How to Weld Inconel 625: TIG, MIG, Filler Metals and Best Practices

Inconel 625 is considered one of the more weldable nickel-chromium-molybdenum alloys, but a sound weld still depends on procedure qualification, joint cleanliness, heat control and filler-metal selection. Its molten weld pool is less fluid than that of carbon steel, so poor torch position or surface oxide can readily cause incomplete fusion. Excessive heat input and restraint can also increase the risk of distortion and solidification-related cracking.

This guide explains practical selection and fabrication principles for Alloy 625 plate, pipe, tube, fittings and fabricated components. It is a technical starting point, not a substitute for a project-specific WPS/PQR, applicable construction code or welding engineer approval.

Inconel 625 Welding at a Glance

Item	Practical starting point
Base material	Inconel 625 / Alloy 625 / UNS N06625
Preferred precision process	GTAW / TIG
Higher-deposition process	GMAW / MIG or pulsed GMAW
Manual covered-electrode process	SMAW
Matching TIG/MIG filler	AWS A5.14 ERNiCrMo-3; EN ISO 18274 S Ni 6625 (NiCr22Mo9Nb)
Matching SMAW electrode	AWS A5.11 ENiCrMo-3; ISO 14172 E Ni 6625 (NiCr22Mo9Nb)
GTAW shielding gas	High-purity argon is a common starting point
GMAW shielding gas	Argon or an argon-helium mixture according to the consumable supplier and qualified WPS
Preheat	Normally not required; warm only enough to remove condensation
Interpass temperature	Common manufacturer guidance: maximum 200°F (93°C), or lower when required by the WPS
PWHT	Not normally required for a matching 625 weld; avoid applying carbon-steel stress-relief practice without engineering review
Essential controls	Cleanliness, oxide removal, short stable arc, controlled heat input, adequate shielding and qualified inspection

Why Inconel 625 Is Weldable but Still Demands Control

Inconel 625 is primarily strengthened by molybdenum and niobium in a nickel-chromium matrix. Unlike age-hardened alloys such as Inconel 718, it does not depend on a full post-weld aging cycle to develop its normal corrosion-resistant fabrication properties. This is one reason Alloy 625 is widely used for welded piping, pressure equipment, offshore components, chemical-processing systems and weld overlay.

Three characteristics still require attention:

1. The weld pool is sluggish. Nickel-alloy weld metal does not wet and flow like carbon steel. The welder must direct the arc deliberately at both sidewalls and maintain suitable joint access.
2. Surface oxides are refractory. Oxides left between passes may remain solid in the next weld pool, creating inclusions or incomplete fusion. Each pass must be cleaned before the next is deposited.
3. Heat and restraint matter. High heat input, wide weaving, poor joint design and heavy restraint can enlarge the heat-affected zone, increase distortion and raise cracking risk.

The result is a material that can produce excellent welds, but only when normal nickel-alloy fabrication discipline is followed.

Which Filler Metal Should Be Used for Inconel 625?

For Inconel 625 welded to itself, the default matching filler is ERNiCrMo-3 for GTAW/GMAW and ENiCrMo-3 for SMAW. These classifications are designed around an Alloy 625-type nickel-chromium-molybdenum-niobium deposit.

Filler-Metal Selection Table

Joint or application	Normal starting selection	Important qualification note
Inconel 625 to Inconel 625 by TIG/MIG	ERNiCrMo-3	Confirm AWS/ASME or EN ISO classification, diameter, lot certification and WPS
Inconel 625 to Inconel 625 by SMAW	ENiCrMo-3	Use the polarity, storage and rebaking instructions provided by the electrode manufacturer
Inconel 625 to 300-series stainless steel	Often ERNiCrMo-3	Check dilution, service temperature, corrosion environment and construction code
Inconel 625 to carbon or low-alloy steel	Often a nickel-alloy filler such as ERNiCrMo-3	Buttering, PWHT sequence and dilution control must be engineered for the specific joint
Alloy 625 weld overlay or cladding	ERNiCrMo-3 is widely used	Deposit chemistry may require multiple layers because the first layer is diluted by the substrate
Service requiring a different corrosion profile	ERNiCrMo-4, ERNiCrMo-10 or another engineered filler may be considered	Do not substitute solely because a filler has more molybdenum; verify corrosion, strength, dilution and code requirements

ERNiCrMo-3: Matching Wire for TIG and MIG

ERNiCrMo-3 is classified by AWS A5.14 and is also identified in EN ISO 18274 as S Ni 6625 (NiCr22Mo9Nb). It is available as TIG rod and MIG wire and is intended to provide an Alloy 625-type weld deposit.

Typical manufacturer data for an ERNiCrMo-3 product may show approximately 21-22% chromium, 8-10% molybdenum and 3-4% niobium plus tantalum, with nickel as the balance. Purchase specifications should rely on the applicable edition of the standard and the actual manufacturer’s certificate rather than a generic web composition table.

ENiCrMo-3: Covered Electrode for SMAW

ENiCrMo-3 is the corresponding covered-electrode classification under AWS A5.11. Under ISO classification it may be identified as E Ni 6625 (NiCr22Mo9Nb). SMAW is useful for field erection and repair where TIG or MIG equipment is less practical, but slag must be completely removed between passes.

Why ERNiCrMo-4 or ERNiCrMo-10 Is Not an Automatic Upgrade

ERNiCrMo-4 and ERNiCrMo-10 have different chemistries and corrosion profiles. They may be appropriate for specific dissimilar joints, overlays or process media, but they are not universal substitutes for ERNiCrMo-3. A filler change can alter weld strength, dilution response, pitting resistance, high-temperature behavior and code qualification. Select it through corrosion and welding engineering review.

TIG Welding Inconel 625

GTAW, commonly called TIG welding, is generally preferred for root passes, thin-wall pipe, sheet, instrumentation tubing and fabrication where penetration and bead shape must be closely controlled.

Recommended TIG Setup Principles

• Use DC electrode negative (DCEN) unless the qualified procedure states otherwise.
• Use high-purity argon as the normal shielding-gas starting point.
• Select thoriated alternatives such as ceriated or lanthanated tungsten in accordance with shop safety policy and the WPS.
• Maintain a short, stable arc to limit atmospheric contamination and excessive bead width.
• Add sufficient ERNiCrMo-3 filler. Autogenous welding should not be assumed acceptable for a production joint unless it has been specifically qualified.
• Use a gas lens where improved shielding coverage is needed.
• Purge the root side of pipe or tube welds when required to prevent oxidation. Purge flow must be established by joint volume, dam arrangement, outlet size and the qualified procedure, not copied from a universal online value.

Step-by-Step TIG Procedure

1. Verify the base material. Confirm grade, product specification, material condition, thickness and traceability before joint preparation.
2. Prepare the joint mechanically. Use the groove angle, root face and root gap defined by the drawing or WPS. Remove plasma-cut oxide and heat tint from the fusion surfaces.
3. Degrease before welding. Remove oil, cutting fluid, marker, paint, adhesive, sulfur-bearing compounds, moisture and penetrant residue with an approved chloride-free solvent.
4. Use dedicated tools. Grinding wheels and stainless-steel brushes should be reserved for nickel alloys and should not previously have been used on carbon or stainless steel.
5. Establish shielding and purge. Confirm gas purity, hose condition and adequate displacement of air before striking the arc.
6. Deposit a controlled root pass. Keep the arc short, feed filler consistently and direct the arc toward the joint faces to avoid incomplete sidewall fusion.
7. Use narrow beads. Stringer beads are generally easier to control than wide weaving. Follow any weave limitation in the WPS.
8. Clean every pass. Remove oxide, arc starts, stops and surface defects before depositing the next layer.
9. Monitor interpass temperature. Do not start the next pass until the weldment is below the WPS limit; 200°F (93°C) is a widely published maximum for this alloy family.
10. Complete specified inspection. Visual, liquid-penetrant, radiographic or ultrasonic examination should follow the applicable code and joint category.

Should TIG Amperage Be Selected by Plate Thickness Alone?

No. A reliable current range depends on electrode diameter, filler size, joint geometry, welding position, root opening, machine characteristics, travel speed and required penetration. A generic table that assigns one amperage range to each thickness can be misleading.

Use the qualified WPS as the controlling document. When developing a procedure, begin with the welding-consumable or alloy producer’s nominal data and qualify the actual combination through a PQR where required.

MIG Welding Inconel 625

GMAW/MIG is used when higher deposition rate is needed for thicker plate, larger fabrications or overlay. Pulsed GMAW can provide better heat control and positional capability than conventional spray transfer, depending on equipment and procedure development.

For example, one current ERNiCrMo-3 consumable data sheet recommends 75% argon / 25% helium and lists the following nominal starting ranges. These are manufacturer-specific examples, not a replacement for procedure qualification.

ERNiCrMo-3 wire diameter	Voltage	Current	Manufacturer-listed gas
0.035 in / 0.9 mm	26-29 V	150-190 A	75% Ar / 25% He
0.045 in / 1.1 mm	28-32 V	180-220 A	75% Ar / 25% He
1/16 in / 1.6 mm	29-33 V	200-250 A	75% Ar / 25% He

Actual voltage, current, wire-feed speed, travel speed, contact-tip distance and shielding gas must be established for the joint, position and transfer mode. Avoid adopting stainless-steel GMAW settings without testing; nickel weld pools behave differently.

SMAW, FCAW and Submerged-Arc Welding

SMAW

SMAW with ENiCrMo-3 is suitable for site work, repair and joints where portability is important. Keep electrodes dry in accordance with the manufacturer’s handling instructions. Remove slag completely, grind starts and stops as required, and keep interpass temperature under control.

FCAW

Nickel-alloy flux-cored consumables are available, but the exact classification, shielding gas, position and mechanical properties are product-specific. FCAW should be adopted only when the chosen consumable has documented suitability and the process is qualified for the intended service.

Submerged-Arc Welding

Some ERNiCrMo-3 wire manufacturers list compatible SAW wire/flux combinations. However, alloy producers also warn that the higher heat input and slower cooling associated with SAW can increase restraint and cracking concerns. For corrosion-critical Alloy 625 fabrication, SAW should therefore be treated as a specialized qualified process rather than a default production method.

Joint Preparation and Cleaning

Cleanliness is one of the strongest predictors of Inconel 625 weld quality.

Before Welding

• Remove grease, oil, cutting fluid, paint, crayon, adhesive, penetrant chemicals, scale and moisture.
• Remove oxide from thermal-cut edges by machining or grinding.
• Avoid sulfur-, lead- and phosphorus-bearing contaminants near the weld.
• Protect cleaned filler wire and prepared joints from shop dirt and condensation.
• Verify fit-up before final cleaning so the cleaned surfaces are not repeatedly handled.

Between Passes

• Remove all visible oxide and slag.
• Grind defective starts, stops or crater areas before continuing.
• Use dedicated nickel-alloy brushes and clean abrasives.
• Reclean any surface exposed to oil, dirty compressed air or handling contamination.

Preheat, Interpass Temperature and Heat Input

Is Preheat Required for Inconel 625?

Preheat is normally not required. Room temperature is generally sufficient. Material stored in a cold environment may be warmed slightly to eliminate condensation, but this is moisture control rather than metallurgical preheating.

What Interpass Temperature Should Be Used?

Published alloy-producer guidance recommends a maximum interpass temperature of 200°F (93°C). A project WPS may impose a lower limit, and that lower qualified value should govern. Temperature should be measured close enough to the joint to represent the weld area before the next pass.

How Should Heat Input Be Controlled?

Heat input must be controlled through the qualified combination of current, voltage, travel speed and process efficiency. For basic comparison, arc energy can be calculated as:

Arc energy (kJ/mm) = Voltage x Current x 60 / [Travel speed (mm/min) x 1000]

Any thermal-efficiency factor required by the governing procedure or standard should then be applied consistently. There is no single universal kJ/mm or kJ/in limit suitable for every Inconel 625 joint. Thin-wall tube, thick plate, overlay and dissimilar joints require different qualified ranges.

Is Post-Weld Heat Treatment Required?

Most matching Alloy 625 corrosion-resistant weldments are used in the as-welded condition, so PWHT is generally not required. Carbon-steel stress-relief cycles should not be applied automatically to an Alloy 625 weldment.

Alloy-producer guidance warns that intermediate heat treatment in approximately 1000-1500°F (538-816°C) can precipitate secondary phases and reduce properties such as corrosion resistance. If heat treatment is required because of a dissimilar base material, construction code, forming history or service condition, the complete assembly must be reviewed by the responsible materials and welding engineer. A full solution treatment may be appropriate in specific cases, but temperature, holding time and cooling must match the material condition and qualified procedure.

Welding Inconel 625 to 316L Stainless Steel

ERNiCrMo-3 is commonly considered for Alloy 625-to-316L joints because it provides a nickel-rich weld deposit with broad corrosion resistance. The final selection must account for dilution from both base metals, design temperature, service medium, galvanic conditions, required strength and applicable code.

Key controls include:

• Place the joint and root geometry under a qualified dissimilar-metal WPS.
• Control dilution through bead placement and heat input.
• Confirm whether buttering is required by design or by the heat-treatment sequence.
• Evaluate ferritic or austenitic filler alternatives only through engineering review.
• Inspect the fusion boundary carefully, particularly where cyclic loading or aggressive media are present.

There is no universal rule that every 625-to-316L joint must first be buttered with 309L. That choice depends on the engineering basis and qualification record.

Welding Inconel 625 to Carbon or Low-Alloy Steel

Alloy 625 is welded or overlaid onto carbon and low-alloy steels in pressure equipment, offshore systems and repair work. These joints require more than a filler-metal match because the ferritic material may have preheat, hydrogen control and PWHT requirements that conflict with the preferred thermal exposure of the nickel alloy.

Before production, define:

• whether the joint is a structural transition, seal weld, overlay or corrosion barrier;
• required minimum deposit chemistry after dilution;
• number and thickness of overlay layers;
• ferritic-base preheat and hydrogen-control requirements;
• whether buttering must be heat treated before final joining;
• hardness, impact, corrosion and NDE acceptance criteria.

Do not prescribe a universal buttering filler or heat-treatment sequence without the governing code and PQR.

Common Inconel 625 Welding Defects and Prevention

Defect	Likely contributors	Prevention
Incomplete fusion	Sluggish pool, poor torch angle, narrow groove, oxide between passes, excessive travel speed	Improve joint access, direct the arc at both sidewalls, clean every pass and qualify travel range
Porosity	Moisture, oil, dirty gas lines, inadequate shielding, contaminated filler	Degrease, keep filler dry and clean, leak-check gas delivery and verify shielding coverage
Oxide inclusion	Failure to remove heat tint or interpass oxide	Dedicated brushing or light grinding before each pass
Solidification cracking or microfissuring	High restraint, unfavorable bead shape, excessive heat input, poor crater termination or contamination	Reduce restraint, control bead geometry and heat input, fill craters and use a qualified sequence
Root oxidation	Inadequate purge, purge loss or premature purge removal	Use suitable dams and outlets, verify purge before welding and maintain it until the hot root is protected
Undercut	Excessive current, long arc, incorrect torch angle or travel speed	Shorten arc, correct angle and remain within WPS variables
Distortion	Excessive weld volume, unbalanced sequence, high heat input and poor fixturing	Minimize weld volume, use balanced sequencing and appropriate fixtures

Inspection and Acceptance

Inspection scope should be stated before welding, not added after fabrication.

Typical Inspection Methods

• VT: joint preparation, fit-up, bead profile, undercut, oxidation and final appearance.
• PT: surface-breaking cracks or linear indications on nonmagnetic Alloy 625.
• RT: volumetric inspection of butt welds where required by the construction code.
• UT: possible for suitable geometries, but technique and reference standards must be appropriate for nickel-alloy weld metal.
• PMI: verifies alloy family and helps prevent filler or base-material mix-up; it does not by itself prove mechanical properties or heat-treatment condition.
• Mechanical and corrosion testing: tensile, bend, impact, hardness, macro examination or corrosion tests may be specified during procedure qualification or production testing.

Applicable documents may include ASME BPVC Section IX for procedure and welder qualification, the relevant construction code for acceptance, AWS A5.14/A5.11 or EN ISO 18274/ISO 14172 for filler classification, and project-specific NDE requirements. Always confirm the edition and project jurisdiction.

Inconel 625 Welding Checklist

Before releasing an Inconel 625 weld for production, confirm:

• Base material grade, specification, heat number and condition are verified.
• Filler classification, diameter, heat/lot and certificate match the WPS.
• Joint design, root gap and alignment meet the drawing and WPS.
• Surfaces are free of oxide, oil, moisture and marking contamination.
• Dedicated nickel-alloy tools are available.
• Shielding and purge gases match the qualified procedure.
• Preheat, interpass and heat-input limits are defined.
• Pass cleaning and crater treatment are specified.
• Dissimilar-metal dilution and any buttering sequence are qualified.
• Required VT, PT, RT, UT, PMI and production tests are listed.
• Repair welding follows an approved repair procedure.

Frequently Asked Questions

What is the best filler metal for welding Inconel 625?

ERNiCrMo-3 is the normal matching filler wire or rod for GTAW and GMAW of Inconel 625. ENiCrMo-3 is the corresponding covered electrode for SMAW. Dissimilar joints or unusual corrosion environments may require another filler, but the change should be supported by engineering review and procedure qualification.

Can Inconel 625 be TIG welded?

Yes. GTAW/TIG is one of the preferred processes for Inconel 625, particularly for root passes, thin-wall pipe, tubing and precision fabrication. Use a qualified ERNiCrMo-3 procedure, inert shielding, suitable root purge, strict cleaning and controlled interpass temperature.

Does Inconel 625 need preheat before welding?

Normally no. Room temperature is generally adequate. Cold material may be warmed enough to remove condensation, but unnecessary preheat increases the temperature of the weldment and can make interpass control more difficult.

What is the maximum interpass temperature for Inconel 625?

Alloy-producer guidance commonly recommends a maximum of 200°F (93°C). A qualified project WPS may specify a lower maximum, in which case the WPS value controls.

Can Inconel 625 be welded to 316L stainless steel?

Yes. ERNiCrMo-3 is commonly considered for this dissimilar combination, but filler selection and joint design must account for dilution, service medium, temperature, strength and the applicable construction code. Buttering is project-specific rather than automatically required.

Is post-weld heat treatment required for Inconel 625?

Most matching Alloy 625 corrosion-resistant welds do not require PWHT. If another component or construction code requires heat treatment, review the complete thermal cycle because intermediate stress-relief temperatures can precipitate secondary phases and reduce corrosion performance.

Why does an Inconel 625 weld show lack of fusion?

Nickel-alloy weld pools are relatively sluggish. Lack of fusion can result from poor joint access, oxide between passes, incorrect torch angle, excessive travel speed or failure to direct the arc at both sidewalls. Joint preparation, interpass cleaning and WPS control are essential.

Related Alloy and Product Resources

• Review the base material: Inconel 625 / UNS N06625
• Compare product forms: Nickel Alloy Fittings, Flanges, Forgings and Wire & Strip
• Review corrosion-service materials: Corrosion Resistant Alloys
• Compare alternative alloys: Inconel 625 vs Hastelloy C-276

Request Material for an Inconel 625 Welding Project

J&A Alloy supplies Inconel 625 plate, sheet, bar, pipe, tube, fittings, flanges, forgings and welding-related material for industrial fabrication. For a quotation, send:

• base material and product form;
• ASTM, ASME, AMS, EN or project specification;
• dimensions, wall thickness and quantity;
• material condition and required inspection certificate;
• filler classification and diameter, when applicable;
• service medium and design temperature;
• NDE, PMI, corrosion-test or third-party inspection requirements;
• destination country and required delivery date.