Abstract

A correct bolted flanged joint tightening procedure includes retorquing to restore short-term creep relaxation and embedment losses; the ASME PCC-1-2019 Tightening Method recommends a minimum of 4 hours of dwell time before retightening the bolts.

It is known that in an industrial plant, maintenance costs come mostly from process downtime in addition to the labor and the tools necessary to perform the operation. Reducing the retorque waiting time would make installation quicker and avoid additional — and unnecessary — costs, returning the plant to revenue operation sooner.

This paper explores whether different gasket styles should have the same dwell time between the installation and retorque, and what would be the dwell time to minimize plant downtime without compromising the gasket performance.

The study was performed using a test rig based on a 4” class 300 ASME B16.5 flange equipped with eight strain-gauged bolts that correlates bolt elongation with applied stress. Four dwell times (15min, 1h, 4h and 24h) and different gasket styles and materials such as PTFE, CFG and metallic gaskets were tested. Additionally, two ASME PCC – 1 installation methods were compared and reported: Legacy Cross-Pattern Numbering System and Alternative Assembly Pattern #3. The former is the typical method for flanged joint tightening operations, while the latter offers a simpler, faster execution.

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