Stainless Steel Coil Tube — TIG Self-Fusion Welding with Back-Side Argon Shielding (TIG Back-Purge Process)

Product Overview

The Stainless Steel Coil Tube, produced by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product designed for demanding industrial applications requiring seamless, high-integrity connections. This product falls under the Installation & Maintenance category, specifically within the Connection Processes and Welding Connections sub-classification. The defining technical feature of this product is its TIG (Tungsten Inert Gas) Self-Fusion Welding with Back-Side Argon Shielding process, which ensures metallurgical purity and maximum corrosion resistance at weld joints.

Unlike conventional welding methods that may introduce filler metals or leave residual oxidation on the internal surfaces, this process employs a pure argon (Ar) shielding atmosphere on both the primary (front-side) and secondary (back-side) of the weld zone. This dual-shielding approach is critical for maintaining the austenitic microstructure of the stainless steel and preventing intergranular sensitization at the heat-affected zone (HAZ).

Material & Properties

Stainless steel coil tubes are typically manufactured from austenitic grades such as AISI 304 (UNS S30400), AISI 316 (UNS S31600), or AISI 321 (UNS S32100), each offering distinct combinations of corrosion resistance, mechanical strength, and thermal stability.

Specifications

Parameter Specification Notes
Product Name Coil Tube (盘管) Sequential No. 220
Welding Process TIG Self-Fusion (GTAW) ISO 4063: 141
Back-Side Shielding Pure Argon (Ar) Back-Purge Dual-side protection
Shielding Gas Flow Rate 8–15 L/min Adjustable per joint geometry
Pre-Purge Requirement Mandatory prior to arc initiation Full displacement of ambient air
Post-Purge Requirement Mandatory until weld cools below 100°C Prevents late-stage oxidation
Filler Metal None (Self-Fusion) Base metal serves as filler
Acceptable Internal Appearance Silvery, clean, no discoloration Indicates successful protection
Reject Criterion Internal wall oxidation / blackening Indicates protection failure
Typical Wall Thickness Range 0.3–3.0 mm Optimal for TIG self-fusion
Typical Outer Diameter Range 3.0–108.0 mm Per customer specification

Manufacturing Process

3.1 Pre-Weld Preparation

Proper surface preparation is the foundation of a successful TIG self-fusion weld with back-side argon shielding. The process begins with thorough cleaning of both the internal and external surfaces of the coil tube at the weld joint area. All contaminants — including oils, grease, oxidation scale, and particulate matter — must be removed using appropriate mechanical and chemical methods. A stainless steel wire brush or abrasive pad is recommended for mechanical cleaning, followed by solvent degreasing.

3.2 Back-Purge System Setup

The back-side argon shielding system must be configured prior to any welding operation. This involves:

  1. Sealing: Appropriate purge blocks or gaskets are installed on both sides of the weld joint to create a confined atmosphere chamber.
  2. Purge Gas Connection: Pure argon gas lines are connected to the purge chamber inlet and outlet ports.
  3. Flow Rate Calibration: The gas flow is set within the range of 8–15 L/min, calibrated to the specific tube diameter and joint configuration. Insufficient flow results in incomplete air displacement; excessive flow can cause turbulent mixing and reduced shielding effectiveness.
  4. Pre-Purge: Argon gas is introduced for a minimum duration sufficient to completely displace atmospheric oxygen and nitrogen from the purge chamber. This step is mandatory and must be verified before arc initiation.

3.3 TIG Self-Fusion Welding

The welding operation utilizes a non-consumable tungsten electrode (typically thorium-free LaB₆ or ZrO₂-stabilized tungsten) with no filler rod. The base metal itself serves as the filler material, ensuring metallurgical compatibility and eliminating concerns related to filler metal composition mismatch.

Key welding parameters include:

3.4 Post-Purge and Cooling

After completion of the welding pass, the back-side argon purge must continue until the weld zone has cooled sufficiently (below approximately 100°C) to prevent post-weld oxidation. Premature cessation of the purge gas is a common cause of internal discoloration and must be strictly avoided.

3.5 Critical Quality Indicator — Internal Weld Appearance

Acceptance Criterion: The internal weld surface must exhibit a uniform silvery or slightly straw-colored appearance, indicating complete argon protection throughout the welding and cooling cycle.

Rejection Criterion: Any visible oxidation, blue/purple discoloration, or blackening on the internal weld surface indicates protection failure. This failure results in the formation of chromium-rich oxide layers that deplete the local area of chromium, leading to irreversible loss of corrosion resistance at the weld joint. A compromised weld joint in a coil tube system represents a critical failure point that can lead to premature corrosion, system leakage, and catastrophic equipment failure.

Applications

Stainless steel coil tubes welded via the TIG self-fusion with back-side argon shielding process are employed in applications where weld integrity and long-term corrosion resistance are paramount:

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality control protocols to ensure that every coil tube product meets international standards for welding integrity and material performance:

Each production batch undergoes comprehensive quality verification including visual inspection of internal weld surfaces, dimensional verification, and, where required, non-destructive testing (NDT) methods such as dye penetrant testing (DPT) or radiographic testing (RT) to confirm weld soundness and absence of internal defects.

Unique Selling Points