Torque Tool Calibration and Verification

Hex Technology conducted a torque tool calibration and verification study with a small refinery. In this study, we analyzed the different types of torque tools used during a turnaround and the accuracy of the calibration process. We concluded that regular verification of calibration in torque tools may be a necessary part of the QA/QC process.

  1. What is Torque Tool Calibration and Validation?
  2. Frequently Used Terms when Discussing Torque Wrench Calibration and Validation
  3. Development of the Calibration and Torque Wrench Verification Knowledge
  4. What Torque Tools are Being Used in the Industry?
  5. How Often Should I Calibrate a Manual Torque Wrench?
  6. How Often Should I Calibrate our Power Tools?
  7. How did Hex Come to These Conclusions for Torque Validation?
  8. Method of Verification 
  9. Torque Verification Recommendations
  10. Conclusion

What is Torque Tool Calibration and Validation?

Calibration of torque wrenches is critical to the reliability of bolted flanged joints when using torque measurement to achieve axial load on a fastener. While ISO 6789 has a proven method of calibration for manual torque wrenches (commonly called “clicker” type torque wrenches), there is no current popular method of calibration for “Powered Equipment” seen in the industrial world. 

These power tools include pneumatic torque wrenches & battery torque wrenches (we consider these pistol grip torque multipliers) and hydraulic torque wrenches. These torque wrenches typically have a torque range from 500 ft-lbs to 5000 ft-lbs. 

Torque validation is when we double-check the accuracy and repeatability of the torque setting on a given torque wrench. We can also use this validation process to audit and examine calibration labs and service companies. 

Note: We do not talk about torque screwdrivers, metrology used for calibration, and what adapters do to change the torque value. 

Frequently Used Terms when Discussing Torque Wrench Calibration and Validation

There is some dirty laundry that we should wash out before we get to the remainder of this paper. Here are some words that calibration labs and service companies who provide torque wrench calibration fly around:

  • ISO 6789 is a calibration standard but only applies to manual torque wrenches. It DOES NOT address Powered Equipment. But it is solid for manual torque wrenches and is commonly used by calibration service companies. 
  • ISO/IEC 17025: The ISO website says, “ISO/IEC 17025 enables laboratories to demonstrate that they operate competently and generate valid results, thereby promoting confidence in their work nationally and worldwide.”
    • Note: Just because a calibration lab has this accreditation, it does not mean that they calibrate the torque wrenches correctly! It just means that they are doing what they say they are doing…even if it isn’t correct.
    • Shocking fact: Most torque wrench manufacturers do not have a calibration standard for their torque tools that they impose on calibration labs! So how can you judge the “valid results”? Only through proper validation of the procedures, which we have not seen much of in the industry. 
  • NIST Traceability: Calibration labs will have torque transducers with a certification for NIST (National Institute of Standards and Technology). While this is important, it means that the torque transducer has been calibrated correctly by proper calibration equipment, not that the actual torque wrenches have been calibrated correctly. 
  • Calibration Certificate: These are great to have, and typically calibration laboratories do a great job on the technical aspects of what they know. They include the NIST traceability of the torque transducer, the confirmation of applied torque achieved, and all the ISO/IEC 17025 accreditation details. But again, how did they develop their calibration methodology, considering there is no standard for power tools? Have they ever put their methods to test on a fastener? 

Development of the Calibration and Torque Wrench Verification Knowledge

Multiple papers have addressed the different aspects of calibration for Powered Equipment, and we list them at the end of this paper.

The questions that we have not been able to answer through previous tests that we were looking at answering with this test are:

  • What types of torque equipment are used within the petrochemical industry, and what frequency? 
  • What is the calibration or torque testing frequency that each wrench should undergo?

While each plant and industry are different, this paper will address these questions based on over 8,000 data points from a refinery turnaround and feedback from manufacturers of power tools.

What Torque Tools are Being Used in the Industry?

In a previous YouTube video we made, we went in-depth about the most used torque tools in the industry during turnarounds. We gathered information from some of our clients that oversaw turnarounds at their plants. 

We discovered in that research that 80% of torque tools used during the turnaround were square drive manual torque wrenches and pistol grip tools (pneumatic and battery-powered). 

20% of the tools used in that study were the hydraulic torque wrenches, including square drive and low profile tools. We are going to concentrate on the 80% as of now!

How Often Should I Calibrate a Manual Torque Wrench?

ISO 6789 states that manual torque wrenches shall be calibrated once every 12 months. But our previous studies have shown that roughly 60% of manual torque wrenches will be out of calibration at the end of 12 months. 

How many fasteners did that torque wrench touch while out of calibration? There is no good way to tell. 

Therefore we found that there are torque testers that you can deploy either in your shop or out in the field to validate the torque values! And they are not too expensive.

The one that we have the most experience with is the NORBAR TruCheck. They have several models out there, but our recommendation is to get one that will do roughly 500 ft-lbs so that all of your manual torque wrenches can be validated.

NORBAR TruCheck verification tool

Another torque verifier that we have found works great to verify powered equipment or can even be brought into the field to verify the accuracy of torque on the flange is a Smart Socket.

Powered Equipment verifier
  • Note: Hex Technology does not get paid if you buy these. This info is what we have found to help out our customers. If you know of another one that we should look into, please contact us at [email protected]

How Often Should I Calibrate our Power Tools?

Until the industry standardizes on a calibration verification method, End Users can use the tools to assess/audit their suppliers to see if their accuracy and calibration method are enough to meet its requirements.

We have found that any method of calibration or verification should be compared with the flange setup that has been written about in previous papers.

How did Hex Come to These Conclusions for Torque Validation?

In the past, the Maintenance Manager from a small Midwest refinery had allowed each contractor for a turnaround to bring their own torque tools for use. After working with Hex Technology for the past three years on the accuracy and repeatability of torque wrenches, they decided that their refinery would supply all the torque wrenches for the turnaround to improve calibration consistency.  

Two central tool trailers were set up in the refinery, one of which was for the hydrofluoric acid (HF Trailer) plant, and the other was for the rest of the plant (Main Trailer), which a chosen vendor staffed. The HF trailer data is not included in the findings here as they were primarily clicker-type wrenches, and this study focuses on Powered Equipment.

The Main Trailer was equipped with transducers to work on manual “clicker” type (clicker) wrenches and hydraulic wrenches.

The pneumatic and battery-powered torque wrench vendor provided a new calibration system for pneumatic, and battery-powered pistol grip wrenches developed from the previous testing results with Hex Technology.

Method of Verification 

During the turnaround, there were two 12-hour shifts over 24 hours. Pipefitters checked out the torque tools during the shift. The pipefitters returned the torque tools at the end of the shift. We tested them on either the torque transducer (hydraulic and clicker wrenches) or the new calibration system (pneumatic and battery wrenches).

We tested all the torque tools at 30%, 60%, and 90% of their total output; we recorded the data daily. If the wrench failed one of the test ranges, it was re-calibrated and put back on the shelf for subsequent use. If the torque tool passed all three test ranges, it was also put back on the shelf for subsequent use.

The turnaround lasted 5.5 weeks, with over 8,000 calibration data points.

Breakdown of Wrench Type and Failures

Breakdown of Torque Tool used in a Turnaround
  • 49% of all wrenches used were pistol grip tools. This was higher than what we expected.
  • 36% were clicker wrenches. This was lower than what we expected.
  • 14% were low-profile hydraulic wrenches. This was lower than we expected.
  • 1% were hydraulic square drive wrenches. This was surprisingly lower than we expected. 

The hypothesis going into the turnaround was that the clicker wrenches would be roughly 60%, while the pistol grip and hydraulic wrenches would split the remaining 40%. However, the data shows that the pistol grip wrenches alone consisted of 50% of the total use. 

After discussions, we determined that there was plenty of battery and pneumatic torque wrenches, and the assemblers found them easier to use than clicker wrenches. This led to higher usage of pistol grip wrenches instead of clicker wrenches.  

Breakdown of Torque Wrench Usage

Amount of Failures Per Each Type of Wrench: Failure was determined if it did not meet +/-5% of the test fixture’s target torque associated with the tool. If the wrench failed one of the three settings, it was considered a failure and re-calibrated.

The above table shows the % of failure per wrench Model and the tool model type. Some tools had less than ten uses, so they should be ignored as, statistically, we don’t have enough data to determine if the failure rate is accurate.

Note: Hydraulic Square Drive tool data is omitted as none of the sizes qualify for 10+ times of use.

Percent Failure Rate Per Type of Wrench

Failure percent of each type of wrench tested

The above table shows that the wrenches did not meet the +/-5% criteria; however, most failures were within +/-10% of our criteria. We found only one tool that was grossly out of calibration.

After further reviewing the battery data, we found that most of the failure rate occurred on the 30% setting. If we removed the 30% setting test from the failure data, the failure rate would be 7.2%. 

In other testings, the accuracy of powered equipment has inherent inaccuracies when set to <20% of torque output. This is why the lowest test settings we conducted were at 30%. However, failure rates that occurred at 30% were only 2-5% off our target +/-5%. This data reinforces that the Powered Equipment’s final passes should be 30-90% of the torque wrenches output.

Torque Verification Recommendations

Hex Technology and the refinery have noticed that “torque verifiers” would suffice as a substitute to a complete re-calibration of the tools. The Torque verifiers we used for square drive tools can handle up to 5,000 ft/lbs of torque. 85% of the tools used in this turnaround could undergo torque verification. 

The NORBAR TruCheck that we have mentioned earlier is great for this kind of torque verification. This device was used in the turnaround to verify that the wrench is accurate and to remind the assembler that this is a precision instrument and to use it correctly.

Smart Sockets can also be used to verify the accuracy of torque with powered equipment on the flange.


It has been noted from previous research that manufacturers do not supply calibration specifications for their Powered Equipment Torque Wrenches, and there is not an industry standard for calibration of these wrenches. This is not good for the bolting industry as it can cause discrepancies in the target torque that translates to bolt/gasket stress that End Users require.

It should also be noted that there is no method of determining the frequency of re-calibration as roughly 5% of all wrenches will be out of calibration during a turnaround, which we would consider moderate usage.

It is good practice to incorporate torque verification tools to ensure that you are using properly calibrated equipment.

Until the industry standardizes on a calibration verification method, End Users can use the tools to assess/audit their suppliers to see if their accuracy and calibration method are sufficient to meet its requirements. We have found that any method of calibration or verification should be compared with the flange setup that has been written about in previous papers.


We want to thank the following companies for assistance in this paper:

RAD Torque Systems for support with torque verification methods and tools.

Torque Tools Inc. for support gathering this data.

C&S Technology for helping put this idea together and collecting the initial data.


Importance of Calibration (2011): “The analysis of data performed for this paper has also demonstrated the usefulness of the calibration procedure in detecting wrenches that should be repaired or replaced. For the manual and hydraulic wrenches studied, several had test results after calibration in excess of 10% above or below the target torque.” [2]

Justification for one standard of calibration (2012): “There are many misconceptions within the industry of when, how, why, by what standards, in what time-frame and by what definition calibration should occur.” [3]

Is there a difference in practical application on performance of Powered Equipment vs. the manufacturers claim for accuracy and repeatability (2017): “None of the tested equipment met its manufacturer’s accuracy claim and only Tool A pneumatic used on the NPS 8 flange met the manufacturer’s repeatability claim. Of the two twin tool sets tested, both sets showed a 7-10% difference in accuracy between twin tools.” [4]

Reinforcement of calibration verification method of using actual flanges for verification process (2018): “Powered torque wrenches (hydraulic and pneumatic) all trended approximately 5% to 30% low on final bolt load. This agrees with the results of last year’s testing presented in PVP2017-65800 “Determining Accuracy and Repeatability of Torque through Powered Equipment” but brings up the question of why powered tools have consistently provided low bolts loads in two separate studies.” [5]

It was confirmed that manufacturers can adjust their calibration methods to achieve better accuracy on actual flanges instead of transducers (2019): This work, along with the studies of the past two years, has provided a workable method to validate calibration of powered equipment through performance testing. In our case, the process of checking the tool’s performance on four different size/pressure rating flanges and checking bolt stresses with a bolt load gage as an indicator provided a good indication of each tool’s performance.” [6]

Corrugated Metal Gaskets, Explained

Corrugated Metal Gaskets (CMGs) are gaskets that we see a lot in heat exchangers where we see plenty of radial shear. Typically, we suggest the use of Kammprofile Gaskets in heat exchanger applications, but but because of the volume of use that we see in applications, we’re going to cover the details of Corrugated Metal Gaskets.

What is a Corrugated Metal Gasket (CMG)?

Breakdown of a Corrugated Metal Gasket

Corrugated Metal Gaskets can be used in specialty flanges such as heat exchangers. Still, CMGs should not be used in piping flanges (standard ANSI flanges) without proper engineering consideration. Even with engineering consideration, we still suggest using better sealing products such as spiral wounds or kammprofile gaskets instead of corrugated metal gaskets!

They’re a sheet of metal that’s manufacturers corrugate to make the corrugated metal core. The gasket should be used with a soft facing which essentially means flexible graphite (that’s what the gasket companies call it, we call it graphite), or another filler material like PTFE on each side.

The corrugated metal core can be made with regular gasket materials such as carbon steel, 304 stainless steel, 316 stainless steel (if you need to go to higher temperatures), and other high-temperature materials.

The filler material typically has a have graphite facing. Other non-asbestos fillers can be adapted to this gasket, but in petrochemical applications, we only see the graphite facing.

While we are not overly familiar with the use of corrugated metal gaskets outside of petrochemical applications, many companies state that these are also made with compressible sealing elements designed to resist high temperature, corrosive chemicals, and thermal cycling.

Note: We will not be discussing – Ring Joint Gaskets (RTJs), elastomeric gaskets, compression packing, o-rings, gasket sheets, and plain graphite gaskets. If you would like to know more about these kinds of gaskets, click here.

Where not to use CMGs?

Unfortunately, some manufacturers recommend corrugated gaskets for pipe flanges instead of spiral wound gaskets. These applications are not a good idea, especially for ASME B16.5 flanges. 

They are not considered superior sealing products to spiral wound gaskets because they are not as resilient to thermal cycling. This is because the recovery in a spiral wound gasket is better for pipe flanges, and CMGs are not commonly used as sealing products for these flanges.

There have been papers about how the graphite sealing element will blow out when thermal cycling, and there is no recovery. With a spiral wound gasket, the graphite sealing element is packed between the windings, and there is a better chance of re-sealing the flange.

What are the Best Uses for a CMG?

We see CMGs and kammprofile gaskets in heat exchangers and some expansion joints in petrochemical applications. The CMG is suitable for heat exchangers and expansion joints because they’re good at resisting radical shear and have a bit of compressibility and recovery.

And they would be an upgrade to double jacketed gaskets, but most petrochemical sites will standardize on kammprofile gaskets as their choice for heat exchangers especially.

Radial Shear example
Radial Shear

We see these applied in exchangers because they’re good at radial shear because of their compressibility and recovery due to the flexible graphite. 

These are good for high temperature & high-pressure exchangers since they can take 45ksi gasket stress. Of course, you would need to calculate your bolt load using ASME PCC-1 Appendix O to make sure you don’t overstress these gaskets. 

CMGs did a great job filling the void back when double jacketed gaskets were the preferred gasket for heat exchangers, as kammprofile gaskets were too expensive. Manufacturers since then have done a great job in reducing the price of kammprofile gaskets over the last twenty years, making the price difference between them and CMGs negligible. Today, we see CMGs being used less and less due to kammprofiles. 

For more information on this subject, please email us at [email protected].

Galvanized Steel Fasteners & Other Corrosion Resistance Coatings

Galvanized vs other corrosion resistance coatings. We talk about the difference between galvanized and black oxide coatings. Click here to read about PTFE studs!

  1. Where do you See Galvanized Steel Fasteners?
  2. What is Galvanization?
  3. What Type of Galvanized Process is Common?
  4. What is the Difference Between Galvanized Steel and Bolts Coated with Black Oxide?

Where do you See Galvanized Steel Fasteners?

Galvanized Fasteners have been in the industrial world for a long time, and I had no clue what to do with them! We see them as fasteners that we can use with flanges, standard fasteners (metric and imperial sizes), Hex Bolts, and Hex Nuts.

But here are some facts that I didn’t know:

  • We don’t see them on flanges as much as we see them on everyday items such as Eye Bolts, U-bolts, structural bolts, carriage bolts, lag screws, rivets, washers, and even self-tapping studs more often than not.
  • We see Grade A and Grade 2 are the most common grades of zinc-plated alloy steel for galvanized bolts and galvanized nuts (which looks like a yellow zinc coating). But while not very common it is a practice to galvanize “black bolts” or regular B7 material.
  • While galvanized steel fasteners are high-strength studs that have the same tensile strength as regular studs, they have, from what I have been told, high corrosion resistance and higher durability with corrosion resistance and rust resistance.
  • Apparently, over time galvanized fasteners have corrosion resistance around chlorinated water. Still, stainless steel (or other high alloy steel) is better for corrosion resistance around saltwater and other marine environments.
  • Galvanized steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel. The higher price for stainless steel fasteners and stainless steel nuts comes from the process of making stainless.
  • Stainless steel bolts are formed when the raw materials of nickel, iron ore, chromium, silicon, molybdenum, and others, are melted together.

But our biggest lesson on hot-dip galvanized steel fasteners this year is that you MUST lubricate them! From our testing, the K-factor without lubrication is all over the board.

Galvanized Studs Lubricated vs Dry K-Factor

You can see in the image above that you have a high k-factor with a lot of bolt scatter if you do not lubricate them properly!!

If you would like more information on k-factor testing of galvanized fasteners, please contact us at [email protected].

What is Galvanization?

So what is Galvanization?

Wikipedia states that galvanization or galvanizing is applying a protective zinc coating to carbon steel or iron for corrosion resistance. The most common method of galvanization is hot-dip galvanizing, in which the parts are submerged in a bath of a molten hot layer of zinc.

Hot-dip galvanizing is done by placing the fastener in molten zinc at 842°F, and “the pure zinc (Zn) reacts with oxygen (O2) to form zinc oxide (ZnO), which further reacts with carbon dioxide (CO2) to form zinc carbonate (ZnCO3)” – Wikipedia.

What Type of Galvanized Process is Common?

Everyone I dealt with for galvanized fasteners in flanges states that you should use only one type of fastener: Hot-dip galvanized steel.

So the first question racking my brain is how many different types of galvanizing are there?

There are different types of galvanization, including:

  • Hot-dip galvanization – immersion of the item in molten zinc
  • Continuous galvanizing is a form of hot-dip galvanization, but it has a thinner zinc layer and less corrosion resistance.
  • Electroplating – using the item and zinc metal as electrodes in an electrochemical cell

FYI: ASTM F2329 is the specification covering hot-dip galvanized fasteners, and ASTM F1941 is the specification covering zinc plated fasteners.

What is the Difference Between Galvanized Steel and Bolts Coated with Black Oxide?

Black Oxide is the converting of a ferrous material with a chemical treatment. Treating fasteners with a black oxide coating adds a soft layer of corrosion resistance.

Black Oxide Corrosion Resistance Coating

We talked with a fastener manufacturer, and they stated that most fasteners come from overseas, so this black oxide is used more for rust resistance.

Apparently the studs sit on a dock in Asia for a month, travel overseas for three months, sit on a dock in America for one month, then come to the plant and sit on the shelves for 3+ months. Because of this shipping process, you can start to see some rust, so manufacturers added black oxide for rust resistance. 

So if you have silver studs, they are most likely made in the USA, while the black oxide studs are made overseas!

From what we have been told, black oxide is not great for corrosion resistance, and that is why you use galvanized steel. However, for regular rust resistance, black oxide is excellent!

We did a study on the k-factor difference between lubricated black oxide and lubricated bare steel fasteners and found no significant k-factor difference between the two!

Other Corrosion Resistant fasteners box and whisker chart

Relaxation Pass in Bolted Flange Joints

Discussing the effectiveness and necessity of relaxation pass and start-up re-torque procedure according to industry research over relaxation behavior. 

  1. Where do “Relaxation Passes” and “Start-up Re-Torque” (Hot torque) Tightening Procedure Come From?
  2. What do we Know About Bolt Stress Relaxation in Gasketed Flange Connections?
  3. Do you Lose Bolt Preload or Bolt Stress at All?
  4. Average Bolt Stress Relaxation After Bolt-Up
  5. What is Gasket Relaxation: Gasket Creep with PTFE Gaskets and Sheet Gasket Materials?
  6. Does Relaxation Happen on High-Temperature Flange Connections?
  7. Conclusion

What are “Relaxation Passes” and “Start-up Re-Torque” (Hot torque) Tightening Procedures?

Relaxation passes and start-up re-torquing procedures are used in specifications to help prevent leakage and increase sealing performance in ANSI pipe flanges, heat exchangers, and other pressure boundary joints.

Relaxation Pass: This is a circular torque pattern on a bolted flange joint assembly at the same torque value as the initial bolt torque, performed after a specific time. 

Note: We typically perform this on a gasketed flange at ambient temperature and steady-state.

Start-Up Re-Torque (formerly known as hot torque): This is also a circular torque pattern on a bolted flange joint assembly at the same initial bolt torque value as it was assembled to, only done between 250F-450F. Be sure not to do this at high temperatures since the K-Factor (some mistakenly call this “coefficient of friction”) changes after 450F!

NOTE: Since there was confusion in the industry between hot bolting and hot torquing, ASME PCC-1 has modified the name of this process to ensure clarity between the two. 

So, when do you perform a relaxation pass and start-up re-torque (hot torquing)? Are they worth every penny? 

What do we Know About Bolt Stress Relaxation in Gasketed Flange Connections?

Hex started learning about bolt stress relaxation when we first read John Bickford’s “An introduction to the Design and Behavior of Bolted Joints.” John Bickford, being the grandfather of bolting. 

We noticed first in the top paragraph that Bickford states experiments should be done before making a specification. 

Article excerpt describing relaxation in bolted joints
Taken from Handbook of Bolts and Bolted Joints – John Bickford

Bickford states structural steel bolts showed a loss of 11% of preload immediately after tightening and another 3.6% and the next 21 days, followed by another 2% over the next 11.4 years. 

NOTE: This applies to structural steel and not a gasketed flange joint! 

If you go down further, Bickford states that the Southwest research Institute suggests that fasteners lose an average of 5% of preload right after tightening in quotes “because of elastic recovery” (this shouldn’t be confused with elastic interaction). 

Do you Lose Bolt Preload or Bolt Stress at All?

We wanted to examine how much bolt preload we might lose to bolt stress relaxation while using metallic gaskets. 

A good friend of ours, who operates a refinery, said they would give us six heat exchangers with the gaskets. We used a torque wrench to do the bolt tightening. We used UT measurement to measure the axial load and monitored the amount of relaxation on the bolted flange connections. 

We used three different gaskets for our test: (4) kammprofile gaskets, (1) double jacketed gaskets, and (1) corrugated metal gaskets. The experiment consisted of using UT measurements on each bolt once every hour for the first day, then once a day for six days, and then once a month for the next two months.

Test results from relaxation pass in bolted flange joints

Average Bolt Stress Relaxation After Bolt-Up 

Now we get a chance to look at the data:

Relaxation in bolted flange joints after two weeks

Suppose you look at the measurements in the first eight hours, about 0.9% preload relaxation. You’ve got to remember that UT is plus or minus 3%, so we’re well within that 3%. We also see the same readings on day one, day two, and even though two weeks of monitoring. 

On average, we saw almost zero creep relaxation on metallic gaskets and no preload relaxation with standard bolt materials (ASTM B7 and B16 bolt material).

NOTE: these pressure vessels have not seen any internal pressure or high temperature!

What is Gasket Relaxation: Gasket Creep with PTFE Gaskets and Sheet Gasket Materials?

To understand this more, Hex had to go over to our friends at TEADIT and ask them to do some research on relaxation since we know sheet gaskets have gasket creep.

Jose Vega and his team at TEADIT went through and looked at when we should do relaxation passes. They used a 4″ 300# flange connected to software that shows the bolt stress on each of the bolts, measuring the bolts’ stress so we can measure relaxation.

TEADIT set the torque wrench to 120 foot-pounds and monitored the gasket relaxation. They performed a re-torque and then waited another 20 hours to record the gasket relaxation. 

Gasket relaxation in bolted flange joints

You can see these re-torque increments are: 

  • 15 minute re-torque – then wait 20 hours to measure the bolt stress
  • 1 Hour re-torque – then wait 20 hours to measure the bolt stress
  • 4 Hour re-torque – then wait 20 hours to measure bolt stress 
  • 24 Hour re-torque – then wait 20 hours to measure the bolt stress.

These are the results:

Corrugated Metal Gasket relaxation in bolted flange joints
Results of Corrugated Flexible Graphite Gasket Stress Loss
PTFE gasket relaxation in bolted flange joint
Results of PTFE Gasket Stress Loss
Spiral Wound Gasket Relaxation in bolted flange joint
Results of Spiral Wound Gasket Stress Loss

As you can see, the corrugated flexible graphite and PTFE gaskets do need a re-torque, while the spiral wound gasket doesn’t! This is because of the effect of gasket creep on the gasket thickness between the flange faces. We tend to call this “cold flow” for sheet gaskets. 

You can see that after the 15 minute re-torque, you make up a decent amount of bolt stress back. 

However, it is interesting that a re-torque after that gives back just a little bit (around 4%) of bolt stress and not as much reward as we thought it would. 

Because of this study, Hex’s recommendation is to wait an hour, go to lunch, return, and re-torque the sheet gaskets. Another practice some refineries have that has been effective for them is to have the next shift, with re-verified torque tools, re-torque the flange.

Does Relaxation Happen on High-Temperature Flange Connections?

Warren Brown and Tze Lim with Integrity Engineering Solutions (a mechanical engineering consulting firm) did an excellent study, where they presented the following information at the ASME Pressure vessel and Piping Conference. Brown and Lim looked at different ASTM A193 bolt materials at 725 degrees Fahrenheit (385 Celsius) to determine how much bolt stress relaxation one should see at that temperature.

Relaxation that occurs after high temperatures
“Quantifying Bolt Relaxation During High Temperature Operation” Warren Brown, Tze-Yew Lim

ASTM A193, B7 bolt material relaxed 60%, B16 bolt material relaxed about 25%, and the B8M bolt material gained a little load. 

Most specifications in plants that Hex works with state they upgrade bolt materials between 700F and 800F process temperature. These are good for a minimum, but if you think that high temperature is a culprit for a flange connection leakage rate, my suggestion is to look at upgrading the bolt material. 

Interesting: Hex Technology has seen that some plants put Heavy Hex nuts on B16 studs instead of Grade 4 or Grade 7 nuts. That’s a bad idea as there is relaxation in the Heavy Hex Nuts that you don’t see in the Grade 4 or Grade 7 nuts. 


Question #1: Should you do a Relaxation Pass on a bolted flange joint?

Answer: Metallic gaskets do not need a relaxation pass. The amount of gasket creep is nominal and within our margin of error for measuring with UT!

Question #2: When should I do a startup re-torque on a bolted flange joint?

Answer #2: The answer to this question has two parts.

  • Part 1: I have been the guy on a live pressure vessel with a torque wrench, and it is not my favorite place. Getting a good gasket leakage buffer should be priority #1, as a slight change in gasket stress can cause a leak, and you have assemblers on the flange. So please work hard on this first. 
  • Part 2: Start-up re-torques on flange connections are great at 250F to 400F degrees. The reason why we put it in that semi-high temperature allows the bolt stress relaxation to start, AND your K-factor (not to be confused with the coefficient of friction) of your lubricant stays the same. At high temperatures, the oil burns off (at about 450 Fahrenheit), and your torque is no good…no matter how calibrated your torque wrench is! 

We typically recommend performing a bolted flange joint analysis before making these a common task in your specification. Mechanical Engineering should look at items like flange material, operating conditions, flange rotation, and possibly even do a finite element analysis to ensure you get the correct clamping force without deformation of the flanges.

Important notes

  1. At the time of this article, ASME PCC-1 is working on both definitions and guidance for “Hot Bolting,” which is now called “Single Stud Replacement.” 
  2. We did not discuss the use of washers during our experiments because they will skew the results as they increase the grip length of the studs. 

For more information about relaxation pass procedure and start-up retorque, don’t hesitate to contact us at [email protected]!

See also:

Flange Stud Bolt Lengths: What do I Need to Know?

Kammprofile Gaskets, Explained

Bolt Lubricant and Torque: A Comprehensive Guide

Flange Stud Bolt Lengths: What do I Need to Know?

Including Pipe Flanges, RTJ’s, Raised Face, and Custom Flanges

Different flange types and sizes require specific stud bolt dimensions. This article will discuss how the stud bolt length can affect flange joint assembly and how to choose the correct studs for your flange type and size.

  1. What is the Effective Length of Studs?
  2. How Does the Stud Bolt Length Affect Flange Joint Reliability?
  3. Standard ASME B16.5 and ASME B16.47 Flange Sizes
  4. Custom Flanges: Non-ANSI and API Flanges
  5. How Do I Fix the Stud Bolt Length Ratio to the Diameter of Bolts?

What is the effective length of studs?

The effective length of an ANSI stud bolt is essentially the middle of the nut to the middle of the nut. We call this the “grip length” of a fastener; this is where the majority of bolt load will reside, no matter the diameter of the bolts.

Most people think that the entire hex nut will hold the load, meaning the whole length of the stud bolts is engaged in maintaining load and gasket stress. But again, it is only the middle of the hex nuts to the middle of the hex nuts that do most of the work! 

Effective length of a stud bolt

Some people will discuss the Nominal Pipe Size (NPS), the use of metric bolts, the unified coarse pitch threads (UNC) of the bolt (or other thread pitches), or even the fact that it’s a Ring Type Joint (RTJ) instead of a Raised Face Flange affects the flange. And they are correct, but for other reasons.

For example, the 150# flange series are mathematically more likely to leak than the higher ratings found in the ASME B16.5 flange series. Why is this? Not because of the stud length, but because the diameter of bolts found in these flanges is minimal compared to the gasket; therefore, it is really hard to get good gasket stress on these flanges.


8″ nominal pipe size in the 150# series flanges is mathematically more likely to leak because there is not enough bolt load than any other nominal pipe size or flange size. To increase the gasket stress, you would have to increase the number of studs or the diameter of studs. The length of the stud has very little to do with the reason these are poor-performing flanges! 

Fun Fact #2: 

3″ nominal pipe size in the 150# series flanges are the second worst for the same reason…low gasket stress. Not because of the length of the stud bolts. 

Items not covered in this article are corrosion issues, different ring gaskets, machine bolts, history of ASTM a193, and stainless steel bolt materials compared to B7 bolt materials. 

How does the stud bolt length affect flange joint reliability?

Short bolt lengths are typically less reliable than longer bolt lengths. The rule of thumb for a desirable stud length is a 5:1 ratio length of the stud to the diameter of the stud, meaning that the length of the stud bolt is five times larger than the diameter of the stud bolts. 

It doesn’t take much deflection when the bolt length is short to relieve the bolt load; however, a longer bolt length with the same spring rate will have to deflect more before the bolt load is lost. 

Therefore, when looking at the bolt circle, we want to see the length of stud bolts 5X greater than the bolt diameter. 

Standard ASME B16.5 and ASME B16.47 Flange Sizes

When looking at a standard flange (ASME B16.5 or ASME B16.47), we don’t see many flanges where the length of the stud has a ratio of less than 5:1 length of stud to the diameter of the stud. This means that we don’t see this as an issue with these types of flange sizes. 

Below is a flange bolt chart that shows that the stud bolt lengths got both ASME B16.5 flanges & ASME B16.47 flanges. It includes the bolt dimensions (including the size of the hex nuts & length of stud bolts), the different lengths of studs needed for RTJ’s and Raised Face Flanges, and the number of fasteners in each flange!

Flange stud bolt length chart

Custom Flanges: Non-ANSI and API Flanges

This becomes more of an issue when we look at custom flanges such as heat exchangers or reactors. As you can see from the video, when we drilled out the threaded tube sheet in the flange, we effectively doubled the length of the stud. Therefore this joint is more reliable when it comes to relaxation.

How Do I Fix the Stud Bolt Length Ratio to the Diameter of Bolts?

Remember, the shorter the bolt, the more deflection and the more “relaxation.” 

How do you cure this if you have a short stud bolt length ratio to the diameter of bolts? 

There are several options… our favorite is spacers for the bolts. These are the easiest to implement and use in the field. But every bolted flange joint is different, so if you would like more help, please email us at [email protected].

See also:

Relaxation Pass in Bolted Flange Joints

Flange Stud Bolt Lengths: What do I Need to Know?

Kammprofile Gaskets, Explained

Kammprofile Gaskets, Explained

Kammprofile Gaskets (also known as grooved metal gaskets or spelled as camprofile gaskets) are our best friends in the heat exchanger world due to their durability. We are going deeper into what they are and answering, “What is a Kammprofile Gasket, and why do we care?”

  1. Kammprofile, aka Grooved Metal Gasket, Camprofile
  2. Strengths of a Kammprofile Gasket
  3. Weaknesses of Kammprofile Gaskets
  4. Kammprofile vs. Spiral-Wound gaskets on Flanges

Kammprofile, aka Grooved Metal Gasket, Camprofile

The kammprofile gasket is made of a solid metal core that can be made with regular gasket materials. These materials are carbon steel, 304 stainless steel, 316 stainless steel (if you need to go to higher temperatures), and other high-temperature materials such as Hastelloy and Inconel.

The gasket manufacturer will machine serrations that look like grooves into the gasket material; that’s where we get the term grooved metal gasket from. These serrations are made to put a facing material on the sealing surface.

The facing material (filler material) is often typically a soft facing material such as graphite facing (flexible graphite is what manufacturers call it). Other non-asbestos fillers include mica (high-temperature applications), PTFE, and other sealing materials.

While they don’t need a guide ring (like the outer ring of a spiral wound gasket), we like to see them on the gasket as it helps the assembler center the gasket during assembly. This can be adapted to this gasket, but we only see the graphite facing in petrochemical applications.

  • NOTE: the guide ring will be loose-fitting, which is a good thing! It allows the solid metal core of the gasket to grow during thermal expansion!

Items not covered in this article: o-rings, compression packing. 

Strengths of a Kammprofile Gasket

Kammprofile gaskets (or camprofile gaskets) are our best friends for heat exchangers and other custom flanges. Kammprofiles are tough, hard to destroy in assembly, they work in high temperatures, they work at high pressures, and they can take large bolt loads.

They are way better than double jacketed gaskets, better than corrugated metal gaskets, and large diameter (B16.47 piping or greater than 24″ flanges) spiral wound gaskets. 

  • NOTE: Large diameter spiral wound gaskets want to buckle and pop out. In contrast, small amounts of graphite pop up on Kammprofile gaskets.

Kammprofile gaskets are also super resilient to radial sheer, which we discussed in our training and other articles.

Probably the best part of these gaskets is how easy it is to adjust the area of the gasket to generate a better seal.

Kammprofiles may be put into many different configurations of flanges, such as flat face flanges and even muffler joints found in vehicles! 

Some manufacturers even offer conversion gaskets for ring joint gaskets to raised face flanges. 

Weaknesses of Kammprofile Gaskets

A drawback of these gaskets is that they are hard and are more susceptible to imperfections in the flange face.

So we need to make sure that our flange sealing surface has minimal dents and scratches and make sure that it’s compliant with PCC-1 Appendix D for flatness tolerances for flange surfaces.

Kammprofile vs. Spiral-Wound Gaskets on Flanges

I have two favorite types of gaskets: Kammprofile and Spiral Wound Gaskets. So, where do you put each of them?

Kammprofile’s are incredible for exchangers, but we are hesitant to put these gaskets in smaller raised face flanges (ASME B16.5 flanges)! While Kammprofiles are technically listed in B16.20 dimensions, they have glaring weaknesses in other applications due to their dependence on a near-perfect flange face and inability to recover. 

Spiral wound gaskets are WAY more flexible and forgiving to piping flanges flange surfaces. 

Then, the question has to be asked, “Why do we have some manufacturers put them into critical piping flanges?”

The answer to that is because when you have a critical system (which typically has excellent QA/QC and procedures), if there isn’t high temperature or thermocycling, we are putting them in a gasket’s heaven! So they should work since we have taken all the bad stuff out of the equation. If you want a robust, suitable gasket for piping flanges, use a spiral wound gasket!! To add to this, if you have metal jacketed gaskets, get a kammprofile gasket, and it will help give you a high-quality seal!

For more thoughts, questions, or concerns about anything in this article, please contact us at [email protected].

See also:

Spiral Wound Gaskets, Explained

Bolt Lubricant and Torque, Explained

Bolt Tensioning Guide: Uses, Safety and Troubleshooting

Bolt Tensioning: An Overview

Hydraulic bolt tensioners more commonly used for bolting applications in Europe than the United States. You’ll typically see hydraulic tensioning used on fasteners with 2″ bolt diameter or greater, but they can operate on studs as small as ¾” bolt diameter

Tensioners are common in subsea (both topside and underwater), wind turbine, and power generation applications, but are less frequently used in the oil & gas industry. Within the oil & gas industry, however, a good use of tensioning tools is on fasteners in critical bolted joints such as heat exchangers and other large pressure vessels

When you use 50% or greater tensioner coverage, you can achieve more even and accurate gasket compression than when you use one (or even 4) torque wrenches.  

One of the main advantages of stud tensioners is that they eliminate the friction factor (or k-factor) on the stud and nut face. In fact, tensioners are more accurate in general, achieving a plus-or-minus 10% accuracy rating compared to 30%

Accuracy of bolt tensioning vs torquing, compared.

It is typically stated that you can also reuse stud bolts more frequently when you’re using hydraulic bolt tensioners, since you don’t have to worry about galling or any frictional forces on the fastener. While this is true in laboratory applications, be aware that in the field, you have to take into account operating conditions like temperature and pressure, which will affect the fasteners over time. 

Using Bolt Tensioners in the Field

One limitation of tensioners is the need for greater spacing. While this typically isn’t an issue on normal piping flanges, you might not have enough space for a tensioner on valves and other custom flanges like you’ll see on heat exchangers

Also, the maximum fastener stress that tensioners can achieve is normally around 50,000-60,000 psi of stud preload. If you plan on tensioning to more than 60,000 psi, you’re probably going to need a specialty tensioner

You also need additional stud length for tensioning. The rule is you need one diameter of the stud sticking above the nut so that the puller bar can grip the stud when the load cell presses on it. Therefore, to calculate the proper size, you take the normal stud length you would use for torquing and add on another diameter of that stud to it. 

Do not use washers with tensioners. The footprint of a tensioner can sit on the washer, bow it up, and the tensioner gets locked on as a result.

Another disadvantage of tensioners is they don’t do well in elevated temperatures. What does that mean? Well, the startup re-torques you might ordinarily do are fine with torque wrenches, but tensioners can’t be used that way because the seals will blow and won’t hold the pressure. So with tensioning, you can assemble the flange at ambient temperatures just fine, but after startup you can’t go back and do what some people call a “hot tension pass”.

NOTE: There are other bolting tensioning tools such as hydraulic nuts that we do not discuss in this article. 

How Hydraulic Tensioning Works

Starting from the bottom of the unit, the basic parts of a hydraulic tensioner are:

Nut: This sits on the flange, while the bridge sits around the nut. As you can see, the bolt protrudes through the nut, and you need to make sure that you have one diameter of that stud sticking above the nut. 

Load cell: This sits above the nut, and has the hydraulic piston inside of it. Attached to the load cell is a nipple for oil to come in at a designated hydraulic pressure from the tensioner pump

Puller bar: This sits on the piston, which is threaded onto the stud. The hydraulic pressure in the pump and the diameter of the load cell determines how much force you’ll exert on the bolt.

Bolt tensioning on 50% and 25% of bolts within a flange.

50% coverage (shown above, left), or one tensioner on every other bolt, is standard. While it’s possible to do 25% coverage (above, right), we don’t recommend this approach because it requires more passes, is harder for the assembler to execute, and your accuracy starts going down. Therefore, when you have 50% coverage, you’re going to have what we call an A pass and a B pass.

BOLT TENSIONING EXAMPLE: Let’s say your target is 50,000 psi bolt stress. First you need to consult with the tensioner and the engineer to make sure you have all your load loss factors figured out. But for this example, you’re going to tension your A pass 20% above what you would do your B pass. Your B pass is your final bolt load. But because we’re only putting load on half the bolts and we’re trying to bring this pipe together and compress the gasket and everything else, we actually kind of have to go over what our target is so that when we bring our B pass in, the load transfer is going to happen and it should equalize out. Now a common practice is to go back to your A’s and just double check that you still have the correct bolt load on there and do your B pass on your A’s.

Hydraulic Tensioning Safety

Safety around hydraulic tensioning is absolutely important. Your primary concern is that you are working with high pressure hydraulic fluid, which goes from the tensioner pump to the load cell and then on to the other tensioners. A high-pressure fluid can cause massive injury, so always ensure that proper storage, cleanliness, and safety measures are taken prior to use. If you see a worn or damaged hose or fitting, please replace it. 

Additionally, your assemblers don’t want to be looking down at the tensioner while it’s in use, because if it pops off because of insufficient thread engagement, stripping, or anything else, it ends up being a bullet. So you always want to make sure you’re on the side of the tensioners, and not looking straight down at the puller bar.

Learn more safety considerations for all hydraulic equipment. 

Maintenance, Troubleshooting, and Calibration

Seals are the most common culprit for issues with a hydraulic tensioner. Just like with hydraulic torque wrench pumps, if you have oil, dirt, or any other gunk running through the hydraulic fluid, those impurities will get into the tools and eat away at the seals, which are then the first things to go. 

Outside of the seals, hydraulic tensioners don’t require a ton of maintenance. The only other big troubleshooting tip is if you’ve got a tensioner that is not working, you need to check your couplers. 

For calibration, all you’ve got to do is make sure the gauge was calibrated within the past 12 months.

Well-trained assemblers produce far more accurate results. Learn how a U.S. refinery achieved more consistent flange makeup.  

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Hydraulic Torque Wrench Use in Industrial Bolting

Hydraulic torque wrenches are a staple in the fastening of industrial bolting applications.

These wrenches are necessary to achieve high torque outputs (greater than 600 ft. lbs.) on a fastener. Manual clicker wrenches capable of reaching 1000 ft. lbs. do exist, but they are brutally difficult to use. Power tools are easier on the assembler and lead to better accuracy and repeatability.

Since hydraulic tools have a high torque output, they need to be powered by a hydraulic pump. This pump or “power pack” relays high-pressure hydraulic force through a hydraulic hose in order to produce the target torque output.

If calibrated correctly, the hydraulic pump will allow the user to change the torque setting accurately. Hydraulic pumps can be powered by either pneumatic (air-driven) or electric power.

Hydraulic torque tools can have a minimum torque of 100 ft. lbs. and a maximum torque of 120,000 ft. lbs.  Both the minimum and maximum torque depend on the capacity and size of the hydraulic equipment. Hydraulic torque wrenches are especially useful on large bolts (1-inch diameter or greater). In the sections below, we’ll explain how hydraulic torque wrenches work, starting with the pumps that power them and working outward to the tools themselves.

Hydraulic Pump (Or “Power Pack”): Where it Begins

A standard pump can generate up to 10,000 PSI, and allow you to adjust the torque setting on the hydraulic wrench. Most pumps work with all major tool brands.

Pumps are either electric or air-driven, though you’ll typically see pneumatic hydraulic pumps used in hydrocarbon processing. Using an electric pump for some bolting applications may require you to get a “Hot Work Permit,” due to the electricity.

For all hydraulic torque wrenches, a hose connects the hydraulic pump to the hydraulic wrench itself. The hose connections (or couplers) are set up so that you cannot hook up the hose incorrectly — the male/female attachments require the right match in order to connect (see photo above). Therefore, connecting the hose to the pump is intuitive and easy.

Hydraulic Hose: Keep an Eye on This Connection


After you power up the pump, you’ll adjust the pressure to match the correlated target torque value on the calibration sheet. The hose attached to the hydraulic tool on what is called the uni-swivel. Logically, the uni-swivel can handle up to 10,000 PSI.

IMPORTANT NOTE: Hydraulic hoses SHALL (i.e. must) be rated for a 4:1 hydraulic pressure, which means rated for 40,000 psi.

There are setting to advance or retract. Advance will fill the piston with hydraulic fluid, which then advances the piston to push on the drive pawls. The drive pawls rotate, which causes the nut to rotate.

ANOTHER IMPORTANT NOTE: Carefully inspect a hydraulic hose for damage or holes before use. If pressurized liquid were to escape through a hole, the stream that would result would be capable of causing severe injury (think: lost fingers or deep cuts).

Square Drive Bolting Tools: Best for Breakouts

The square drive bolting tool is the most common hydraulic torque wrench in industrial bolting. Square drive sizes include ½”, ¾ “, 1″, 1 ½”, 2 ½”. Size dictates the maximum torque output that these tools can generate.

Experience shows square drives are best suited for breaking out, as square drives are more robust and have fewer moving parts than low profile wrenches, making them less prone to breakage.

A square drive tool’s reaction arm places it further away from the flange (due to the impact socket and square drive), therefore square drives are more difficult to use for assembly than a low profile hydraulic torque wrench.

Low Profile Bolting Tools: An Assembler Favorite

Low profile hydraulic wrenches consist of two parts: A powerhead and a link. The link makes low profiles unique because each set of links fit over a specific size of nut. You can change the link by pulling the link pin, then sticking on a differently sized link.

Low profile wrenches go upward from 2,000 ft. lbs. to 4000, 8000, 16,000, and so on. You need a link for every wrench of that size, meaning you might need multiple links for a 2,000 ft. lb. version, multiple links for the 4,000 ft. lb. version, and so on. Links for different model tools are not interchangeable.

As you might guess from the name, Low Profiles are absolutely awesome when dealing with low clearance issues. The reaction point for a low profile is right up against the next adjacent nut. The low-profile wrench may be the assembler’s favorite hydraulic tool because it is easier to use than a square drive.

Hydraulic Torque Wrench Safety

With the high-pressure fluid and extremely powerful mechanical reaction arms, there is great potential for injury with improper hydraulic equipment wrench use. Hex Technology recommends any site that uses hydraulic tools first undergo safe use and operation training.

Always depressurize the hydraulic hose prior to use. Store hydraulic hoses in a circle wrapped end to end, and do not screw the ends on one side together. As mentioned above, if you see any steel braiding bins, cracks, burns or kinks, do not use that hose.

The other major safety concern for all hydraulic torque wrenches is pinch points resulting from reaction points. You know enough physics to know that for every action, there is an equal and opposite reaction. In bolting, this means that if an assembler is applying 1000 ft. lbs. to a bolt, the reaction arm is applying that same amount of force to the adjacent nut. You do not want any part of your body caught between those two pieces of metal.

There are two major types of hydraulic tool designs out there: Those with holding pawls and those without holding pawls. A holding pawl allows the tool to ratchet without using the “wind up” on the fastener. The holding pawl will get bound up on the fastener at some point, and while the tool will ratchet, it will be hard to take off the flange.

When this happens: DO NOT take a hammer to the tool. Instead, power up the tool through the hydraulic pump then depress the holding pawl, and the hydraulic tool will release.

Hydraulic Torque Wrench Maintenance

An important aspect of hydraulic torque wrenches maintenance are watching the seals. Often, these seals are the first thing to break. If you see oil in your hydraulic pump that looks milky, full of water, dirt, or grime, those impurities will travel along with the hydraulic fluid through your tool and eat away at your seals.

The second maintenance factor to mind are the hydraulic hoses. The couplers on hoses regularly get grime and gunk and everything else put through and onto them. Then people will place channel locks or pipe wrenches onto the couplers to try and tighten them. Please clean the fittings with each use so you don’t have to do this, as channel locks will damage and eventually ruin the couplers.

If you have to replace a fitting, please make sure to follow the hydraulic hose manufacturer’s requirements.

The hydraulic pump doesn’t usually require in-field maintenance, but may require some troubleshooting. Air-driven hydraulic pumps will have an FLR, or “filter lubricator regulator.” When you hook up air to your hydraulic pump, there’s a little nozzle on the bottom of the filter. Dump all the water and gunk and grime out before you start running your tool. Because if that gunk and grime go through your FLR, it will travel through the hose into your air motor, and tear up the motor.

You’ll see the FLR has a little sight glass that allows you to see the oil going in. Make sure the oiler is putting in one drip of oil every 10 seconds.  This oil lubricates the air motor, ensuring it doesn’t bind. Having the oil drip more frequently will lead to oil exhaust on the handle, but if the tool doesn’t oil frequently enough, it will bind up the pump and you’ll eventually have to swap the pump out.

It is our recommendation that you reach out to the torque wrench manufacturer. They normally do a safe use and operation and troubleshooting course on their tools, as each different manufacturing and each different model of tool has its own quirks and purposes for each individual part.

After any maintenance on a hydraulic torque wrench, you have to recalibrate the tool. It’s necessary to re-grease both the drive pawls and the side plates so the pawl can move back-and-forth easily against the side plate, doesn’t get bound up, and doesn’t gall.

Calibration: When and what’s required

There are two elements of a hydraulic torque wrench that need to be calibrated:

  1. The actual wrench itself.
  2. The gauge on the hydraulic pump.

Both of these components should be calibrated at least once every 12 months. Once the tool is calibrated, a new torque chart needs to be generated. The updated chart is what your crews will need to use with that tool from that point on. Always check the serial number and date to ensure you have the correct calibration chart for that tool.

If you have questions or your site needs training on the use of hydraulic torque wrenches, contact Hex Technology.

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The Forgotten Essential Worker

One of the few upsides of the COVID-19 pandemic is a greater collective appreciation for essential workers.

Drive down any street and you’ll see yard signs singing the praises of “front line heroes.”

Many interpret the label to mean those working in health care or grocery stores. Some also understand it to mean truckers and delivery workers who keep stores and hospitals alike stocked with supplies. These people all deserve our gratitude. Praise for them is long overdue.

But amid the tributes of the past year, another group of deserving heroes goes unrecognized.

“We’d die of starvation, basically.”

By every possible definition, the women and men laboring on America’s oil and gas supply lines are essential.

This shouldn’t require great imagination to understand. About half of all homes in the U.S. are heated by natural gas. The other half use electricity – although keep in mind, natural gas is responsible for nearly 40% of electricity production, too. Meanwhile, petroleum products drive more than 90% of all transportation.

In short: Without oil and gas workers, we would freeze inside our homes and be stuck with unmovable vehicles.

While he’s known for mass-producing electric cars, Elon Musk recognizes the importance of oil and gas workers and what they do. “We can’t stop instantaneously and not have oil and gas,” Musk said recently. “You know, like, we’ll likely die of starvation basically.”

Indeed, the machines that plow our fields. The trucks and airplanes transporting those crops from farm to market. They all depend on refined products.

The same goes for your Amazon delivery van or the Instacart driver who brings you groceries. Nearly all of our modern conveniences depend on oil in some way.

The Unsung Hero Fighting COVID-19

While most people can easily see the connection between oil and transportation, the vital and irreplaceable role oil and natural gas refining play in the fight against COVID may not be as apparent. But it’s every bit as real and significant.

It starts in the emergency room, where the N-95 masks protecting our doctors and nurses depend on multiple plastics derived from oil and natural gas.

The same is true for protective face shields, gowns, rubber gloves, and shoe covers.

In fact, nearly all PPE involves plastics and other refinery derivatives in some way. The American Chemistry Council draws a direct connection between the gear protecting our medical professionals on the front line with oil and gas refining.

Vaccines Depend on Refining

Now the world looks on as an unprecedented vaccine rollout gets underway. COVID vaccination clinics are a source of hope that the world might return to “normal” soon.

Those clinics, and the vaccines administered within them, are also only a reality thanks to the men and women in our refineries.

The Moderna, Johnson & Johnson, and Pfizer vaccines all must be stored at extremely low temperatures. (Moderna and J&J need to be kept at -20%, Pfizer at -70%.) The refrigerants making cold storage possible are typically isobutane, propane, and propylene – all of which are derived from oil & gas.

Administering those shots to everyone in the U.S. who needs one will require an estimated 850 million plastic syringes. Specifically, those syringes are an injection-molded form of polypropylene derived from naphtha, and naphtha – you guessed it – comes from oil refining.

And of course, the entire distribution network responsible for transporting vaccines from production centers to patients relies on oil & gas.

A Uniquely High Level of Pain

So to summarize: Our heated homes, every method of transportation, and our only hope for a return to normalcy and freedom from COVID fears all depend on oil and gas.

More accurately, they all rely on the work the women and men in our refineries and other production units.

But to date, their only reward for this essential work has been greater economic uncertainty.

Perhaps no sector has borne as much financial pain during the COVID crisis as oil and gas. During 2020, more than 160,000 people involved in oil and gas production in the U.S. lost their jobs. A string of U.S. refinery sites closed or were idled, from Martinez, California to Gallup, New Mexico to Convent, Louisiana. Many other sites have been forced into layoffs.

Those who’ve been spared from these losses continue to show up for work each day, performing the work that makes the work of every other front-line hero possible.

But there are few (if any) signs thanking them.

Why is that?

What We Don’t See

You could argue oil and gas workers have been overlooked because of politics, or the fight over climate change. But I’m so tired of politics and fighting. And I imagine you are too.

So I want to believe that the reason is far less nefarious:

People just don’t see them.

While anyone can see the work of their doctor and grocer, the essential tasks being performed inside the United States’ 131 operating oil refineries and hundreds of production rigs are hidden from public view. Almost no one stepped inside of a refinery or onto a rig other than the workers themselves even before COVID. That’s even more true now.

The efforts of these vital workers goes unrecognized because it’s unseen.


I’m asking you to see them.

I’m asking that you set aside the debates and noise and see these workers for what they are: Women and men who go into a tough environment to do work we all rely on.

They are essential.

They are valuable.

And they are just as worthy of our praise and gratitude as every other worker on the front line.

To all those in oil and gas who may be reading this: Thank you.

Hex Technology helps industrial sites operate more safely, efficiently, and profitably through specialized training for reliability and maintenance. We’ve saved sites millions of dollars and helped them earn awards for excellence. Read our most recent case study here

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Bolting Applications with Pistol Grip Torque Wrenches

Roughly 25 years ago, pneumatic torque wrenches (a.k.a. pneumatic torque gun or pistol grip) torque wrenches were commercialized enough to make them one of the main staples for bolting solutions found in oil & gas or power generation.  We have seen the pneumatic torque wrench technology move to both battery and electric powered pistol grip torque wrenches to improve the accuracy and repeatability in bolting applications.  

The oil & gas bolting industry has seen an increase in pistol grip tools as they are ergonomic, heavy duty, have an adequate torque range for most fasteners, and have high-speed continuous rotation without having to ratchet.  This makes them faster than other controlled torque options (such as hydraulic torque wrenches).

We typically see pistol grip wrenches in heavy duty applications because in order to achieve a high torque output (typically greater than 500 to 600 ft-lbs) on a fastener you should where it is easier on the assembler and you can generate better accuracy and repeatability than with an impact wrench or other unregulated “torque tools.”

Pistol Grip torque wrenches consist of a motor (typically powered by air pressure, battery power, or electricity), a gearbox design (planetary gearbox or gearbox) which acts as a torque multiplier,  a square drive, and a standard reaction arm

  • NOTE: These pneumatic tools should not be confused with impact wrenches as impact wrenches do not have an FRL (filter-regulator-lubricator) or another regulated power source (electricity or battery power).
  • Since these pistol grip wrenches have a high torque output typically ranging from 50 ft-lbs to 15,000 ft-lbs. Both the min and max torque range is dependent on the capacity and of the square drive size. Each one of these pistol grip torque tools has a calibration certificate specifically for each tool (serial number and not model) that has the readout of the input vs. the torque value (typically found in ft-lbs or Newton-Meters).  

NOTE: Hex Technology has had significant experience with pistol grip torque wrenches and suggests contacting us if you have further questions after this article.

NOTE: See our articles on Hydraulic Torque Wrenches and Stud Tensioners for other power tool options to achieve high loads on fasteners. 

Pneumatic Pistol Grip Torque Wrenches

The first type of pistol grip torque wrenches that we will discuss is the pneumatic torque wrench. These are powered by air pressure that goes through the air motor, and at the end of the gearbox is a reaction arm that is used to absorb the torque and allows the tool operator to use it with little effort (thus making it ergonomic). These guys are great because they have a very high torque output and they’re normally smaller than an impact wrench as well. 

These advantages include being relatively easy to use. If you’ve used an impact wrench, the only difference with a pneumatic torque wrench is that you’ve got to do is dial your torque with the FRL Some of the best reasons to use pneumatic torque wrenches is they have no vibration, operate at less than 80 decibels, are ergonomic, and they have a higher torque output than what impact wrenches do.  

NOTE: All pneumatic tools are not the same. An impact wrench does not have accuracy or repeatability while pneumatic torque wrenches do. 

Battery-Powered Pistol Grip Torque Wrenches Work

Battery-powered pistol grip tools are more common in the oil & gas industry now than they were 10 years ago, and I project that they’re going to be even more common than pneumatics in the next couple of years because it was just so convenient to use.  

Since they are battery-powered, you do not need an air hose or electrical socket!  They are typically more accurate and repeatable as they have a digital gauge and not a dial gauge.

Electric Powered Pistol Grip Torque Wrenches

The pistol grip wrench that we’re going to talk about is electronic torque wrenches. We don’t see these a lot in the oil & gas industry because it needs electricity, which means you need a hot work permit. We see them more in the power industry, wind industry or structural steel industry, but you can see right here that it’s got an entire box dedicated to setting the torque value and then there’s an output to the wrench itself. Each manufacturer has got strict calibration requirements for these, so please contact them if you’ve got any questions. Do not go into that box and try to adjust it yourself, as that will be a very expensive mistake.

Pistol Grip Torque Wrench Safety

The first thing we’re going to talk about when using these wrenches is safe use and operation. Pinch points are a common safety hazard around the reaction arm of these tools. The reaction arm swings over and reacts against the next nut or possibly the flange. That is not a handle, do not use it as a handle. Keep your hand as far away from the reaction arm as possible. If the torque wrench is putting out a thousand foot-pounds, that reaction force on the reaction arm is going to be a thousand foot-pounds and you’re going to lose a finger.

It is also important that the user have a solid reaction point. Curved or bad reaction points can cause the tool to bind up and put excess load on the gears within the tool. Multiple reaction arms are available from the manufacturer to achieve proper reaction arm placement if the standard reaction arm is not suitable for your application. 

Pistol Grip Torque Wrench Maintenance 

When talking about the maintenance of these tools, you have to remember that they are precision instruments and should be treated that way. Don’t just leave them in the back of the truck overnight. Make sure that they are in an environmentally controlled place so that rain doesn’t get on them, water doesn’t get on them when they’re not in use.

Preventative maintenance will give early detection of worn-out tolerance in these tools and prevent premature failure. For pneumatics, one of the things that we like to do is make sure that when you plug the air in on the FRL, there’s a little nozzle on the filter that you can loosen and it spits out all of the water and all of the dirt that you’ve gotten inside of the hose. Also, make sure that your lubricator is filled with air tool oil. You can see one drip every 10 to 15 seconds from the sight glass of the lubricator.

Unfortunately with the electric and the battery-powered, there’s not a lot of preventative maintenance that you can do on these tools as everything is pretty much closed circuit. The one thing I do not want you to do is go in and try to fix that planetary gear set yourself. It is super complicated with hundreds of moving parts, and you’ll probably end up buying a new tool if you do that. 

Also if you hear anything not working properly, it’s making a grinding noise, don’t keep pulling the trigger because that’s $500 a piece, and get it to a licensed repair shop to get fixed and recalibrated.

Pistol Grip Torque Wrench Calibration Certificate

Calibration certificates for all of the pistol grip wrenches are pretty much the same, and while there is no industry requirement, the standard is to calibrate these once a year. However, these tools should be load verified throughout that calibration year. Meaning you should put them on a Skidmore (or equivalent) and test their accuracy and repeatability just to make sure that the tool is staying within its calibration certificate‘s torque readout.


In conclusion, pistol grip torque wrenches are absolutely awesome to use in the field as they’re super convenient and are high speed (because they do not have to ratchet) compared with other bolting torque methods. With the battery torque wrench, you don’t have to have a hose, you don’t have to have a box, so they’re really easy for the one off flanges. They will probably break down more frequently than the pneumatics just because the handle is not as robust. However, all these wrenches are great for piping flanges, heat exchangers, manhole covers, and any heavy duty bolting applications found in oil & gas

All pistol grips are square drive tools, so If you can fit an impact in there, you can fit one of these torque wrenches in there.

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