Stress corrosion well casings

A program for acoustic emission under the name Monopac was developed for external and internal corrosion, stress corrosion cracking and weld cracking.55 This program consists of the test procedures as well as case histories. 

The stress-corrosion cracking (SCC) mode of failure was later observed even in the case of ferritic stainless steels. The only clear message from this is that the exact mechanism of failure by this mode is not well established. Alloys containing >34% Ni were found to prolong the time of SCC failure. Ferritic type alloys 430 and 434 are resistant to SCC both in MgCl2 and NaCl environments in the mill-annealed condition, but not in welded conditions. Also, welding impairs the ductility and their resistance to SCC. 

Other somewhat parallel cases can be cited to expand the argument that basic science is needed. For example, stress-corrosion is a common mode of failure in ceramics and metals, as well as polymers. The mechanisms are different yet the need for basic understanding is essential in developing practical, reliable predictive measurements and tests. 

Stainless steels are unpredictable in sea water. In some circumstances, certain grades have stood up well but in other cases rapid attack has occurred. Stainless steels are prone to stress-corrosion cracking and susceptible to attack due to crevices and deposits. The consensus seem to be that stainless steels may be excellent in certain cases but must be used with caution. 

Many corrosion phenomena are related to the formation of a barrier-type film on metal surfaces. In most cases this is an oxide or a hydroxide layer. Phosphate layers are important as well, especially as a primer for organic coatings. Under certain conditions, these passivating layers may be destroyed locally, which leads to special corrosion phenomena like pitting corrosion, crevice corrosion, and stress corrosion cracking. Although passivity is discussed in detail in Chap. 3 of this Volume, an introduction is given in order to understand these localized corrosion phenomena. 

In this case, the SCC threshold temperatures can be raised significantly (by 15 to 80 °C, or 27 to 144 °F) by microstructin al refinement and/or minor ( 0.1%) additions of palladium (R.W. Schutz, M. Xiao, and T.A. Bednarowicz, Stress Corrosion Behavior of the Ti-3Al-8V-6Cr-4Zr-4Mo Titanium Under Deep Sour Gas Well Conditions, Paper No. 51, presented at NACE Corrosion 92, Nashville, Apr 27-May 1,1992). 

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