Laser Peening Components Increases Inspection Intervals

Laser Peening:  The new EPRI report, Materials Reliability Program: Topical Report for Primary Water Stress Corrosion Cracking Mitigation by Surface Stress Improvement (MRP-335 Revision 2), published August 13, 2015 states:
“The objective of this report is to define appropriate inspection requirements and intervals for certain components – Alloy 600 reactor pressure vessel head penetration nozzles and Alloy 82/182 dissimilar metal welds in primary system piping – that have been treated by surface stress improvement (SSI) methods (that is, peening) for the purpose of mitigating primary water stress corrosion cracking (PWSCC)… Given the demonstrated effectiveness of SSI techniques such as laser peening and water jet peening (aka cavitation peening), relaxation of the inspection requirements for these components is appropriate after SSI treatment.”
The report provides a general review of laser peening as a surface enhancement process that imparts deep compressive residual stresses via the interaction of the laser strike and plasma, and the resulting shock wave producing pressures above the yield strength of the material causing plastic deformation.  Laser peening effects are achieved through a precision control of the laser energy, pulse duration, spot size, location on a part, and the number of times the area is covered.  Laser peening is concluded to be effective based shot peening data and considering the substantiation provided in these details:

• “Extensive industrial experience shows that peening of many types is effective at inhibiting the initiation of both fatigue and stress corrosion cracks”
• “These peening processes do not result in growth of any pre-existing flaws during peening, and that they prevent growth of flaws with depths less that the depth of the compressive stress field developed by peening”
• “No adverse effects have been identified”

Click here for the free download of the entire report.