Mitigation of stress corrosion and fatigue by surface conditioning

Abstract

Method and apparatus for surface conditioning a metal surface typically having irregular surface contours, by rubbing the metal surface with a surface conditioning device having a plurality of bristles which contact the metal surface during the rubbing and effect tensile stress reduction or degraded layer removal in the metal surface.

Description

[0001]The present invention relates to a method and apparatus for providing mitigation of stress-corrosion cracking (SCC) and fatigue initiation in metallic components, including for example base metals and welds in austenitic stainless steels and nickel-base alloys. In particular, the invention provides a method and apparatus for mechanical surface conditioning of metals to mitigate susceptibility to crack initiation or growth of small cracks due to tensile surface stresses.BACKGROUND OF THE INVENTION[0002]Stress-corrosion cracking (SCC) in metals is generally known to be caused by the simultaneous presence of a susceptible material, an aggressive environment, and tensile stresses. In the past, mitigation of SCC has focused on reducing or eliminating one or more of these causes, either in the bulk state or locally at the exposed work surface.[0003]Conventional peening and burnishing processes, including water-jet peening, laser shock peening, shot peening, hammer peening, and rolle...

AI Technical Summary

Benefits of technology

[0007]It has now been discovered, surprisingly, according to the present invention, that it is possible to effect surface conditioning of a metal surface by rubbing the metal surface with a surface conditioning means comprising a plurality of abrasive bristles. The stretching action of the abrasive in the bristles on the metal surface during the rubbing causes tensile stress reduction in the metal surface.

Problems solved by technology

Conventional peening and burnishing processes, including water-jet peening, laser shock peening, shot peening, hammer peening, and roller or ball burnishing, are known to locally reduce surface stresses, but do not reduce the micro-structural, micro-chemical, or micro-geometrical susceptibility of the material surface, and do not refresh degraded surfaces due to abusive fabrication practices or to service in an aggressive environment.

Conventional peening methods do nothing to remove existing degraded surface conditions, such as from frequently abusive fabrication processes, including forming methods such as rolling or bending, and surfacing methods such as machining or grinding, or from exposure to normally aggressive in-service environments, including high-temperature oxygenated water or from exposure to contaminated water.

In fact, these methods add to the undesirable cold work that is already present.

However, none of these or other known SCC surface mitigation methods provides both stress-reduction and surface-conditioning redundancy in reducing susceptibility to SCC, especially in the critical crack-initiation phase.

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