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Guidelines for In-Situ Characterization of Cracks
Stress Corrosion Cracking (SCC) theory postulates two mechanisms for crack growth and initiation; intergranular crack propagation associated with classical or high pH SCC and transgranular crack propagation associated with near-neutral pH SCC. Metallography is a method for distinguishing between the two forms of SCC by observing the mode of crack propagation.
The purpose of this project was to establish a practical metallographic protocol to distinguish between high pH SCC and near-neutral pH SCC in the ditch. The protocol addresses how to distinguish the crack propagation modes. In addition, the protocol addresses procedures for preparation of sample location areas for analysis through the use of mechanical, electrical, and chemical means considering the quality of results, ease of use, portability, and reliability.
Key Results
An “in-the-ditch” SCC identification and characterization protocol was developed that included identification of surface breaking cracks with magnetic particle inspection and metallography. A conventional grind-polish and etch surface preparation procedure coupled with in-situ microscopy and a crack mode assessment methodology was established for in-the ditch use.