Discussion on the implementation issues of the new GB/T 25198-2023 standard \"Pressure Vessel Heads\"

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The new version of GB/T 25198 has been in effect for 1 month now. The more common and challenging issues that arise during the implementation of this standard are listed below. We welcome everyone to actively discuss other problems encountered during implementation in the comments section: 1. The standard for end caps specified in the design drawings is GB/T 25198-2010; the manufacturing of these end caps took place in March. Is it appropriate to follow the old standard or the new one? 2. Can the end caps stored last year still be used this year or next year? 1) Mandatory standards: There is a transition period between the date of issuance and the date of implementation of the new version of mandatory standards. During this transition period, enterprises may apply either the old version of these mandatory standards or the new version. However, after the transition period, that is, starting from the date of implementation of the new mandatory standards, the new mandatory standards must be complied with. Due to the mandatory nature of **standard enforcement rules, the date on which the new version of the mandatory standard comes into effect is also the date when the old version of such standard is repealed. Recommended national standards refer to a type of standard that is voluntarily adopted in aspects such as production, exchange, and use through economic means, also known as voluntary standards. 2) Recommended standards: Any organization has the right to decide whether or not to adopt recommended national standards; violating such standards does not entail any economic or legal consequences. However, once it is accepted and adopted, or agreed upon by all parties to be included in the economic contract, it becomes a technical basis that all parties must abide by, carrying legal binding force. 3) In summary: Which version of the standard should be followed, the new one or the old one? Since GB/T 25198 is a recommended **standard, refer to the article published on this official account titled “Pressure Vessel Engineers – Can the old standards still be used after the revision of GB/T 24511-2017?” Is it effective? > The interesting comment from the friend in the comments section with the nickname ‘Dragon🐉’: it is reasonable to follow the design date specified in the drawings – use the old standards before March 1st, and the new standards after March 1st. As for the new version of the standard for design, can the old version still be used in practice? A reasonable approach is to compare the old standards with the new ones, adding additional inspection items if necessary; if the products made under the old standards meet the requirements of the new standards, or if the users and designers agree and provide relevant written documentation, then those products can be used. 1. The manufacturer of the head: Considering the need to ensure the quality of raw materials as well as the ability to procure them, the procurement, inspection, cutting, and welding of raw materials for pressure vessel heads are generally carried out by the pressure vessel manufacturing plant. However, some pressure vessel manufacturers, due to constraints such as equipment limitations or mold issues, entrust specialized head manufacturing units to produce the heads. The manufacturing plant formulates a reasonable processing procedure based on factors such as the structure and material properties of the head, the manufacturing capabilities of the head manufacturer, transportation costs, and overall costs; where necessary, it also establishes heat treatment procedures for hot working and after shaping. 2. Head forming method: Cold stamping forming is widely used due to its advantages such as precise dimensions, low cost, and good appearance. It is mainly applied to heads with a diameter of 6 meters or less and a thickness of 40 mm or less, and can be used for carbon steel, low-alloy steels such as Q345R, and stainless steel. In China, the maximum thickness achievable in hot stamping forming is 380 mm. The dimensions of hot-stamped heads are difficult to control; heating not only affects the properties of the material but also is energy-intensive and environmentally unfriendly. The stamping thinning rate is usually highest at the areas of the elliptical head with high curvature, ranging from about 8% to 10%. The thinning rate is usually greatest in the range of 20° to 30° near the bottom of the hemispherical head or spherical cap, at approximately 12% to 14%, with a conservative estimate of 13% to 15%. Spin forming is mainly suitable for heads with relatively thin thicknesses, as it does not require stamping dies. Spin forming is divided into cold spin forming and hot spin forming; currently, cold spin forming is the more common method, and it is primarily used for carbon steel, low-alloy steels such as Q345R, and stainless steel materials. The spinning thinning rate of elliptical heads ranges from 13% to 16%, being proportional to the diameter and inversely proportional to the thickness. When the capacity of stamping or spinning equipment is insufficient, or overall transportation is limited, large-sized end caps are generally manufactured by pressing them in segments and then welding them together. Split-pressing end caps require the creation of molds, which takes a long time; moreover, these end caps have many seams, resulting in a large amount of welding work that can significantly affect the quality. The thinning rate of the segments in a segmented head is relatively low, generally below 5%. If the top circular plate is formed by pressing it into a perfect circle, its thinning rate is around 8% to 10%. In addition to being pressed into a perfect circle or being welded together first and then pressed, the top circular plate can also be formed by pressing it into strips first and then welding those strips together. 3. Major technical changes in the new version of GB/T 25198-2023 \"Pressure Vessel Heads\": Terms and definitions have been added ； The nominal diameter DN of the head has been changed to the head diameter D (the inner or outer diameter of the head) ； The shapes and parameters of the elliptical heads and disc heads, which are based on the outer diameter, have been modified ； The head type parameters were modified, the code for the conical head type was changed, and a conical head type without straight edges was added ； Changed the header marker ； Added requirements for risk assessment and control in the manufacturing environment and head manufacturing, as well as for supervision and inspection ； The content related to raw material preparation has been modified; the information on materials has been moved to the sections on manufacturing, inspection, and acceptance, and provisions regarding material cutting and labeling have been added ； Added requirements for pressure vessel heads made of zirconium material ； Requirements for composite panel materials have been added; requirements for ensuring the performance of materials after processing have been introduced and clarified; requirements for corrosion resistance testing have been modified ； The requirements for grinding and patch welding have been changed ； The requirements for groove preparation and the surface have been changed ； Changed the requirements for the layout of joint panels and welds) ； The specifications regarding the surface color of welds and heat-affected zones in titanium and titanium alloy heads have been modified, and new specifications for the surface color of welds and heat-affected zones in zirconium heads have been added ； The content related to head forming was modified, and forming inspection was added ； The heating methods and general requirements have been changed; requirements for process heating, regulations for determining the effective heating area, and requirements for heat treatment measurement records have been added. The requirements for the heating medium have also been adjusted ； Requirements regarding the temperature control during heating of zirconium and zirconium clad plates have been added ； Added recommended temperatures for warm forming of austenitic stainless steel heads ； Added a control requirement specifying that for closures made of composite panels, the inner circumference or inner diameter should be used as the alignment reference ； The diameter range, outer circumference, and inner diameter tolerance requirements have been changed ； The tolerance requirements for the shape and dimensions of the end caps have been changed, and the use of other measurement methods has been permitted ； Added control and measurement requirements for the ferrite content in austenitic stainless steel heads designed for temperatures below -40°C and subjected to strain strengthening treatment ； Added requirements for heat treatment documents and automatic recording of heat treatment temperatures ； Value of the deformation rate used to determine whether annealing is required after cold forming of oval, disc, and conical end caps made of aluminum-magnesium alloys and aluminum-magnesium-silicon alloys, titanium and titanium alloys, and brass (except H96) ； It adds consideration of the impact of flat plate deformation rate on head manufacturing ； Added requirements for heat treatment specimens of product test pieces/base materials ； Added non-destructive testing methods and modified the relevant requirements ； The requirements for the factory data have been changed ； Added the product logo.