General Process Specification for Heat Treatment of Steel Pressure Vessels.pdf

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General Process Specification for Heat Treatment of Steel Pressure Vessels – Yixing Sanmu Chemical Equipment Co., Ltd. General process document, Document No.: ZZ.2003-15 1. Scope This standard specifies the post-weld heat treatment processes for welded components made of carbon steel and low-alloy steel. This standard applies to post-weld heat treatment of carbon steel and low-alloy steel products used in boilers and pressure vessels, which is carried out with the main purpose of improving joint performance and reducing welding residual stresses. The post-weld heat treatment for other products can also be followed as a reference. 2. Referenced Standards The provisions contained in the following standards become part of this standard by being referenced herein. At the time of standard publication, all versions shown are valid. All standards will be revised, and those using this standard should consider the possibility of adopting the latest versions of the following standards. GB9452-1988 Method for determining the effective area of heat treatment furnaces. 3. Requirements 3.1 Personnel and Responsibilities 3.1.1 Heat treatment operators must undergo training, pass assessments, and obtain a certification before they can carry out post-weld heat treatment operations. 3.1.2 The post-weld heat treatment process is prepared by the heat treatment technician, and reviewed by the heat treatment responsible engineer. 3.1.3 Heat treatment operators shall strictly follow the post-weld heat treatment procedures and carefully fill in the original operation records. 3.1.4 The engineer responsible for heat treatment is tasked with reviewing the original operation records of post-weld heat treatment (including the automatic time-temperature recording curve), verifying whether they meet the requirements of the post-weld heat treatment process, and signing and stamping them after confirmation. 3.2 Equipment 3.2.1 Various post-weld heat treatment methods and equipment shall meet the following requirements: a) They must be capable of fulfilling the requirements of the post-weld heat treatment process ； b) It has no harmful effect on the heated parts during post-weld heat treatment ； c) It can ensure uniform heating throughout the heated part of the object ； d) Ability to accurately measure and control temperature ； e) After welding and heat treatment, the deformed part meets the design and operational requirements. 3.2.2 The post-weld heat treatment equipment can be one of the following: a) Electric heating furnace ； These regulations have been in effect since October 2003. Page 1 of 4. General Process Regulations for Heat Treatment of Steel Pressure Vessels – Yixing Sannmu Chemical Equipment Co., Ltd. General process document; Document number: ZZ.2003-15 b) Covered gas furnace ； c) Infrared high-temperature ceramic electric heater ； d) Other heating devices that can meet the requirements of the post-weld heat treatment process. 3.3 Post-weld heat treatment methods 3.3.1 Heat treatment in a furnace a) Heat treatment after welding should preferably be carried out by heating in a furnace, and such heat treatment furnaces must comply with the relevant provisions of GB9452. Once the relationship between furnace temperature and the temperature of the parts being heated has been established, during heat treatment in the furnace, it is generally acceptable to use the furnace temperature to estimate the temperature of those parts. However, for special or critical welded products, temperature measurement should be based on thermocouples installed on the parts being heated. b) The items to be heated should be properly placed within the effective heating area of the furnace, to ensure uniform heat distribution and flow inside the furnace. When heat-treating in a flame furnace, it should be avoided for the flame to directly hit the workpiece. c) To prevent the occurrence of restraint stresses and deformation, the supports for the heated components should be arranged properly. For large thin-walled components as well as those with significant variations in structure and geometric dimensions, additional supporting fixtures should be used to increase stiffness and maintain stability. 3.3.2 Segmented heat treatment: Post-weld heat treatment can be carried out in segments within the furnace. When heat treatment is carried out on the heated part in segments, the repeated heating length shall be no less than 1500 mm. The portion of the heated component outside the furnace should be fitted with appropriate insulation measures to ensure that the temperature gradient does not affect the structure and properties of the material. 3.3.3 Overall furnace-based heat treatment: When carrying out overall furnace-based heat treatment, in addition to meeting the requirements of 3.2.1, attention should also be paid to: a) considering the adverse effects on heat treatment caused by factors such as climate changes and power outages, as well as emergency measures ； b) Necessary measures shall be taken to ensure a uniform and stable temperature of the heated parts, thereby preventing restraint stresses and deformations in those parts, as well as in the supporting structures and bases, due to thermal expansion and contraction. 3.3.4 Local heat treatment: Local heat treatment methods are permitted for welding joints of types B, C, and D, welding joints of type A where spherical heads are connected to cylinders, as well as areas that have been repaired due to defects. During local heat treatment, the heating width on each side of the weld should be no less than 2 times the thickness δs of the steel material (δs being the thickness of the steel at the welded joint) ； When the joint is welded to the shell, the heating width should not be less than 6 times the thickness δs of the steel material. This procedure has been in effect since October 2003. Page 2 of 4. General Process Specification for Heat Treatment of Steel Pressure Vessels – Yixing Sanmu Chemical Equipment Co., Ltd. General process document; Document number: ZZ.2003-15 Insulation measures should be taken in the area near the heating zone to prevent the temperature gradient from affecting the structure and properties of the material. 3.4 Post-welding heat treatment process parameters 3.4.1 The temperature of the parts to be heated when they are introduced into or taken out of the furnace shall not exceed 400°C; however, for parts with large thickness variations, complex structures, high requirements for dimensional stability, and low requirements regarding residual stress levels, the temperature inside the furnace at the time of introducing them into or taking them out of the furnace should generally not exceed 300°C. 3.4.2 After the welded joint is heated to 400°C, the heating rate in the heated area shall not exceed (5000/δs) °C/h, nor shall it exceed 200 °C/h; the minimum value may be 50 °C/h. 3.4.3 During heating, the temperature difference over any 5000 mm length within the heating zone shall not exceed 120°C. 3.4.4 During insulation, the difference between the highest and lowest temperatures in the heating area should not exceed 65°C. 3.4.5 During the heating and holding period, the atmosphere in the heating area should be controlled to prevent excessive oxidation of the weld surface. 3.4.6 When the furnace temperature is above 400°C, the cooling rate in the heating zone shall not exceed (6500/δs)°C/h, nor shall it exceed 260°C/h; the minimum value may be 50°C/h. 3.4.7 After being taken out of the furnace at the temperature specified in 3.4.1, the welded parts shall continue to cool in still air. 3.4.8 The recommended holding temperatures and holding times for post-weld heat treatment for common steel grades are shown in Table 1. Steel grade; Thickness δs requiring post-weld heat treatment, in mm; Post-weld heat treatment temperature, in °C; Post-weld heat treatment holding time, in hours. No preheating before welding; Preheating before welding at 100°C. Q235-A.F, Q235-A, 10, 20, 20R, 25: >32, >38; 600, 640. 1) When the thickness δs is ≤50 mm, the holding time is (δs/25) hours, but it must not be less than 1/4 hour. 2) When the thickness δs is greater than 50 mm, it is h 09MnD —— —— 580.620; for 16Mn, 16MnR, 16MnD, and 16MnDR, the value is >30 >34 600.640. For 12CrMo, it applies to any thickness: 640.680. 1) When the thickness δs is ≤125 mm, the formula used is (δs/25)h. For 15CrMo and 15CrMoR, it applies to any thickness: 640.680. This specification has been in effect since October 2003. Page 3 of 4. General Process Specification for Heat Treatment of Steel Pressure Vessels by Yixing Sanmu Chemical Equipment Co., Ltd. General process document – Document number: ZZ.2003-15. For 1Cr5Mo, it applies to any thickness: 720.760. However, the minimum time required is not less than 1/4 hour. 2) When the thickness δs > 125 mm, it is h. Note: 1. For welded joints with different steel thicknesses, the thickness δs is based on the thinnest component. 2. For welded joints formed by joining different steel grades, the requirement shall be determined according to the more stringent heat treatment specification. 3. When performing post-weld heat treatment on quenched and tempered steel, the holding temperature should generally be lower than the tempering temperature of the steel. However, post-weld heat treatment for which the holding temperature is higher than the tempering temperature is not restricted, as the properties of the steel still meet the requirements for product use. 4. The heat treatment thickness δs refers to: a) the thickness of the thinner part when the shell is joined to the head ； b) Shell thickness welded to flanges, tube sheets, or other similar structures ； c) Thickness of the shell or head welded to the take over ； d) Thickness of the weld at the joint when a non-compressed member is welded to a compressed member ； e) Depth of the repair weld. 5. The insulation time can be accumulated. 3.5 Requirements for test plates regarding post-weld heat treatment: For containers that require heat treatment, the test plates shall undergo post-weld heat treatment along with the containers. 3.6 Requirements for the retention period of records on post-weld heat treatment: The records of the time and temperature profiles for post-weld heat treatment must be kept for at least 7 years. These regulations have been in effect since October 2003. Page 4 of 4