TWI was approached by a Research Member to give an independent assessment of major components in a refinery that they were considering for purchase. The plant had been built in the 1960s to the ASME codes and operated for over 100,000hr in various campaigns during a 14 year life. Economic circumstances then led to the plant being shut down for several years. The plant was refurbished and run for a further period (less than one year) before finances again led to it being shut down. TWI staff visited the plant to collate the fabrication, operation and maintenance information that was available in the plant records. The site visit included visual inspection of various items of plant that were considered critical to the viability of the refinery.
From the temperature and pressure records available for the reactor pressure vessels, piping and furnaces, it was possible to build up a reasonable picture of the service exposure seen by these components. The fabrication drawings revealed the materials used, and the design operating conditions. Ultrasonic inspection records showed the vessel wall thicknesses (even following the corrosion loss due to 100,000hr service) still exceeded the specifications. A preliminary Remaining Life Assessment (RLA) calculation showed that only a very small fraction of the available life had been consumed in all of the pressure vessels and most of the tubing.
One furnace was found to have tubes which had been running at temperatures in excess of the design specification. The cumulative life fraction calculation for this tubing was large compared to the other components assessed, indeed, it exceeded unity, indicating that failure would have occurred if the material had been 'lower bound' in its creep resistance. Visual inspection of this furnace revealed severe sagging and bulging of the lower rows of tubes, ie considerable creep strain accumulation. Metallographic examination during the refurbishment had revealed extensive creep cavitation damage. It was recommended that this furnace should be at least partially retubed before it entered further service.
With the exception of the one furnace described above (where problems with the layout of the burners had led to excessive service temperatures), it was thus possible, as a result of the RLA (which took less than one week), for the prospective buyers to gain considerable confidence that there was a worthwhile operating future for the plant.