Bolt Lubricant and Torque: A Comprehensive Guide

For the past 40 years, when the oil and gas industry thought of bolt lubricant, it focused on disassembly — i.e. the breakout torque seen at the bolt head or at the nut of the fastener.

What went unexplored until recently was how lubricant affects the Nut Factor on a fastener, which then affects tightening torque, and therefore effects the bolt tension.

But that’s just the beginning.

Through years of research and first-hand experience, we have found that many lube manufacturers don’t know how their lube performs in the field. They often don’t understand the difference between friction coefficient and Nut Factor.

That’s a problem, because you reach the applied torque on your fastener through understanding your Nut Factor. If those numbers are off, then your final torque values will be incorrect no matter what your torque reading might be.

In this article, we’ll help you avoid those problems by explaining:

  1. What is Bolt Lubricant?
  2. A Brief History of Bolt Lubricant
  3. Why You Use Bolt Lubricant
  4. How Much Bolt Lubricant to Use
  5. How to Apply Bolt Lubricant
  6. Bolt Lubricant Torque Chart

What is Bolt Lubricant?

Any lubricant is designed to reduce friction and wear between two surfaces in contact. Bolt lubricant is a little more complicated than that.

In the past, bolt lubricant has been associated with disassembly, and therefore many in the oil and gas will refer to it as “anti-seize.” But bolt lubrication is also crucially important for assembling flanges properly.

Using proper bolt lubrication practices will allow assemblers to achieve the ideal torque with a low degree of bolt scatter (which we define as differences among torque levels on different bolts holding together the same flange).

Proper bolt lubrication means:

  • Consistent frictional properties: In order to determine your torque value, you have to understand, and solve for your K-factor. K-factor, which can also be called “nut factor,” is an experimental number. It is not adequate to use a friction coefficient or a friction factor calculation. In fact, PCC-1 just took out Appendix J which is the Friction Factor Calculation.
  • Adequately Lubricated Fasteners: There are very few situations in bolting together flange joints where you can over-lubricate a stud. You should always be able to see a bead of lube “squish” out the bottom of the nut. This means that you have put adequate lubricant on all surfaces that need it.
  • Lower Breakout Torques (no galling): Galling is a form of wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there’s large amount of force compressing on the surfaces together. Certain lubricants, such as nickel lubricants, can actually cause galling.
  • Physical and chemical stability: In the past, the petrochemical industry used copper-based lubes in the past as their standard. However, they discovered these types of lubes don’t play well with hydrogen and can lead to hydrogen embrittlement, which can corrode, crack, or otherwise deteriorate surfaces. Then the industry moved to nickel-based lube, but there was another problem: It causes galling to accelerate. Now the industry has moved to moly lube. Moly lube is technically a mineral, helps prevent galling, and is good for most environments.
  • Ease of application: The ability to apply lubrication is a different subject than adequate lubrication. Why? If the lube can’t come out of the can because it’s a solid at lower temperatures, an assembler won’t be able to apply it adequately.

A Brief History of Thread Lubricant

As we mentioned earlier, bolt lubricants were initially thought of as anti-seize. Companies like Jet-Lube have produced anti-seize thread lubricants for 70+ years for the upstream industry. To this day, the use of copper-based lubricant Kopr-Kote(TM) is the standard lubrication in the field.

Therefore it doesn’t seem unreasonable that when the rest of the petrochemical and power industry started to focus on anti-seize products for a bolted joint, they turned to those copper-based lubricants. But they discovered copper lube was not good for all systems because it doesn’t play well with hydrogen.

Instead, the industry then turned to nickel-based lubricants. This type of lube was considered good because of its high-temperature rating, up to 2500 degrees Fahrenheit. (But note: That is the melting point of nickel and not a good method for determining what a good lube looks like.)

Recently the petrochemical industry has moved to molybdenum disulfide, which is also called “moly” lube. Currently this is the best type of lube for assembling bolted joints, because it does not cause hydrogen embrittlement if mixed with the correct chemicals.

(Note: Pure moly lubricants are not recommended around hydrogen. Check with the manufacturer.)

Why Use Bolt Lubricant?

There are two main reasons why lubricated fasteners are better than non-lubricated fasteners.

1. Galling

Galling demonstrated on a small bolt.
Galling demonstrated on a small bolt. (Image courtesy of Misumi.)

Galling is one of the most frustrating things we run into in the field as assemblers.

The true definition of galling comes from ASTM G40, and it says galling is form of surface damage arising between sliding solids distinguished by microscopic, usually localized roughening and creation of protrusions, i.e. lumps, above the original surface.

So what does that mean to the assembler?

It means we’re grinding steel on steel to stretch steel. That’s what we’re doing when we use torque. So if we want to get rid of galling, one of the best ways to is to properly lubricate.

The other part of preventing galling is in what type of lubricant you are using. That’s why you’ve seen an increase of molybdenum disulfide lubricants (a.k.a “moly” lubricants) in the industry.

2. Achieving Proper Bolt Torque: An Introduction to K-Factor

Here we need to discuss:

  1. Non-Lubricated Bolts (a.k.a. Dry Torque)
  2. Partially Lubricated Bolts
  3. Properly Lubricated Bolts

But before we talk about these items, or get to our torque chart, it is imperative you understand the working definition of K-Factor (or “Nut Factor”). ASME PCC-1 states:

“K is an experimentally determined, dimensionless constant related to the coefficient of friction.”

Translation: You need to have experimental data on what Nut Factor you have. DO NOT rely on just the coefficient of friction numbers. Some manufacturers will say they are the same, or they will not have done Nut Factor testing at all. PLEASE do your homework on this.

“Published tables of experimental nut factors are available from a number of sources; however, care must be taken to ensure that the factors are applicable to the application being considered.”

Translation: You need to make sure any previous testing was done on applications that represent what you are working with. For example, we once saw a company do a test on 1/4 inch bolts. The problem: The average size bolt in the petrochemcial industry is 3/4 inch. So those tests weren’t especially helpful.

“It should also be noted that recent research has shown there to be nut factor dependence on bolt material, bolt diameter, and assembly temperature. These factors can be significant and should not be ignored when selecting the nut factor or anti-seize compound. The user is advised either to seek test results conducted on similar bolt and anti-seize specifications or to conduct nut factortrials (size and material) with their own conditions.”

Translation: Get your hands on their research! It’s the only way you can verify that they have done their homework.

(Beyond ASME PCC-1: Learn what today’s bolting professionals need to know.)

Non-Lubricated Bolt Nut Factor:

It’s not possible to determine an accurate Nut Factor for dry threads. Unfortunately, when you don’t have lubricant, there are many other substances that may act as lubes on your fastener that you might not be able to see.

One of them is the oil used on them during manufacturing. For example, we have seen a stud where the oil has been “baked off” using an oven have a Nut Factor of about .26, while a stud that still has oil residue is about a .20. (It’s worth noting that particles of solids still on the stud that will also affect your Nut Factor).

That is a big discrepancy.

Hex Technology recommends that you do not try to solve this problem unless you have the proper equipment and understand the “Turn of the Nut Method.”

Partially Lubricated Bolt Nut Factor:

Let’s say you’ve done your homework and understand the nut factor for your lube. If that lubricant isn’t applied generously/properly, the dry parts of the fastener will increase your Nut Factor and result in different bolt loads on each of your fasteners.

So you might be using a calibrated torque wrench, and have a known Nut Factor, but if your lube isn’t applied properly, your torque value (bolt tension) will have changed.

(Learn more about how to properly use clicker wrenches.)

Properly Lubricated Bolt Nut Factor:

When testing your Nut Factor, you put it in the best and most repeatable condition, then you replicate those conditions in the field. By properly lubricating fasteners, you achieve the correct ft-lbs, clamping force/preload, and gasket stress.

How Much Lubricant Should You Use?

Proper lubrication means that you’ve put lubricant on every thread so that the valley of the stud is full. See the demonstration at the 1:20 mark in the video below (click here to jump to it, but note: that link will take you to YouTube):

Notice how we lubricate enough so that when you hand rotate the nut down, there’s a little bead of lube that squishes out. This means that we’ve put lubricant on all the parts that will experience friction when we apply torque.

How to Apply Bolt Lubricant

When you apply lubricant, be certain that all valleys of the stud bolt threads are filled.

Once the nut is hand tightened, you should see a bead of lubricant extruding from beneath the nut. This indicates that the lubrication has been applied to all working surfaces.

In this screenshot from the video above, notice how the varying levels of bolt lubrication lead to better results:

This graph shows the different degrees of bolt scatter experienced under three conditions: bolts with no lubricant, bolts with improper lubricant, and fully lubricated bolts. Fully lubricated have the best torque values.

No lubrication: You will see that, without lubricant, bolt stress is lower than our target bolt stress of 40 Ksi. In the video above, our test on unlubricated studs test averages 28.8 Ksi, with the low amount being 27.3 and a high of 31.

Partial lubrication: Inconsistent or only partially lubricating the studs will result in unfavorable bolt stress. In the second test, by using lubricant the average bolt stress increased by 5.4 Ksi, but still came up short of our target of 40 Ksi. Bolts that are not lubricated in the same fashion will have a greater variation in the bolt load.

Proper lubrication: Properly lubricated studs will result in a tight bolt load at our desired stress target. Notice how bolt load has increased, and we’re now achieving bolt loads much closer to the target bolt load of 40 Ksi. And notice how the variation among the bolt loads (a.k.a. bolt scatter) has drastically reduced when all working surfaces are properly lubricated.

Bolt Lubricant Torque Chart

PCC-1 published Table O-3.2-1 “Reference Values (Target Torque Index) for Calculating Target Torque Values for Low-Alloy Bolting Based on Unit Prestress of 1 ksi (root area) (Inch Series Threads).

This was done to ensure you can use it to determine and adjust to stainless steel fasteners that have a lower tensile strength.

This table displays torque values for numerous bolt sizes with three different K-Factors.

NOTE: The above chart shows you how to determine your torque IF you have either a 0.15, 0.18, OR 0.2 Nut Factor. But again you need to experiment with what lube you have and confirm the Nut Factor is in order to make a torque specification.

Learn more about the technical aspects of bolted flange joint assembly.

Hex Technology trains bolting assemblers, specialists and inspectors. We’ve committed to making the world’s refineries and industrial plants safer through better bolting practices. We offer online training 100% free. To start, claim your spot in Level 1 training here.

The Clicker Wrench Guide: Torque Ranges, Calibration and More

What is a Clicker Wrench?

The Clicker-type torque wrench is the most commonly used torque wrench in the oil and gas industry today.

There’s a good reason why: A clicker wrench is an affordable and extremely accurate tool — so long as you use it properly.

Clicker wrenches are not power tools, but a manual method to achieve proper torque (a.k.a. bolt load) on your fastener. They should be a part of any assembler’s collection of hand tools in every oil and gas plant.

How do Clicker Wrenches Work?

Click Type Torque Wrenches are a ratcheting adjustable torque wrench, meaning you can adjust the applied force up or down within a given range.

Clicker wrenches have a housing that shows such force in either inch-pounds (in-lbs), foot-pounds (ft-lbs) or Newton Meters (Nm), which is used for metric torque settings.

In this article, we’ll concentrate on foot-pounds/Newton Meters, and not micro-clicker torque wrenches (also called micrometer torque wrenches), which measure in inch-pounds because they are typically not used in heavy-duty industrial applications.

The typical click-type torque wrench comes with a manual adjustable setting, but there are also digital torque wrenches available. People may refer to these as electronic torque wrenches. Any of them can help an assembler achieve the desired torque on a fastener.

Most clickers are square-drive torque wrenches. They typically have a ratchet head with drive sizes of 3/8″, 1/2″, or 3/4″. However, most assemblers need to have open-ended attachments for the low clearance issues whey often encounter in the field.

When a clicker wrench is pulled to the point of the torque setting, the lever inside the wrench rolls over a cam and hits the inside of the wrench handle wall. This effect makes the “click” sound, and tells the operator that they have reached the desired torque value.

A Brief History of Clicker-Type Torque Wrenches

It’s generally accepted that the first clicker wrench was created by Conrad Bahr at the New York City Water Department in 1918. He was tired of having inconsistent bolt loads on his fasteners, so he decided to fix it by making a torque wrench that would apply the same load consistently.

(FUN FACT: Torque Wrenches are 100+ years old and most people still don’t know how to use them properly!)

Bahr wasn’t the first to attempt to patent the idea, however. The first patent for a torque wrench was filed by John H. Sharp in 1931. What he then called a “torque measuring wrench” is what we today know as a beam-type torque wrench.

A beam type torque wrench has a torque gauge near the handle.
A beam type torque wrench. (Source: Shutterstock)

But Bahr was not to be left behind. In 1935, Bahr and George Pfefferle patented an adjustable wrench that had ratchet head and that would provide the assembler “audible feedback” — i.e. the “click.”

Bahr also made sure to include a mechanism that prevented the wrench from back-ratcheting when the desired torque on the fastener was achieved.

I would say that Conrad Bahr is a hero in the torque wrench world!

Torque Range for Clicker Wrenches

The preset torque ranges for clicker wrenches range from 10 ft-lbs to 2,000 ft-lbs. Different torques come in different drive sizes. The typical sizes you’ll see in heavy industrial applications are:

  • 3/8″ square drive size: Typical torque range of 10-150 ft-lbs. These are great for areas that you have wrench clearance issues for the length of the torque wrench.
  • 1/2″ square drive size: Typical torque range of 30-250 ft-lbs. These are the most used in the industry and every assembler should have one, or at least have access to one. Also this is the drive size we typically see the low profile adapters used with.
  • 3/4″ square drive size: Typical torque range of 100-600 ft-lbs. While these can produce a good amount of torque on the fastener, they are about 4 feet long, so they might not fit on every application.

Through years of tracking use in the field, Hex Technology has found that 82.3% of applications in the Oil and Gas Industry can be assembled with a click torque wrench that can achieve 250 ft-lbs. That’s nearly the same percentage for the Chemical Industry too.

While manufacturers do make 1,000-foot-pound and 2,000-foot-pound clicker wrenches, they should be treated as a last resort, used only when there is no other option.

Why? Simple: These wrenches are a BEAST on assemblers.

You have to generate 200 to 300 pounds of force on the end of the wrench in order to make achieve your torque. That requires a lot of strength — especially when you consider that they might have to touch 24 studs 4 times if you are using the star method of assembly.

So while a high-torque manual clicker wrench seems like an ok idea in theory, in practice, in order to achieve that level of force, the assembler is either going to have to bounce on the wrench in order to get it to click, or will just become exhausted during the assembly.

Bottom line: If you’re in a situation that requires a 1,000-foot-pound torque wrench or greater, see if you can opt for powered equipment to achieve the torque you are trying to reach.

Clicker Torque Wrench Accuracy, Calibration and Recalibration

Standard ISO 6789 covers the construction and calibration of hand-operated torque tools, including standard torque wrenches and even screwdriver-type torque wrenches.

The standard states that re-calibration for tools used within their specified limits should occur every 12 months. In cases where the tool is in use in an organization which has its own quality control procedures, then the calibration schedule can be arranged according to company standards.

Each calibration sheet should be marked with their torque range, the unit of torque, the direction of operation for unidirectional tools (some tools only allow you to go in the clockwise direction) and the manufacturers mark.

If a calibration/recalibration certificate is provided, the tool must be marked with a serial number that matches the certificate or a calibration laboratory should give the tool a reference number corresponding with the tool’s calibration certificate.

The accuracy of clicker wrenches should be between 3 and 5%, depending upon the manufacturer. And as with any other tool under ISO 6789, they should be calibrated at a minimum of every 12 months.

NOTE: It is common practice — and a very good idea — to also field check the accuracy of these tools between calibration dates.

To do this, you can request a load verifier from the tool manufacturer, place it within your plant, and use it to check that your wrench hasn’t fallen out of calibration.

How to Use a Clicker Wrench

While Clicker Wrenches are accurate, the inaccurate part is the human being. So you’ve got to watch out.

We’ll often combat inaccuracy by putting clicker wrench checkers in the field. Not only does this validate that the wrench is doing what it’s supposed to do, but it also helps to make sure that the human operating the tool is doing what he or she is supposed to do.

Before using a clicker wrench, you want to check that the wrench is set to the desired torque value. When applying force to the wrench, you want to do so evenly — not by jerking, yanking, or jumping on the implement.

Also note: torque wrenches are pretty sensitive. You need to take care when using and handling them. Dropping, hitting, or banging the wrench can change the output of the calibration.

Also, if you don’t completely unwind it to less than 20% of the total scale, you can bend the internal works too much, and they won’t return to their original shape. That will affect your torque value, and may invalidate your calibration.

Other Torque Wrenches You May See

Complexity is the enemy of completion.

Where many people think that technology can compensate for a lack of training or skill, we’ve seen time and again that it doesn’t. Which is why manual click-type torque wrenches remain the go-to tool for the bolting industry.

If you combine this relatively simple tool with a well-trained assembler, you’ll achieve good results.

There are several other types of wrenches available, which we’ll describe below. However please be aware these tools might complicate your procedure process.

Electronic torque wrench

An electronic torque wrench displays a torque value on a digital screen.
An electronic torque wrench displays a torque value on a digital screen. (Source: Shutterstock)

With electronic (indicating) torque wrenches, have a strain gauge attached to the torsion rod, which sends a signal to the transducer and is then converted to a torque value. They typically have a digital display.

Programmable electronic torque/angle wrenches

These are very similar to the electronic torque wrench, but they use a low torque value followed by moving the nut a certain amount of an angle.

The angle measurement is done by a sensor or electronic gyroscope. This design of torque wrench is highly popular with wind power and automotive manufacturers for documenting tightening processes requiring both torque and angle control.

Mechatronic torque wrench

Torque is achieved in the same way as with a click-type torque wrench but it has a digital readout screen (like an electronic torque wrench).

These wrenches also typically have some sort of wireless data transmission with a computer interface so that you can document what torque was applied. We joke that they beep, vibrate, and have flashing lights, so all that’s missing is your old man sitting behind you saying “Stop, stupid!”

There are also manufacturers that are really good at making micrometer torque wrenches like Tekton and GearWrench, but typically we see CDI (a Snapon Company) or Proto Tools in the oil and gas industry for manual wrenches.

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Gasket Types in Oil and Gas, Explained

What is a Gasket?

A gasket is meant to form a mechanical seal that fills the space between two or more mating surfaces. Its goal is to prevent leakage from, or into, the joined objects while under compression.

Gaskets allow for less-than-perfect mating surfaces on machine parts. They can fill irregularities and increase the likelihood of sealability — especially in high-pressure applications and flanges that have a high differential temperature range (cyclic flanges).

There are many different types of gaskets used in the oil and gas (petrochemical) industry and other heavy industry. They include both standard ANSI/ASME pipe flanges (an example is ASME B16.5 flanges) and gaskets used in heat exchangers.

What Nachos Can Teach You About Proper Gasket Assembly

What most people don’t know is that the gasket stress is what we care about the most! Not the bolt load.

We use this analogy when training people: “What is the purpose of the chip in chips and queso? It’s the vehicle that gets the queso to the mouth.”

That is the purpose of the bolt: To be the vehicle to gets the gasket stress correct.

What are the Most Common Types of Gaskets Used in Oil and Gas?

Here are the 8 types of gaskets you will see the most often:

1. Envelope Gasket (Double Jacketed Gaskets)

Envelope Gaskets can be either double jacketed gaskets, or they can have PTFE (some call it Teflon but that is a trademarked name) on the outside of a stainless steel metal core. However, they don’t have a lot of compression or recovery, and do not hold up to radial sheer (slipping of the flanges on the gasket during high-temperature fluctuations).

2. Flat Metal Gaskets

Flat metal gaskets of various dimensions stacked against a wall.
Source: Shutterstock

These gaskets usually have a stainless steel core without any filler material, and are used in low criticality applications. They also don’t have a lot of compressibility or recovery.

3. Non-Asbestos Sheet Material Gaskets

Non-asbestos sheet material is typically found with full-face flanges and have elastomeric properties, although they can be just graphite gaskets in few cases. One can have high chemical resistance sheet gaskets such as a PTFE/ePTFE gasket that has great compressibility and a little bit of recovery if you don’t overstress them.

Normally, these gaskets are used with low pressure and low temperature, but they can be also put in put in flanges where chemical resistance is needed. Most gasket manufacturers stock a wide range of elastomeric, non-elastomeric, PTFE/ePTFE, graphite gaskets, and compressed sheet material in both sheets and rolls.

4. Ring Type Joint

2 Ring Type Joint Gaskets on white background
Source: Shutterstock.

Ring Type Joint gaskets are also called RTJ gasket, ring gasket or ring joint gaskets. They come in oval or octagonal shapes, which can be used in API 6A applications.

RTJ gaskets were traditionally found in high pressure and high-temperature applications, as sheet material elastomers can not hold up in those types of applications. But today RTJ gaskets are being phased out of high pressure and high-temperature applications, as spiral wound gaskets with inner rings are now the preferred gasket.

However, if you are using ring type joint gaskets, know that they are typically made of a soft stainless steel gasket material, and should be replaced after every use due to the plastic deformation that it sees in the flange. If you don’t replace it, you are jeopardizing the sealability of the gasket.

5. Kammprofile Gasket

Interior of a Kammprofile gasket
Courtesy of Salmarcon.

You’ll also see Kammprofile spelled “camprofile gasket,” and they are sometimes called grooved metal gaskets. These types of gaskets are commonly found in heat exchangers in the oil and gas industry.

They are much more reliable than jacketed gaskets (double jacketed gaskets). Kammprofile gaskets are typically made of a stainless steel metal core with a flexible graphite filler material.

The area (a.k.a cross-section) of the gasket can be easily changed to achieve good gasket stress while withstanding a high bolt load. Kammprofile gaskets are also really great for radial sheer which is seen when the flanges slip on each other (really the flexible graphite filler) during flange expansion and contraction (due to temperature).

This gasket material is a solid metal gasket, and the metal core can be made of stainless steel or other exotic materials so that it can be put in high pressure and high-temperature flanges.

6. Spiral Wound Gaskets WITH an Inner Ring

Two green spiral wound gaskets on white background.
Source: Shutterstock

These types of gaskets are the best metal gaskets for all pressure ratings of pipe flanges, especially ASME B16.5 flanges.

I would argue that they are also great for heat exchangers due to their sealability tolerances with imperfections in flanges, and because they can be made for high pressure and high-temperature applications.

These spiral wound gaskets have a stainless steel inner ring, a carbon steel outer ring, and the metal core is made of stainless steel windings. The filler material is typically flexible graphite, but you can also have an elastomeric filler material such as PTFE if chemical resistance is needed.

Spiral wound gaskets are more also flexible than Kammprofile gaskets so they tend to also have more compressibility and recovery, but they are harder to place in a flange at larger diameters so it is advisable to move to Kammprofile gaskets.

7. Spiral Wound Gaskets WITHOUT an Inner Ring

These types of gaskets should not be used in typical pipe flanges, and especially not in high-pressure rated pipe flanges (such as 600 pounds or greater).

The reason: Spiral wound gaskets without inner rings can buckle under high gasket stress, such as what you’ll see when there is a lot of bolt area and little gasket area.

There are instances when a spiral wound gasket without a stainless steel inner ring or carbon steel outer ring can be used for groove flanges such as male/female flanges, but we will typically see that they will compress enough to not allow for recovery.

8. Corrugated Metal Gaskets

Corrugated metal gasket on white background.
Courtesy of Garlock.

These gasket types can be made to have a minimum of 0.5″ cross-section and have been used to change gasket area. They are better than metal jacketed gaskets for heat exchangers, but should not be used in standard piping flange gaskets.

How to Identify a Gasket: A Color-Coded Chart

Most piping flange gaskets in the oil and gas industry today are spiral wound gaskets made of stainless steel for the metal core material with either PTFE or graphite filler material. ASME B16.20 offers a Color Coding Chart that is part of the standard for inspection purposes.

The color coating on the outer ring (which is typically carbon steel) is painted on the outside of the ring so that an inspector can identify the windings material.

Typically 316 stainless steel is used as the standard in petrochemical applications, as it is better for high-temperature applications. While 304 stainless steel could be used, most End Users in the petrochemical industry err on the conservative side for the 316 stainless steel which has a green color on the carbon steel outer ring.

The most common filler material is flexible graphite, and that is indicated by the grey stripe on the green outer ring.

The ASME B16.20 color chart above indicates what the gaskets are made of. NOTE: there is no marking for gaskets that do not have a stainless steel inner ring, so it is prudent that ALL spiral wound gaskets have an inner ring.

For an even deeper dive into spiral wound gaskets, check out this resource.

Hex Technology trains bolting assemblers, specialists and inspectors. We’ve committed to making the world’s refineries and industrial plants safer through better bolting practices. We offer online training 100% free. To start, claim your spot in Level 1 training here.

Bolted Flange Joint Assembly: Learning the Technical Aspects

In 2005 I started selling hydraulic torque wrenches. Like many young salesmen, I instantly thought I was a “Bolted Flange Joint Expert.”

(Today I consider myself a recovering Bolting Expert.)

When customers asked about how flanged joints worked, my go-to response was, “well, target torque is the only thing that matters.” I didn’t consider things we now know are essential, like…

  • assembly procedure
  • tightening sequence
  • the guidelines in ASME PCC-1

I just looked at bolt stress (really, the percent yield of the stud), and a little bit on the “cross pattern” (a.k.a. the star pattern), but that was it. If you gave me a torque value or bolt load, I wouldn’t necessarily know why or how it was generated. I just knew how to apply the tightening method to the appropriate fastener size.

What “Bolting Experts” Often Miss (or Misunderstand)

It’s a problem that still occurs today. Despite being one of the oldest assembly practices in industry, bolting techniques are often learned on-the-job, delivered from seasoned assemblers to greener staff. While this may cover some of the basics, word-of-mouth training often fails to address fundamental concepts such as…

And really, that’s just the beginning. The field of bolted flange joint assembly goes far deeper. More than 15 years later I’m still learning new things about bolted flange joint assembly (BFJA).

Often, I get asked a question that was on my own mind back at the beginning: “Where can I go to learn about BFJAs (both pipe flanges and heat exchangers)?”

Best Resources for Understanding Bolted Flange Joint Assembly

A close up of bolts in a bolted flange joint.

There are good authors and publications, and bad ones, within bolting. I’m not going to waste your time by listing resources that aren’t worth reading. Instead, I’ve collected materials about the past, present and future of the bolting industry you ought to know. However, this list is always growing so don’t just stop here!

(NOTE: These books are for references to concepts. They aren’t a recipe for the assembly of BFJA’s or proper flange assembly practices.)

The Classics: John Bickford is the first author of BFJA books. Some of the material is outdated now, but they still are good reference material. He has three and the below listing is in order and not rank with a description of each book. They are not cheap ($200+ each) and you can find them both on Amazon:

  • An Introduction to the Behavior of Bolted Joints – This is the first book he published. It’s my second-favorite of his works because it talks about basics but the book that followed it (listed below) has a better scope of concepts.
  • Handbook of Bolts and Bolted Joints – Bickford takes his best articles from his first book and adds about 30 more articles from what were then “trusted resources” within the industry. Some of the articles are a little biased since they were written by the manufacturers of the products, but it will give you a good idea of how each topic functions.

The Present: The American Society of Mechanical Engineers (ASME) has published PCC-1 (Post Construction Committee -1) which is titled, “Guidelines for Pressure Boundary Bolted Flange Joint Assembly.”

This is the industry standard on how to assemble BFJA’s and is great for calculating gasket stress, K-Factors, training, etc. One should be very familiar with this document and is a good jumping point for a holistic understanding of bolted flange joints.

You should also read “Welding Research Council Bulletin 538” which has the background on many topics in ASME PCC-1.

For Upstream Applications, you should also read through API 6A.

Also for the Present: My new favorite book that has been updated frequently is published by Jose Veiga and it is titled “Industrial Gaskets.” You can download it for free at that link.

The Future: The American Society of Mechanical Engineers has an annual conference where BFJA’s receive their own section. You can find the research being done here.

Refine the search to “Bolted Flange Joints,” then narrow down by author. I highly recommend Dr. Warren Brown, who was my engineering mentor and is widely regarded as the foremost expert in the world on bolted joints today. However, you can filter by your topic and author on whatever you might be looking for.

NOTE: These articles normally cost $25 each.

Conclusion: BFJA Essentials

Today there are still many people in the BFJA industry who claim to be “experts.” Most are…on own products. But many of these individuals don’t possess a holistic understanding of all the parts that go into proper bolted flange joint assembly.

After many years of reading through the work of these experts and their opinions, I’ve found that sticking to the basics is the best path. Therefore, my recommendation is to follow ASME PCC-1 guidelines as the standard and use the different references to understand the items in ASME PCC-1. (Find more on ASME PCC-1 Training, and how to use it in your organization, here.)

When you research these topics, please remember: Keep it simple. Also, beware if someone tells you any of the following:

  • “We have had 100% success…” (<-No, no you didn’t.)
  • “This product brings together the best from X product and Y product…” (<-If it brought together only the “good,” where did the “bad” go?)

Also remember: You can’t out-procedure a lack of training. ASME PCC-1 Appendix A discusses the joint assembly procedures that all bolted joint assembly personnel should know, and serves a good syllabus for all individuals associated with BFJA’s to understand.

RELATED: Read our guide to clicker-type wrenches.

Other useful resources for understanding Bolted Flange Joint Assembly are our Level 1 and Level 2 training courses. Both are available for you 100% free when you sign up here.

PTFE Coated Studs: Do They Work?

PTFE Coated Studs: A Little Background

PTFE is short for Polytetrafluoroethylene, a chemical applied to common bolting materials (such as B7 stud bolts) to provide corrosion and chemical resistance.

Some other common coatings for PTFE coated fasteners are Teflon® and Xylan®. In this article, we’ll refer to all of them as PTFE.

PTFE coated studs have been used for many years within the bolting industry, especially in any application that requires corrosion resistance or in offshore applications (salt spray is hard on Grade B7 material). PTFE is also useful if you’ve had “galling” and need a lower breakout torque for safe removal.

PTFE should not be used in high-temperature applications. Fluoropolymer coatings manufacturers use temperatures in the 400F-500F as the maximum temperatures, so you typically do not see alloy steel bolts (such as B8) with PTFE coatings.

While PTFE coated studs (including Xylan® coated studs) have corrosion-resistant properties, which are functionally understood by assemblers, the technical aspects of fluoropolymer coatings are often misunderstood.

For example, as an assembler, I was told that the PTFE coaching acted as a lubricant, which meant I didn’t have to mess with lubricating them after I put them into a flange.

It sounds like the perfect solution. The only problem is: That advice was wrong.

Way wrong, in fact.

Yet many front-line assemblers today still think it’s correct.

Thankfully, in the decades since I first started putting together flanges, smart minds both in the lab and on the front lines have given us a much more accurate picture of how PTFE coated studs work.

In this article we’ll bust some myths, provide practical advice, and address some of the most common questions we hear from craft assemblers today, including:

  1. Are all PTFE coated studs the same?
  2. Do I lubricate PTFE coated studs?
  3. Can I re-use PTFE coated studs?
  4. Why do PTFE studs have low friction and lower break out torque than regular studs? (Grade B7 with 2H hex nuts for example)
  5. Does the PTFE coating help with corrosion resistance?

Click any of those questions above to jump directly to the answer you want. Or read on to get the complete picture of how PTFE coated studs affect assembly.

1. Are all PTFE coated studs the same?

Absolutely not.

While PTFE is the same as Teflon® on a chemical level, they are not applied the same way by each manufacturer. There also are several different types of base coats.

Therefore, the thickness of the coating on the fastener is not a standard — and quite frankly, it’s not controlled.

As a result, you must choose one manufacturer and test your k-factor for their product, and recognize that those values do not transfer to other PTFE coated stud manufacturers.

2. Do I lubricate PTFE coated Studs?


At 30,000psi bolt load (not to be confused with 30% tensile strength), you start stripping your coating. Also, the coating will start binding. Therefore, you’ll have better accuracy and less bolt scatter (or differences in bolt loads on each bolt) by using lubricating them.

However, you will have to test your lubricant and manufacturer combination in order to correctly determine your K-Factor. Note: Don’t confuse K-Factor with low coefficient of friction, which is not used for this calculation.

(Learn proper lubrication techniques in our Level 1 course — now available free.)

3. Can I re-use PTFE coated studs?

You shouldn’t.

If you were to re-use PTFE coated studs, the corrosion-resistant coating on the threads will most likely be at least somewhat degraded or damaged, meaning your K-Factor will change again.

Physically the bolt might still hold up to corrosion. So visually, they would still look good, which would lead someone to think that the life expectancy of the stud would be longer. But appearances can be deceiving, and you shouldn’t reuse PTFE coated studs.

4. Why do PTFE studs have low friction and lower break out torque than regular studs?

What would you say if I told you that, in order to fit the nut on the stud with the PTFE coating, you must drill a bigger threaded hole (tap) through a 2H nut? Yes, it’s true. And there is are no technical specifications on this.

I couldn’t believe it either, but you will be effectively taking 30%-50% of the contact surface away. Therefore, it is not the PTFE that makes it easier to disassemble (and you have a low friction between stud and nut on assembly). This phenomenon is due to having considerably less contact area!

5. Does the PTFE coating help with corrosion resistance?

Yes…to an extent.

Let’s say you have a B7 stud (ASTM A193) and 2H nuts. The application process and proprietary materials of the PTFE coating is intended to help with corrosion resistance. However, since the coating is proprietary to the manufacturer, it is hard to say how well it helps with corrosion resistance.

One way to test this is with a salt spray test with ASTM B117, which sprays the stud bolts up to 3,000 hrs while not freezing the nuts.

A Brief History of PTFE

Before PTFE coated bolts came along, the petrochemical industry used other methods of making corrosion-resistant bolting components, such as hot dip, galvanized, cadmium or zinc-plated fasteners.

Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The most well-known brand name of PTFE-based formulas is Teflon by Chemours. Chemours, a spin-off from DuPont, originally discovered the compound in 1938.

PTFE (polytetrafluoroethylene) coatings are considered non-stick coatings. Therefore you need a process to apply the “non-stick” coating to the “B7 stud material”. Therefore, the typical manufacturing process is a three-step process.

  1. Apply a corrosion resistant base coating
  2. Apply an adhesion coating
  3. Apply a polytetrafluoroethylene nonstick topcoat

It’s unclear exactly when the bolting industry started using PTFE coated studs, but they have been around for a while. They tend to be used in highly corrosive environments.

Once the bolts prove themselves, people start placing them all around the plant — regardless of whether or not they should or need to.

Bottom Line: I am not very fond of using PTFE coated studs as it increases the complexity of a bolted joint, you don’t have a consistent K-Factor (not “low coefficient of friction”). Unfortunately, PTFE coated studs are over-prescribed since most people don’t know how they actually work.

A Real-World Test of PTFE

A cooling tower pours condensation onto our test bolts. When we started researching PTFE studs, we took standard B7s, B7s coated with PTFE, and a set of B7 Doxsteel studs. We then put them in the worst part of a plant: In the way of drift from a cooling tower. (If you notice in the photo at left, you’ll see an icicle hanging above the test flanges.)





Here’s what happened:

b7 studs with doxsteel coating during a corrosion test B7 studs with a PTFE coating during a corrosion test. Standard B7 studs during a corrosion test.

(From left: B7s coated with Doxsteel, B7s coated with PTFE, and standard B7s.)

So, out of the three pictures above, which would you say has the easiest break-out torque (some call it a low kinetic friction coefficient)?

My thoughts were: Doxsteel, PTFE, and then B7 studs.


The B7 studs with PTFE were easier to break loose. I asked the CEO of Doxsteel about the testing, and why his studs were second best, and this is what he showed me.

Oversizing Nuts to Make PTFE Studs and Nuts Fit

One of the biggest issues in bolting is K-Factor, as it deals with how the friction when applying torque and proper lubricant will help with safe removal of the studs during disassembly.

We’ve found through testing that at about 30,000 psi of bolt load, you start to tear that PTFE coating off the stud and heavy hex bolts. (Learn more about high psi applications in our free course on Powered Equipment.) The coating ends up binding on the bottom of the nut and threads. This changes the binding of the PTFE, makes the K-factor change, and your bolt scatter is more dispersed.

Why does this happen? Well, it works together with a lower break out torque. The nuts are over-tapped!

Yup, as you can see in the picture on the top above, you will see normal engagement of a B7 stud. Then the picture on the bottom shows how PTFE manufacturers over tap the nut so that the coating can fit.

You can normally see 20%-40% less engagement of the threads. So it is not the PTFE that makes it easier to break loose, but actually the lack of engagement!

Other References to Review

It’s hard to find material on this topic that wasn’t published by a manufacturer. But here are a couple of interesting resources:

  1. Doxsteel. These guys are responsible for the pictures above and testing with Hex.
  2. Here’s a video I found on the application of PTFE. I can’t confirm, but I think that this is how all manufacturers apply it (which seems less technical than I ever thought).

You can get access in-depth guidance on bolting and bolt components through our free online training. Sign up today. 

Beyond ASME PCC-1 Training: What Today’s Bolting Professionals Need to Know

Introduction: What is ASME PCC-1?

ASME is short for the American Society of Mechanical Engineers. PCC-1 stands for “Post Construction Committee 1”. PCC-1 addresses “Guidelines for Pressure Boundary Bolted Flange Joint Assembly.”

It’s a consensus document, which means it was written by several experts across the bolting injury.

The document addresses many factors involved in bolting principles and the assembly of bolted flange joints. The scope of ASME PCC-1 states:

These guidelines for bolted flange joint assemblies apply principally to pressure-boundary flanged joints with ring-type gaskets that are entirely within the circle enclosed by the bolt holes and with no contact outside this circle.

These guidelines may be selectively applied to other joint geometries. By selection of those features suitable to the specific service or need, these guidelines may be used to develop effective joint assembly procedures for the broad range of sizes and service conditions normally encountered in industry.

This document uses the most up-to-date bolting principles for the integrity of bolted joints on pressure vessels. They discuss assembly, disassembly, quality assurance (documentation), bolting safety and tool handling, gaskets, torque, fasteners, washers, tensioning.

One of the most important parts of the document is, “Appendix A -Training and Qualification of Bolted Joint Assembly Personnel.”

This appendix is the basis for a training program for assembler qualification. Successful completion of training for bolted joint assembly may be the most important part of ASME PCC-1.

At Hex Technology, we’ve provided bolting training for several years. Our leadership serves on the PCC-1 committee. In this article, we will explain

ASME PCC-1 Appendix-A Training: Background and Why it Matters

The whole point of ASME PCC-1 was to ensure assemblers understood the principles of bolted joints. The goal is to provide them with the knowledge they need to solve problems in the field.

Since it would be impossible to “write the rules” for every type of flanged joint used in every type of industry, the committee wrote a guideline. This guideline serves as a template for the bolting industry. The guideline is inclusive of not only the principles of a bolted joint, but also the bolter’s ability to assemble flanges.

End Users

For an End User (meaning a refinery or other industrial plant), there are typically four departments that should go through bolting training: Engineering, Maintenance, Inspection, and Operations. All of these individuals have a part to play in a successful and safe bolting program.

Below is a path showing how End Users might use this training. At Hex Technology, we recommend three additional levels of training that Appendix A does not stipulate (Bolting Inspector, Bolting Assembler, & On-Boarding Training), as experience shows they lead to a better-informed organization (and therefore, better results).

  • On-Boarding Training (Level 1): Anyone working in a plant ought to know how to properly assemble a bolted flange joint. They also should be familiar with the factors affecting their working conditions. A Level 1 training provides that basic, but essential, knowledge. Some topics covered include: proper lubrication, stud installation, gasket installation, and general inspection of flange facing.
  • Bolting Trainee (Level 2): This training is important, as it helps assemblers to understand the fundamental concepts of a bolted flange joint. While PCC-1 provides some specifications around training, how that training is carried out from plant-to-plant can vary widely. As a result, a person who’s “Level 2” at one plant may have a vastly different understanding than someone who’s been designated a similar level at another plant. This is one of the reasons why we’ve sought to provide free Level 2 training online. (You and your staff can sign up for Level 2 here, but note: Completion of Level 1 is required before you test for the Level 2 certificate. Level 1 training is also free.)
  • Bolting Inspector (Level 3): Inspection staff may be required to inspect flanges, bolts and gaskets on a periodic basis. They also monitor joint assembly progress and effectiveness. This level is not intended to teach individuals how to assemble flanges but how to inspect the effectiveness of assembly. This is normally completed through a final examination of the flange through a checklist.
  • Qualified Bolting Specialists (Level 4): At least one individual — and, ideally, multiple people — in each plant ought to earn qualified bolting specialist certification. This person would be a good asset for equipment flanges (that tend to be more of a hassle) and to also help management with contractors and growing their bolting program organically. PCC-1 states that a QBS would need to recertify every 3 years
  • Qualified Senior Bolting Specialists (Level 5): Every End User ought to have at least one Level 5 individual in their organization. Why? Someone who’s trained to this level will understand the unique, and sometimes random, challenges bolted flange joints can present. Bolted flange joints are more complicated than welded joints. A good example is with heat exchangers, which nearly always feature custom flanges. A QBS level 5 can understand every aspect of bolting, and therfore fix such custom flanges, helping your plant avoid potentially costly leaks, LOCs or shutdowns. A Level 5 individual can also support your plants with bolting needs and help direct the overall bolting program.
  • Qualified Bolting Specialist Instructor (Level 6): Bolted Joints are a small portion of what End Users must monitor and account for. Due to joint integrity being new within the industry, this level takes not only deep experience but continual study. Currently, End Users should rely on a 3rd party individuals or companies that are thoroughly competent on the principles of the bolted joint to complete training courses of their individuals on Appendix A unless they can afford to dedicate one to two individuals to continual upkeep of what Appendix A recommends for this position.

PCC-1 Training Guidelines for Contractors

There are three major types of bolting contractors who operate in industrial plants:

  • General
  • Specialty
  • Inspection

Each type of contractor ought to have achieved a specific level of training within their workforce. Below is an explanation of each category of contractor, along with their needs.

Specialty Contractors

Typically Specialty Contractors are hired to assemble or “torque” critical flanges and flanges that need powered equipment. However, it has been seen by Hex Technology that many of these companies (in general but there are a few exceptions) have not trained their organization on Appendix A of ASME PCC-1. They tend to rely on using their “expertise” on powered equipment (usually given in one manufacturer training session) to qualify themselves as experts.

It is Hex Technology’s recommendation that each Specialty Contractor improves its current bolting program and meet the following guidelines:

  • On-Boarding Training (Level 1): For Specialty Contractors, this should be a preliminary step for a “casual” worker who might help with bolted assemblies but is not a supervisor on a job to complete. There will be many occasions where a bolted flange joint assembler will need a second person to help with equipment. Therefore it is up to the contractor how many of these individuals they might need in cross-training.
  • Bolting Assembler (Level 2): The goal of a Specialty Company is to eventually put the remaining of their bolting individuals through some sort of training in order to start getting their knowledge base up. This will then set them up for a career path to move into Qualified Bolting Specialist level. During this time, it would be of benefit to start teaching the individuals not only the academic/practical aspects of their job but to also teach them: paperwork, project management, powered equipment, exchangers, and piping aspects outlined in ASME PCC-1 Appendix A. (*50% of Specialty Contractors total employment should be considered for this role.)
  • Bolting Inspector/Supervisor (Level 3): This level depends on the QA/QC policies of their own program, and if they are planning on being a 3rd party inspection company.
  • Qualified Bolting Specialists (Level 4): There should be more of these individuals than just a couple in Specialty Contractors (both large and small). These individuals would be used on smaller “turn-around” and normal maintenance. It is not the intent of Hex Technology to state that these individuals are on every job but thinks it is reasonable that 30% of bolting individuals should be trained to this level. (*30% of Specialty Contractors total employment should be considered for this role.)
  • Qualified Senior Bolting Specialists (Level 5): Specialty Contractors should have multiple individuals who can fulfill this role. This is intended for individuals to be able to run entire “turn-arounds” worth of bolting, where a plant may be working on thousands of piping flanges and hundreds of heat exchangers at one time. Therefore, it would be in the Specialty Contractors interest to have a problem solver on these bigger jobs. (*15% of Specialty Contractors total employment should be considered for this role.)
  • Qualified Bolting Specialist Instructor (Level 6):  Determine a time frame that at least one individual obtains this level in order to train the many individuals that they might have in their organization. This will take time, and a 3rd party might be needed until one can be properly trained. (*1-2% of Specialty Contractors total employment should be considered for this role.)

General Contractors

General contractors are typically hired to assemble and torque 80% of flanges in a plant turnaround. You want them to have a baseline skillset in which you are confident.

It should be a minimum that they teach their individuals on both the “On-Boarding Training” and should strive to determine how to administer “Bolting Trainee” training (both mentioned above).

It should be noted that General Contractors typically assemble flanges, and one individual (normally considered the “project manager”) should be trained to the “Bolting Specialist” level to make sure his crew is assembling flanges correctly in their specific work environment. (*100% of staff working on bolted flange joint applications should be trained to at least the On-Boarding Level.)

Inspection Contractors

Inspection contractors are the individuals are there to make sure the assembly of a flange follows procedure, from pre-assembly to assembly to post-assembly.

It should be a minimum that Inspection Contractors train their individuals on the above mentioned “Inspector Training” as they are responsible for making sure that the components and assembly of the flange is completed. (*100% of their staff that works on bolted flange joint applications should be trained to at least the Inspection Level.)

Summary of Appendix A

A1.1.1 – Background / How should I use this?

The first part of this appendix states “The recommendations outlined in this Appendix are intended as a guideline, and they may be applied differently by different user organizations.”

Some individuals have expressed that they want ASME to “tell them what they should know,” however this document is intended to serve all Industry, not just a single one (such as the petrochemical industry). Therefore, not all items may apply. End Users and Contractors are responsible for determining the level of knowledge that they would like their organization to know.

Example: A pipeline company/contractor wouldn’t necessarily need to make their assemblers have the “Exchanger Endorsement” included in this Appendix.

Do all my assemblers need to be “Qualified Bolting Specialists”?

Appendix A states that you can determine what quantity of each level you would like working in your organization.
“User organizations who choose to utilize provisions of this Appendix should specify the level of qualification required. Examples include the following:

  • (a) An organization may require only one Appendix A–Qualified Bolting Specialist who works with a number of bolting assemblers.
  • (b) An organization may require that a group of Appendix A–Qualified Bolting Specialists work in the organization.
  • (c) An organization may require each assembly team working in a plant to be, as a minimum, led by an individual who is an Appendix A–Qualified Senior Bolting Specialist.”

Example: An End User could state that each plant would have one Qualified Bolting Specialist on each shift to make sure that other individuals are assembling bolted flange joints properly.

A.1.1.3 – How do I qualify my assemblers to this Appendix

This has been a sticky point for End Users that haven’t been around this document for long. ASME DOES NOT qualify Bolting Specialists. There is only one company out there (to my knowledge) that has followed Appendix A to be considered a Qualifying Organization who can qualify not only assemblers but organizations to train their assemblers to Appendix A.

To become a Qualifying Organization, the two main points that should be followed are:

  1. Qualifying Organization: an organization that undertakes the training, demonstration, and practical and theoretical examinations outlined in this Appendix to qualify a bolted joint assembler.
  2. Review Organization: an independent organization that conducts quality control reviews of the Qualification Program. Guidance for selection of Review Organizations is provided in para. A-5.3.2.

The Organization should have their training reviewed by an Independent Review Organization to ensure that the content is correct. This DOES NOT mean by a good friend, or an organization that is not in the bolting industry! It is meant to be done by industry-known subject matter experts to make sure that the information being presented is correct and free from commercial bias.

A.1.2 – What are the definitions of all these terms?

  • Bolting Assembler: a person meeting the experience qualifications of para. A-2.2 who is engaged in the assembly of bolted joints in accordance with the recommendations contained in ASME PCC-1 but has not yet received training and qualification from a Qualifying Organization. This means that an individual hasn’t completed formal training but is preparing to do so. Below are the descriptions of what this individual should be prepared to learn and be tested on.
  • Senior Bolting Assembler: A person meeting the experience qualifications of para. A-3.1 who is engaged in the assembly of bolted joints in accordance with the recommendations contained in ASME PCC-1 but has not yet received training and qualification from a Qualifying Organization.
  • Bolting Instructor: A person meeting the experience qualifications of para. A-4.1 who is engaged in the assembly of bolted joints and the training of bolting assemblers in accordance with the recommendations contained in ASME PCC-1 but has not yet received training and qualification from a Qualifying Organization.
  • Bolting Trainee: A person undergoing training to become a Qualified Bolting Specialist.
  • Qualified Bolting Specialist: A person qualified by a Qualifying Organization as meeting the requirements of section A-2 of this Appendix.

A-2.2 – This section contains the items that an individual shall be trained on. There are several (listed below).

Qualification: they should know the items from A-2.2 – A.2.6

Experience: they should have previously had 6 months full time (or the equivalent). A sticking point for some companies is the fact that this section states, “The experience should be documented by references from Senior Bolting Assemblers, Qualified Senior Bolting Specialists, or Qualified Bolting Specialist Instructors indicating that the field experience obtained meets the requirements of this Appendix.”

Commentary: Since the industry is young and most companies have not recorded individual’s experiences in the field. A company should use their judgment to determine who should complete this training as a “rookie” would not be able to understand many concepts if they don’t have proper experience.

A-2.3 Training of Fundamentals: This part of the training is the “meat” of the information that a Qualified Bolting Specialist should know. There are roughly 150 academic items that are discussed in this section.

A-2.3.1 Piping Specific Training: This is training on how to assemble different types of pipe and what is important to each standard type. Some items discussed are: Raised Face, Flat Face, Ring Type Joint, etc. Issues often encountered when you assemble a Flat Face to a Raised Face flange.

A-2.3.2 Powered Equipment Training: This training is intended to make sure individuals are trained on more than just manual “clicker” type wrenches. Some of these include: Hydraulic Torque Wrenches and Stud Tensioners.

A-2.3.3 Heat Exchanger Training: This training is intended to train individuals on the different make ups of exchangers. Some of these include: Confined vs. non-confined gaskets; Shell to tube sheet vs. channel head to tube sheet gaskets.

A-2.3.4 Special Joint Training: This section is intended to be vague as there are special types of joint in different industries that individuals should be trained on for that industry. Some examples include:

  • Lens Rings – primarily in Nitrogen Plants
  • “Grayloc” flanges – primarily in “upstream” applications

A-2.4 Practical Examination: The demonstrations are designed to highlight significant aspects of the training curriculum and are to be performed in the presence, and to the satisfaction, of a Qualified Bolting Specialist Instructor. In addition, a practical examination of each candidate, requiring the assembly of at least two joints, shall be required.

Several different demonstrations by the trainee should be observed, and it is the Appendix’s recommendation that they complete at least one and observe the others (at a minimum).

  • Gasket placement
  • Joint alignment
  • Different Bolting Patterns
  • Bolting Patterns vs. Different Gasket Types

2.5 Duties: This section is brief but explains the expectations of what Bolting Specialists should be able to do in the field.

2.6 Maintenance of Qualification: This section gives examples of how a Specialist can pursue continual learning on their trade, and pass the “Training Fundamentals” testing every three years.

Qualified Senior Bolting Specialist: A person qualified by a Qualifying Organization as meeting the requirements of section A-3 of this Appendix. This section is more of an administrative section. Here are some highlights from this section to qualify for this position you must complete:

  • Two years as a Qualified Bolting Specialist
  • Take an active role in fixing bolting issues within plant(s) and can apply them in the field
  • Provide “on the job” training for bolting assemblers and trainees (A-3.2.1)
  • Maintain records on Bolting Specialists
  • Prepare procedures for trouble joints
  • Conduct on-site “introduction” to established bolting procedures
  • Spend 20% of their time in the field with Bolting Specialists

Qualified Bolting Specialist Instructor: A person qualified by a Qualifying Organization as meeting the requirements of section A-4 of this Appendix. This individual should have ample experience of not only “academic” teaching but field experience in order to relate to the assemblers that they are training. Many Vendors offer “training” and think that their individual should be teaching others. However, it is my experience that if you have not been on a turnaround and/or have worked in general maintenance in a plant, they will teach the concepts that only can be applied in “sterile” environments.

There are several items that need to be completed to achieve this:

  • Have 4 years’ experience as a Qualified Senior Bolting Specialist
  • Demonstrate administrative and problem-solving skills

Ready to improve your organization’s bolting program? Right now we’re offering online bolting training for Level 1 and Level 2 individuals, with enricher courses on Powered Equipment and Heat Exchangers. Start today and get access to all four here.

Spiral Wound Gaskets, Explained

What are Spiral Wound Gaskets?

A Spiral Wound Gasket is the most common metallic gasket used in industrial plants. A properly selected and installed spiral wound gasket can withstand high temperatures and pressures, preventing leaks throughout their intended lifespan. 

A spiral wound gasket consists of three elements:

  1. Outer ring. Made of carbon steel, this outer ring is sometimes called the centering ring or guide ring. It’s used to center the gasket when you insert it into a bolted flange joint. 
  2. Inner ring. The inner ring is pivotal for the gasket because it prevents windings from buckling inside the pipe. When a gasket buckles, parts of it get sucked into the pipe. From there, pieces of the gasket will typically flow through the pipeline until they get caught on something. Often, they’ll get wrapped around rotating equipment like a pump. The mess that results is known as a “bird’s nest.” Inner rings help you avoid this problem. 
  3. Sealing element. As you might guess from the name, the sealing element creates the seal that prevents leaks. A sealing element encompasses both windings and filler material. Most spiral wound gaskets in oil and gas refineries will use a flexible graphite filler material rated for high temperatures. A flexible graphite filler also allows the gasket to be more tolerant of flange distortion and joint misalignment. Polytetrafluoroethylene (PTFE) is another common filler material. PTFE is not rated for high-temperature applications, however. Meanwhile, most winding materials in refineries will be stainless steel and monel

Spiral Wound Gasket Markings

An illustration explaining the markings on a spiral wound gasket.

Spiral Wound Gaskets have several different markings on them. Each tells you something specific and important about the gasket itself. Starting from the top…

ASME B16.20 

At the top of a spiral wound gasket, you ought to see a marking that states “ASME B16.20.” this indicates the gasket is made to the ASME B16.20 standard, which is the standard governing metallic gaskets for pipe flanges (which includes spiral wound gaskets).  


First, the manufacturer’s name is usually positioned on the right-hand side of the gasket. This tells you who made the gasket. 

Winding Material and Filler Material

Indicates what the gasket is made of. Gasket color also tells you a lot about these materials — more on that in a moment. 

Diameter and Pressure class 

These markings tell you the size of the gasket, along with the load the gasket can handle. 

There are different pressure classes: 150, 300, 400, 600, 900, 1500 and 2500. Higher numbers indicate the ability to tolerate greater pressures. 

Spiral Wound Gasket Color Codes

A chart showing each color of spiral wound gaskets, and their corresponding material.

Colors play an important role on spiral wound gaskets. The color of the outside rim, and the color of the stripe along the rim, both are important indicators of the material within the gasket. 

  1. Outside rim colors indicate the gasket’s windings materials
  2. Rim stripe colors tell you the gasket’s filler materials 

For example, the following outside rim colors indicate specific windings materials: 

  • Yellow means 304 stainless steel gasket material. That means the inner ring and metallic windings are made of 304 stainless steel.
  • Green is 316 stainless steel
  • Turquoise is 321 stainless steel
  • Blue is 347 stainless steel
  • Orange means that it’s made out of Monel
  • Black is Alloy 20
  • Silver is carbon steel
  • Brown is Hastelloy B
  • Beige is Hastelloy C
  • Gold is Iconel
  • Red is Nickel
  • Purple is Titanium

NOTE: If you work in the oil and gas industry, most of the time you will see one of three colors: Yellow (304 stainless steel), Green (316 stainless steel), or Orange (monel). Monel is an alloy of nickel and copper that, in addition to tolerating high-temperatures, also is resistant to corrosion. 

Meanwhile, rim stripe color tells you the gasket has one of the following filler materials:

  • Pink indicates mica paper
  • Gray indicates graphite
  • White indicates PTFE
  • Light Green green indicates ceramic

NOTE: If you work in the oil and gas industry, most of the time you will see Gray, indicating graphite.

Why Spiral Wound Gaskets are in use

Spiral Wound Gaskets have been around since 1912, but they were not used regularly in industrial piping until the 1990s.  

On July 12, 1989, the EPA issued a final rule banning most asbestos-containing products. That included gaskets.  At the time, asbestos gaskets were used in applications under lower temperatures and pressures because they weren’t at risk for blowout under those conditions. Ring Joint Gaskets were used in the high-temperature (~500+ degrees Fahrenheit) and high-pressure applications. 

In the early 1990s, the petrochemical industry went in search of a type of gasket that would be  as effective as asbestos. Spiral wound gaskets were a strong option because they allowed the use of materials capable of handling the demands of the oil and gas industry. 

After about 5 years, the industry moved to make spiral wound gaskets the standard in ASME B16.20

An amendment to ASME B16.20 in May 2008 made the use of inner rings within spiral wound gaskets standard. The standard states:

“…Inner rings shall be furnished with all spiral-wound gaskets having PTFE (polytetrafluoroethylene) filler material. Inner rings for flexible graphite filled spiral wound gaskets shall be furnished unless the purchaser specifies otherwise. For all filler materials, inner rings shall be furnished in spiral wound gaskets for: a) NPS 24 and larger in Class 900 b) NPS 12 and larger in Class 1500 c) NPS 4 and larger in Class 2500 Inner rings are required for these gaskets due to high available bolt loads, which may result in outer ring damage.” 

The reason ASME B16.20 requires inner rings is because the flange faces create enough gasket stress that the additional compression causes the metal windings and filler material to push against the outer ring (also known as the guide ring).  

The outer ring is a solid piece of carbon steel. and the stainless steel windings are shaped in a “Chevron V” (refers to the shape, not Chevron the company). The shape aids in pushing the winding material to project into the inside diameter of the pipe. This will interfere with the process. If additional compression (roughly 22ksi gasket stress) is met, the metal windings will completely fail. Often, a “birds nest” (where the metal windings fall into the pipe and get tangled up) results.  The bad part about that is that they will travel until they reach some sort of rotating equipment and/or valve.   

Spiral Wound Gaskets are incredible gaskets for both piping (preferred gaskets in ASME B16.5 and B16.47 flanges). While the Kammprofile gasket gets a lot of attention for heat exchangers, spiral wound gaskets are also great for them.

Compressibility and recovery are what make spiral wound gaskets the best metallic gaskets for most flanges. They are now the metal gasket that has taken favor over Ring Type Joints for even high-pressure flanges including ASME B16.5 2500 series flanges.  

Installing Spiral Wound Gaskets: Things to Know

The outer ring is not a compression stop

While some manufacturers call the outer ring a compression stop, it  IS NOT.  If your gasket has enough seating stress to compress to the outer ring, you essentially have a flat metal gasket, which gives you little to no recovery for when your plant cycles and the flange faces move apart due to thermal expansion. 

Flange faces do not come down on the sealing element as flat as most people think. 

Flange faces actually rotate a little bit. What do we mean by rotate? If you look at the flange faces of a raised face flange the raised face is actually pivot point to a lever. The end of the lever is where the nuts are actually clamping down together. 

So what you do is you rotate your flange — i.e. you “bird mouth” your flange a little bit. Now they should bird mouth equally, but sometimes they don’t. One flange face typically bends to the other. 

This leads to what we call dishing. Some people have called it cupping, but the technical term is dishing. That’s when the outer ring bends down. 

Now there are a lot of conspiracy theories on this. Some people say, “Oh, It gets caught up in the bolt threads.” That’s not what happens at all. 

What happens is since the flange is rotating, it rotates maybe a degree or two. Depending on the length of your outer ring, that determines how much deflection you see at the end of it.

More on what to do when you see “dishing”

So let’s discuss some practical applications of when you see dishing. Let’s take a 2″ 300 and a 2″ 600 gasket. What gasket do you go grab when you need to assemble one of those flanges? You grab the same gasket. But what’s the difference between those two flanges? 

Well, the difference is the fact that a 300 has got 1/16″ raised face wall. The 600 has got a ¼” raised face, so what you’ve effectively done is quadrupled the height of your raise face, which makes it even a longer lever, which we will see more dishing on the 600 than you will on the 300.

Another place that we see this is on the 2500 and 1500 series flanges. That outer ring is so long that just one degree of rotation is exaggerated even further on those gaskets. So when this happens, an inspector will come by and say, “Hey, you over-torqued that flange. You need to go back and retorque it.” And as the assembler, we do that, and what happens? The exact same thing. This is a mechanical interaction. It is going to keep happening. Flange rotation is where the flange rotates, pushes on that outer ring just a little bit and you see dishing.

RELATED: Learn more about the gasket types used in the oil and gas industry.

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