Weld Residual Stresses and Primary Water Stress Corrosion Cracking in Bimetal Nuclear Pipe Welds

Pressure Vessel ◽

Large Diameter ◽

Corrosion Cracking ◽

There have been incidents recently where cracking has been observed in the bi-metallic welds that join the hot leg to the reactor pressure vessel nozzle. The hot leg pipes are typically large diameter, thick wall pipes. Typically, an inconel weld metal is used to join the ferritic pressure vessel steel to the stainless steel pipe. The cracking, mainly confined to the inconel weld metal, is caused by corrosion mechanisms. Tensile weld residual stresses, in addition to service loads, contribute to PWSCC (Primary Water Stress Corrosion Cracking) crack growth. In addition to the large diameter hot leg pipe, cracking in other piping components of different sizes has been observed. For instance, surge lines and spray line cracking has been observed that has been attributed to this degradation mechanism. Here we present some models which are used to predict the PWSCC behavior in nuclear piping. This includes weld model solutions of bimetal pipe welds along with an example calculation of PWSCC crack growth in a hot leg. Risk based considerations are also discussed.

Primary water stress corrosion cracking in alloy 600 and intergranular crack growth rate

Metals and Materials International ◽

10.1007/s12540-010-0416-x ◽

2010 ◽

Vol 16 (2) ◽

pp. 267-271 ◽

Cited By ~ 5

Author(s):

Y. C. Jung ◽

H. S. Chung ◽

K. S. Lee ◽

N. H. Heo

Keyword(s):

Growth Rate ◽

Water Stress ◽

Crack Growth Rate ◽

Stress Corrosion ◽

Crack Growth ◽

Intergranular Crack ◽

Corrosion Cracking ◽

Alloy 600 ◽

Stress Corrosion Cracking (SCC) of Nickel-Base Weld Metals in PWR Primary Water

Materials Science Forum ◽

10.4028/www.scientific.net/msf.747-748.723 ◽

2013 ◽

Vol 747-748 ◽

pp. 723-732 ◽

Cited By ~ 2

Author(s):

Ru Xiong ◽

Ying Jie Qiao ◽

Gui Liang Liu

Keyword(s):

Residual Stresses ◽

Stress Corrosion ◽

Surface Condition ◽

Cold Work ◽

Corrosion Cracking ◽

Pressurized Water ◽

Weld Metals ◽

Surface Residual Stresses ◽

This discussion reviewed the occurrence of stress corrosion cracking (SCC) of alloys 182 and 82 weld metals in primary water (PWSCC) of pressurized water reactors (PWR) from both operating plants and laboratory experiments. Results from in-service experience showed that more than 340 Alloy 182/82 welds have sustained PWSCC. Most of these cases have been attributed to the presence of high residual stresses produced during the manufacture aside from the inherent tendency for Alloy 182/82 to sustain SCC. The affected welds were not subjected to a stress relief heat treatment with adjacent low alloy steel components. Results from laboratory studies indicated that time-to-cracking of Alloy 82 was a factor of 4 to 10 longer than that for Alloy 182. PWSCC depended strongly on the surface condition, surface residual stresses and surface cold work, which were consistent with the results of in-service failures. Improvements in the resistance of advanced weld metals, Alloys 152 and 52, to PWSCC were discussed.

Mechanical Stress Improvement Process (MSIP) Used to Prevent and Mitigate Primary Water Stress Corrosion Cracking (PWSCC) in Reactor Vessel Piping at V.C. Summer

Aging Management and Component Analysis ◽

10.1115/pvp2003-2160 ◽

2003 ◽

Author(s):

E. A. Ray ◽

K. Weir ◽

C. Rice ◽

T. Damico

Keyword(s):

Water Stress ◽

Stress Corrosion ◽

Mechanical Stress ◽

Reactor Vessel ◽

Corrosion Cracking ◽

The Other ◽

Water Reactor ◽

Improvement Process ◽

During the October 2000 refueling outage at the V.C. Summer Nuclear Station, a leak was discovered in one of the three reactor vessel hot leg nozzle to pipe weld connections. The root cause of this leak was determined to be extensive weld repairs causing high tensile stresses throughout the pipe weld; leading to primary water stress corrosion cracking (PWSCC) of the Alloy 82/182 (Inconel). This nozzle was repaired and V.C. Summer began investigating other mitigative or repair techniques on the other nozzles. During the next refueling outage V.C. Summer took mitigative actions by applying the patented Mechanical Stress Improvement Process (MSIP) to the other hot legs. MSIP contracts the pipe on one side of the weldment, placing the inner region of the weld into compression. This is an effective means to prevent and mitigate PWSCC. Analyses were performed to determine the redistribution of residual stresses, amount of strain in the region of application, reactor coolant piping loads and stresses, and effect on equipment supports. In May 2002, using a newly designed 34-inch clamp, MSIP was successfully applied to the two hot-leg nozzle weldments. The pre- and post-MSIP NDE results were highly favorable. MSIP has been used extensively on piping in boiling water reactor (BWR) plants to successfully prevent and mitigate SCC. This includes Reactor Vessel nozzle piping over 30-inch diameter with 2.3-inch wall thickness similar in both size and materials to piping in pressurized water reactor (PWR) plants such as V.C. Summer. The application of MSIP at V.C. Summer was successfully completed and showed the process to be predictable with no significant changes in the overall operation of the plant. The pre- and post-nondestructive examination of the reactor vessel nozzle weldment showed no detrimental effects on the weldment due to the MSIP.