Full Description

This Bulletin documents a European experimental study conducted on behalf of the "pressure vessel equipment industrial piping commission of CETIM". This experimental work was conducted, funded and published in French by CETIM. The PVRC BFC initiated Project 01-BFC-01 to provide detailed English interpretation of this important work. The work itself was inspired by PVRC BFC Project 97-04 "Effect of Bending Moments on the Tightness of Bolted Flange Gaskets", now published within WRC Bulletin 473. It demonstrated that external moments applied to a joint have little effect on the tightness of a properly tightened joint, raising the question: to what degree would flange misalignment affect the tightness of the same joint and assembly bolt loads?

In this study, the tightness of a CEN joint with fiber reinforced and expanded graphite gasket sheets and graphite filled spiral wound gaskets was measured for various types and degrees of flange facing misalignment. These misalignment "defects" were axial (10mm), radial (10mm) and angular (1.5, 2.5). Upon the application of "proper" bolt loads, leak tightness was directly measured for each defect case over a range of internal pressures up to 4 MPa (580 psi). The CEN study joint is similar to an ASME B16.5 NPS 8 Cl 300 pipe joint.

The spiral wound gasket was the most alignment sensitive, and angular (non-parallel facing) misalignment defects had the most influence on assembled joint tightness. The 2.5 defect could not be sealed for the spiral wound gasket! Although this finding is for a specific test system or "piping system stiffness", and a less stiff system may have sealed adequately, it is nevertheless useful to have a direct experimental conformation of specific angular misalignment effects. A similar study for an ASME B16.5 NPS 8 Cl 300 joint has been proposed but remains un-funded.

The reader of this Bulletin may find sufficient information to formulate a rule for the allowable amount of misalignment in piping system joints with known stiffness and gaskets. It could be argued that angular flange misalignment sufficient to be excessive for a critical pump nozzle flange might also be excessive for flanged joints in general. Therefore the alignment rule for critical pump nozzle flanges suggested by Appendix 1 of WRC Bulletin 449 might also be considered useful for application to piping system joints in general given the findings of this Bulletin.

Product Details

Published: 2006 Number of Pages: 48 File Size: 1 file , 2.7 MB