I am looking for empirical data or equations that predict the increase in fastener tensile load that results from chisel peening flange edges to stop leaks.
A class 150, 3"nps cast aluminum valve on a 90 psig x 140 degF seal oil system has 3/4" thick FF flanges bolted to 1-1/2" thick wrought steel FF pipe flanges. Each valve to pipe flanged joint is held together by four 5/8" 11 UNC bolts and nuts that compress an O-ring that sits in a groove inside the bolt circle. The seal oil leak is due to a defective O-ring.
A sealant injected enclosure has been considered but determined to be too complex and the risk of sealant ingress to the process too high. Peening the edge of the aluminum into the 'sandwich' created by the steel flange and grade 8 fasteners is considered to be low risk.
The line peen will be made using a small rounded slot chisel in a pneumatic peening gun directed at the edge of the aluminum flange to cause very localized plastic flow and create a compression ridge next to the thick steel flange.
Does the line peen create a compressive load equal to the flange perimeter x depth of peen x poisson ratio x ultimate stress of aluminum? Would this force divided by the total bolt tensile area predict the increase in fastener stress?
