General process of heat treatment of steel pressure vessel

1, scope

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

This standard is applicable to the post-welding heat treatment of carbon steel and low-alloy steel products of boilers and pressure vessels for the main purpose of improving joint performance and reducing welding residual stress. The post - welding heat treatment of other products can also refer to the implementation.

2. Reference standards

The following standards contain provisions which, by reference in this standard, constitute provisions of this standard. At the time of publication of the standard, all editions shown are valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards.

Method for determination of effective zone in heat treatment furnace.

3, requirements


3.1 personnel and responsibilities

3.1.1 heat treatment operators shall pass the training and examination and obtain the post work certificate before conducting post-welding heat treatment operations.

3.1.2 post-welding heat treatment process shall be prepared by the heat treatment technologist and reviewed by the responsible engineer for heat treatment.

3.1.3 the heat treatment workers shall operate in strict accordance with the post-welding heat treatment process, and fill in the original operation records carefully.

3.1.4 heat treatment responsibility engineer shall be responsible for reviewing the original operation record of heat treatment after welding (including time-temperature automatic recording curve), verifying whether it conforms to the process requirements of heat treatment after welding, and signing and sealing after confirmation.


3.2 equipment

3.2.1 all kinds of post-welding heat treatment and devices shall meet the following requirements:

A) it can meet the requirements of post-welding heat treatment process;

B) in the process of post-welding heat treatment, there is no harmful effect on the heated part;

C) it can ensure uniform heat penetration of the heated part;

D) able to accurately measure and control temperature;

E) after heat treatment after welding, the deformation of the heated part can meet the design and use requirements.


3.2.2 post-welding heat treatment equipment can be one of the following:

A) electric heating furnace;

B) hooded gas stove;

C) infrared high temperature ceramic electric heater;

D) other heating devices that can meet the requirements of post-welding heat treatment process


3.3 post-welding heat treatment method


3.3.1 heat treatment in furnace

A) the method of heating in the furnace shall be preferred for post-welding heat treatment, and the heat treatment furnace shall meet the relevant provisions of GB9452. In the case of the accumulation of the furnace temperature and the heated parts of the corresponding relationship between the value, the furnace heat treatment, it is generally allowed to use the furnace temperature to calculate the temperature of the heated parts, but for special or important welding products, the temperature measurement should be based on the thermocouple placed on the heated parts.

B) the heated parts shall be placed neatly in the effective heating area of the furnace, and the heat in the furnace shall be evenly distributed and circulated. During the thermal treatment in the flame furnace, the flame should not be directly sprayed onto the workpiece.

C) in order to prevent the occurrence of restrained stress and deformation, the supports of the heated parts should be properly arranged. For large thin-walled parts, structures and geometric sizes with large variations, necessary support and other tools should be added to increase rigidity and balance stability.


3.3.2 staged heat treatment

Post - weld heat treatment is allowed in sections of the furnace. The reheating length of the heated part shall not be less than 1500mm when the heated part is subjected to segmented heat treatment. Suitable insulation measures shall be taken for the outer part of the heated part so that the temperature gradient will not affect the structure and performance of the material.


3.3.3 overall heat treatment outside the furnace

In the process of heat treatment outside the overall furnace, on the basis of meeting the requirements of 3.2.1, it should also be noted that:

A) considering the adverse effects of climate change, power failure and other factors on heat treatment and emergency measures;

B) necessary measures shall be taken to ensure the uniform and stable temperature of the heated parts, so as to avoid the restrained stress and deformation caused by expansion and contraction of the heated parts, support structure and base


3.3.4 local heat treatment

Local heat treatment is allowed for class B, C and D welded joints, class A welded joints with spherical heads connected to cylinders, and defective welding repair parts. During local heat treatment, the heating width of each side of the weld shall not be less than 2 times the thickness of the steel s (s is the thickness of the steel at the welded joint); When the connection is welded to the shell, the heating width shall not be less than 6 times the thickness s of the steel. Heat preservation measures should be taken near the heating zone so that the temperature gradient does not affect the structure and properties of the material.


3.4 technological parameters of post-welding heat treatment


3.4.1 the temperature of the heated part shall not exceed 400℃ when it enters the furnace or comes out of the oven. However, for the heated part with a large thickness difference, complex structure, high requirement for dimensional stability and low requirement for residual stress value, the temperature in the furnace when it enters or comes out of the furnace shall not exceed 300℃ generally.

3.4.2 the heating rate of heating zone shall not exceed (5000/ s) ℃/h, and shall not exceed 200℃/h, and the minimum temperature may be 50℃/h.

3.4.3 when heating up, the temperature difference within any length of 5000mm in the heating zone shall not be greater than 120℃.

3.4.4 during thermal insulation, the difference between the highest and lowest temperatures in the heating area shall not exceed 65℃.

3.4.5 during the heating and insulation period, the atmosphere in the heating area should be controlled to prevent excessive oxidation of the welding surface.

3.4.6 when the furnace temperature is higher than 400℃, the cooling speed in the heating area shall not exceed (6500/ s)℃/h, and shall not exceed 260℃/h, and the minimum temperature may be 50℃/h.

3.4.7 the welding piece shall be cooled in still air after it is baked at the baking temperature of 3.4.1.

3.4.8 recommended post-welding heat treatment heat preservation temperature and heat preservation time for common steel Numbers are shown in table 1


Steel grade

Thickness s, mm to be heat treated after welding

Post - welding heat treatment temperature ℃

Heat treatment holding time after welding, h

Not preheating before welding

Preheat 100℃ before welding

Q235-A.F、Q235-A、

10、20、20R、25

>32

>38

600〜640

1) when thickness

The delta s 50 mm or less,

Is (s/25) h, but the minimum time is no less than 1/4h.

2) when thickness

The delta s > 50 mm,

Is [2+1/4× (s-50) /25]h

09MnD

——

——

580〜620

16Mn、16MnR

16MnD、16MnDR

>30

>34

600〜640

 

12CrMo 

——

Any thickness

640〜680

1) when the thickness s is no more than 125mm, it is (s/25) h, but the shortest time is no less than 1/4h.

2) when the thickness s> is 125mm, it is [5+0.25× (s-125) ÷25]h

15CrMo、15CrMoR

——

Any thickness

640〜680

1Cr5Mo

——

Any thickness

720〜760


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