SEDL / STP / STP755-EB / STP28410S

Design Properties for Steels Used in Coal Conversion Vessels

Landes, JD
Advisory Engineer and Senior Engineer, Westinghouse R&D Center, Pittsburgh, Pa.

McCabe, DE
Advisory Engineer and Senior Engineer, Westinghouse R&D Center, Pittsburgh, Pa.

Pages: 25    Published: Jan 1982

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Abstract

A fracture-mechanics related approach was used to evaluate the performance of 2¼Cr-1Mo in simulated coal conversion environments. Two heats of ASTM A 387 and ASTM A 542 were prepared in the form of commercially produced weldments on 178-mm (7-in.)-thick plate. Base metal, weld metal, and heat-affected zone (HAZ) were investigated. In addition, a simulation of Type 347 stainless steel weld overlay was prepared.

The sensitivity to environmentally enhanced crack growth was evaluated by rising load test for exposure in 6 percent H²S-Balance H². The temperature range covered was from room temperature to 727 K (850°F), and pressures were from 5.5 to 24.1 MPa (800 to 3500 psi). Fixed-displacement wedge-loaded specimens were exposed in 100 percent H² at 24.1 MPa for six months.

Results indicate that 2¼Cr-1Mo in all metallurgical conditions will be sensitive to environmental cracking in 6 percent H²S-Balance H² at room temperature. At 588 K (600°F) effects due to 6 percent H²S-Balance H² are minimal, but at 727 K significant environmentally assisted plasticity develops.

Fixed-displacement specimens in high-pressure hydrogen were found to have severely degraded postexposure toughness. The mechanism of degradation is believed to be hydrogen-assisted cracking. It also was found that highly preloaded and cracked specimens of 2¼Cr-1Mo will develop creep at temperatures as low as 727 K.