This paper was presented as ASME-65-PET-13 at the Petroleum Mechanical Engineering Conference, Houston, Tex., Sept. 19–22, 1965, of The American Society of Mechanical Engineers. Permission has been granted by ASME to present it at the Deep Drilling and Development Symposium of the Society of Petroleum Engineers, to be held at Monahans, Tex., march 31, 1966. Permission to publish all or any part of this paper must be obtained from the American Society of mechanical Engineers, United Engineering Center, 345 East 47th Street, New York, N. Y. 10017.
Economical operations at well depths below 10,000 ft and increasing completion pressures demand excellent performance of tubular goods at extremely high stresses. Performance of high-strength tubular goods may be affected adversely by hydrogen embrittlement which can be caused by normally accepted manufacturing practices. Subjecting tubular goods to some processes or environments may cause diffusion of atomic hydrogen into the steel and result in intergranular cracking and failure of high-strength steel at stresses considerably below the unaffected material strength. Tests indicate that elimination or control of processes and environments promoting diffusion of atomic hydrogen into steel may be necessary to insure satisfactory high-strength pipe performance.
A V-150* casing string, carefully ordered, transported, inspected, and run using procedures to insure satisfactory performance, recently parted at a tensile load less than one half of the ultimate connection strength. One week after setting the casing, V-150 coupling failures shown in Figs. 1 and 2 were found at 1,632 and 1,950 ft, respectively. The drilling rig had moved off the well after setting and cementing the casing string; within 8 hours after rigging up to complete the well, a workover rig detected the casing failure. A work string run to circulate mud out of the casing was stopped at 1,652 ft by the lower section of the failed casing string; subsequent circulating resuited in fluid returns on the production casing-protective casing annulus.
Investigation of the failure indicates that normally accepted manufacturing practices, mill-acid cleaning and electroplating of coupling threads, caused hydrogen embrittlement of two V-150 couplings resulting in parting of the casing string. Acid cleaning and electroplating of coupling threads used by manufacturers to minimize thread galling and improve pressure-sealing characteristics cause diffusion of hydrogen into the steel which can result in intergranular cracking and failure of high-strength steel at stresses considerably below the unaffected connection strength.
In the presence of a sustained tensile stress above some minimum level, such as represented by the hoop stress of a coupling made up on casing, atomic hydrogen which is free to move or diffuse in the steel can cause a brittle failure to occur. High-strength steel is more susceptible to hydrogen embrittlement than low-strength steel since the minimum stress required for failure decreases as the steel strength level increases. These fractures are sometimes referred to as "hydrogen-induced, delayed, brittle failures" and occur with no appreciable ductility even though the material may exhibit normal ductility in a tensile test. Hydrogen embrittlement, like electricity, is not fully understood; however, the following commonly held concept, which lacks complete agreement with some of the experimental data, explains the general idea of hydrogen embrittlement: