API RP 941-2016 pdf free download

API RP 941-2016 pdf free download.Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants.
1 Scope This recommended practice (RP) summarizes the results of experimental tests and actual data acquired from operating plants to establish practical operating limits for carbon and low alloy steels in hydrogen service at elevated temperatures and pressures. The effects on the resistance of steels to hydrogen at elevated temperature and pressure that result from high stress, heat treatment, chemical composition, and cladding are discussed. This RP does not address the resistance of steels to hydrogen at lower temperatures [below about 400 °F (204 °C)], where atomic hydrogen enters the steel as a result of an electrochemical mechanism. This RP applies to equipment in refineries, petrochemical facilities, and chemical facilities in which hydrogen or hydrogen-containing fluids are processed at elevated temperature and pressure. The guidelines in this RP can also be applied to hydrogenation plants such as those that manufacture ammonia, methanol, edible oils, and higher alcohols. The steels discussed in this RP resist high temperature hydrogen attack (HTHA) when operated within the guidelines given. However, they may not be resistant to other corrosives present in a process stream or to other metallurgical damage mechanisms that can occur in the operating HTHA range. This RP also does not address the issues surrounding possible damage from rapid cooling of the metal after it has been in high temperature, high pressure hydrogen service (e.g. possible need for outgassing hydroprocessing reactors). This RP discusses in detail only the resistance of steels to HTHA. Presented in this document are curves that indicate the operating limits of temperature and hydrogen partial pressure for satisfactory resistance of carbon steel and Cr-Mo steels to HTHA in elevated temperature hydrogen service. In addition, it includes a summary of inspection methods to evaluate equipment for the existence of HTHA.
3 Operating Experience 3.1 Basis for Setting Integrity Operating Windows Figure 1 illustrates the resistance of steels to attack by hydrogen at elevated temperatures and hydrogen pressures. HTHA of steel can result in surface decarburization, internal decarburization, fissuring, and cracking, or a combination of these (see Section 4). Figure 1 gives the operating conditions (process temperature and hydrogen partial pressure) above which these types of damage can occur. Figure 1 is based upon experience gathered since the 1940s. Supporting data were obtained from a variety of commercial processes and laboratory experiments (see the References to Figure 1). While temperature and hydrogen partial pressure data were not always known precisely, the accuracy is often sufficient for commercial use. Satisfactory performance has been plotted only for samples or equipment exposed for at least 1 year. Unsatisfactory performance from laboratory or plant data has been plotted, regardless of the length of exposure time. The chemical compositions of the steels in Figure 1 should conform to the limits specified for the various grades by ASTM/ASME. Owners/operators should develop integrity operating windows (IOWs) (as outlined in API 584) to manage risks associated with HTHA by using operational experience presented in this document. Since the original version of Figure 1 was prepared for API in 1949 [1] , further experience has enabled curves for most commonly used steels to be more accurately located. All information relevant to 0.5Mo steels (C-0.5Mo and Mn-0.5Mo) is summarized in Annex A. The Fifth Edition of this RP also added three data points, which show HTHA of 1.25Cr-0.5Mo steel below the current 1.25Cr-0.5Mo curve. See Annex B for more discussion of 1.25Cr-0.5Mo steel. Annex C gives a similar discussion for 2.25Cr-1.0Mo steel. This Eighth Edition adds 12 data points and a new curve labeled as “Carbon steel (welded with no PWHT)” for HTHA of carbon steel not subjected to postweld heat treatment (PWHT.