INTER-GRANULAR STRESS CORROSION CRACKING IN THE HEAT AFFECTED ZONE OF THE PRESSURIZER SPRAY LINE PIPING OF A PRESSURIZED WATER REACTOR

Abstract

A circumferential crack was detected during an in-service inspection of the pressurizer spray line piping of a pressurized water reactor (PWR). Destructive investigation revealed an inter-granular crack with a depth of 4.4 mm, which was propagated in the weld heat affected zone (HAZ) of a 316 stainless steel. The line is filled with hydrogenated PWR primary water, assuming oxygen stagnation is not a primary cause. The detailed initiation mechanism is still unclear, and the propagation was considered inter-granular stress corrosion cracking of extremely high hardened HAZ. The potential cause of the high hardness is the superimposition of high heat input and constrain condition of nozzle shape.

The result of crack growth simulations using EPRI MRP458 explained reasonably the cracking process. The calculated propagation of a tiny crack from 0.5 to 4.4 mm depth was 9 years, which is within the operation time of the Ohi-3 (i.e., 19.3 effective full power year).