welded steel pipe welds quality inspection, steel pipe welds quality control

How to implement the quality control of welded steel pipe welds in production?

Date:2025-04-30

The quality inspection of welded steel pipe welding involves not only the assessment of welded joints but also a comprehensive inspection of the entire welding process. This includes pre-welding, in-process, and post-welding stages. A detailed explanation of each phase is provided below.


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I. Pre-Welding Inspection of Welded Steel Pipes

Before welding, the following elements must be strictly controlled to ensure the quality of the welding process:

Personnel Qualification
Welding operators must possess the required technical proficiency and hold valid qualification certificates. Their welding activities must fall within the scope permitted by their certifications.

 

Welding Equipment and Tools
The welding equipment should be in good condition with a stable power supply. Instruments such as ammeters and voltmeters must be calibrated and valid. Auxiliary tools—grounding wires, tungsten electrodes, and welding torches—must be intact and operational.

 

Materials Inspection

Base Materials: The base material, used for welded joints, should be verified against the material list for specifications, grade, and heat treatment condition. Groove dimensions should meet drawing requirements, and groove surfaces within 20mm must be polished to metallic luster.

 

Welding Materials: This includes welding rods, wires, fluxes, shielding gases, and broken wires. These materials must be checked for specification, brand, and quantity. Welding rods and fluxes must be dried before use and stored in insulated containers. Typically, if not used within 4 hours, re-drying is required.

 

Welding Method Validation
Common welding techniques include arc welding, TIG/MIG, plasma arc welding, submerged arc welding, resistance welding, laser welding, and electron beam welding. The selected method must conform to the welding procedure specifications (WPS).

 

Welding Environment Assessment
The environment significantly affects weld quality, especially for Cr-Mo heat-resistant steels, which are prone to cold cracking due to rapid cooling. Preheating and insulation are essential. Welding is prohibited under the following conditions unless protective measures are taken:

Relative humidity≥90%

Base metal temperature < -10℃

Ambient temperature < 5℃

Rain, snow, or wind≥8 m/s for arc welding,≥2 m/s for gas-shielded welding

 

Welding Measurement and Process Monitoring
Process inspection involves monitoring various parameters—equipment condition, material use, environment, welding methods, and settings—to ensure they comply with the WPS. Dedicated quality inspectors typically carry out these inspections.

 

Applicability Check
Verify that the welding procedure, base material, fixtures, positioning methods, and environmental conditions are suitable for the welding operation.

 

II. In-Process Welding Inspection

Welder Self-Inspection
Welders should closely monitor the weld, especially during multi-layer or multi-pass operations, and promptly remove any defects. If high-frequency defects are detected, they must be reported immediately.

 

Monitoring Welding Parameters
Carefully control and record current, voltage, travel speed, inter-pass temperature, and gas flow rate—especially when impact toughness or hardness is critical.

 

Equipment Performance
Ensure all welding equipment and instruments are responsive, calibrated, and functioning properly during welding.

 

Weld Monitoring
Check weld cleanliness, bead shape, number of passes, sequence, deformation control, and overall fit-up. Dimensional checks are essential throughout the process.

 

III. Post-Welding Inspection of Welded Steel Pipes

After welding, a thorough inspection must be performed to evaluate whether the welded joints meet acceptance criteria:

Visual and Dimensional Inspection
Use a 5×magnifying glass to examine the weld surface. Cracks, porosity, slag, incomplete penetration, or lack of fusion are not allowed. For stainless and low-temperature steels, undercut is unacceptable. Use weld gauges to measure weld dimensions (width, reinforcement, undercut, misalignment).

 

Non-Destructive Testing (NDT)

Surface Testing: PT (penetrant) and MT (magnetic particle) are used for surface flaw detection.

Internal Testing: UT (ultrasonic) and RT (radiographic) are standard.

Advanced Methods: TOFD, phased array UT, and digital radiography can be employed for higher precision or specialized applications.

 

Destructive Testing
When feasible, physical and chemical destructive tests can accurately determine the weld's mechanical properties and compliance with design specifications.

 

Leak Tightness Testing

Liquid Leak Test: For non-pressurized welded steel pipes and vessels.

Air Tightness Test: Compressed air is introduced, and external soapy water detects leaks via bubbles.

 

Strength Testing
Includes hydraulic or pneumatic pressure testing. Hydraulic tests use water with pressure 1.25–1.5×the design pressure to verify strength and integrity.

 

Conclusion

The welding quality of welded steel pipes directly impacts the safety and reliability of the piping system. A strict, multi-phase inspection regime—from pre-welding to post-welding—is essential for ensuring compliance with engineering standards, avoiding hidden defects, and enhancing long-term performance. Proper implementation not only guarantees weld quality but also safeguards the system's structural integrity under real-world conditions.

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