ASME PTB-3-2010 pdf download.Section VIII – Division 2 Example Problem Manual.
The subject of Examination Groups is covered in Part 7, paragraph 7.4.2. The assignment of a welded joint to a particular Examination Group is dependent on the manufacturing complexity of the material, the maximum thickness, the welding process, and the selected weld joint efficiency. The Examination Groups are defined in Table 7.1. There are three Examination Groups defined within VIII-2, which are then further subdivided in sub-groups “a” and “b” to reflect the crack sensitivity of the material. The required method and extent of nondestructive examination is defined Table 7.2 based on the Examination Group, the joint category, and the corresponding permissible joint type. Also introduced in Part 7, paragraph 7.4.2 is the concept of the governing welded joint, which is defined as that welded joint within a given vessel section (such as a shell course or vessel head) that, as a result of the selected joint efficiency, determines the thickness of that vessel section. For example, in a given shell course, the longitudinal weld seam would control the thickness of that shell course in most cases and would be the governing welded joint. However, if the component was subject to significant longitudinal stress from wind, seismic, or other external loadings such that the circumferential seam dictated the thickness of the shell course, then it would be the governing welded joint. Since it is possible for a pressure vessel to have more than one governing welded joint, it is also possible to have a pressure vessel with multiple Examination Groups. The requirements for the case of a single vessel containing a combination of Examination Groups are covered in Part 7, paragraph 22.214.171.124.b. In each vessel section, the Examination Group of the governing welded joint shall be applied to all welds within that vessel section, including any nozzle attachment welds.
7.1 Example Problem E7.1 – NDE Requirements: Vessel with One Examination Group Designation A plant engineer is tasked with developing a design specification for a new pressure vessel that is to be constructed in accordance with VIII-2. Based on the anticipated design data, materials of construction, and welding process, the engineer selects Examination Group 1a to set the joint efficiency and NDE requirements for the entire vessel. A sketch of the vessel showing nozzle sizes, orientation, and weld seams is shown in Figure E7.1.
The requirements for operation of PWHT are provided in paragraph 6.4.4. The operation of postweld heat treatment shall be carried out by one of the procedures given in paragraph 6.4.3 in accordance with the following requirements. a) When post weld heat treatment is performed in a furnace (see paragraph 126.96.36.199), the temperature of the furnace shall not exceed 800°F at the time the vessel or part is placed in it. b) Above 800°F, the rate of heating shall be not more than 400°F/hr divided by the maximum metal thickness of the shell or head plate in inches, but in no case more than 400°F/hr, and in no case need it be less than 100°F/hr. During the heating period there shall not be a greater variation in temperature throughout the portion of the vessel being heated than 250°F within any 15 ft interval of length.
The requirements for postweld heat treatment are found in paragraph 6.4.2. Material specification SA-537 Class 1 is a P-No. 1, Group No. 2, material. Therefore, in accordance with paragraph 188.8.131.52.e, the PWHT requirements are provided in Table 6.8. The definition of nominal thickness governing PWHT is provided in paragraph 184.108.40.206. For pressure vessels or parts of pressure vessels being postweld heat treated in a furnace charge, the nominal thickness is the greatest weld thickness in any vessel or vessel part which has not previously been postweld heat treated. Therefore, the governing nominal thickness is that of the cylindrical shell, 3.3592 in . The procedures for postweld heat treatment are found in paragraph 6.4.3. PWHT of the vessel will be performed by heating the vessel as a whole in a closed furnace in accordance with paragraph 220.127.116.11.