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Structural Integrity Associates, Inc. (SI), of San Jose, California, announced a service that permits power plants to operate safely without repairing piping flaw excavations. The need to weld repair excavations made for surface flaw removals is usually determined by whether the remaining wall thickness satisfies ASME pressure thickness code. This conservative criterion results in repairing excavations that, in actuality, do not degrade safe plant operation. Such repairs add unnecessary time and costs to plant outages.

Relying on related ASME Code design rules for local thin areas, SI developed a methodology and software for rapid evaluation of these excavations. Typically, evaluations using this methodology show many excavations as acceptable without weld repair, even though net thickness is less than Code required pressure thickness.

The need to weld repair excavations made for removing surface cracks and other defects is typically determined by whether the post-excavation net wall thickness satisfies ASME Code for pressure thickness (Section I for boilers, Section VIII for pressure vessels, B31.1 Code for piping). This criterion is restrictive since many components do not have pressure thickness much above Code.

Relying on related ASME Code design rules for local thin areas, SI developed a methodology and software for rapid evaluation of these excavations. The software performs a three-dimensional finite element stress analysis for stresses due to pressure, deadweight, and thermal effects, and compares these stresses to Code allowables for local thin areas.

A sample evaluation performed for a utility indicated that a 6-inch long excavation in the girth weld of a hot reheat pipe was acceptable without weld repair, even though the net thickness in the excavation was only 85% of Code required thickness. The methodology was reviewed and approved for use on high-energy piping and pressure vessels by the utility's insurance carrier.

SI offers this evaluation as a service. Results can typically be provided in short turnaround, allowing plant personnel to make a quick decision concerning the need for weld repair (subject to approval by the applicable state agency).

Structural Integrity Associates, Inc., headquartered in San Jose, California, with offices and affiliates in five states, has been providing engineering consulting and inspection services to the utility and other industries for over 15 years. The company is well known for its expertise in the prevention, control, and repair of structural failures for a broad range of industries.