Author: Scott Hamilton

Bolted Flange Joint Assembly: Learning the Technical Aspects

Last updated on by Scott Hamilton

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 Some of the material is outdated now, but they still are good reference material.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.

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Spiral Wound Gaskets, Explained

Last updated on by Scott Hamilton

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).  

Manufacturer

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.

The Stud Bolt Guide: B7s, B8s, B16s and More

Bolt Lubricant and Torque, Explained

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The Clicker Wrench Guide: Torque Ranges, Calibration and More

Last updated on by Scott Hamilton

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.

RELATED: 

Bolt Lubricant and Torque, Explained

The Myth About Bolt Yield

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Join Industry Leaders!

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Torque Calibration in the Lab and the Field

Last updated on by Scott Hamilton

Why Torque Calibration Matters

The torque wrench is the most-used product for achieving proper load on a fastener. Research shows all torque equipment — manual tools and power tools alike — requires calibration both upon purchase and periodically after use. They will not remain accurate infinitely throughout their lives.

Torque wrench calibration is a critical step in assembly, therefore, because even if you have a great process and skilled labor, your results won’t be good if you don’t have accurate tools.

In fact, the inaccuracies that can result from improperly set torque tools can be huge. We’ve seen in the field that, sometimes, wrenches will “click” at their target of 200 ft-lbs while being off by as much as 50 ft-lbs.

Usually these discrepancies are the result of damage during use. But that damage is often invisible, and therefore undetectable — unless you have some way of testing the tool’s calibration.

In this article, we’ll first review the essential practices of torque calibration. We’ll then discuss common torque tools used in industry, including manual torque wrenches and powered equipment (hydraulic, pneumatic, and battery torque wrenches). Then we will discuss methods for the field verification of these torque tools.

There are some new torque testers that are great for torque applications in the field. We will also discuss the frequency of torque wrench calibration and give you a brief explanation of how it works.

NOTE: The examples of equipment and manufacturers are from our experience only. There might be other options found in the industry.

Torque Tools Calibration: The Basics

All torque tools need to be calibrated by a calibration lab. However, since there is no standard for torque wrench calibration for Powered Equipment, and all torque wrenches experience uneven use, Hex Technology has done research on how to verify your torque wrenches repeatable accuracy while using field testing equipment.

It seems that anyone who performs torque calibration services would verify their calibration lab and methods, but Hex Technology has found that most manufacturers do not verify the calibration process of their employees and distributors. While these companies have NIST traceability on their torque transducers, they often don’t know how the tool actually stalls on the torque application.

It is not hard to do with either a micrometer on a standard fastener (measuring lbf vs. load), force gauges (like a Skidmore) with a fastener, or create their own torque sensor that has been verified. Some manufacturers have done this, but others are behind the curve.

Therefore, while we do not sell these products, Hex Technology recommends verifying your torque calibration service providers with the following methods.

Manual Torque Wrenches

Manual Torque Wrench Calibration Guidelines

Manual torque wrenches or “clicker wrenches” are the most common torque products in the marketplace, the most accurate type of torque wrenches, and have a standard to calibrate to (unlike powered equipment).

The manual torque wrench should not be used when you’re trying to achieve torque over 600 ft-lbs of torque. There are 1000 ft-lb and 2000 ft-lb clicker wrenches are available in the marketplace, but those are beasts for assemblers to use. So please use no greater than 600 ft-lbs.

The accuracy of clicker wrench torque products is between 3 and 5% depending upon the manufacturer. They shall be calibrated every six months per ISO 6789, “Assembly Tools For Screws And Nuts – Hand Torque Tools – Part 2: Requirements For Calibration And Determination Of Measurement Uncertainty.”

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 after use, the load in the spring mechanism inside the torque wrench will get damaged and your torque wrench will need calibration yet again.

There are many different manufacturers of these wrenches but the ones that we have tested and have worked well are CDI (a Snap-on company), Mountz, and Proto.

Field Calibration for Manual Torque Wrenches (i.e. Clicker Wrenches)

We typically use the NORBAR torque testing equipment (we call them clicker checkers) at the beginning of shifts or use to ensure that the torque wrenches are within +/-5% within their stated torque target. If the wrench does not meet these criteria, you should send it in to your calibration lab for examination. When using these clicker checkers, note that the assembler can have a big effect on its accuracy, so a little training on how to properly use clickers should be a part of this process. We offer free online training for assemblers here. 

Finally, for recalibration, ISO 6789 states that you shall calibrate these tools once a year, regardless of how much (or how little) you may have used them.

Powered Equipment

Electronic torque wrench

The Electronic torque wrench is fairly new to the marketplace. While more expensive than manual torque wrenches, electronic torque wrenches feature a digital display with buttons, so that the predetermined torque value is effortless.

These torque wrenches usually feature ratcheting square drives and many times also include a flexible head. The wrench can make a variety of different indications when the desired torque is met. It can beep and turn colors to alert you. The only thing missing is the old man on your crew sitting behind you saying, “Stop, stupid.”

These wrenches have been seen to be more fragile than typical manual torque wrenches. They are also susceptible to the same damage mechanisms (dropping, etc.).

Hydraulic Torque Wrench (low profile and square drive)

Hydraulic Torque Wrench Calibration Guidelines

The hydraulic torque wrench has been around for a long time and was commercialized by Hytorc in 1968. Since then many other manufacturers have emerged, including Torsion X, BoltTech Mannings, and Enerpac.

These torque wrenches can do up to 180,000 ft-lbs and all the way down to 50 ft-lbs. They come in two styles: low-profile and square drive. Most manufacturers claim to have a +/-3% accuracy (of the full scale of the wrench) with 2% repeatability.

When repair services are completed on hydraulics they shall be recalibrated, according to standard, as it will affect accuracy.

Pneumatic Torque Wrench

The pneumatic torque wrench was commercialized by New World Technologies (RAD Torque Tools) 25 years ago and these are gear boxed torque multipliers. These were a step up in speed and ease of use since they weren’t attached to a hydraulic torque wrench pump.

Now there are other manufacturers — Hytorc, Mountz, NORBAR, and many more.

These torque wrenches can produce up to 15,000 ft-lbs and can also go to 50 ft-lbs. They are all square drive tools and claim to have a +/-5% accuracy (of full scale of the wrench) with 2% repeatability.

These are always re-calibrated after repair but you should ensure that they are with your chosen calibration lab.

Battery-Powered Torque Wrench

Pistol Grip Torque Wrench Calibration Guidelines

Our first experience with these was in the early 2000s with RAD Torque Tools in their earlier form. Today, the major manufacturers in the pneumatic marketplace are also making these torque wrenches.

These torque wrenches are becoming far more common in torque application. They are easier to use than pneumatic torque wrenches because they don’t need a basket and air hose to run the motor. Because their use is becoming more widespread, it is critical that the industry understands them better.

These torque wrenches are very sensitive to how stiff the torque application is. Meaning, they perform differently on gasketed torque applications than they do on structural steel torque applications.

They can produce up to 10,000 ft-lbs, but also go down as low as 100 ft-lbs. They are also square drive tools that claim to have +/-5% accuracy (of the full scale of the wrench) with 2% repeatability.

These torque products need to be calibrated after every repair. Thankfully, it’s easy for calibration labs to adjust them.

Calibration for Powered Equipment

Strange but true: There is NO calibration standard in the marketplace for Powered Equipment. Therefore, just because a calibration lab states that they are ISO/IEC 17025 Accredited, it does not mean they know how to calibrate tools correctly. They just follow their procedure. It’s very much like ISO 9000 accreditation. Their torque transducers can simulate either the stiffness of a structural steel joint or a gasketed joint (which is softer). But which are they using?

So we have found that if you want to test a wrench in a lab or shop you can use NORBAR torque sensors which will allow you to verify that your wrench is within +/-10% accurate. This accuracy is acceptable for torque wrench verification.

If you would like to test your tool on an actual torque application, we have used the RAD Smart Socket. This will fit on any size square drive and they make it for different size nuts.

To use the Smart Socket, you just insert your square drive into the socket, turn it on and apply your torque. It will read the torque value and as long as you are +/-10% accurate, you can consider that a win for torque verification.

RELATED: 

The Clicker Wrench Guide

K-Factor: How to Use and Understand This Essential Calculation

PTFE Coated Studs: Do They Work? 

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The Stud Guide: B7s, B16s, and Other Common Bolt Materials found in ASME Pressure Vessels and Piping

Last updated on by Scott Hamilton

At first glance, the names of fasteners used in bolting for ASME pressure vessels and piping can sound like something out of the old-school board game “Battleship.”

B7, B8, 2H, A193..dangit, you just sunk my destroyer.

Each of these labels are meaningful, and can indicate the use of different materials (such as alloy steel or stainless steel) with different mechanical properties.

The names also indicate which will perform better in certain environments, such as high-temperature and high-pressure applications.

In this article, we’ll discuss several different relevant aspects of these fasteners, including:

  • tensile strength
  • stainless steel (grade B8) vs. carbon steel (grade B7 & B16)
  • heavy hex nuts (2H nuts, or Grade 4 & 7 nuts)

But we’ll start with an overview of the standards governing the use of nuts and bolts in industrial applications.

Summary of Standards for Common Fasteners

Industrial fasteners can be called stud bolts or — of course — just plain ol’ bolts. They are governed by three main industry standards:

  • ASTM A193: “This specification covers alloy steel and stainless steel bolting material for pressure vessels, valves, flanges, and fittings for high temperature or high-pressure service, or other special-purpose applications. Ferritic steels shall be properly heat treated as best suits the high-temperature characteristics of each grade.”
  • ASTM A320: “This specification covers alloy steel bolting materials and bolting components for pressure vessels, valves, flanges, and fittings for low-temperature service.”
  • ASTM A194: “This specification covers a variety of carbon, alloy, and martensitic and austenitic stainless steel nuts. These nuts are intended for high-pressure or high-temperature service, or both.”

NOTE: Items that we will not cover in this article include: coating practices such as zinc plated, PTFE or Xylan(R) coating, hex bolts, or hex cap screws or machine screw nuts and coupling nuts found in ASME B18.2.2, as these have nothing to do with industrial bolting.

Stud and Nut Combinations

B7 Studs and 2H Nuts

ASTM A193 Grade B7 bolts are made of chromium-molybdenum steel. The bolts are quenched and tempered (a.k.a heat treated) to develop the desired tensile strength (mechanical properties).

Grade B7 Stud Bolts are used in pressure vessels that do not need corrosion resistance, aren’t susceptible to stress corrosion cracking, and for temperatures typically less than 750F. However, these bolts can have many different types of finishes, including:

  • plain finish for standard applications
  • hot-dip galvanized process
  • zinc plated and/or have a PTFE or Xylan coating for corrosion resistance

NOTE: Typically a coated stud will have a lower temperature rating than plain finish stud bolts. (See our article “PTFE Coated Studs: Do They Work?” for more.)

Size and strength:

  • ASTM A193 B7 stud bolts with a diameter of 2.5 inches or less will have a yield strength of 105,000 PSI.
  • Grade B7 fasteners with a stud diameter of 2-5/8″ to 4″ diameter have a lower yield strength of 95,000 PSI.
  • 4″ to 7″ inch stud bolts have an even lower yield strength of 75,000 PSI.

The nut material for Grade B7 bolts is typically ASTM A194 heavy hex nuts (2H nuts).

Various bolts a bolting assembler must identify.
This is supposed to be a stack of B7s on a job site. Can you find the B16 mixed in?

A194 Grade 2H Nuts

2H nuts work in combination with B7 Studs and are stronger than the stud bolt. Therefore you should see failure on the stud before you see failure in the nut.

NOTE: This does not include over tapping of the nut for coated materials as it would change the strength of the nut.

2H nuts, also known as Heavy Hex Nuts, are very common in the industry and easy to procure.

Grade B7M Studs and Nuts

ASTM A193 Grade B7M studs are identical in chemistry to Grade B7, as they are quenched and tempered carbon steel to achieve a lower hardness. However, they have a lower tensile strength than B7 studs.

We typically see Grade B7M bolts in hydrogen stress corrosion cracking (SCC) applications such as hydrofluoric acid or in Floating Head Heat Exchangers.

ASTM A194 GRADE 2HM are similar to 2H nuts, except this grade is recommended for use in stress corrosion cracking environments.

Grade B16 Studs

ASTM A193 B16 stud bolts are used primarily for high temperature applications of 751-1100F. They are manufactured from a chromium-molybdenum-vanadium alloy steel,

Although A193 Grade B16 bolts and studs have similar strength requirements as Grade B7, the fasteners retain strength under high temperatures, and also experience less relaxation at those high temperatures.

There are two nut combinations you can use for B16 stud bolts. They are:

  • ASTM A194 GRADE 7: These are also heat-treated chrome-molybdenum steel nuts that are also suitable for sub-zero service conditions and have minimum Charpy impact values in accordance with ASTM specifications.
  • ASTM A194 GRADE 4: These were taken out of ASTM A194 in 2017, but were heat treated molybdenum steel nuts.

It is imperative that you use Grade 7 (or 4) nuts with B16 studs, because they have similar properties. 2H Nuts, on the other hand, will relax more. So if you have high temperature and 2H nuts you will see increased relaxation, or loss of bolt load. (Not sure how to handle bolt relaxation? Contact us. We can help.)

B8 Studs Class 1 and Class 2: What’s the Difference?

ASTM A193 B8 studs are commonly used in high temperature applications (roughly 1101F to 1500F) . However, you have to be cautious because there is a difference between B8 Class 1 and B8 Class 2 studs.

Grade B8 stud bolts are made of AISI 304 stainless steel. These type of fasteners are made with austenitic stainless steel and require carbide solution treatment.

The carbide solution treatment, also known as solution annealing, is the process in which fasteners are heated and then water-quenched to assure maximum corrosion resistance.

Class 1 stud bolts are not strain-hardened, and have a yield strength of 30 KSI, or 30,000 PSI. However, Class 2 stud bolts are strain-hardened and have a 95,000 PSI or 95 KSI yield strength.

How can you tell a Class 2 versus a Class 1 bolt? The B8 symbol on a Class 2 will have a line underneath it, while a Class 1 will not have an underline. Please look for the line on a B8 class 2.

ASTM A194 GRADE 8 Stainless steel nuts required for these fasteners.

B8M Studs

ASTM A193 Grade B8M fasteners are manufactured the same way as B8 fasteners. The difference is in the materials that they are made of.

B8M fasteners are manufactured from AISI 316 stainless steel as opposed to AISI 304 stainless steel. The 316 form of stainless steel is better for corrosion resistance because it has more molybdenum.

ASTM A193 Grade B8M Class 1 fasteners require a carbide solution treatment, while Class 2 fasteners require an additional strain hardening just like B8 fasteners.

ASTM A194 GRADE 8M Stainless steel nuts are required for these fasteners.

ASTM A320, Grade L7 and Grade L7M

ASTM A320 Grade L7 and L7M fasteners are recommended for use in low temperature environments typically found to be -50F to -150F. These fasteners also require Grade 4 or Grade 7 nuts.

RELATED:

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

The Myth About Bolt Yield

A Guide to Bolt Lubricant and Torque

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