1. This standard specifies the heat treatment process for post-welding of carbon steel and low-alloy steel welded structures.

This standard applies to carbon steel and low-alloy steel products for boilers and pressure vessels, implementing post-weld heat treatment primarily for improving joint properties and reducing residual welding stress. The post-weld heat treatment for other products may also be carried out in accordance with this standard.

2. The provisions of the referenced standards are incorporated into this standard by reference. The versions indicated at the time of publication of the standard are considered valid. All standards are subject to revision; parties using this standard should explore the possibility of using the following standards.

GB9452-1988 Method for Determining the Effective Area of Heat Treatment Furnaces

Strainers, tube sheets, and tube sheet processing

3. Requirement

3.1 Personnel and Responsibilities

3.1.1 Operators of heat treatment procedures must be trained and pass an assessment to obtain a certification before they can perform 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 responsibility engineer.

3.1.3 The heat treatment operator should strictly follow the heat treatment process after welding and carefully fill out the original operation records.

3.1.4 The heat treatment responsibility engineer is responsible for reviewing the original operation records (including time-temperature automatic recording curves) after welding heat treatment, verifying if it meets the post-weld heat treatment process requirements, and signing and stamping after confirmation.

3.2 Equipment

3.2.1 Various post-weld heat treatments and equipment should comply with the following requirements:

Meets post-weld heat treatment process requirements.

b) The heat treatment process after welding has no harmful effects on the heated parts.

c) Ensures even heat penetration in the heated parts.

d) Accurately measure and control temperature;

The heated component, after welding and heat treatment, meets the design and usage requirements in terms of deformation.

3.2.2 Post-weld heat treatment equipment can be one of the following types:

Electrically heated furnace

b) Cover Gas Stove

Infrared high-temperature ceramic electric heater

d) Other heating equipment that can meet the post-weld heat treatment process requirements?

3.3 Post-Weld Heat Treatment Method

3.3.1 Furnace Heat Treatment

Post-weld heat treatment should preferably be carried out by heating within an oven, and the heat treatment furnace must comply with the relevant provisions of GB9452. Once the corresponding values between oven temperature and the heated parts have been accumulated, during oven heat treatment, it is generally permissible to estimate the temperature of the heated parts based on the oven temperature. However, for special or critical welding products, temperature measurement should be based on thermocouples placed on the heated parts.

b) The heated items should be neatly arranged within the effective heating zone of the furnace, ensuring uniform and proper heat distribution. When undergoing heat treatment in a flame furnace, it is advisable to avoid direct flame喷射 onto the workpieces.

c) To prevent the occurrence of restraint stress and deformation, the supports for the heated parts should be properly arranged. For large thin-walled components and structures with significantly different structural and geometric dimensions, additional supports and fixtures should be added to enhance rigidity and balance stability.

3.3.2 Post-weld heat treatment allows for segmented processing within the furnace. When the heated parts undergo segmented heat treatment, the repeated heating length should not be less than 1500mm. The external part of the heated parts should be insulated properly to ensure that the temperature gradient does not affect the material's structure and properties.

3.3.3 During the overall heat treatment outside the furnace, ensure that...

On the basis of 3.2.1, it is also important to note:

Considering the adverse impacts of climate change and power outages on heat treatment, as well as emergency measures.

b) Necessary measures should be taken to ensure uniform and stable temperature of the heated parts, to avoid the generation of restraint stresses and deformation due to thermal expansion and contraction of the heated parts, supporting structures, and bases, etc.

3.3.4 Local heat treatment is permitted for B, C, and D class weld joints, A class weld joints where spherical heads are connected to cylindrical sections, and for defect repair areas. During local heat treatment, the heating width on each side of the weld should not be less than twice the thickness of the steel (δs) at the weld joint; when welding a header to a shell, the heating width must not be less than six times the thickness of the steel (δs). Insulation measures should be taken near the heating area to ensure that the temperature gradient does not affect the material's structure and properties.

3.4 Post-weld heat treatment process parameters

3.4.1 The temperature of the heated part upon entering or exiting the furnace shall not exceed 400°C. However, for heated parts with significant thickness variations, complex structures, high dimensional stability requirements, and low residual stress values, the furnace temperature upon entering or exiting the furnace is generally not recommended to exceed 300°C.

After the welding piece is heated to 400°C, the heating zone's temperature rise rate must not exceed (5000/δs) °C/h, and it should not exceed 200°C/h. The minimum temperature rise rate can be 50°C/h.

During heating, the temperature difference within any 5000mm length of the heating zone must not exceed 120°C.

During insulation, the temperature difference within the heating zone should not exceed 65°C.

During the warming and insulation period, the atmosphere in the heating zone should be controlled to prevent excessive oxidation of the weldment surface.

When the furnace temperature exceeds 400°C, the cooling rate in the heating zone must not exceed (6500/δs) °C/h, and it should not exceed 260°C/h; the minimum cooling rate can be 50°C/h.

3.4.7 Weldments

The 3.4.1 batch should be allowed to cool further in still air after being removed from the production temperature.

3.4.8 The recommended heat treatment insulation temperature and time for post-welding heat treatment of common steel grades are listed in Table 1.