(128b) Transfer Line Exchanger Fitness for Service Analysis Case Study: Assessing Erosion for Remaining Life Prediction

Ethylene furnace transfer line exchangers (TLE’s) are often designed with minimal erosion or corrosion allowance on the tubes in order to keep the tubes as thin as possible. This is done to keep the high tube side gas temperatures from overheating the tubes which receive cooling from the boiler feed water on the shell side. Typically, when the tube wall loss from inner diameter erosion (or other damage mechanisms) or outer diameter corrosion causes the tube thickness to fall below design thickness, the tube must be replaced. Alternatively, if the thinning is confined to a small local area, a fitness for service (FFS) analysis may allow for continued safe operation with tubes thinned below the design thickness, provided the FFS established local area minimum thickness is not exceeded. This paper provides a case study of a FFS analysis that provided for continued safe operation of TLE tubes that were thinned beyond the original design thickness. The owner/user, TLE OEM, and a 3^rd party engineering contractor collaborated in this analysis. The paper will discuss how the results of this analysis can be used to replace tubes selectively and continue safe operation.