Handling and Storage of Welding Fluxes

Correct flux management is one of the most overlooked factors in submerged arc welding (SAW) quality. Flux that has absorbed moisture — even in small quantities — introduces hydrogen into the weld pool, which is a primary cause of hydrogen-induced cracking (HIC) in high-strength steels and restrained joints. The consequences of poor flux handling are not always immediately visible: HIC is a delayed failure that can develop hours or days after welding is complete, making it particularly dangerous in structural, pressure vessel, and offshore applications.

This guide covers the three key functions of flux, how flux baking works, and the specific storage, handling, recycling, and rebaking requirements for Exaton SAW fluxes. For guidance on flux-cored and metal-cored wire selection, see our Flux-Cored and Metal-Cored Wire Guide.

The Three Functions of Flux in Welding

Before addressing handling and storage, it is worth understanding what flux actually does — because the handling requirements flow directly from these functions and what compromises them.

1. Cleaning

Flux removes oxides, grease, moisture, and other surface contaminants from the metals being joined. Oxides on the base metal surface prevent the molten filler metal from bonding effectively — flux dissolves these chemically, creating a clean, reactive surface for the weld to form against. Even a brief period between pre-cleaning and welding can allow re-oxidation to begin, which is why flux-protected processes such as SAW are particularly valuable on scale-prone materials.

2. Protection

During welding, flux forms a protective barrier — either as a slag layer or, in SAW, as a physical granular blanket — that shields the molten weld pool from atmospheric oxygen and nitrogen. Without this protection, the weld pool would rapidly oxidise, producing porosity, inclusions, and a mechanically compromised joint. In SAW, the granular flux blanket completely covers the arc and weld pool, providing both atmospheric protection and thermal insulation that contributes to the controlled cooling rate of the weld.

3. Facilitation

Flux acts as a wetting agent, reducing the surface tension between the filler metal and the base metal. This improved wetting allows the molten filler to spread evenly and form a strong metallurgical bond across the joint. Flux also lowers the effective melting temperature of the filler, enabling it to flow into tight joint geometries more easily and fill the joint completely.

Why Flux Baking Matters

In submerged arc welding, moisture absorbed by flux during storage or handling is one of the most serious process variables. When moist flux is heated in the arc, the moisture dissociates and releases hydrogen into the weld pool. This dissolved hydrogen migrates to points of high stress concentration — typically the weld root, the fusion line, or the HAZ — and can cause cracking that develops well after the weld appears sound.

Hydrogen-induced cracking is particularly dangerous because:

• It is a delayed phenomenon — cracks may not appear until hours or days after welding
• It is not detectable by visual inspection of the completed weld
• It is most severe in high-strength steels, thick sections, and highly restrained joints — exactly the applications where SAW is most commonly used

Flux baking removes absorbed moisture and volatile substances by subjecting the flux to a controlled heating cycle, restoring it to its optimal condition before use.

General flux baking procedure

1. Preheat the oven — set to the temperature specified by the flux manufacturer. Always refer to the specific product data sheet; using the wrong temperature can fail to remove moisture or alter flux chemistry
2. Spread the flux evenly — place flux in a shallow metal tray in a single even layer no deeper than 50 mm. Do not stack or overlap — uneven layers prevent adequate airflow and uniform heating, leaving moisture trapped in the centre
3. Bake for the specified duration — baking time depends on flux type and composition; follow the manufacturer's instructions precisely. Underbaking leaves residual moisture; overbaking can alter flux chemistry and basicity
4. Cool in a clean, dry environment — allow flux to cool to room temperature with adequate ventilation. Do not expose cooling flux to damp or humid conditions — freshly baked flux is highly hygroscopic and will begin reabsorbing moisture immediately
5. Store correctly after baking — transfer baked flux to sealed dry containers or a flux holding oven. Rebaking is required if flux is left exposed for an extended period before use

Exaton SAW Flux: Storage and Handling Requirements

Exaton fluxes are manufactured with carefully controlled raw material selection and optimised production conditions, ensuring a guaranteed as-delivered moisture content from the factory. To maintain this condition for as long as possible, the following handling and storage requirements must be observed.

Transport

• All flux must be transported in covered vehicles — exposure to rain or high humidity during transit is sufficient to compromise moisture content
• Unbroken pallets must be kept shrink-wrapped in plastic or in their wooden crates throughout transport
• If packaging is damaged during transit, unprotected containers must be repacked within one hour — beyond this, the flux should be scrapped or rebaked before use
• A maximum of two pallets may be stacked on top of one another

Storage

Unopened flux drums must be kept under the following controlled storage conditions:

• Temperature: 20 ± 10°C
• Relative humidity: as low as possible, not exceeding 70%
• Flux stored correctly under these conditions has a maximum shelf life of 5 years
• The contents of unprotected flux hoppers must, after each 8-hour shift, be placed in a drying cabinet or heated flux hopper maintained at 150 ± 25°C
• Remaining flux from opened drums must also be kept at 150 ± 25°C until next use

Recycling

SAW flux is typically recovered and recirculated during welding. To maintain flux quality through the recycling process:

• Moisture and oil must be removed from the compressed air used in any recirculation system — oil or moisture carried through the compressed air system directly contaminates the flux
• The addition of new flux must be maintained at a ratio of at least one part new flux to every three parts recycled flux — recycled flux progressively depletes in active ingredients and must be replenished to maintain consistent arc performance and weld chemistry
• Foreign material — mill scale, dross, slag fragments — must be removed by sieving before recycled flux is returned to the hopper

Rebaking Exaton Fluxes

When handled and stored correctly according to the requirements above, Exaton fluxes can generally be used as delivered without rebaking. However, rebaking is recommended in two situations:

• Severe applications — where the material specification or procedure qualification calls for the lowest achievable hydrogen levels (e.g. H5 or H4 classification), rebaking immediately before use provides an additional safeguard
• Flux that has been exposed to unfavourable conditions — if flux has been stored incorrectly, exposed to elevated humidity, or left in an open hopper beyond the permitted period, rebaking can return it to its original condition

Rebaking procedure for Exaton fluxes

• Temperature: 350 ± 25°C
• Duration: minimum 4 hours
• Layer depth: flux must be spread on shallow trays with a maximum depth of 50 mm — deeper layers prevent uniform heating and leave moisture in the lower portions of the flux bed
• After rebaking: flux not immediately used must be placed in a holding oven or drying cabinet at 150 ± 25°C until required — do not allow rebaked flux to cool and be exposed to ambient conditions before use

ESAB SAW Fluxes and Packaging

ESAB's submerged arc welding flux range is available in the BlockPac™ format — a high-moisture-resistance packaging system for fluxes such as OK Flux 10.65 and OK Flux 10.66, designed to maintain flux condition during transport and storage and reduce the frequency of baking required in controlled environments.

For stainless steel and nickel alloy SAW applications, OK Flux 10.99 is a neutral agglomerated basic flux designed for austenitic stainless steels and compatible with nickel-based alloy wires for demanding corrosion-resistant applications.

For SAW wire selection guidance, see our Welding Consumables Selection Guide or contact your local ESAB representative.