Sulfide stress cracking susceptibility of nickel containing steels
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I.
INTRODUCTION
LOW-alloy steels and weld fillers containing greater than 1 pct nickel are not used in sour oil and gas service, because these materials are considered susceptible to sulfide stress cracking (SSC). A sour environment is defined I as one where the fluids contain HES at a partial pressure greater than 345 Pa. This restriction is based mainly on one body 2 of data obtained nearly two decades ago. Because of this restriction a large group of nickel-containing low-alloy steels which can be heat treated to high toughness, such as the 43xx and 46xx series steels, cannot at present be used in sour applications. However, there have been other experimental data, as noted later, which show that in certain heattreated conditions nickel-containing low-alloy steels are as resistant to SSC as those not containing nickel. The present study was undertaken in the belief that a systematic study of the performance of heat-treated nickel-containing lowalloy steels (commonly termed "low-nicker' steels) in sour environments would reveal heat treatments that would give these steels adequate SSC resistance. Such knowledge would widen the assortment of low-alloy steels that can be used in sour environments, especially for applications where a high notch toughness at low temperatures is also required. The objective of this study was to compare the performance of selected nickel-containing low-alloy steels in a standard nES environment with that of nominally nickel-free AISI 4130 steel at comparable strength and hardness levels (yield strength (Y.S.) --690 MPa, HRC -< 22). Five commercial low-alloy steels with nominal nickel contents ranging from 0 to 3 pct were selected. These were quenched and tempered to the desired hardness. In addition, five different tempering treatments were used for one of the steels (AISI 4330) to establish the effect of minor microstructural changes on the sulfide stress cracking susceptibility. Much of the available data on SSC resistance of low-alloy steels has been obtained using stressed beam specimens in H2S-saturated media. In a study by Treseder and Swanson 2 short beam specimens with two small holes drilled at midsection were exposed to 0.5 pct acetic acid solution satuJ.H. PAYER is Professor, Department of Metallurgy and Materials Science, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106. S. P. PEDNEKAR, Research Scientist, and W. K. BOYD, Senior Research Leader, are with Battelle-Columbus, 505 King Avenue, Columbus, OH 43201. Manuscript submitted August 30, 1985. METALLURGICALTRANSACTIONS A
rated in H2S. A critical stress was calculated from the results obtained at varying beam deflections. A number of steels of proven or potential application in oil field service were tested at different hardness (and, hence, different strength) levels. Based on field experience, a lower limit on critical stress for acceptability of medium-strength steels was set, and using this criterion, the steels found unacceptable at hardness levels of below 235 BHN (HRC 22) were those cont
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