Advancements in engineering design and analysis tools have allowed many new products to be developed for maintaining and operating gas turbines. They are not only safer, but they also allow for faster and easier operation as well as cost savings. Some of these enhancements have become best practices in the industry.

One specific area of improvement is seen in critical fastening applications. A critical fastening application is any bolted joint that requires accurate and uniform bolt loading.

Heat and Slug Wrench Method

In early years of turbomachinery, it was common practice to tighten a nut and bolt through thermal expansion. This process, sometimes referred to as “heat and beat”, was done by heating the stud or bolt to cause the material to expand in length. You tighten the nut with a slug wrench and a large hammer.

Bolt Torque Method

Another method used to tighten fasteners is to apply torque. It is common to see stud sizes well above one inch in diameter, a mechanical torque wrench used by a single person cannot supply enough torque.

To achieve high torque values on studs of larger size, the hydraulic torque wrench was developed. Using hydraulic pressure, it transmits far more torque than a mechanical torque wrench. This enables better bolt loading of large studs.

Hydraulic Bolt Tensioning Method

An alternative to stud heating and hydraulic torque wrenches that has become accepted as a best practice is hydraulic bolt tensioning. Benefits include repeatability and accuracy, as opposed to the high variance in pre-load that exists with both the heat and slug wrench method, as well as the bolt torque method.

A standard hydraulic bolt tensioner fits over the stud and nut. Its threaded adapter grips the exposed threads above the nut.Using hydraulics, the stud is stretched, and the nut can be freely turned down to the flange face.

The problem of friction between threads is another area that is resolved by bolt tensioning. Friction develops in threads of the nut and bolt, as well as when the nut is being tightened onto the flange itself. This tends to gall the material. As a result, the nut can stick and needs to be cut off.

Even if the nut does not gall and stick, friction remains a problem. The amount of friction can vary from bolt to bolt which leads to preload variation. Friction also tends to cause the bolt to wind up, which relaxes over time and loses its initial clamping force. Hydraulic bolt tensioning eliminates this issue.

For applications that do not have enough spacing between the studs for a tensioner, or there are not enough threads exposed above the nut for a standard tensioner to grip onto, a hydraulic rod tensioner can be used. The hydraulic rod tensioner was developed for applications with a very tight radial foot print.

The hydraulic rod tensioner needs a foot print no bigger than that of the original heavy hex nut. This kind of tensioner allows the stud to be as close as possible to one another, which is often the case with many of today’s flange designs.

The perforated nut makes it possible to tension studs that were originally done with torque and therefore did not have the stud length to allow proper thread exposure above the nut for the standard tensioner to grip onto.

There are many different types of hydraulic bolt tensioners available on the market. Various supplier have developed tools which can be used in many different situations. As well as off-the-shelf items, there are specialty designs.

Riverhawk Company is well known as an engineered solutions provider. We have been challenged over the years to develop solutions across many industries: Petrochemical, Oil & Gas, Nuclear, Wind, Industrial and more. General Electric challenged us to upgrade our tooling and develop a safer solution.

The GE legacy tooling manufactured by Riverhawk for the GE Frame 6, 7 and 9 is commonly identified with the yellow guard surrounding the tool. The newly designed tooling, known as the Hydraulic Safety Interlock Guard tensioner (HSIG), has a new guard design that is orange to allow very quick identification.

This new tooling has been designed to provide users with a significantly reduced lift weight during use and a new safety interlock to secure the tensioner in place during the tensioning process. The design reduces the potential for operator error that might cause the tensioner to disengage the stud. In the unlikely event of such disengagement the new guard design will contain the impact and remain clamped on the flange to prevent operator injury. The system is compatible with existing hardware and will be used on all new installations.

The new HSIG tensioner was also designed to address a few key issues customers were having with the older legacy tooling. The issues that Riverhawk addressed were:

Leaking Issues
One issue customers were having was that the legacy tensioner had a tendency to leak. This leaking was a result of over stoking the tensioner. With the new Riverhawk HSIG tensioners, they have been designed to stop the tensioner from getting damaged when over stroked. No longer can you over stroke the HSIG Tensioner, as it has stops to prevent the over stroke condition.

Tensioner Jumping Issues
The other important feature that the HSIG has is its ability to greatly reduce the likelihood of the tensioner jumping. The old legacy tensioner was a one-piece design, so in some applications it was difficult to attach it to the flange and hardware. It was also difficult to see and/or feel if you had the puller screw fully engaged into the stud to be tensioned. The new HSIG Tensioner is assembled onto the stud to be tensioned, in pieces (modular design). This allows the puller screw to be installed by itself and makes it easy to see if the puller screw is fully engaged in the stud.

Riverhawk is dedicated to supplying the very best solutions to our customers. If you are currently experiencing a pain that has no solution, please reach out to our engineering team to discuss.

Strain Gage Accuracy

Measuring torque in a rotating shaft can be done in a variety of ways. Riverhawk has been producing a strain gage based torque measuring system since the late 1970’s (formerly known as Indikon). Strain gages remain the most accurate and direct way to measure strain in a shaft.

Manufacturers of other devices typically use phase shift technology that measures twist across an entire coupling from flange to flange. Over the years, these companies have tried to convince users that the strain gage technology is unreliable.

Riverhawk Torque Meters

Strain gages do fatigue just like any other material. And just like any other material, they will not fatigue if used within the endurance limit of the material. Riverhawk Torque Meters are the only ruggedized strain gage based torque measuring devices that have over 30 years in service with the original strain gages. We work with all major coupling manufacturers to make slight modifications to the coupling spacer tube that limit the strain to well below the endurance limit of the strain gage. We have also developed proprietary mounting and protection techniques that ensure the strain gage will provide reliable output for the life of the coupling.

Benefits of Strain Gage Riverhawk Torque Meters

There are several benefits to a Riverhawk strain gage-based torque meter system….

• Cost Less and Require Less Modification to the Coupling and Coupling Guard
• Measure Torque at Zero Speed
• Add Far Less Weight to the Coupling With a Lower Overhung Load or Moment
• Include Two Complete Calibrated Systems for Redundancy in the Event of Malfunction
• Movement or Location of Mechanical Parts Does Not Affect Accuracy of the Torque Measurement
• Dynamic Torque Option for Instantaneous Measurement, Torsional Vibrations, and Start or Peak Torques

Riverhawk Strain Gage System Upgrades

Riverhawk recently performed an upgrade on a system that was over 20 years old. The old analog electronics were re-vamped and upgraded. The strain gages themselves were left un-disturbed as originally mounted. We simply upgraded to the newer digital electronics package and factory calibrated the system to an accuracy of .25% traceable to NIST standards.

If you have an application and have design questions, our Technical Support Team would be glad to help. Our design engineers have hands on experience with torque measurement systems and can help in several ways. Please contact me, Rick Donegan, if you have product questions or would like additional information on our torque measurement systems.

Hydraulic External Tensioner (HET)

HET’s are tools that apply hydraulic preloads to studs by gripping the exposed threads above an existing nut. It does this by creating axial loads using hydraulic pressure to stretch the stud rather than torqueing the nut. The stud is hydraulically preloaded, the nut is tightened down by hand and the hydraulic preload is released.

Characteristics

• Interchangeable puller screws allow you to use a single tensioner for similarly loaded studs
• Puller screws can be made to fit any type, size and pitch thread
• Any number of tensioners can be linked “daisy-chained” for simultaneous and even loading
• HET can be customized for special applications

Full range of standard HET Tensioners:

• 6 Frame Sizes
• Thread Sizes: 3/4″ up to 4″
• Can Produce Hydraulic Tensioning Loads Up to 890,000 LBF

External Tensioning Nut (ETN)

ETN’s are used with HET’s as a retrofit to existing hardware. When tensioning on the stud is not an option, ETN’s are used to replace the original nut and are externally threaded to allow tensioning. The HET is then threaded onto the ETN to apply hydraulic preload.

Characteristics

• Retrofittable for joints not originally designed for hydraulic tensioning
• Externally threaded nut eliminates the need for studs to be extended above the hex nut
• Can reduce the radial footprint of the nut
• Allows external tensioner to be used on nuts in counter-bored holes
• Utilizes standard HET tensioning platform

HET’s and ETN’s are commonly used in many applications which include:

• Steam Turbine Casings
• Centrifugal Compressor Casing
• Windmill Structure Base Bolts
• Gas Turbine Compressor Tie Rods
• Reciprocating Compressor Crosshead Connections

This blog was written by Shaun LaPolla in the Riverhawk Business Development group. If you have any questions, please contact Shaun or anyone in the Riverhawk Sales group for more information.

Over the past several months, Riverhawk has been performing some extensive testing with a new environmentally safe hydraulic fluid. This potential new fluid is biodegradable and therefore much more environmentally friendly. We have undergone numerous test with this oil to make sure it is compatible with the components we use it in. To date, Riverhawk has completed testing evaluating the oils coefficient of friction, compatibility of being mixed with existing oil, effects on the different seal materials and different coatings. We have also tested its ability to mix with water. All the completed testing has gone well and we intend to replace our existing oil with this new environmentally safe oil in the coming months. We believe this change will be a welcomed improvement by many customers as environmental safety becomes a much more important topic in today’s world. More importantly, there is no cost impact to do this. If you have any thoughts or concerns with this change, please be sure to contact Riverhawk.

This blog was written by Business Development Manager Pat McCormack. He is heavily involved in the testing and evaluation of the environmentally safe hydraulic fluid. Please feel free to contact Pat if you have any questions.

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Sample #3 – Coating 2

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The Riverhawk Torque Blocker is a mechanical fuse that can be installed in a drive train. When a torque overload occurs, the Torque Blocker will release and allow the driver and load equipment to coast down separately without damaging downstream equipment. A torque overload might be caused by short circuit conditions in an electric generator, running restart of electric motors, jams in rolling mills, or liquid slugs in compressors. Either way, the Torque Blocker will release at a preset torque value to protect your equipment. After a release occurs, the Torque Blocker can be reset quickly. An operator pumps up the hydraulic clamp, resets the mechanical pins, drains the oil, and the reset is complete. Although hydraulic pressure is used to set the unit, no hydraulic pressure is used during operation so there is no oil spray upon release.

Riverhawk Torque Blockers are well suited for applications that range from 14,000 to 5 million inch-pounds of torque. We are able to adapt to all kinds of shaft connections. Riverhawk can also provide a turnkey coupling and Torque Blocker combination by connecting our Torque Blocker to most any manufacturers flexible, rigid, or gear coupling.

Please take a moment to check out the animation on our website at the link below to see how a Torque Blocker works and contact Riverhawk Engineering with any questions you might have.

This Blog was written by Riverhawk’s Applications Engineering Director Rick Donegan who can be reached directly at extension 136.

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