With today's machinery, getting torque wrong can have consequences for production, safety, and liability. Michael Wuensch, Stanley Proto's product manager for wrenches and torque products, talks about new calibration and measurement tools that ensure accuracy.
Accurate torque measurements are critical to the energy industry. After all, applying the wrong torque to a critical fastener can cause an expensive piece of machinery to fail, halting production and possibly causing injury to workers.
Maintaining accurate torque is a challenge in all industries, but it's especially so in high torque environments like those found in the oil and gas business, where torque multiplication needs to be used on large fasteners. Fortunately, Stanley-Proto has introduced new equipment that makes it easier to maintain accurate torque in any environment. But before explaining how that equipment works and why it's important, I need to review some basic concepts.
Despite its importance, torque is widely misunderstood on the jobsites and in the boardrooms of today's corporations. In fact, Stanley Proto's field representatives hear the same basic questions again and again. "What exactly is torque?" "Why can't I just tighten the connection as much as I can?" "Do we really have to calibrate torque wrenches?" "How often?"
I will answer these questions below.
Why torque is important
In its simplest form, torque (T) is a force times a distance (T = F x D). The force (F) is you pushing or pulling on the handle of a wrench. The distance (D) is the length between the centre of your hand and the centre of the fastener. So, if you apply a 100 Newton force to a wrench, with your hand one metre away from the fastener, you are applying 100 Newton-meters of torque, or 100Nm. Similarly, 50 Newtons applied two meters away produces the same 100Nm torque load.
The purpose of applying torque is to produce tension between two parts of a connection – whether bolts on a pipe flange or valve seat, motor mounts on a pump, or lug nuts on a wheel. The proper tension will be enough to keep the connection together without damaging the components.
From the field worker's perspective, ensuring the proper torque can be a hassle. Torque wrenches have to be treated with more care than most other tools; torque values have to be set before applying the torque; and careful records may have to be kept of the torque values being applied.
But this effort has real payoffs. If there's too little tension in a connection it can come loose; if there's too much, the fasteners can strip out, the bolt heads can shear off or the fasteners can prematurely fail. Both situations frustrate mechanics, waste valuable time, and create potentially serious safety risks. Proper torque application helps prevent these costly problems.
That makes the old advice not to be "penny-wise and pound-foolish" truer than ever. Trying to save a few dollars on a bargain basement torque wrench can potentially cost tens or hundreds of thousands of dollars when production stops or equipment fails (or when the lawyers come knocking at your door) because the improper torque was unknowingly applied to a critical piece of equipment. You can minimise such problems by purchasing top-quality torque tools from reputable companies.
Maintaining accuracy
Even top quality tools require regular care and maintenance. Proper calibration of a quality torque wrench will ensure that the torque setting on the wrench produces the proper torque value when applied to a fastener.
The American Society of Mechanical Engineers (ASME) publishes Industry standards that specify certain acceptable limits of performance for torque wrenches (ASME B107.14). These specifications include the tolerances of how accurate the torque wrench needs to be at various settings. The standard calls for a +/- 4% accuracy in the clockwise direction. That means a 100Nm setting can apply as little as 96Nm or as much as 104Nm and still pass the standards' requirements.
Regular calibration is one of the most important steps in maintaining this level of accuracy. The Hand Tool Institute's "Guide to Hand Tools" recommends that torque wrenches be calibrated approximately every 5,000 cycles. In practice, however, calibration schedules vary widely. They can range from weekly torque calibration (whether it's needed or not) at an in-house metrology lab, to torque wrenches that have been in the field for 20 years without ever having been calibrated. While these are extremes, there is an easily achievable middle ground that can fulfill the ever-increasing requirements for proper torque application.
New calibration equipment allows small shops and tool cribs to check the calibration of their torque wrenches on site at an affordable price. Proto's new series of -all-in-one torque testers combine both a transducer to measure the torque and a meter to display the applied torque in one rugged metal frame. Cost effective devices like these allow the smaller sized companies to beef up their calibration efforts and record keeping with a minimal investment.
Solving the torque multiplication problem
As mentioned above, special challenges are posed by high torque environments like those found in the energy industry, where large fasteners can require torque application in excess of 1,300Nm. Most high-end tool manufacturers offer torque wrenches of 1,000Nm or more, but these tools are very large, sometimes almost 2 meters in length, and can't always be worked in a limited space. In those cases the only way to achieve enough torque is with a torque multiplier.
A torque multiplier uses a series of gears and a reaction arm to multiply the input torque anywhere from 3.3 to 52 times, depending on the model. While this is impressive, it also introduces additional unavoidable inaccuracies inherent in the process of multiplying torque.
Consider a fastener connection that requires 2,500 Nm of torque to meet engineering design requirements. Using a Proto J6234 Torque Multiplier with a 13.6X multiplication factor (+/- 5% accuracy), the torque wrench providing the input must be set to 184Nm. Let's calculate a worst-case scenario for the resultant output torque. If each tool reads on the low end of calibration, the torque wrench's actual output (-4%) will be about 176 Nm and the multiplier output will be affected by an additional -5%. The resulting applied torque will be only 2,274 Nm, nearly 225Nm lower than the target torque. And remember that these are properly calibrated tools that meet industry specifications! In some cases, this variance from target torque is acceptable – but only if the engineering specs say it's acceptable.
When such variances from design specifications are not acceptable, one new tool that can help users avoid such problems is the Proto Torque Multiplier Display Unit (J6352). It's placed between the output of the torque multiplier and the socket itself. Because it measures and displays the actual applied torque to the fastener – up to 2700 Nm – there's no need for calculations or guesswork. It has an accuracy of +/- 1%, which virtually eliminates final torque errors. The user need only set the target torque level and apply the input torque (even with a standard ratchet); a green light will illuminate and a buzzer will sound when the target torque is reached.
New tools like these meet an important need in the pipeline industry. They make it easier for everyone to meet the torque accuracy requirements so crucial to maintain safety and keep product flowing.
Michael Wuensch graduated in 1989 with a degree in Mechanical Engineering from the University of Texas in San Antonio and has worked in engineering design for 16 years. He has been with Proto for five years – first as a tool designer, then as product manager for wrenches and torque products, providing technical training and introducing new and innovative products into the industrial tool market.
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