Misaligned Stress Review With Stress Paper and Analysis Software

Abstract In fluid transfer systems where piping is connected by bolted flanges, alignment of flanges and correct application of gaskets is essential to achieving a proper seal. Excessive misalignment causes high gasket stress on one side, while the other side of the flange could have stress below minimum gasket seating requirements or an actual gap. Each company has their own standards of misalignment acceptability that could conform to industry standards or be more stringent. This project has incorporated new tools and methodologies to bring additional insights to the industry. Per A SME PCC-1-2022, NONMANDATORY APPENDIX E, the maximum tolerance for the misalignment of flanges is 1/32″ from parallel. With two flanges facing each other, but slightly misaligned, as seen in PCC-1-2022 Figure E-2-3 Parallelism, this misalignment is measured as the difference in gap size from the larger span to the smaller span, often called “bird-beak”. There are many factors that contribute to misalignment such as, but not exclusively, ground settlement or tremors, insufficient supports, unintentional impacts, uneven bolting or relaxing of the system, or material creep. The objective of this study is to understand how different parallelism offsets (0″, 1/64″, and 1/32″) affect gasket performance employing the Multifunction Testing Device TEMES FL.AI1 from AMTEC. This study incorporated shims between an upper and lower plate to mimic the different sizes of an offset. In the gaps between the plate-to-gasket and gasket-to-shim, stress paper is placed. This paper responds to different stress levels by producing various shades of coloring where imprinted, increasing where greater stress is present. Each sheet of stress paper is then processed through a scanner and analysis software. The result is a visually enhanced layout of measurable gasket stresses across the various surfaces where gaskets have been imprinted. Each gasket type is designed, made, or constructed to seal differently and each compensates for various or uneven gaps to different extents. The stress distribution tests with the range of parallelism offsets were conducted on five gasket types: spiral wound gasket with inner and outer ring, high density spiral wound gasket with inner and outer ring, grooved metal gasket with soft facing, optimum recovery corrugated gasket, combination gasket comprised of both grooved metal and optimum recovery corrugations with soft facing. This study and the results advocate for careful consideration of gaskets, particularly where flange misalignment exists. Gaskets with the ability to conform to uneven forces performed better with single sided compensation of misalignment. These results serve as a guide for engineers and industry professionals seeking to optimize sealing solutions, enhancing reliability and performance.