Woodside had been experiencing intermittent blockages in 4/5 S1406 LNG trains since September 2008 and had been unable to pinpoint the source of the problems.
Repeated hydrate formations were leading to reduced productivity and the existing process monitoring instrumentation had failed to confirm moisture breakthrough on the beds. The site's existing Panametrics portable moisture analysers had proven susceptible to drift in both use and storage, exhibiting large hysteresis errors. Tests proved they were very slow to settle at the low moisture concentrations of interest making them unfit for such a diagnostic purpose.
A specialist in trace moisture measurement was contracted to carry out an independent moisture audit and performance assessment of the existing process monitoring moisture analysers in order to determine the source of water leading to the hydrate formations.
In order to determine the root cause there was a need to work through the process, starting at the mol sieve drier beds and systematically work downstream in order to quantify the contribution from each stage of the process and validate each test result against a known reference moisture source, before proceeding to the next test.
MCM. the contractor, provided the necessary moisture measuring instrumentation and validation techniques needed to confirm the source and quantity of any unexpected moisture found during the audit.
Woodside's process engineers requested MCM to focus on 3 areas of potential sources of water ingress, these being;
- The driers which could, if incorrectly packed, lead to channelling in the desiccant;
- The mercury guard beds and C02 scrubbers in the analyser house; as these were known to take a long time to reach equilibrium and may have been put into service prematurely by being insufficiently dried down;
- The defrost systems on both trains, which, if compromised could be leaking.