Medium-carbon steel piping, after about 200,000 hr of service, and carbon–0.5 molybdenum steel piping, after about 150,000 hr of service, have been evaluated to determine the effect of prolonged service on the stress-rupture, creep, tensile, and impact properties of the materials. The carbon steel was in main steam service at 825 F, 600 psi, and the carbon–0.5 molybdenum steel at 900 F and 800 psi. All of the material tested would meet requirements for new piping; the original differences that probably were present in the piping as a result of fabrication or heat-treatment appeared modified as a result of service.

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