What happened?
During a recent inspection at a facility, an NOPSEMA inspector observed vibration-induced fatigue cracking and evidence of rectification work carried out on several small-bore connections on seawater cooling pipes. On further investigation, it was discovered that there had also been a recent fatigue failure on the hydrocarbon test separator header. Fortunately, the operator had detected hydrocarbon leaking out of the crack and the line was repaired without any major release of hydrocarbons. The operator of the facility initially did not report the incident as a dangerous occurrence (damage to safety critical equipment), as it was considered only a “minor weep”.
What could go wrong?
In certain situations, vibration-induced fatigue could lead to a loss of containment of a significant quantity of hydrocarbons, which if ignited could result in a major accident event involving multiple fatalities.
Key lessons:
- The risk of vibration-induced fatigue on hydrocarbon facilities must be thoroughly assessed. All types of excitation should be considered, including:
- flow induced turbulence
- mechanical excitation
- pulsation from reciprocating and positive displacement pumps and compressors, rotational stall, and flow induced excitation
- High-frequency acoustic fatigue
- surge/momentum changes due to valve operations
- cavitation and flashing.
The Energy Institute, based in the United Kingdom, has developed guidelines for the avoidance of vibration-induced fatigue failure in process pipework. The guidelines can be used from the design stage through to the operational stage in the life of a facility to identify and address pipework at risk of vibration-induced fatigue.