Sulfide Stress Cracking of High-Strength Steels In Laboratory and Oilfield Environments

High-strength steels commonly used in drilling, completing, and producing' gas and oil wells exhibit catastrophic, brittle failures when exposed to environments containing hydrogen sulfide. This phenomenon is known as sulfide stress cracking (SSC). SSC has long troubled the petroleum industry by placing restrictions on the use of petroleum industry by placing restrictions on the use of high-strength steels in handling sour gas and crude in these applications. As wells become deeper and encounter higher temperature and higher pressure formations, these high-strength steels are needed for effective, economic, and safe completions. High priority is placed on comprehensive design guidelines for commonly used highstrength steels that will allow selection of these materials for specified conditions of temperature and H2S concentration.

Many previous studies have used laboratory tests incorporating artificial H2S environments (100 percent H2S, NaCl, HCl, H2SO4, etc.) to investigate the various parameters that affect SSC of steels. Often these studies parameters that affect SSC of steels. Often these studies have failed to relate the laboratory data to observations made in real oilfield environments. Generally, SSC data for many conventional oilfield materials are not available. This paper summarizes the results of an examination of the SSC susceptibility of selected API and nonAPI grades of high-strength steels subjected to extensive laboratory and field tests. The objective of these tests was to determine the limits of SSC susceptibility for these materials in real oilfield environments and to correlate these results with laboratory data.

Table 1 lists the materials tested in the present study, along with their chemical compositions. Five API grades of steel tubulars were tested: J-55, C-75, N-80, P-110, and V-150. The non-API steels tested included MOD N-80 (trade mark), SOO-95 (trade mark), SOO-125 (trade mark), and SOO-140 (trade mark). Also included in this examination was a sample of AISI 410 in wrought tubular form. All materials with the exception of the SOO-140 were in the form of 3 1/2- to 4 1/2-in. casing. The SOO-140 was in the form of 7-in. casing. The mechanical properties of these steels are given in Table 2. All materials were heat treated by the supplying manufacturer.

All materials with the exception of the SOO-140 were tested in the form of notched C-rings. An example is shown in Fig. 1. The C-rings were approximately 4 1/2-in. in diameter (3 1/2-in. diameter for SOO-125) with a 0.25-in. wall thickness. The outside surface of each specimen contained a Charpy V-notch, which had a depth of 12 1/2 percent of the specimen thickness. The SOO-140 was tested in the form of notched beam specimens (3.5 X 0.3 X 0.1-in., 12 1/2 percent Charpy V-notch). Such a specimen is also shown in Fig. 1. All specimens were stressed by mechanical deflection using carbon-steel bolts, while neglecting the effect of the C-ring notch.

JPT

P. 1483