The in-situ SSM system performs nondestructive field measurements of local key mechanical properties of pipeline base materials and welds. These properties include the yield strength (which determines the grade of the pipeline steel material and the maximum safe operating pressure), true-stress versus true- plastic-strain curve, strain hardening exponent (uniform ductility), strength coefficient, ultimate tensile strength, and initiation fracture toughness (which determines the critical size of service-induced sharp cracks). The SSM technology has been reviewed by the US Office of Pipeline Safety (OPS) of the Department of Transportation (DOT) and is recommended for use by the pipeline industry.
The SSM system utilizes an ABI® technique that is nondestructive, fast, and very accurate. The ABI® test requires a reasonable localized polishing of the test area for indentation testing. The spherical indentations produced on the pipeline surface are shallow, smooth depressions (i.e., no sharp edges and, hence, no stress concentration sites). Furthermore, the ABI® test leaves a compressive surface residual stress that retards crack initiation (similar to the shot peening process used routinely in the aerospace industry). Therefore the ABI test, although a true/robust mechanical test, is considered for practical purposes nondestructive. Thousands of ABI® tests have been conducted on ferritic steel samples, including grades from B to X100 of pipeline steels, at various test temperatures. Also, numerous ABI® tests have been conducted in the field (at ambient temperatures) on pipelines in the USA, Europe, Africa, and Asia. The integration of the SSM-measured key mechanical properties with the crack sizes and/or the maximum depth and spacing of corrosion pits, measured using ultrasonic and other techniques, allows a deterministic structural integrity assessment (DSIA), the calculation of the maximum safe transmission pressure for these pipelines, and will allow safe up-rating (increased transmission throughput).