(203b) Avoiding Risks of New Brittle Fracture Susceptibility in Carbon Steel Pipe, Fittings and Flanges That Meet ASME Code

Severe reductions of toughness properties of new fabrication carbon steel piping components have created a new brittle fracture risk in the last few years. The issue is becoming widespread globally, affecting up to 30 percent of materials tested with a smaller percentage exhibiting cast iron like properties. This phenomenon contradicts the ASME Code which assumes, based on historical material properties, that these materials behave in a ductile manner where instead they behave in a brittle fashion at temperatures between -29^oC (-20^oF) to +15^oC (+59^oF). Ethylene facilities that operate at the low end of this temperature range are at an increased risk for this “break before leak” brittle phenomenon. ASTM and ASME require no testing to mitigate risks to brittle fracture at these temperatures and wall thicknesses using the impact testing exemption curves that are based on fracture mechanics.

Laboratory test results of parent carbon steel pipe, fitting, and flanges in ASME B31.3 refinery and gas plant construction and facility start-ups reveals unexpected low toughness of 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at -10^oC (14^oF) to -29^oC (-20^oF). Others are independently testing and globally reporting similar results. Hydrotest and in-service failures are starting to surface with low toughness and brittle transgranular cleavage cracks.

Analysis of these failures shows no obvious correlation with location of manufacture or country of origin. Some manufacturers are not experiencing this issue. This phenomenon creates a new brittle fracture risk that needs to be addressed by the plant owners, Engineering/Procurement/Construction (EPCs), component suppliers, steel manufacturers, and regulators as the uncertainty of not knowing suitability for service at temperatures down to -29^oC (-20^oF) is concerning for reliability and safety. Steel components that behave in a ductile fashion are an important aspect in the design, fabrication and safe operation of pressure equipment and piping. Low toughness can result in brittle fracture of the material during hydrostatic tests, cold start-ups, cold operation and low temperature upset conditions.

Additionally, a small percentage of ASTM A350 LF2 CL1 forged flanges certified to -46^oC (-50^oF), experienced parent metal hydrostatic test failure and examination found brittle failure with 3J (2.2 ft-lb) to 7J (5.2 ft-lb) at -46^oC (-50^oF). A dependency to trace elements and forging technique was found. ASTM testing methodology was found insufficient to identify sub-standard material and was addressed by developing a new modified sampling procedure.

An advanced new technology non-destructive ultrasonic test was developed to accurately evaluate components and operating systems to the risk of brittle fracture and has demonstrated greater than 95% correlation with laboratory test results.

This paper briefly discusses historical literature, metallurgical investigations, findings, and factors that contribute to susceptibility to brittle fracture. Guidance to avoid low toughness and mitigate risks of in-service brittle fracture to ensure that components are suitable for service is provided.