Technical Bulletin

Effective Management of Seam Welded Cold Reheat Piping

A recent catastrophic failure of a cold reheat piping system has raised awareness and concern for the existing condition and long-term serviceability of these systems. This represents the second reported failure in the last seven years in these systems. Initial information released on the incident indicates an ID initiated fatigue failure along a longitudinal seam weld toe downstream of an attemperator during normal operation of the unit. Additional evaluations of the failure are on-going.

Historically, these systems have not been part of High Energy Piping Risk Management Programs since they typically operate at temperatures below the creep regime. However, due to these failures it is now apparent that additional evaluations of CRH piping systems are prudent.

Structural Integrity Associates has long been known as the industry leader in comprehensive Asset Management through the application of an integrated, multi-disciplined approach to critical component assessment. To address these new concerns SI has analyzed the available system, component and damage mechanism information to develop the most economical, effective, and quantitative assessment methodology.

The result of this effort indicates that that a systematic evaluation of unit operational history combined with quantitative inspections of the welds is the preferred approach. Inspections should include examination of the attemperator condition, piping geometry, and weldments. Weldment inspections should include techniques capable of identifying both OD and ID initiated cracking at longitudinal seam and girth welds. The inspection of the OD surface should include magnetic particle testing. The Time of Flight Diffraction (TOFD) ultrasonic technique provides the ideal attributes for the detection and quantitative characterization of ID initiated cracking in CRH piping weldments. TOFD can detect, accurately size, and characterize indications in a single scan. TOFD is capable of distinguishing between original fabrication flaws and service related damage. As importantly, TOFD provides a digital record of the entire inspection that can be used with results from subsequent inspections to develop unit specific damage trends. TOFD applied to CRH welds offers productivity rates unmatched by conventional methods. Imaging of 200 plus feet of weld a day per team are typical and include not only indication detection but also accurate flaw classification and sizing.

To discuss your CRH Piping Assessment Program contact Matthew Dowling at info@structint.com.

Actual field TOFD Image of a fatigue crack in a weldment.