Zhuojin Pipe Fitting Co., LtdTIG Welding Repair Technology for Small Diameter Spiral Welded Pipes
Literature Overview
The technical paper by Jiang Yongfeng, Ren Hu, Feng Zongze, Chen Lei, Liu Wei, and Ren Chao from Jiangsu Yulong Steel Pipe Technology Co., Ltd. presents a practical solution for TIG welding repair of small diameter spiral submerged arc welded pipes. Published in Steel Pipe in 2024 (Volume 53, Issue 6, pages 40-45), this work addresses a long-standing industrial challenge: the difficulty of repairing internal weld defects in small diameter spiral pipes where conventional welding methods cannot be applied.
Core Technical Challenge
Problem Statement
Small diameter spiral submerged arc welded (SAW) pipes present unique repair challenges due to spatial constraints. The internal diameter is too small for workers to access the inner weld surface using conventional shielded metal arc welding (SMAW) techniques. This limitation has historically been a bottleneck for manufacturing quality, as internal weld defects cannot be effectively repaired, leading to product rejection or reduced service life.
Traditional Limitations
| Method | Applicability | Limitation |
|---|---|---|
| SMAW (Saw) | Large diameter pipes | Cannot access small diameters |
| SAW (internal) | Requires access to inner weld | Not feasible for small diameters |
| No repair | N/A | Product rejection, quality loss |
| TIG (external only) | Surface defects | Cannot achieve full penetration |
TIG Repair Technology Development
Process Concept: Single-Side Welding with Double-Sided Formation
The core innovation is the application of TIG welding for single-side welding with double-sided formation on the external surface of small diameter spiral pipes. This approach achieves full penetration and a formed weld on the internal surface without requiring internal access.
Key Process Parameters
The researchers optimized the following welding parameters for the repair process:
| Parameter | Value/Range | Purpose |
|---|---|---|
| Welding Current | Optimized for penetration | Achieve full penetration |
| Welding Speed | Controlled for heat input | Prevent burn-through |
| Shielding Gas | Argon (high purity) | Prevent oxidation |
| Filler Metal | Compatible with base material | Ensure weld integrity |
| Tungsten Electrode | Appropriate diameter and composition | Stable arc, good penetration |
| Back Purging | Argon or nitrogen | Protect internal weld surface |
Welding Material Selection
The selection of appropriate welding materials is critical for ensuring compatibility with the base pipe material and meeting the required mechanical and corrosion resistance properties. The filler metal must match or exceed the base material's composition and mechanical properties to ensure a sound weld joint.
Quality Verification and Standards Compliance
Applicable Standards
The repaired products were verified against GB/T 9711-2023 PSL2 standard and customer technical requirements. This standard governs the requirements for steel pipes for pipeline transportation systems, with PSL2 representing a higher product specification level requiring more stringent quality criteria.
Non-Destructive Testing Requirements
| Test Method | Purpose | Acceptance Criteria |
|---|---|---|
| Radiographic Testing (RT) | Detect internal defects | Per GB/T 9711-2023 |
| Ultrasonic Testing (UT) | Detect volumetric defects | Per relevant standard |
| Magnetic Particle Testing (MT) | Detect surface defects | No linear indications |
| Visual Inspection (VT) | Surface quality assessment | No cracks, porosity, undercut |
Mechanical Property Requirements
The repaired welds must meet the following mechanical property requirements:
| Property | Requirement |
|---|---|
| Tensile Strength | ≥ Base material minimum |
| Yield Strength | ≥ Base material minimum |
| Impact Energy | ≥ Specified minimum at test temperature |
| Hardness | Within specified range |
Engineering Practice and Implementation
Operational Skill Requirements
The TIG repair process for small diameter spiral pipes requires specialized operator skills:
- Precise torch control and travel speed management
- Consistent filler metal deposition technique
- Ability to maintain arc stability in confined spaces
- Knowledge of back purging techniques for internal weld protection
- Skill in achieving proper weld bead profile without excessive reinforcement
Construction Plan and Measures
The researchers proposed a comprehensive construction plan including:
- Pre-Weld Preparation: Surface cleaning, defect characterization, fit-up verification
- Welding Execution: Optimized parameter application, sequence planning
- Post-Weld Inspection: NDT verification, dimensional checks
- Documentation: Complete traceability of welding parameters and inspection results
PDCA Cycle Application
Applying the Plan-Do-Check-Act cycle to the repair process:
| Phase | Activities | Key Deliverables |
|---|---|---|
| Plan | Parameter selection, material selection, procedure development | Welding procedure specification |
| Do | Execute repair welding per procedure | Repaired pipe |
| Check | NDT inspection, mechanical testing | Quality verification report |
| Act | Parameter adjustment based on results | Improved procedure |
Study Insights and Independent Reflection
This research addresses a practical and economically significant problem in the steel pipe manufacturing industry. The ability to repair internal weld defects in small diameter spiral pipes without requiring internal access represents a substantial advance in manufacturing capability. The successful application of TIG welding for single-side, double-sided formation demonstrates the versatility of the TIG process and its suitability for challenging repair applications.
The achievement of compliance with GB/T 9711-2023 PSL2 standard validates the technical approach and demonstrates that the repair technology produces welds of equivalent quality to the original pipe. This is particularly important for pipeline applications where the integrity of every weld is critical for long-term safe operation.
From a manufacturing perspective, this technology reduces product rejection rates and enables the repair of otherwise scrap material, providing significant economic benefits. It also enhances the manufacturer's capability to address customer concerns and maintain quality reputation in competitive markets.
Reference Value and Outlook
The TIG repair technology for small diameter spiral welded pipes represents a practical solution to a long-standing industry challenge. Future development should focus on further optimization of welding parameters for different pipe diameters and wall thicknesses, development of automated repair systems for increased productivity, and extension of the technology to other pipe types and materials. As pipeline infrastructure continues to expand globally, robust repair technologies are essential for maintaining asset integrity and extending service life. The successful application of this technology demonstrates the continued importance of skilled manual welding in modern manufacturing, even as automation advances in other areas of the industry.