When using A516 Gr70 for boiler manufacturing, operators must strictly adhere to its standard requirements. Relevant personnel must rigorously control material acceptance, welding quality, heat treatment, and inspection processes to ensure compliance with the high-temperature, high-pressure operating conditions of boilers.
Prior to production, technical personnel must review raw material qualification documents, such as product compliance reports, to confirm adherence to ASTM A516/A516M standard requirements for Gr70. Key indicators including chemical composition and mechanical properties must be verified. Subsequently, material performance must be tested through chemical analysis, tensile testing, and impact testing. Non-compliant materials are strictly prohibited. Additionally, inspect the surface quality of steel plates. Defects such as cracks, laminations, or scale are not permitted. Thickness deviations must comply with standard specifications to avoid compromising structural strength.
Production personnel must pre-determine welding procedures to ensure parameters like current, voltage, welding speed, and preheating temperature meet joint performance requirements. Welders must hold valid certification for the specific project and strictly adhere to approved process parameters during welding.
Prior to welding, clean contaminants like oil and rust from the groove and surrounding areas. Perform preheating based on plate thickness and ambient temperature to prevent welding cracks.
Conduct hydrogen removal promptly after welding, especially for thick plates or low-temperature environments, to avoid hydrogen-induced cracking. The hydrogen removal temperature is typically 250-350°C, with holding time determined by plate thickness.
For steel plates exceeding 40mm in thickness, normalizing treatment must be performed during manufacturing to refine grain size, homogenize microstructure, and ensure a balanced strength-to-toughness ratio.
Welded joints require post-weld heat treatment (PWHT) as specified, typically involving high-temperature tempering at 595-650°C to eliminate residual welding stresses and improve weld microstructure.
During heat treatment, heating rate, soak time, and cooling rate must be strictly controlled to prevent performance degradation or deformation caused by temperature fluctuations.
Non-Destructive Testing: Welded joints require 100% radiographic testing (RT) or ultrasonic testing (UT), focusing on detecting internal cracks, lack of fusion, lack of penetration, and other defects. Testing standards must comply with relevant boiler manufacturing codes.
Visual Inspection: After welding completion, inspect the weld appearance to ensure proper formation without surface defects like porosity, slag inclusions, or undercut. Weld dimensions must meet design requirements.
Hydrostatic Testing: Upon boiler fabrication completion, conduct hydrostatic testing at the design pressure specified. This verifies overall boiler integrity and structural strength. During testing, pressure must be increased gradually while observing for leaks or structural deformation.
Determine the boiler's operating temperature and pressure. A516 Gr70 is suitable for medium-to-low temperature applications, typically with a design temperature not exceeding 450°C. If the boiler operates continuously at higher temperatures, evaluate the material's high-temperature strength and creep properties. Replace with a more suitable heat-resistant steel if necessary.
If the boiler medium is corrosive, additional anti-corrosion measures must be implemented or corrosion allowance incorporated into the design to prevent material corrosion failure.
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