Post Welding Heat Treatment of Large Pressure Vessel : Key Technologies and Applications

Welding Residual Stress

Welding Residual Stress---The self-balancing internal stress generated in the weldment under the action of non-uniform temperature field, strong restraint, and drastic phase transformation. It is invisible and intangible, and is the "invisible killer" threatening the structural integrity of pressure-bearing equipment.

Challenges Brought by Large-scale Equipment

Manufacturing process                                                                                                                                                       Service process

Challenges Brought by Large-scale Equipment

The diameter and wall thickness are extremely large, and the number of weld passes is high, which generates significant residual stress, leading to stress corrosion, creep, and fatigue cracking!

To enhance the inherent safety of major pressure-bearing equipment: It is urgent to eliminate welding residual stress!

Challenges Brought by Large-scale Equipment

          Overall heat treatment                                                Segmented overall heat treatment                             Local heat treatment of joint welds

On-site Local Heat Treatment Difficulties

                     Unequal thickness structures presents                                                                           

Thin walls lead to excessive deformation

Pressure-bearing Equipment Difficulties

Why do large pressure-bearing equipment still leak despite strict design, manufacturing, and inspection?

Accurate and Efficient Calculation of Residual Stress

Work1-1：In-plane integration and out-of-plane variable length equivalent heat source model.

Accurate and Efficient Calculation of Residual Stress

Work1-2：Welding residual stress steady-state 

Micro-indentation testing technique

Work2：Residual stress testing by energy indentation method

Advantages：

mprovement of local post-weld heat treatment

Main and auxiliary heating distribution

Induction heating uniformity control method

Induction heating principle

Rib reinforcement deformation control method

Achieve 70% reduction in maximum expansion deformation