Existing C-0.5Mo steel equipment in hydrogen service is still a concern in industries due to its high susceptibility to hydrogen attack at elevated temperature. High Temperature Hydrogen Attack (HTHA) has been one of the major problems in petroleum and petrochemical industry because of its metal degradation phenomena. HTHA occurs in carbon and low carbon steels exposed to high partial pressure of hydrogen at elevated temperatures. Since the original Nelson Curve was published in 1949 to define the operating limits for steels used in hydrogen service to avoid HTHA, a number of research and investigation activities on HTHA have been carried out around the world.

API summarized these data as API RP 9411 - “Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants” in 1970 and, since then, it has been widely used for material selection in hydrogen service in petroleum refining and petrochemical plants. Some of the common materials included in API RP 941 are carbon steel (CS), C-0.5Mo, 1.25°Cr-0.5Mo, 1.0Cr-0.5 Mo, 2.25°Cr-1.0Mo, etc. Particularly of interest are components made out of C-0.5Mo Steels whose curve has been removed from the updated API 941 and is assessed based on the CS curve. This has been done due to unfavorable service experiences of C-0.5Mo in the past. The C-0.5Mo equipment that operates above the CS curve should be either replaced or regularly inspected to detect HTHA.

In one of the refineries a 10” diameter C-0.5 Mo process gas bypass pipe in a waste heat boiler exchanger of a hydrogen production plant was found leaking and further investigations and analysis revealed that the failure took place due to long term exposure to hydrogen rich gas coming from the reformer.

This paper describes the methodology adopted for detection and failure investigation of the above mentioned process gas bypass pipe, inspection for HTHA in susceptible regions and also to establish the mechanical integrity of the waste heat boiler exchanger for further service.

Subject
High temperature hydrogen attack, Materials, Piping, Inspection, Base metals, Scatter, Heat, Steel, Equipment, Boilers, Cracks, Wastes, Hydrogen
Keywords:
High Temperature Hydrogen Attack, C-0.5 Mo steel, TOFD, Advanced Ultrasonic Back Scatter, Phased array UT
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2014
Association for Materials Protection and Performance (AMPP)
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