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

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