Weld Overlay Repair of Laminations in 16MnReR Low-Temperature Pressure Vessel Base Material

Literature Overview and Technical Context

This 1990 publication by Liu Xiaoxian and Sun Liancheng from Shenyang Construction Machinery Factory Installation Company addresses the repair of laminations (inclusions) in 16MnReR low-temperature pressure vessel base material through weld overlay. 16MnReR is a normalized low-alloy steel specifically designed for low-temperature service, with guaranteed impact toughness at -40°C. Laminations are planar defects that occur during steelmaking and rolling, caused by the inclusion of non-metallic inclusions or insufficient bonding between layers of the steel slab.

The technical significance of this work lies in its demonstration of a practical repair method for a critical defect in a pressure vessel material. Laminations are particularly dangerous in pressure vessels because they can act as stress concentrators and crack initiation sites, leading to catastrophic failure. The weld overlay repair method allows the removal of the laminated region and replacement with sound weld metal, thereby restoring the structural integrity of the component.

Defect Analysis and Repair Strategy

Laminations in steel plates are classified according to their size, orientation, and severity. The classification system used in this work is based on the following criteria:

The repair strategy for Grade 3 laminations involves the following steps:

1. Defect identification: Use ultrasonic testing (UT) or radiographic testing (RT) to identify the location, size, and orientation of the lamination.
2. Defect removal: Machine or grind the laminated region to remove all affected material. The removal depth should extend beyond the lamination by at least 5 mm to ensure complete removal.
3. Weld groove preparation: Prepare a suitable weld groove geometry to ensure adequate fusion between the repair weld and the base metal. A U-groove or J-groove is preferred for deep repairs.
4. Weld repair: Apply the repair weld using a suitable filler metal and welding process. The filler metal should be matched to the base material to ensure compatibility of mechanical properties.
5. Post-weld treatment: Apply PWHT to relieve residual stress and restore the mechanical properties of the repair area.
6. Inspection: Perform NDT and mechanical testing to verify the quality of the repair.

Filler Metal Selection

The selection of filler metal for 16MnReR repair is critical to ensure compatibility with the base material. The following filler metals are recommended:

The filler metal should have a minimum impact energy of 47 J at -40°C to match the toughness requirements of 16MnReR. The carbon equivalent should be limited to ≤ 0.40% to ensure weldability and reduce cracking susceptibility.

Welding Process and Parameters

The welding process for 16MnReR repair should be selected based on the size and location of the repair. The following processes are commonly used:

• SMAW (Shielded Metal Arc Welding): Suitable for small repairs and field applications. Provides good control and flexibility.
• SAW (Submerged Arc Welding): Suitable for large repairs and deep welds. Provides high deposition rates and good quality.
• GTAW (Gas Tungsten Arc Welding): Suitable for root passes and thin sections. Provides excellent arc control and low heat input.

The recommended welding parameters for 16MnReR repair are:

The preheat temperature is critical to reduce the cooling rate and prevent hydrogen-induced cracking. The interpass temperature should be maintained at or below the preheat temperature to prevent excessive grain growth. The post-weld temperature is applied to relieve residual stress and improve toughness.

Quality Assurance and Testing

The quality of the weld overlay repair must be verified through a comprehensive testing program that includes:

• Ultrasonic testing (UT): Verify the absence of laminations and other internal defects in the repair area.
• Radiographic testing (RT): Verify the fusion and penetration of the repair weld.
• Magnetic particle testing (MT): Detect surface and near-surface defects in the repair area.
• Mechanical testing: Verify the tensile strength, hardness, and impact toughness of the repair weld.
• Hydrostatic testing: Verify the pressure integrity of the repaired pressure vessel.

The acceptance criteria for the repair weld are:

• Tensile strength: ≥ 490 MPa (matching 16MnReR base metal)
• Hardness: ≤ 300 HB (to prevent cracking)
• Impact energy: ≥ 47 J at -40°C (matching 16MnReR requirements)
• UT acceptance: No laminations or other defects per NB/T 47013
• RT acceptance: No porosity, slag inclusion, or incomplete fusion per NB/T 47013

Study Insights and Engineering Implications

The work by Liu and Sun demonstrates the feasibility of weld overlay repair for laminations in low-temperature pressure vessel materials. The key insight is that lamination repair requires a systematic approach that addresses defect identification, removal, welding, and quality assurance.

From a metallurgical perspective, the repair of 16MnReR requires careful attention to the carbon equivalent and cooling rate to prevent hydrogen-induced cracking. The low temperature service requirement also demands that the repair weld maintain adequate impact toughness at -40°C, which requires careful selection of filler metal and welding parameters.

The economic implications of lamination repair are significant. The cost of repairing a laminated pressure vessel is typically 20-40% of the cost of a new vessel, making repair an attractive option for critical components. However, the repair must be performed with the utmost care to ensure the long-term reliability of the pressure vessel.

This literature study reinforces the importance of systematic approach to lamination repair, emphasizing the need for careful planning, process optimization, and quality assurance to achieve reliable and cost-effective results in low-temperature pressure vessel fabrication.