Maintenance of pressure safety valves (PSVs) requires them to be taken out of service, tested and then refurbished. This is a costly process and the requirement for the PSV to be removed from service can drive the need for a shutdown with a far bigger cost. The customer challenge is to optimize the PSV maintenance while maintaining or even improving safety.
DNV GL solution
The approach taken was to ensure that the risk from potential failure of each PSV to operate (lift) if required was below a threshold by setting a maximum maintenance interval and then to use as wide a set of relevant data as possible to determine if this maximum was justifiable, or if a reduced interval was required. This process included:
- Defining categories of PSVs operating under similar conditions such that good performance within a group of PSVs could be used to increase the interval for those with a lack of data
- Cautiously increasing the interval if there is sufficient evidence of good performance
- Gathering data at regular intervals to update the RBI results.
Outcome and benefits
The consistency of the approach allowed 4,000 PSVs to be assessed within a month. In the first year of the assessment, a 15% maintenance reduction was achieved, combined with an improvement in safety due to maintenance efforts being concentrated (lower maintenance intervals) on the worst performers. In subsequent years, further reductions in maintenance were achieved while safety was maintained, with the client also having total visibility of the justification for any changes.