Trace Moisture in Welding

Application Note

Welding quality depends on a controlled environment, as even small amounts of moisture in gases or on metal surfaces can cause defects that weaken the weld. Measuring trace moisture at very low levels and using sensors in gas lines or storage helps manufacturers spot and fix issues early, ensuring strong, reliable and consistent welds.

Welding, a vital fabrication process

Welding is a vital fabrication process used to permanently bond two or more materials, most commonly in metals or thermoplastics. The process uses heat, pressure or both to merge the materials into a single, unified piece. Most welding methods melt the base materials and often add a filler metal, creating a robust, fusion-based joint. To ensure the weld remains pure and protected from atmospheric gases, shielding gases or flux are typically applied to the molten weld pool.

Welding is crucial across many industries, including aerospace, automotive, construction, energy, manufacturing and maintenance. In these industries, the need for strong, durable bonds is essential.

Industrial gases in welding

Shielding gases – protecting the weld from impurities and contamination.
Fuel gases – providing the high temperatures needed for various welding techniques.

For instance:

MIG (Metal Inert Gas) and MAG (Metal Active Gas) welding use inert or active gases to stabilise the arc and enhance weld quality.
TIG (Tungsten Inert Gas) welding relies on inert gases for precision and clean welds, especially on sensitive metals.
Plasma and laser welding require tightly controlled gas environments to ensure optimal arc stability.
Oxy-fuel processes depend on fuel gases mixed with oxygen for both cutting and joining metals.

Choosing the right welding gases and managing them carefully, is essential for achieving strong, defect free joints in any application.

The role of moisture measurement in welding

Why moisture matters in welding
Moisture can enter the welding process from atmospheric humidity, contaminated gas lines or poorly stored consumables. When exposed to welding temperatures, water vapour breaks down and releases hydrogen. This hydrogen is absorbed into the molten weld pool, increasing the risk of weld defects. Key problems caused by excess hydrogen include:

Porosity, gas pockets forming within the weld.
Hydrogen induced cracking, fractures that can occur long after welding, threatening structural integrity.
Brittleness and reduced ductility, making welded joints stiffer and more susceptible to sudden failure.

Impact beyond structural integrity
Moisture contamination doesn’t just affect strength; it also degrades the weld’s appearance and mechanical performance. Results can include unsightly weld beads and weak spots that may fail under stress. Furthermore, moisture can alter shielding gas characteristics, destabilise the welding arc and trigger unwanted chemical reactions, all of which undermine weld quality.

The solution: stringent moisture control
For robust, reliable welds, controlling moisture at every stage is vital. Careful handling of materials, ongoing monitoring and strict compliance with industry standards help ensure consistently strong and high quality results across all welding applications.

Moisture is one of the most significant contaminants in welding applications; even trace amounts can severely impact weld quality, mechanical properties and long-term reliability. To maintain high standards and ensure process integrity, strict adherence to established protocols is essential. Standards such as ISO 14175, which sets limits on moisture in shielding gases and industry certifications such as NADCAP for aerospace and defence, are crucial for demonstrating best practices in safety critical sectors.

Common sources of moisture and why they matter

Maintaining weld quality requires constant vigilance against moisture contamination, which can lead to hydrogen absorption and serious weld defects. Moisture can enter the welding process from a variety of sources:

Shielding gases – moisture impurities may persist in gas cylinders that have not been properly purified or maintained, making shielding gases a significant source of contamination.
Leaks and permeation – atmospheric moisture can infiltrate through leaks during cylinder changes or within gas lines. Components such as rubber hoses and regulators are also susceptible to moisture permeation, introducing water vapour into the gas stream.
Cylinder valves and fittings – imperfect seals can allow ambient air to enter the system, further increasing moisture levels.
Supplied gas moisture content – even gas provided by vendors can contain measurable parts per million (ppm) of moisture unless specifically purified for welding use.
Pipelines and condensation – in long or uninsulated pipelines, condensation can form and later vaporise as gas flows through, contributing additional moisture.
Filters and regulators – if not regularly maintained, filters can trap and release accumulated water. Regulators that vent to the atmosphere may draw humid air back into the system.
Cylinder surfaces and depressurisation – cylinder exteriors can adsorb moisture from humid environments; rapid depressurisation can also cause chilling, leading to moisture formation inside cylinders.

Proactive moisture control at every stage of the gas supply chain is essential for minimising hydrogen contamination and for consistently achieving strong, defect free welds.

How to minimise moisture contamination in welding

Preventing moisture contamination is essential for maintaining weld integrity and quality. Here are proven strategies to keep your welding process moisture free:

Purge gas lines with dry shielding gas – use dry gases such as argon or nitrogen to purge lines and ensure your gas delivery system is both leak free and moisture free
Monitor with trace moisture analysers – install trace moisture analysers to directly measure moisture levels in your shielding gas or purged areas. This ensures conditions remain within strict, acceptable limits.
Install desiccant dryers or gas purifiers – adding dryers or gas purifiers to your shielding gas supply removes residual moisture before it can reach the weld pool.
Optimise shielding gas flow rate – set the flow rate carefully. Too much flow can cause turbulence, bringing in humid air, while too little fails to protect the weld adequately.
Regular maintenance and inspection – frequently check hoses, regulators and gas delivery components for leaks or damage. Use low permeability hoses and promptly replace any worn parts to minimise the risk of moisture ingress and maintain consistent weld quality.

By implementing these best practices, you can significantly reduce the risk of moisture related welding defects and ensure strong, high quality welds in every application.

Measurement solutions

Trace moisture analysers should be strategically placed in welding setups to ensure shielding gas and environmental conditions remain dry enough to prevent weld defects.

Shielding gas supply line
Use portable trace moisture analysers at the welding torch head. This ensures the gas is dry at the point of use, preventing hydrogen induced cracking and porosity.

Gas cylinder or manifold outlet
For centralised systems, install an online trace moisture analyser for continuous measurement at the outlet of the gas manifold or regulator to monitor bulk gas dryness before distribution.

Purge gas lines
For pipe or vessel welding, when purging with argon or nitrogen, install moisture sensors in the purge line or exhaust to verify the moisture content during setup and welding.

Trace moisture measurement is essential for ensuring welding quality, reliability and safety. Detecting water vapour at ppm levels helps prevent defects such as porosity and hydrogen induced cracking. Using suitable sensor technology, integrating it correctly into gas supplies and maintaining calibration ensures optimal performance. Real time moisture monitoring supports weld integrity, simplifies troubleshooting, reduces waste and helps meet industry standards.