Enhanced methodologies used for the assessment of high-temperature header girth welds

Abstract

Inspections performed during 2003 and 2004, have shown a significant increase in the number of occurrences of advanced cracking in superheater and reheat header girth welds. These cracks have been observed: • at several plants within different utilities • in both header body girth welds and header-to-tee girth welds • in headers of different manufacturers and • in headers with and without ligament or stub tube weld cracking. In addition, there has also been an increase in the number of main steam and hot reheat piping girth weld failures that exhibit characteristics similar to the aforementioned header girth weld cracking. In a number of incidences cracking has been confirmed to have initiated mid-wall and in some cases propagated to through-wall failure. The use of linear phased array ultrasonic testing (UT) has been shown to be effective • in determining girth weld profiles, • in the detection and sizing of macro-cracking, and • in locating macro-damage relative to the weld geometry. Similarly, annular phased array UT has been shown to be effective in the detection of incipient creep cavity development before the onset of microcracking. In addition, long-range guided wave UT has been used on piping systems to determine the location and type (e.g., field or shop) welds without extensive scaffolding or insulation removal and with the anticipated advantage of being a screening technology for welds with extensive cracking. This paper will present Structural Integrity Associates (SI) experience with high-temperature header girth weld cracking and the enhanced non-destructive examination (NDE) techniques applied to the detection and quantification of damage.