(186e) Fatigue Cracking of Small Diameter Branch Connection at Pressure Relief Valve

Small diameter branch connections for instrumentation and bleeders are a necessity in piping systems
but also a vulnerability, in particular around sources of vibration. Operating plants have multiple
sources of vibration, for example, rotating equipment often provides sufficient input frequency to excite
natural harmonics of small branch connections. A discharging Pressure Relief Valve (PRV) can also lead
to similar issues.

These vibrations can lead to fatigue cracking and separation resulting in significant downtime and
Process Safety Risk. This paper will present one such case, where a small diameter connection adjacent
to a PRV cracked at the pipe wall following a series of relieving events during unstable operations.

This paper aims to raise awareness by sharing a case where vibrations are generally not observed
(during the act of PRV relieving) and can result in a small diameter piping failure in a relatively short
duration. The paper will also share some mitigations pursued following this event to reduce the
potential for vibrations and some measures to limit the risk should they occur.