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Date：2025-04-03 16:14:29
Author: DTI
Core Standards for Welding Procedure Qualification of Overlay Welding
International Standards
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ISO 15614-6: This standard is specifically designed for the qualification of overlay welding procedures. It provides detailed regulations on the qualification process, testing methods, inspection requirements, and assessment procedures for overlay welding.
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AWS D1.1/D1.6: These standards provide additional requirements for overlay welding of steel and stainless steel. They are widely used in structural steel applications such as construction, bridges, and other infrastructure projects, focusing on corrosion resistance and mechanical properties.
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ASME IX: Part of the ASME Boiler and Pressure Vessel Code, this section specifies the rules for welding and brazing procedure qualifications. It is widely applied in industries such as power generation, oil and gas, shipbuilding, and aerospace.
Chinese Standards
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NB/T 47014 (replacing JB/T 4708): This standard is used for the qualification of overlay welding for pressure equipment, such as boilers, pressure vessels, and pressure pipelines. It covers various welding methods, including shielded metal arc welding (SMAW), submerged arc welding (SAW), gas tungsten arc welding (GTAW), and gas metal arc welding (GMAW).
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GB/T 19869.1: This is a general standard for welding procedure qualification, applicable to a wide range of welding processes.
Classification of Overlay Welding Qualification
By Purpose of Overlay Welding
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Corrosion-resistant Overlay Welding (e.g., stainless steel, nickel-based alloys): The focus is on evaluating chemical composition and intergranular corrosion resistance.
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Wear-resistant Overlay Welding (e.g., tungsten carbide, high-chromium cast iron): The emphasis is on hardness and wear resistance (e.g., ASTM G65 wear test).
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Transition Layer Overlay Welding (welding of dissimilar steels): Evaluation of bond strength and control of dilution rate.
By Welding Process
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Arc Welding (SMAW, SAW, GTAW, GMAW)
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Plasma Arc Welding (PAW)
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Laser Cladding
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Thermal Spraying + Remelting (e.g., flame spray welding)
By Combination of Base Material and Overlay Material
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Homogeneous Overlay Welding (e.g., 304L overlay on a 304 base)
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Heterogeneous Overlay Welding (e.g., Inconel 625 overlay on carbon steel)
Key Test Items for Overlay Welding Qualification
Mandatory Test Items
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Macro Metallography: Examination of fusion lines, porosity, cracks, and slag inclusions.
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Hardness Testing (HV/HRC): Evaluation of wear resistance and prevention of embrittlement in the heat-affected zone.
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Chemical Composition Analysis (using a spectrometer): Ensuring that the alloy elements in the overlay layer meet the required standards.
Additional Test Items (Depending on Application)
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Corrosion Testing: Such as ASTM A262 (intergranular corrosion), salt spray testing.
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Bend Testing: Evaluation of the bonding performance of the overlay layer (side bend test is more stringent).
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Dilution Rate Determination: Calculated through metallography or chemical composition (usually required to be ≤10% to 20%).
Scope of Qualification
Grouping of Base Materials
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Base materials are grouped according to the standard (e.g., P1 to P11 groups in NB/T 47014), and materials within the same group can be qualified by a single evaluation.
Overlay Materials
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Different alloy systems (e.g., nickel-based vs. cobalt-based) require separate evaluations.
Welding Parameters
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Changes in current, voltage, wire feed speed, preheat temperature, etc., exceeding ±10% require requalification.
Typical Welding Parameters
| Parameter | Arc Welding (GTAW) | Plasma Welding (PAW) |
|---|---|---|
| Current | 80-150A | 50-120A |
| Powder Feed Speed | - | 20-50g/min |
| Shielding Gas | Ar (99.99%) | Ar + H₂ (5%-10%) |
| Dilution Rate Control | ≤15% | ≤5% |
Notes
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Interpass Temperature Control: Avoid excessive temperatures that can cause cracking (e.g., stainless steel overlay should be ≤150℃).
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Post-Weld Heat Treatment: Some materials require stress relief treatment (e.g., nuclear power overlay layers require PWHT).
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Documentation: Retain welding parameters and inspection reports to comply with ISO 3834 or EN 1090 requirements.
Note: If you need specific qualification report templates or interpretations of standard clauses, please provide further details on the application scenario (e.g., oil pipelines/nuclear valves).
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