welded steel pipe residual stress,welded pipe residual stress

What is the residual stress of welded steel pipe?

Date:2024-09-03

The manufacturing of welded steel pipes typically involves primary processes such as uncoiling, straightening, trimming, forming, and welding, along with a series of auxiliary processes like flaw detection, flattening, and pressure testing. Residual stress is often introduced during the rolling of the steel plate, meaning that residual stress exists in the material even before the pipe-making process begins. Operations such as uncoiling, straightening, and trimming redistribute this existing stress and may generate additional residual stress to a small extent.

 

Impact of Residual Stress on Steel Pipe Properties

Reduced Load-Bearing Capacity: Residual stress can diminish the steel pipe’s ability to bear loads, compromising its structural integrity.

Affected Fatigue Strength: The presence of residual stress can lower the fatigue strength of the steel pipe, making it more susceptible to failure under cyclic loading.

Stress Corrosion Cracking: Residual stress can lead to stress corrosion cracking, particularly in environments where the steel is exposed to corrosive substances.

 

Methods for Eliminating Residual Stress

To mitigate the adverse effects of residual stress in welded pipes, various methods can be employed to reduce or eliminate it. The choice of method should be based on the specific requirements of the welded pipe and evaluated through economic and technical comparisons.

 

- Natural Aging

Description: This method leverages natural temperature variations to gradually release residual stress in the welded pipe.

Advantages: Simple, easy to implement, and cost-effective.

Disadvantages: It is time-consuming, requires long-term allocation of resources, and may not yield significant results in the short term.

 

- Overall High-Temperature Tempering

Description: Involves heating the welded pipe to a specific temperature, maintaining that temperature for a set duration, and then cooling it slowly.

Effectiveness: Properly selected tempering parameters can significantly reduce residual stress.

Challenges: High cost and difficulty in implementing on the production line, making it generally unsuitable unless special requirements exist.

 

- Local Heating

Description: This method applies localized heating to reduce the peak residual stress, though it cannot completely eliminate it.

Effectiveness: The success of this method depends on the temperature gradient, which is influenced by the heating range.

 

- Mechanical Stretching (Overload Method)

Description: Each steel pipe undergoes a hydrostatic test, where pressure is maintained for a certain period. This process checks the quality of the welded pipe and helps eliminate some residual stress.

 

- Other Methods

Internal Control Molding: Some manufacturers use internal control molding instead of traditional external control, transforming the inner wall stress from tensile to compressive, thereby reducing overall residual stress levels.

Sandblasting: When performing anti-corrosion treatments, sandblasting not only removes rust but also helps reduce residual stress.

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