Materials Engineering, Evaluation, and Inspection

Stress Corrosion Cracking

Stress corrosion cracking (SCC) is cracking induced by the combined influence of tensile stress and corrosive environments. SCC can affect materials in a number of ways, from dry cracking to catastrophic failure. Tensile stresses may be directly applied residual, and the problem is often very complex. The formation of SCC in buried pipelines is particularly complicated.

NACE estimates that over 98% of pipelines are buried. No matter how well these pipelines are designed, constructed and protected, once in place they are subjected to environmental abuse, external damage, coating disbondments, inherent mill defects, soil movements/instability and third party damage.

SCC can be very deceptive, and unlike a wall thinning rupture can often involve no loss of pipeline metal. Locating and removing SCC cracks before the pipeline bursts is obviously in the best interests of all concerned. While SCC can occur in both gas and liquid pipelines, it is seen more frequently and with more disastrous results in gas pipelines.

Spectrum provides proven methods for locating external pipeline SCC involving a combination of high quality data collection and thorough evaluation of information from a variety of pipeline parameters and survey procedures.

Stress Corrosion Cracking Direct Assessment

Stress corrosion cracking direct assessment (SCCDA) is a NACE process intended to assist pipeline companies in assessing the extent of SCC on a section of buried pipeline. Guidance is provided in NACE documentation (part A3 of ASME(1) B31.8S,1) which identifies several options for inspection and mitigation activities. The recommended practice for SCCDA presented in standard NACE RP0204-2004 addresses the situation in which a pipeline company has identified a portion of its pipeline as an area of interest with respect to SCC based on its history, operations, and risk assessment process and has decided that direct assessment is an appropriate approach for integrity assessment.

The standard provides guidance for managing SCC by selecting potential pipeline segments, selecting dig sites within those segments, inspecting the pipe and collecting and analyzing data during the dig, establishing a mitigation program, defining the re-evaluation interval, and evaluating the effectiveness of the SCCDA process. Spectrum assists your SCCDA program with very experienced, highly skilled specialists performing appropriate NDT activities at your facility while preparing the documentation necessary for the success of your SCCDA objectives.