While many questions still surround this widespread and widely studied problem, there are a number of control measures you can take to help minimize losses from it in your operations.

Stress-corrosion cracking (SCC) is one of the most prevalent—and one of the most studied—forms of metallic materials failure. This phenomenon is responsible for significant economic losses in many industries and operations, including chemical and petroleum processing, nuclear and fossil fuel power generation, pulp and paper production, underground pipelines and commercial and military aircraft. Materials subject to SCC include mild and low alloy steels, stainless steels and alloys based on nickel, copper, aluminum, titanium or magnesium. (As discussed later in this article, a related process is hydrogen embrittlement [HE].)

Although SCC has received more fundamental study than any other form of corrosion-related attack, many questions still remain. This article is a brief introduction to the topic. It will review a few of the important characteristics of SCC, as well as some related cracking processes in common materials, and show how these results can be used to help minimize loses. References provided at the end of the article list some sources for more in-depth inquiries.

Keep in mind that guaranteed SCC prevention is impossible. Unexpected combinations of the governing factors commonly occur and control measures are not 100% effective. Certain actions, however, can be taken to reduce the frequency of failures. As in many equipment reliability improvement areas, the keys to significant initial progress are first to gain awareness and then to apply known but often under-utilized information.

The general nature of SCC
SCC is a synergistic failure process that occurs due to the combined actions of corrosion and mechanical cracking. The three vital interacting factors are the alloy, local stress level and local

environment. One of its unique features is that a specific combination of a particular corrosive and a particular alloy is required for SCC to occur. Table I lists several of the combinations of materials and corrosive media where the process has occurred. Note that certain corrosive media cause SCC on specific classes of materials, but they have no similar effects on other alloys.

Cracks produced by SCC are caused by tensile stresses— not by compressive stresses. Compressive surface stresses retard SCC and shot peening; imparting these helpful stresses is one control method that can help.

The minimum level of tensile stress necessary...(Read whole article)