Life Extension of Equipment

1Q. What is meant by Life Extension of Equipment?

1A. As pressure vessels, tankage, piping and similar equipment age they undergo various degradations. Corrosion or the wasting away of the metal, weld cracking, pitting, and other mechanisms reduce the life of a vessel with time. While processing plants may be initially designed for 20 years operation, they always seem to exceed that by a factor of 3 or more. Purchasing new vessels and piping would be prohibitive for most plants. To extend the life of these vessels analytical methods are available in publication such as API 579. These methods determine if the deteriorated area is still acceptable or what should be done if it is not. For example, if a large tank has corrosion at the soil line it may be possible to just blend grind the area, protect it from further corrosion with a coating or treatment, lower the fill height and continue to operate. This could be more cost effective than having to take the tank out of service, cut out the section and weld in a new course and perform a hydrotest.

2Q. What is Life Extension of a machine?

2A. Let's use the example that during an inspection of a compressor a crack is found in the shaft, and can't be repaired. A new shaft can be fabricated in two weeks. A large production loss will occur if the compressor has to remain out of service for this period. In four weeks however a planned outage is scheduled for another grade change. Can the compressor be brought back into service and continue to run until then. A failed shaft would result in a catastrophic failure with a long downtime. Using crack growth calculations it can be determined how long it will take, under the operating stresses, for the crack to grow to and unacceptable size. Many times it can continue to operate and the engineer becomes the production managers good friend. It works the other way too.

3Q. Are Life Extension methods always complex?

3A. No. Many times with corrosion they involve sandblasting or wire brushing, inspecting, applying a protective coating, such a paint and defining the next inspection and recording it all.