Preparation of surface replicas is considered a type of visual test.  It has proven to be a valuable tool for analysis of fracture surfaces and microstructure and for documenting certain types of corrosion wear.  HRSG applications are typically to determine whether creep damage is occurring in susceptible high temperature steam piping including the HP Steam and Reheat piping.  In these applications, surface replication is used to attempt to quantify the localized strain in steels that have been exposed to high temperature and stress for long periods. 

Surface replicas are typically obtained by wetting cellulose acetate tape with acetone, allowing it to soften and applying it to a carefully prepared and etched section of the piping surface.  When the tape is removed, the topography of the surface is preserved and it can be examined in the laboratory under an optical microscope or scanning electron microscope (SEM) to evaluate changes in the metal microstructure that are indicative of the various stages of creep damage. This technique should be performed by qualified individuals who have been trained to prepare surface replicas.  It should not be attempted by plant staff or general mechanical contractors; this is a technique that requires a specialist.  Contact an inspection contractor who is experienced in the use of this technique for power boiler applications.

References

[1] Jackson, P. Moelling, D. Malloy, J. Taylor, M. HRSG Inspection Planning Guide - Second Edition, 2006. ISBN 0-9719616-2-X