David Reeves

The Effect of Bolt Size on the Assembly Nut Factor

This paper details recent testing that was performed as an extension of earlier work on nut factor and high temperature breakout performance of selected anti-seize products. Comparison is made between results obtained using bolt diameters from 3/4 inch to 2 inch, two different anti-seize products (Molybdenum and Nickel) and two different bolt materials (ASTM A193-B7 & ASTM A193-B8M). In addition, common equations used for the determination of achieved bolt load from a given torque are examined and compared from a practical perspective in light of the nut factor test results. The test methods that were used are designed to closely mimic actual bolt assembly in a process plant environment. The paper, therefore, presents useful information that will enable more accurate assembly of bolted flanged joints on pressure vessels and piping in any process plant environment.Copyright

Considerations for Selecting the Optimum Bolt Assembly Stresses for Piping Flanges

In order to minimize the likelihood of leakage from flanged piping joints, it is a good practice to maximize the initial bolt assembly stress. Present bolting guidelines (ASME PCC-1 [1]) use a standard percent of bolt yield to set the assembly stress level. This approach does not allow for the difference in strength between standard pipe flange sizes, differences in material yield strengths (carbon steel versus stainless steel), raised face (RF) versus ring type joint (RTJ) flange configurations and the actual gasket stress achieved across all flange sizes and classes. Since there is no assessment of stresses, such an approach may cause failure of joint components. In addition, because the standard percentage of bolt yield technique does not look at gasket stress, it is prone to gasket leakage due to low stress or gasket destruction due to over-compression for some joints. In addition, some joints may require bolt loads well in excess of the standard value to develop an acceptable gasket stress level in order to prevent leakage. This paper examines an alternative approach, based on the actual gasket and flange stresses. The approach examines the minimum and maximum gasket stress levels to determine what bolt stress range is acceptable and then looks at the flange stresses and flange deformation issues to ensure that the flange will not be permanently damaged, while maximizing the specified bolt load. The practical application of this method is in the development of standard bolt assembly stress (or torque) tables for standard pipe flanges using a given gasket type.Copyright

Pressure Energized Gasket (PEG) Behavior and Seating Stress

This paper summarizes the effect pressure and temperature have on a Pressure Energized Gasket’s (PEG’s) ability to seal, or more specifically the PEG’s gasket seating stress.Copyright

Common Misunderstandings About Gasket and Bolted Connection Interactions

Unfortunately most people’s knowledge about bolted connections comes more from information that has been “passed down” from a variety of sources than a solid understanding of the physics and science that impacts pressure boundary bolted connection reliability. A correct understand of bolt and gasket interactions gives a person the skills to reliably solve a variety of sealing application problems. This paper looks at some of the more significant misunderstandings that inhibit people’s ability to effective resolve and prevent problems with bolted connections.Copyright

A Simple Recipe for Solving all Refinery Sealing Issues

Hundreds of papers have been written and presented over the years about bolted connections, what impacts reliability and how to get them to operate leak free. Are bolted connections really that complicated that only experienced, dedicated and highly educated engineers should be involved with the joint design, as well as the assembly of connections out in the field? Clearly not, or hundreds of companies could not stay in business. This paper summarizes some simple steps for making all kinds of bolted connections leak free, including heat exchangers and pipe flanges, and just about any other pressure boundary bolted connection found in a refinery.Copyright

Anti-Seize, Friend or Foe, the Properties That Really Matter!

There is a lot of misinformation published about anti-seize compounds around friction (or K factors) factors and temperature limits. Anti-seize materials exist to serve two functions, to help even out stud stresses/preloads during assembly, and most importantly, allow the components to be taken apart after they have been exposed to heat. This paper looks at how different anti-seize materials are affected after being exposed to enough heat to burn off the grease base.Copyright

The Influence of Winding Density in the Sealing Behavior of Spiral Wound Gaskets

Spiral wound gaskets are used worldwide in piping and equipment flanges and can be manufactured in several combinations of materials, and in a wide range of dimensions, winding densities and shapes. This paper shows the sealability influence of winding densities, which are not specified by the current Spiral Wound B16.20 gasket standards, including flexible graphite filler thickness, height and number of windings. The effect of the flange rotation is also shown.Copyright

Spiral Wound Versus Flexible Graphite Faced Serrated Metal Pipe Flange Gaskets in Thermal Cycling and Pressure Comparative Testing

Spiral Wound gaskets have been successfully used in ASME B16.5 pipe flanges. However, in the last few years, to increase the reliability and safety, there has been a trend to replace them by graphite faced serrated metal gaskets. These are assumed to be better in terms of relaxation and installation. This paper shows a comparison between these two gasket styles. Relaxation and leak tests were performed using standard studs and flanges to simulate actual field conditions.© 2010 ASME

Heat Exchanger Gaskets Radial Shear Testing

Due to the high incidence of leaks in Shell and Tube Heat Exchanges that are in thermal cycling service, there have been studies of the suitability of gasket styles for this kind of application. This paper researches several gasket styles in a test rig developed to simulate the radial shear caused by the differential thermal expansion of the flanges in a Heat Exchanger.Copyright

An Update on Selecting the Optimum Bolt Assembly Stress for Piping Flanges

In order to minimize the likelihood of leakage from flanged piping joints, it is a good practice to maximize the initial bolt assembly stress. Present bolting guidelines (ASME PCC-1 [1]) outline the use of a percent of bolt yield across all flange sizes and classes to set the assembly stress level. These guidelines do indicate that aspects such as component strength and gasket stress should be considered, however the most common application of the approach is to use a standard percentage of bolt yield across all flange sizes and classes. This approach does allow for adjustment for differences in material yield strengths (carbon steel versus stainless steel) and raised face (RF) versus ring type joint (RTJ) flange configurations. It does not, however, adjust for the difference in strength between standard pipe flange sizes nor the actual gasket stress achieved across all flange sizes and classes. Since there is no assessment of flange strength, such an approach may cause failure of joint components. In addition, because the standard percentage of bolt yield technique does not look at gasket stress, it is prone to gasket leakage due to low stress or gasket destruction due to over-compression for some joints. In addition, some joints may require bolt loads well in excess of the standard value to develop an acceptable gasket stress level in order to prevent leakage. This paper is a continuation of the paper presented during PVP 2006 in Vancouver (Brown [2]), which examined the variables that must be considered and drew some preliminary conclusions regarding the use of flange stress limits in determining the maximum allowable bolt load for a given flange size. Subsequent to writing that paper, further investigation found that the code calculated flange stresses are a poor indicator of the maximum acceptable bolt load. The most practical measure of this load is obtained by using elastic-plastic finite element analysis (FEA) to determine the point of gross plastic deformation of the flange. This paper details the maximum bolt load limit results of elastic-plastic FEA on most sizes of standard ASME weld neck flange sizes. The practical application of this method is in the development of standard bolt assembly stress (or torque) tables for standard pipe flanges using a given gasket type. In addition, a new code equation and additional limits are developed, by comparison to the elastic-plastic FEA results, which allow the determination of the maximum assembly bolt load for non-standard weld-neck flanges and standard weld-neck flanges with different bores, materials or gaskets than used in the elastic-plastic FEA presented in this paper.Copyright