CLADDING TECHNOLOGY SHANXI CO., LTDRepair Welding of Laminations in 16MnReR Low-Temperature Pressure Vessel Base Material
Overview of the Technical Challenge
The fabrication of low-temperature pressure vessels demands exceptional material integrity, particularly at the base metal level where laminations can critically compromise structural performance. 16MnReR is a widely used low-temperature structural steel conforming to GB/T 1591 and relevant pressure vessel standards, designed to maintain ductility and toughness at temperatures as low as -40 °C. Laminations in rolled steel plates arise from incomplete bonding of oxide inclusions during the rolling process and represent a fundamental material defect that can propagate under cyclic or impact loading. When such defects are detected in pressure vessel shells, the repair strategy must address both the physical removal of the lamination and the restoration of the base metal's low-temperature mechanical properties through weld overlay.
Core Technical Analysis
The repair process typically involves grinding out the lamination to a smooth, oxide-free surface, followed by weld overlay using a matching or slightly higher-grade consumable. The key challenge lies in controlling the weld thermal cycle to avoid further degradation of the base metal's low-temperature impact toughness. The preheat temperature for 16MnReR is generally maintained between 100 °C and 150 °C, with interpass temperature not exceeding 250 °C. Post-weld heat treatment (PWHT) at 590 °C to 620 °C is often required to relieve residual stresses and restore the tempering characteristics of the weld metal.
| Parameter | Typical Value | Notes |
|---|---|---|
| Base material | 16MnReR | Low-temperature structural steel |
| Preheat temperature | 100–150 °C | Prevents cold cracking |
| Interpass temperature | ≤ 250 °C | Controls HAZ hardness |
| PWHT temperature | 590–620 °C | Stress relief and toughness restoration |
| PWHT duration | 2 h per 25 mm thickness | Minimum holding time |
| Impact test temperature | -40 °C | Per GB/T 150 requirements |
| Impact energy requirement | ≥ 34 J at -40 °C | Minimum for low-temperature service |
Defect Analysis and Countermeasures
The root cause of lamination repair failures often traces back to incomplete removal of the lamination cavity, leading to residual voids that become stress concentrators under pressure. Non-destructive testing using ultrasonic testing (UT) in accordance with JB/T 4730 should be performed before and after repair to confirm complete removal. Magnetic particle testing (MT) is also recommended to detect any surface-breaking cracks that may have propagated from the lamination during grinding operations.
The weld metal selection is critical. Using a consumable with slightly higher carbon equivalent than the base material can introduce excessive hardness in the HAZ, reducing low-temperature toughness. A recommended approach is to use a low-hydrogen flux-cored wire or covered electrode with a carbon equivalent below 0.42%, ensuring the weld metal's impact energy meets or exceeds the base metal specification at the design temperature.
Engineering Practice Insights
In my experience, the most common failure mode in lamination repairs is hydrogen-induced cracking (HIC) in the HAZ during or after welding. This is particularly problematic in low-temperature service where hydrogen embrittlement susceptibility is elevated. Countermeasures include thorough drying of electrodes, limiting arc time per layer, and applying post-weld baking at 200 °C to 250 °C for 2 to 4 hours to allow hydrogen diffusion. The repair procedure should be qualified per NB/T 47014 with appropriate impact testing at the minimum design temperature.
A systematic approach following the PDCA cycle is recommended: Plan the repair procedure with full qualification; Do the repair under strict parameter control; Check with full NDT and mechanical testing; Act on any deviations by revising the procedure. This disciplined methodology has proven effective in achieving zero-rework repair rates in critical low-temperature vessel applications.
The study of lamination repair in 16MnReR reinforces the principle that material integrity at the base metal level is the foundation of pressure vessel safety, and that repair welding must be treated with the same rigor as primary fabrication.