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10 Tips for Using a Torque Wrench Correctly
Tips and Tricks

10 Tips for Using a Torque Wrench Correctly

  • Katarina Knafelj Jakovac

    October 27, 2023

Proper use of professional tools is of great importance in machinery and equipment repairs, overhaul work, and general servicing.

Incorrect tool usage during machine assembly can lead to a shortened machine lifespan and pose risks to worker safety, as well as environmental hazards due to an increased risk of unexpected malfunctions. In extreme cases, machines can seize, explode, or disintegrate.

The most common failures of rotary machines resulting from improper tool use include bearing failures due to reduced clearances, the occurrence of initial cracks in housings due to over-tightening of screws, parts loosening due to inadequate tightening torque, and overloading of bolted connections on flanges.

The main way to prevent such failures is the proper use of a torque wrench, often colloquially known as a kilo wrench.

What is a torque wrench and what is its purpose?

A torque wrench is a type of precision tool designed to apply the appropriate tightening force to a bolted joint.

Its name comes from the fact that when tightening, we apply a torque expressed in Newton-meters to a lever of a specific length, depending on the tool's size. The term kilo wrench derives from the old unit of force measurement known as kilopond.

It was invented by Conrad Bahr in the early 20th century and has since been used in various industrial sectors and technical branches due to its versatile application, compactness, and precision.

There are mechanical, electric, and pneumatic torque wrenches on the market, but here we will focus on the proper use of mechanical torque wrenches.

The most commonly used manual type is known as a click-type torque wrench, as shown in Figure 1. When the mechanism in the torque wrench head reaches the previously defined and set torque value while tightening a nut or screw head, a clicking sound is heard. More advanced torque wrenches have a user or a quality control technician who determines the torque value for the bolted joint.

There are also mechanical torque wrenches designed exclusively for verifying the tightness of bolted joints.

Glavni dijelovi jednostavnog klik moment ključa.png
Picture: Main components of a simple click torque wrench (Source: Author's archive)

Professional mechanical torque wrenches must have a scale for setting the torque and a brake on the handle, while the digital version allows manual input of the torque value using buttons.

Mehanički moment ključ sa skalom i kočnicom.png
Picture: Mechanical torque wrench with scale and brake (Adapted from: Source)

Mehanički moment ključ sa digitalnim unosom.png
Picture: Mechanical torque wrench with digital input (Adapted from: Source)

Electric torque wrenches, like the one in the picture, are powered by lithium-ion batteries and come with numerous advanced features such as automatic head angle adjustment, data storage for torque values, and a brushless built-in electric motor.

Električni moment ključ

Image: Electric torque wrench (Source)

I would like to draw attention to the torque wrenches available in general consumer goods stores. Such torque wrenches are suitable for tightening simple flange connections, such as those on household pipes, where precision work is not crucial, and the exact torque value is not required.

However, their main drawbacks are uncertain origins, unknown material quality, which leads to faster tool wear and breakage, lack of calibration, and the absence of annual calibration checks.

The steel's chemical composition is particularly problematic, as manufacturers of such tools often save on vanadium and chromium.

When these elements are insufficient, the tool may break under a higher-intensity force, leading to additional costs to replace the broken tool to continue working. On the other hand, for tightening tasks in industrial facilities, it is essential to use torque wrenches from reputable manufacturers of professional tools.

Such tools come with a warranty, are made from high-quality steels according to ISO6789 or ANSI/ASME B107/14 standards, GGG 686D, and JJG 707. The torque tolerance can be a maximum of ±3%.

Regardless of the type of torque wrench you use, you will need a set of socket wrenches, known in everyday speech as "gedores", and suitable adapters.

Moment ključevi sa setom nasadnih ključeva (gedora) i adapterima

Image: Torque wrenches with a set of socket wrenches (gedora) and adapters (Source: Author's archive)

How to use and maintain torque wrenches?

Whether you're tightening nuts on bolts that connect a housing and the cover of a centrifugal pump or tightening nuts on bolts on an 8-cylinder diesel engine block, it's essential to use a torque wrench correctly.

When working, use protective work gloves and safety glasses.

Every specialized manufacturer of mechanical machines and equipment provides a range of permissible torque values, defines the tightening sequence, and specifies how many times the nut should be tightened or loosened to evenly distribute the force on surfaces in their user manuals for operation and maintenance.

The torque wrench table shows examples of torque values for bolted joints on a 6-cylinder marine diesel engine. The bolt strength class is 8.8 or 10.9.

Korisnički priručnik za motor Wartsila RT-flex58T-D

(Source)

The first column lists the nominal screw thread diameters according to ISO 261 and ISO 262 standards. The right side of the table lists the corresponding torque values for the bolt according to the bolt class.

Depending on the nominal screw size, you should apply the appropriate torque value and set the torque wrench to that value. For an M8 bolt, you need to set the torque wrench to 20 Nm and then tighten it, for an M10 bolt, you adjust the torque wrench to 40 Nm, and so on.

You should also pay attention to lubricating the threads and the age of the bolts and nuts used, as these factors significantly affect the torque value.

For instance, when it comes to tightening bolted joints on equipment operating at high temperatures and high pressures of working media, industry practice is to use entirely new bolts and nuts taken from stock every time, and a special type of grease is applied during the assembly of flange connections.

Recommendations for correct torque wrench usage:

  1. Follow the manufacturer's instructions for mechanical equipment, which specify the tightening direction when using a torque wrench (clockwise or counterclockwise) and the appropriate torque values as listed in tables.

The sequence of tightening, depending on the number of bolts, is important, as shown in the image.

Bolt tightening sequence depending on the number

Image: Sequence of tightening screws depending on the number

The manufacturer will also specify the number of required tightening and loosening cycles and recommend the use of the appropriate lubricant or Molykote paste on the threads.

Usually, manufacturers and distributors of professional tools offer shorter seminars, training, and educatio to their customers and users on the correct use and maintenance of their tools. You should inquire with your distributor to arrange a customized training for you and your employees once a year.

This way, you will gain valuable information, enhance your employees' skills, learn about the latest tool innovations in the market, and try out new mechanical tools.

Additionally, you have the opportunity to provide feedback to the distributor or manufacturer based on your experiences using their tools in real working conditions, such as tightening bolted joints on car tires or flange connections on a petrochemical heat exchanger.

  1. Use the torque wrench to apply the specified torque value to bolted joints during the final assembly of machines or equipment.

Under no circumstances should you use the torque wrench as the primary and only tool for tightening and loosening bolted joints because it's convenient and readily available. If you are in a hurry to finish the job and do not want to fetch another suitable tool, avoid using the torque wrench inappropriately.

  1. Do not exceed the torque wrench's range. The reliability of measurements is based on the percentage of the working range, and most mechanical torque wrenches have a working range of 20% to 100%.

  2. Do not use an extension handle or additional lever when tightening, unless specified by the torque wrench manufacturer.

Each torque wrench has a specific length, so you should grip it in the middle of the handle. If you use both hands, grasp the middle of the handle with one hand over the other.

When using an adapter, one hand should tighten while the other hand simultaneously supports the adapter, as shown in the image.

Pritezanje sa adapterom

Image: Tightening with an adapter (Source)

  1. Turn the torque wrench slowly and evenly. Avoid making sudden movements, shaking the wrench, or rapidly pulling it.

Any sudden and uneven handling of the torque wrench will damage the tightening mechanism of the head and disrupt the calibration.

  1. When the torque wrench "clicks" during tightening or when it signals (if you are using an electric torque wrench), it means that you have tightened the bolted joint to the desired torque value, and you should stop tightening and remove the torque wrench, socket wrench, and adapter if used.

  2. Regularly inspect the tool for signs of damage or wear. Replace socket wrenches or gedores that are damaged as soon as possible.

  3. Avoid dropping or striking the torque wrench on hard surfaces because impacts can cause calibration disturbances and irreversible damage.

On several occasions, I have seen the head of a manual torque wrench used to lightly tap a gasket to make it sit better on a flange surface.

A torque wrench should by no means be a substitute for a common hammer or a pry bar!

Doing so will irreversibly damage the tightening mechanism and electronic components of the torque wrench.

If you doubt the calibration's correctness due to the wrench's fall, send it for testing to an authorized service, an accredited calibration laboratory, or the manufacturer if the tool is under warranty or you have a maintenance and calibration agreement.

  1. Always store the torque wrench in its original case, protected from moisture, heat, corrosive atmospheres, and dust when not in use.

Moment ključ Komplet u zaštitnoj kutiji

Picture: Complete set in a protective case (Source)

If you have a "click" torque wrench, store it with the working range set to the lowest value.

  1. Calibrate the torque wrench once a year or after every 5,000 cycles (whichever comes first) at an authorized and accredited calibration laboratory according to ISO/IEC 17025 standard.

Keep a record of when the torque wrench was last calibrated.

If you have your authorized service workshop and also wish to obtain an ISO certificate, authorized certification bodies will, among other things, request calibration certificates for precision tools during the inspection of your workshop, so it is essential to have up-to-date calibration certificates.

Simplifying Tool Data Management

When you have a large number of precise professional tools, keeping track of their maintenance, calibration, working hours, and usage records becomes a complex and demanding task.

Previously, records were kept on paper, followed by tracking through Excel spreadsheets. Advanced companies now use computer programs for maintenance management, also known as CMMS (computer maintenance management system) or EAM (Enterprise asset management).

Several types of computer programs with different characteristics and capabilities are available on the market, depending on the manufacturer.

Each program has various modules tailored to the user, including a module for tracking work orders, spare parts, fault records, and inventory status.

One module is dedicated to maintaining tool records and necessary auxiliary equipment for repairs, services, and other required work.

Torque wrenches, gedore sets, and adapters can be easily documented in such a module using a tool card, an example of which is shown in the following image and must contain the following details:

  • Tool type: Torque wrench
  • Manufacturer: Company Ltd.
  • Socket wrench attachment size: 1/2
  • Length: 450 mm
  • Range: 28-210 Nm
  • Calibration certificate according to ISO 6789:2017 is attached to the tool card.

Conclusion

Proper handling and care are essential for tools.

Every craftsman or technician achieves the quality of their work through their skill combined with professional tools.

A torque wrench is an essential part of the toolkit in many trades.

Proper use of a torque wrench and maintenance of the tool in good condition contribute to quicker repairs, reliable operation after repair, longer machine lifespan, and, consequently, lower maintenance costs.

Katarina Knafelj Jakovac
Katarina Knafelj Jakovac social media icon
October 27, 2023

Katarina Knafelj Jakovac holds Master degree in Mechanical engineering with long term work experience in Oil industry. She is Certified Reliability Leader specialized for mechanical equipment and operational excellence. Author of blog Strojarska Radionica (Mechanical Workshop) where she shares professional knowledge and personal experience in maintaining various rotating machines, machine systems and process equipment. Adores mechanics, thermal engineering and internal combustion engines. She is dedicated to the continuous improvement of machine maintenance and quality management of physical assets.