API TR 934-D-2010 pdf download.Technical Report on the Materials and Fabrication Issues of 1 1 / 4 Cr- 1 / 2 Mo and 1Cr- 1 / 2 Mo Steel Pressure Vessels.
This API document provides background information and guidance on the implementation of API 934-C, Materials and Fabrication of 1 1 / 4 Cr- 1 / 2 Mo Steel Heavy Wall Pressure Vessels for High Pressure Hydrogen Service Operating at Temperatures at or Below 825 °F (426 °C) and API RP 934E, Materials and Fabrication of 1 1 / 4 Cr- 1 / 2 Mo Steel Heavy Wall Pressure Vessels for High Temperature Service Operating Above 825 °F (426 °C), and should be used as a supplement to these recommended practices. In recent years it has been recognized that there are important distinctions that need to be considered for 1 1 / 4 /1Cr- 1 / 2 Mo steels. Whereas API 934-A continues to provide materials and fabrication requirements for new 2 1 / 4 /3Cr-1Mo and 2 1 / 4 /3Cr-1Mo- 1 / 4 V steel heavy wall pressure vessels in high temperature, high pressure hydrogen service, different material, and fabrication requirements have been developed for 1 1 / 4 /1Cr- 1 / 2 Mo steel heavy wall pressure vessels. These requirements are covered in RP 934-C and 934-E. This document contains a description of key damage mechanisms that relate specifically to 1 1 / 4 /1Cr- 1 / 2 Mo pressure vessels used in a variety of services. These damage mechanisms include elevated temperature damage mechanisms such as “reheat cracking” or “creep embrittlement” as well as other damage mechanisms that may occur at lower temperatures. Not all services are affected by the same damage mechanisms due to significant differences in service conditions. For example, Hydrofiner Reactors tend to operate at lower temperatures and higher pressures than Catalytic Reformer Reactors, and Coke Drums and FCC Reactors do not see hydrogen service. Also, as a result of the different services causing different damage mechanisms, the fabrication requirements also differ.
4.2 Past In-Service Cracking and Toughness Problems with 1 1 / 4 /1Cr- 1 / 2 Mo Steels In-service cracking problems have been noted for 1 1 / 4 /1Cr- 1 / 2 Mo steel equipment including pressure vessels and piping.  These problems were experienced in both the refining and electric power industries and were related to weld cracks. Nearly all cracking was in reactors and piping, listed in Table 2 and Table 3. Whereas most problems in the refining industry were related to pressure vessels, the electric power industry experienced cracking in longitudinal weld seams of high temperature steam lines, which operated primarily at or above approximately 850 °F (454 °C). Most notable in the refining industry was creep related cracking of Catalytic Reformer reactors. This was reported in Japan,  and led to other studies in the United States.  It was categorized as creep embrittlement (a term that will be discussed later on). Several papers were published that described this cracking and other property changes. Table 4 lists the previous literature, experience, and data that describe these issues. In December 1986 there was an MPC workshop on “Embrittlement of Low Alloy Steels During Exposure at Elevated Temperature Service”. Shortly afterwards API/MPC surveyed refineries worldwide on these cracking problems.  More than 70 incidents were reported from 25 companies. In all cases where deep cracks were found and major repairs required, the reactors were replaced within a few years. In the majority of cases, crack initiation was at major nozzle to reactor welds. Cracking was predominantly in heat affected zones (HAZ) and was intergranular. Creep fissuring was also found. Initially the term “creep embrittlement” was used to describe this phenomenon. In some cases where CVN toughness measurements could be made low toughness values were also reported. Low toughness values in the range of 5 ft-lb to 10 ft-lb (at room temperature) were reported for both plate material and forgings.
Thicker pressure vessels, such as hydrofiner reactors, are often designed and constructed to ASME Section VIII, Division 2 allowable design stresses. Table 7 and Table 8 give a comparison between the allowable design stresses for vessels designed to the 2004 and earlier editions of Division 2 and the 2010 edition of Division 2, respectively. Although the 2004 and earlier editions of Division 2 did not have provisions for design of vessels in the creep range, designs in the creep range were permitted by ASME code case 1489-2 using the allowable stresses permitted for Division 1 vessels, provided the vessel or part was exempt from fatigue analysis by the provisions of AD-160.1 of Division 2.