API TR 942-B-2017 pdf free download

API TR 942-B-2017 pdf free download.Material, Fabrication, and Repair Considerations for Austenitic Alloys Subject to Embrittlement and Cracking in High Temperature 565 °C to 760 °C (1050 °F to 1400 °F) Refinery Services.
1 Technical Approach/Report Organization and Scope As a basis of this report, technical literature, industry experience, and published case studies were reviewed. The review included materials of construction, damage mechanisms, and component-specific fabrication and repair issues. The scope of this report includes the following wrought austenitic alloys: Alloys 800, 800H, 800HT ® , and 300 series austenitic stainless steels, and corresponding welding consumables. Limits in chemical composition, microstructural requirements, and heat treating practices that mitigate susceptibility to embrittlement and cracking are identified. Potentially viable upgrades to commonly used alloys are identified where applicable. The remainder of this report is organized as follows. Section 3, Process Units, gives a brief process overview followed by an explanation of the various damage mechanisms found in that unit. Component specific considerations and examples of in-service damage are also included. Inspection recommendations and general repair method considerations are also included. Section 4, Damage Mechanisms, contains detailed discussions of high-temperature damage mechanisms; including fundamental details of the solid state reactions, their rate of reaction, and recommended mitigation measures. Section 4 also incorporates fabrication and repair practices that can be used for cracked or embrittled equipment. NOTE Excluded from the scope of this document are Hydrogen Reformer catalyst tubes, outlet pigtails and outlet headers. With the exception of catalyst tubes, these are covered in TR 942-A, Materials, Fabrication, and Repair Considerations for Hydrogen Reformer Furnace Outlet Pigtails and Manifolds. Also excluded are expansion bellows in elevated temperature service.
3 Process Units 3.1 General Table 1 summarizes common embrittlement mechanisms in each of the listed refinery process units. Implications for specific equipment are discussed in more detail in the section for each respective process unit. Information on damage mechanisms can be found in API 571 and in Section 4 of this document. 3.2 Fluid Catalytic Cracking Units (FCCUs) 3.2.1 Process Description FCCUs are used to process heavy feedstocks, converting them to gasoline, diesel, and furnace oils. A simplified process flow diagram for the FCCU is shown in Figure 1 [1]. The catalytic reaction occurs mostly inside the riser prior to reaching the reactor at temperatures ranging from approximately 480 °C to 565 °C (900 °F to 1050 °F). In modern FCCUs, the “reactor” functions as a hydrocarbon/catalyst separator. During the process, the catalyst becomes deactivated as it becomes coated with carbon (coke). The catalyst is sent to the regenerator where it is exposed to air, promoting the burn off of coke at approximately 650 °C to 780 °C (1200 °F to 1475 °F). Inside FCCU reactors and regenerators are cyclones which are used to separate the catalyst from the overhead vapor streams. Most regenerators have multiple sets of primary and secondary cyclones. Primary cyclones direct the vapor flow from inside the reactor or regenerator in a centrifugal pattern, forcing the heavier catalyst particles outward against the inside wall, and allowing the catalyst particles to then fall down into the catalyst bed. The lighter vapor stream exits out the top of the primary and into the secondary cyclone to remove residual catalyst from the vapor stream. Primary and secondary cyclones can be seen in Figure 2 [2].
There are two modes of regenerator operation: Complete Carbon-monoxide (CO) Combustion (CCC) or Partial CO Combustion (PCC). Both types of operation are subject to upsets (including “afterburns”) that can cause rapid localized temperature excursions. Afterburn (CO combustion) in a regenerator can lead to localized high temperatures, up of 900 °C (1650 °F) or hotter, which can cause major damage to regenerator internals. Causes of afterburn in a PCC Regenerator include the following. — Lack of promoter activity that causes oxygen slip to the dilute phase. (Promoters are catalyst additives that enhance control of CO, SO x , and NO x .) — Excessive air/coke ratio (too close to the stoichiometric ratio). Regenerators are intended to operate either with clearly less than stoichiometric air (PCC) or with excess air (greater than 1:1) where there is CCC operation. Afterburns tend to be more of a problem with CCC operation. Reasons for afterburn in a CCC regenerator include: slow CO combustion in the dense bed, due to lack of promotion activity and localized deficit in the air supply to the bed, either from asymmetric design or air grid damage.