What Should Be Done About “Moisture Absorption” in Submerged Arc Welding Flux? An Analysis of Key Storage and Drying Techniques

As a critical auxiliary material in the submerged-arc welding process, the moisture absorption of flux directly affects weld quality. Experimental data show that when the moisture content of the flux exceeds 0.1%, the porosity of the weld increases by more than 40%, and the risk of hydrogen-induced cracking rises significantly (data source: GB/T 12470-2023 “Flux for Submerged-Arc Welding”). How can we scientifically address flux moisture absorption? This article provides an analysis from three key perspectives: the hazards of moisture absorption, storage specifications, and drying procedures.

I. Moisture-Absorption Hazards: From Microscopic Defects to Macroscopic Failure

Submerged-arc welding flux is primarily composed of silicates, fluorides, and other substances, which readily undergo physical adsorption or chemical reactions with moisture in the air, leading to two major core issues:

Porosity and Cracks: Under the high temperature of the electric arc, water decomposes into hydrogen and oxygen; hydrogen atoms diffuse into the molten pool, forming porosity, and during cooling they can trigger delayed cracking.

Reduced arc stability: Moisture absorption alters the flux’s conductivity, leading to arc blow and insufficient penetration, thereby reducing welding efficiency.

Take a pressure vessel manufacturing enterprise as an example: improper storage of welding flux resulted in porosity exceeding the specified limit in the circumferential welds of the vessel shell, increasing rework costs by RMB 120,000 per batch.

II. Storage Management: Triple-Layered Defense to Control Moisture Content

1. Environmental Control

Temperature and humidity: The warehouse temperature shall be maintained between 10°C and 30°C, with relative humidity not exceeding 60%, and equipped with automatic temperature and humidity monitoring instruments.

Isolation and protection: Keep away from volatile substances such as acids and alkalis to prevent cross-contamination;

Ground moisture protection: Use a raised floor space of at least 30 cm or install moisture-barrier mats; direct contact with the ground is prohibited.

2. Packaging Specifications

Unopened flux: packaged in double-layer plastic sealing with a desiccant inside; the outer packaging is marked with “Moisture-Proof” and “This Side Up.”

Opened flux: Store in vacuum-sealed drums; once opened, use within 48 hours, and re-vacuum-seal any unused portion.

3. Inventory Management

Adhere to the “first-in, first-out” principle, with an inventory turnover period not exceeding six months;

Conduct regular random inspections of moisture content, with a sampling rate of no less than 5% per batch (reference standard: AWS A5.17).

III. Drying Process: Precise Balance of Temperature and Time

1. Drying Parameters

Common welding flux: bake at 300–350°C for 1–2 hours; post-baking moisture content ≤0.1%.

Low-hydrogen flux: Bake at 350–400°C for at least 2 hours; moisture content must be ≤0.06%.

Drying equipment: Preferentially select recirculating-air drying ovens to ensure uniform heat distribution.

2. Operating Procedures

The flux layer thickness shall not exceed 50 mm to prevent localized overheating or insufficient drying.

Immediately transfer the dried material to a warming box (80–110°C) and retrieve as needed.

The flux must be used within 4 hours after drying; if this time limit is exceeded, it must be re-dried.

3. Technical Verification

A steel structure company improved the pass rate for flux drying from 78% to 96% and increased the first-pass welding qualification rate by 15% by implementing an infrared moisture analyzer.

IV. Long-Term Prevention and Control: Establishing a Standardized Management System

Documenting the system: Develop the “Welding Flux Storage and Drying Operation Instruction,” clearly defining responsible personnel and operational procedures;

Equipment Intelligence: Implementation of an intelligent warehousing system with humidity alerts for real-time monitoring of warehouse environmental conditions;

Personnel Training: Conduct annual specialized training on flux management to strengthen frontline employees’ awareness of moisture prevention.

Conclusion

Moisture-control management of submerged-arc welding flux is the “invisible battleground” of welding quality control. Enterprises must establish a systematic solution encompassing storage conditions, drying procedures, and operator practices to mitigate quality risks arising from moisture absorption. With the widespread adoption of smart sensing technologies and the Industrial Internet, the refined, digitalized management of welding flux throughout its entire lifecycle will inevitably become the industry’s prevailing trend.