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PRCI Report 173
- Evaluation of Stress-Corrosion Cracking Resistance of Newly Developed Grade X70 and X80 Line Pipe Steels
- Report / Survey by Pipeline Research Council International, 08/01/1988
- Publisher: PRCI
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L51563e
Battelle Memorial Institute
Need: Previous research programs sponsored by Pipeline Research Council International, Inc. have investigated the performance of several higher strength, line pipe steels. These steels, in the X70 and X80 grades are produced by microalloying, controlled rolling, and accelerated cooling. They have been shown to have excellent strength, toughness, and resistance to hydrogen sulfide attack. The stress-corrosion cracking (SCC) resistance of these steels has not yet been investigated. Since carbonate-bicarbonate stress-corrosion of buried pipes is a serious safety consideration for evaluating any new line pipe steel, the NG-18 Committee has undertaken this study of the stress-corrosion resistance of several of these new steels.
Benefit: The report describes the results of an evaluation of the stress-corrosion cracking (SCC) resistance of three high-strength, line pipe steels. These steels included an X70 grade containing Mn, V, and Cb, with a ferritic-bainitic microstructure; an X70 grade containing boron (B), with a bainitic structure; and a ferritic X80 grade microalloyed with Mo, Cb, V, and Ti. All three of these steels have been shown, in previous PRCI research programs, to have excellent strength, toughness, and resistance to hydrogen sulfide attack.
Result: The specimens were evaluated using the standard taper-tension specimen test, in which a specimen of varying cross-section is cyclically stressed in a hot carbonate-bicarbonate solution at a cracking potential. After cycling, the specimen is examined for cracking and the threshold stress level for stress-corrosion is determined. The B-free X70 steel had a stress-corrosion threshold stress of at least 42 ksi (60 percent SMYS). The B-containing X70 steel had a threshold stress of 50 ksi (70 percent SMYS). The X80 grade had the highest threshold, both in terms of absolute stress (60 ksi) and fraction of SMYS (75 percent). In addition, the crack growth rates for the X70 steels appeared to be lower than those of more conventional grades, although those rates could not be accurately quantified in this program.
The X70, B-containing grade and the X80 steel both appear to have significantly better SCC resistance than conventional steels. In particular, the X80 grade may provide a threshold stress for SCC that exceeds the normal operating hoop stress of the pipe.
Battelle Memorial Institute
Need: Previous research programs sponsored by Pipeline Research Council International, Inc. have investigated the performance of several higher strength, line pipe steels. These steels, in the X70 and X80 grades are produced by microalloying, controlled rolling, and accelerated cooling. They have been shown to have excellent strength, toughness, and resistance to hydrogen sulfide attack. The stress-corrosion cracking (SCC) resistance of these steels has not yet been investigated. Since carbonate-bicarbonate stress-corrosion of buried pipes is a serious safety consideration for evaluating any new line pipe steel, the NG-18 Committee has undertaken this study of the stress-corrosion resistance of several of these new steels.
Benefit: The report describes the results of an evaluation of the stress-corrosion cracking (SCC) resistance of three high-strength, line pipe steels. These steels included an X70 grade containing Mn, V, and Cb, with a ferritic-bainitic microstructure; an X70 grade containing boron (B), with a bainitic structure; and a ferritic X80 grade microalloyed with Mo, Cb, V, and Ti. All three of these steels have been shown, in previous PRCI research programs, to have excellent strength, toughness, and resistance to hydrogen sulfide attack.
Result: The specimens were evaluated using the standard taper-tension specimen test, in which a specimen of varying cross-section is cyclically stressed in a hot carbonate-bicarbonate solution at a cracking potential. After cycling, the specimen is examined for cracking and the threshold stress level for stress-corrosion is determined. The B-free X70 steel had a stress-corrosion threshold stress of at least 42 ksi (60 percent SMYS). The B-containing X70 steel had a threshold stress of 50 ksi (70 percent SMYS). The X80 grade had the highest threshold, both in terms of absolute stress (60 ksi) and fraction of SMYS (75 percent). In addition, the crack growth rates for the X70 steels appeared to be lower than those of more conventional grades, although those rates could not be accurately quantified in this program.
The X70, B-containing grade and the X80 steel both appear to have significantly better SCC resistance than conventional steels. In particular, the X80 grade may provide a threshold stress for SCC that exceeds the normal operating hoop stress of the pipe.
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