Welding Flux

medium 79 / 79 models (Inspector)

Submerged arc welding flux shields the molten weld pool from air instead of a gas, melting into slag that also alloys the weld metal, while brazing flux does a different job entirely - dissolving oxide films so molten filler can wet and flow into a joint that is never fully melted.

Read more — Welding Flux explained ▾

What makes this type distinct

Flux is not one product but two different jobs depending on process. Submerged arc welding (SAW) flux is a granular mineral compound poured over the joint ahead of the arc; it melts to form a slag blanket that shields the weld pool from atmospheric nitrogen and oxygen, and it also transfers alloying elements into the weld metal, so the flux composition is chosen alongside the wire, not as an afterthought. Brazing flux works differently again - the base metal never melts in brazing, so the flux's job is purely chemical, dissolving the oxide film on both surfaces so the molten filler alloy can wet and flow into the joint by capillary action. Confusing the two, or substituting a general-purpose flux for the specific base metal and process, is a common cause of weld defects at sea.

Submerged arc welding flux process — Cross-section of submerged arc welding showing the electrode wire fed through the contact tip, the flux hopper laying a flux blanket ahead of the hidden arc and weld pool, the solidified slag over the finished weld bead, and the base metal joint, with the direction of travel.

Main components

SAW flux types

Fused flux, melted and granulated during manufacture, gives consistent composition and handles moisture pickup better; agglomerated flux is chemically bonded at lower temperature and allows more alloying flexibility but absorbs moisture more readily and needs stricter storage.

Flux basicity

Rated on a basicity index; acidic flux gives good bead appearance and high deposition rate, basic flux gives better weld metal toughness and lower hydrogen content, relevant for thick, highly stressed hull sections.

Brazing flux

Formulated for a specific temperature range and base metal - copper alloys, stainless steel, and cast iron each need a different flux chemistry to dissolve the relevant oxide.

Packaging and storage

SAW flux is supplied in sealed bags or drums; once opened, it must be kept dry or re-baked before use, since absorbed moisture is a direct source of hydrogen-induced weld cracking.

Selection and sizing

Flux is matched to the wire grade and the parent steel first, then to the joint design and welding position - SAW is a flat or horizontal-vertical process, so flux choice also depends on whether the joint allows the flux bed to sit in place. Basicity is selected against the required weld metal toughness and the risk of hydrogen cracking on thick or high-strength steel sections common in hull repair. Brazing flux is selected by base metal and the brazing temperature range of the chosen filler rod, printed on the filler rod's own specification, not guessed from the metal colour.

Compatibility with the wire or filler rod grade already qualified for the repair
Basicity index against required toughness and hydrogen control for SAW flux
Moisture content and re-baking requirements before use
Base metal match for brazing flux - copper, stainless, or cast iron are not interchangeable
Shelf life and storage condition, since flux is a consumable that degrades in a humid engine room store

Regulations and class

Structural repairs made with SAW consumables on class-surveyed hull or pressure-retaining components must use a welding procedure and consumables qualified to the relevant class society's welding rules, with the flux and wire combination tested together, not separately, since the deposited weld metal properties depend on both. Welders performing class-relevant repairs at sea or in a yard must hold a current welder qualification certificate covering the process and position used. Consumables used for repairs later surveyed by class should be traceable - batch and certificate on file - in case the repair is queried.

Typical faults

Fault	Consequence
SAW flux not re-baked after moisture pickup	Hydrogen-induced cracking in the weld or heat-affected zone
Wrong basicity for the joint thickness	Reduced toughness, porosity, or poor slag detachment
Brazing flux residue not fully cleaned off	Corrosion at the joint, especially on stainless steel, over time
Flux and wire combination not qualified together	Weld metal properties fall outside what the procedure claims
Old or contaminated flux reused from an open bag	Porosity and inconsistent bead appearance

What to look for in a supplier

Certificates showing the flux and wire combination tested together against a recognised weld procedure
Clear basicity index and recommended re-baking temperature on the data sheet
Batch traceability for repairs that may later face class survey
Packaging suited to long-term storage in a ship's stores, sealed against humidity
Stock of the specific brazing flux grades matching the vessel's common base metals, not one general-purpose tin

Never assume an opened bag of SAW flux from last year's repair is still dry enough to use - a quick re-bake before a structural weld costs an hour, a hydrogen crack in a hull frame costs a lot more.

Inspector Mode Show All 79 / 79 with inspector value

5 manufacturers · 79 models

Lincoln Electric

FLUXOFIL 21 HD / C1

Model Number

TAW00004SV

Technical Specifications

Aws-klassifizierung: E7018 H4R (Excalibur MR), E6013, E7014, E7024 depending on series - strength 490-710 MPa
Wasserstoffgehalt: H4 = max. 4 mL/100g Schweißgut (Niedrigwasserstoff für Druckbehälter/Schiffe)
Feuchtigkeitswiderstand: R-Designation: Non-hygroscopic coating, max. 0.4% moisture absorption after 9h at 80°F/80% r.h. (vs. standard: 4h max.)
ISO 2560:2020: Internationale Klassifizierung für SMAW-Stabelektroden (Zugfestigkeit, Zähigkeit, Wasserstoff, Stromart)
Lagerbedingung: Sealed hermetic containers; after opening: oven min. 100-150°C or batches to be discarded (max. 4-9h air humidity exposure)
Trocknung/rekonditionierung: Low-Hydrogen (E7018): 2h at 450-500°C (232-260°C); higher classes: max. 3x 1h at 700-800°C; holding temperature ~150°C after drying

Product Lines

Excalibur (7018 MR/H4R - Niedrigwasserstoff, feuchtigkeitsresistent)
Fleetweld (37, 5P+, 180 - verschiedene Anwendungen)
Murex (7014, 7024 - Rutilbeschichtung/Hochleistung)
LincolnWeld (880M and others for shipbuilding)
Stainless Steel Lines (308L-17, 316L-15 für Korrosionsbeständigkeit)

Common Failures & Inspection Points

Area: Moisture absorption covered electrodes - coating sticky/damp or odor indication
Check: Visual: check coating for dryness; tacky test (touch); odor test; for H4R: up to 9 h permissible at <80°F/<60% r.H. (otherwise oven/discard); document with moisture meter
Area: Coating defects - cracks, spalling, contamination (rust/wear)
Check: Surface inspection: check coating for cracks/breaks; check color/gloss (discoloration=moisture); compare storage duration; batches >6 months dry before use; discard defective batches
Area: Classification conformity and approval - deviation from DNV/ABS/Lloyd's approval
Check: Check documentation: certificate number DNV/ABS/Lloyd's on container; AWS/ISO classification (e.g. E7018 H4R M 3 YH5); review batch papers; query DNV Approval Finder; check certificate expiration date; reject batches <approval date
Area: Batch traceability and storage management - no marking or lost origin
Check: Etiketten sichtbar/lesbar: Chargennummer, Verfallsdatum, Lagerdatum, Lagerort, Temperatur/Feuchte-Protokoll; Materialtestzertifikate (MTR) verfügbar; Schweißprozedur (WPS) + Schweißerqualifikation (WQR) dokumentiert; Logbuch Ofen-Ein-/Auszeiten führen
Area: Drying/reconditioning documentation - temperature, time, holding temperature not validated
Check: View oven protocol: check achieved temperature (E7018: 450-500°C, observe tolerance); holding time from reaching nominal temperature; holding temperature ~150°C after cooling; demonstrate thermometer calibration; temperature data logger; avoid over-drying (coating breaks)
Area: Storage environment not suitable - high air humidity/salt mist (maritime) or mechanical damage
Check: Storage conditions on site: temperature, air humidity (hygrometer), ventilation, salt spray protection; container integrity (dents/scratches=rust risk); location on ship: near engine room (<50°C ideal); seal containers after opening; compare storage duration versus expiration date

Type-universal inspection/service points for Welding Consumables (Lincoln Electric Europe, Mega-Swarm 2026-06). Per-model specs not auto-filled.