Thread Content
Feel free to follow: Cr-Mo steel is widely used in high-temperature hydrogen-rich environments. The selection of Cr-Mo steel is typically based on the Nelson curve specified in API 941. The diagram below shows the Nelson curve from the eighth edition of this standard; it helps to determine the appropriate category of Cr-Mo steel depending on the hydrogen partial pressure and temperature of the application environment. A well-known engineering company specified a temperature design margin of 50F (27.8C). The temper embrittlement of Cr-Mo steels used in high-temperature, high-pressure hydrogen environments is primarily controlled through factors such as the chemical composition of the base metal (the J coefficient, also known as the Watanabe coefficient), the chemical composition of the weld metal (the X coefficient, also known as the Bruscato coefficient), and impact toughness ； Reheat cracking in Cr-Mo steel is controlled by the K factor. The recommended control values provided by Kobelco, a well-known supplier of welding materials, are as follows (for 2.25Cr-1Mo material): The figure below shows the control values established by a renowned engineering company for 2.25Cr-1Mo and 3Cr-1Mo materials: J factor = (Si + Mn) (P + Sn) x 10^4 ≤ 120 (Si, Mn, P, and Sn are expressed in weight percent); Cu = 0.15 percent maximum; Ni = 0.2 percent maximum; Si = 0.3 percent maximum. The control criteria specified in API 934A, third edition (2019), are as follows: According to API’s recommendations, carbon steel materials can be used in hydrogen-containing environments at room temperature up to pressures of 90 MPa.