Stainless steel 316 and 316L are among the most weldable austenitic grades — but “weldable” does not mean “forgiving.” Get the process, filler, or heat input wrong and you will end up with sensitised grain boundaries, sugared weld roots, hot cracks, or a joint that corrodes faster than the base metal it was meant to join.
This guide is written for practising fabricators, welding engineers, and procurement teams specifying TIG wire and MIG wire for SS 316 / 316L projects. Everything here is practical and process-specific. For full grade properties and specifications, see Ambica Steels’ SS 316 & 316L material grade page.
1) Why Welding Stainless Steel 316 / 316L Is Different
Stainless steel behaves fundamentally differently from mild steel under a welding arc — and understanding those differences is what separates a sound, corrosion-resistant weld from an expensive failure.
Lower thermal conductivity. SS 316 conducts heat at roughly one-third the rate of carbon steel. Heat concentrates in the weld zone rather than spreading away — this means higher local temperatures, greater distortion risk, and a wider heat-affected zone (HAZ) relative to the energy input.
Higher thermal expansion. Austenitic stainless steels expand roughly 50% more than carbon steel when heated. This amplifies distortion in thin sections and drives residual stress in constrained joints. Proper fixturing and sequencing matter more here than in carbon steel work.
Electrical resistivity. SS 316 has about seven times the electrical resistivity of mild steel. This means welding parameters — particularly for resistance and spot welding — need adjustment; for GMAW/FCAW, use lower wire extension (stickout) than you would on carbon steel.
Sensitisation risk. The most critical difference. Carbon in the alloy can form chromium carbides at grain boundaries if the steel is held in the 425–860°C range — a problem unique to stainless and the reason 316L exists. See Section 2.
2) Understanding Sensitisation — The #1 Risk
Sensitisation is the single most important concept in stainless steel welding. Every decision you make — choice of grade (316 vs 316L), filler wire, heat input, post-weld treatment — ultimately comes back to managing this risk.
What Happens
When stainless steel is heated and held within the “sensitisation range” of 425–860°C (800–1580°F), carbon in the alloy migrates to grain boundaries and bonds with chromium to form chromium carbides (Cr₂₃C₆). This “robs” chromium from the zone immediately surrounding each grain boundary. Where the bulk alloy contains 16–18% chromium, the depleted zones drop to as low as 9–10% — below the threshold for passive film formation. The result: those zones corrode preferentially, and the joint fails by intergranular corrosion.
Why Stainless Steel 316L Solves It
Grade 316L was developed specifically to address sensitisation. By reducing carbon from the 316 maximum of 0.08% down to a maximum of 0.03%, there simply is not enough carbon available to form a damaging chromium carbide network. This is why 316L is the preferred base metal for welded fabrications in corrosive service — and why ER316L filler wire is the correct choice when joining either grade.
3) Choosing the Right Welding Process
SS 316 and 316L are compatible with most fusion welding processes. Process selection depends on section thickness, joint configuration, production rate requirements, and the service environment of the finished component.
The highest-quality process for SS 316/316L. Precise heat control, excellent arc stability on thin sections, and clean welds. Mandatory for pipe root passes (with argon purge), pharmaceutical equipment, and food-contact surfaces. Slow but delivers the best metallurgical results.
High deposition rate for production welding of medium to heavy sections. Use short-circuit transfer for thin material, spray transfer for thicker sections. Requires ER316LSi filler for improved weld pool fluidity. Shielding gas must be tri-mix or Ar+2%CO₂ — never pure CO₂ (causes carburisation).
Field welding and repair work where TIG/MIG equipment is unavailable. Use E316L-16 or E316L-17 electrodes. Weld quality is lower than GTAW due to slag inclusion risk and less precise heat input. Post-weld slag must be completely removed before any passivation treatment.
Plasma arc welding offers deeper penetration than TIG at comparable heat input. Used for keyhole welding of medium-thickness pipe (3–8 mm) in a single pass. Excellent for mechanised/automated applications in pharmaceutical and chemical plant construction.
High deposition rate for heavy plate (>10 mm) and longitudinal seam welding. Flux selection is critical — use a neutral or slightly basic flux. Not suitable for thin sections or positional welding. Rarely used for 316/316L except in large pressure vessel fabrication.
Oxyacetylene welding is explicitly not recommended for Stainless Steel 316/316L. The process introduces carbon from the flame into the weld pool, directly causing sensitisation and severely degrading corrosion resistance. Never use on any austenitic stainless steel in corrosive service.
4) Filler Wire Selection
Selecting the correct filler is not optional — the wrong choice can make the weld deposit the least corrosion-resistant part of the assembly.
| Filler Wire | AWS Classification | Process | Best For | Use? |
|---|---|---|---|---|
| ER316L | AWS A5.9 ER316L | TIG / GTAW | All Stainless Steel 316/316L joints in corrosive service. The first-choice filler for TIG welding. Low carbon prevents sensitisation. | ✔ Preferred |
| ER316LSi | AWS A5.9 ER316LSi | MIG / GMAW | MIG welding of SS 316/316L. Added silicon improves weld pool fluidity and bead appearance. Same corrosion resistance as ER316L. | ✔ Preferred (MIG) |
| ER316 | AWS A5.9 ER316 | TIG / MIG | Permitted when joining 316 base metal not exposed to sensitisation temperatures. Not preferred — use ER316L instead wherever possible. | ⚠ Acceptable |
| E316L-16 / E316L-17 | AWS A5.4 | SMAW / Stick | Stick welding of SS 316/316L. -16 suffix = rutile coating (AC/DC+). -17 suffix = improved low-hydrogen formulation. | ⚠ Acceptable |
| ER308L | AWS A5.9 ER308L | TIG / MIG | For joining SS 304/304L base metal only. Do not use on Stainless Steel 316/316L — contains no molybdenum, so the weld deposit will have significantly lower pitting resistance than the base metal. | ✖ Do Not Use |
| ER309L | AWS A5.9 ER309L | TIG / MIG | Dissimilar metal welding: joining SS 316/316L to carbon steel or low-alloy steel. Provides a buffer layer in clad plate welding. | ⚠ Dissimilar only |
5) Pre-Weld Preparation
More weld defects in stainless steel originate before the arc is struck than during welding itself. Pre-weld discipline is non-negotiable.
01 Dedicated Tools Only
Never use grinding wheels, wire brushes, or files that have previously been used on carbon steel or other metals. Embedded iron particles will rust on the stainless surface and initiate corrosion. Keep all stainless tooling clearly labelled and segregated.
02 Degrease Thoroughly
Remove all oil, grease, cutting fluids, and marking ink from the weld zone and surrounding area using acetone or a dedicated stainless steel cleaner. Any organic contamination will carburise the weld and cause porosity. Wipe clean just before welding — do not allow solvent residue to remain on the surface.
03 Mechanical Cleaning
Oxide scale and discolouration from prior heat exposure must be removed. Use dedicated stainless steel wire brushes or scotch-brite pads. For pipe bevels, a clean file or carbide burr works well. Never use an abrasive that has touched carbon steel.
04 Joint Fit-Up & Gap Control
Maintain consistent root gaps as specified in your WPS. Gaps that are too tight increase the risk of lack of fusion; gaps that are too wide increase distortion. For pipe TIG welding, a 1.5–2.5 mm root gap with 1.6 mm root face is typical. Tack welds must use the same filler wire as the production weld.
05 No Preheat Required
Unlike carbon and low-alloy steels, SS 316 / 316L does not require preheating. In fact, starting with a cold joint (at ambient temperature) is preferred — it helps limit heat buildup and reduces sensitisation risk. If the component has been in cold storage, allow it to reach ambient temperature to avoid condensation under the arc.
06 Protect from Contamination During Welding
Keep the weld area clean of spatter from adjacent carbon steel grinding or welding operations. Stainless steel is particularly susceptible to iron contamination — a tiny embedded particle from carbon steel spatter can initiate rust and corrosion even on otherwise perfect Stainless Steel 316L.
6) Shielding Gas Selection
Shielding gas choice directly affects arc stability, weld bead appearance, penetration profile, and — critically — the risk of oxidation and carburisation of the weld deposit.
| Gas / Blend | Process | Notes | Rating |
|---|---|---|---|
| Argon 100% (Ar) | TIG / GTAW | Standard shielding gas for GTAW. Use 99.99% purity minimum. Also used as purge gas for pipe root protection. | Best for TIG |
| Ar/He 70/30 or 50/50 | TIG / GTAW | Helium addition increases arc energy and penetration for thicker sections. Useful on heavy-wall pipe and pressure vessels. Higher cost. | Good |
| Ar + 2% CO₂ | MIG / GMAW | Most common MIG blend for SS 316/316L. Low CO₂ maintains oxidising potential for stable arc without carbon pickup. Good bead appearance. | Best for MIG |
| Ar/He/CO₂ (Tri-mix) e.g. 90/7.5/2.5 |
MIG / GMAW | Tri-mix blends give improved weld fluidity, faster travel speeds, and reduced spatter vs. Ar/CO₂. Preferred for production MIG welding of Stainless Steel 316. | Preferred (MIG) |
| Ar + 2% N₂ | Purge gas | Small nitrogen addition to the back purge gas slightly increases pitting resistance of the weld root in duplex-adjacent specifications. Not standard for 316L but used in some pharmaceutical and nuclear applications. | Specialist use |
| Pure CO₂ | MIG | Never use pure CO₂ on stainless steel. The excess carbon causes carburisation of the weld deposit, drastically reducing corrosion resistance — effectively replicating sensitisation damage. | Never use |
Back Purging for Pipe Welds
For pipe welding, argon back purging is essential — not optional — in any application where the weld root will be exposed to a corrosive environment. Without purging, the back of the root pass oxidises (“sugars”) during welding. This sugared surface is rough, unpassivated, and highly susceptible to corrosion — and it cannot be removed by post-weld pickling on the outside of the pipe alone.
7) Heat Input & Interpass Temperature
Heat management is the most important in-process variable for welding Stainless Steel 316 and 316L correctly. Too much heat — or heat applied too slowly — increases sensitisation risk, causes excessive distortion, and can reduce mechanical properties.
Interpass Temperature: Maximum 150°C
On multi-pass welds, the temperature of the previously deposited weld metal and adjacent HAZ must be allowed to cool to 150°C or below before the next pass is deposited. This is called the interpass temperature limit. On thin sections, 100°C or even lower is preferable.
Use a contact thermometer or temperature-indicating crayons (tempilsticks) — do not estimate by feel or colour.
Heat Input Formula
Heat input is calculated as: HI (kJ/mm) = (Amps × Volts × 60) ÷ (Travel Speed mm/min × 1000). For SS 316/316L, target heat inputs are typically lower than equivalent carbon steel joints — high heat input increases time in the sensitisation range and worsens distortion.
Practical Techniques to Limit Heat Buildup
- Intermittent welding: Deposit short weld runs (100–150 mm), then move to the opposite end or side of the joint — “backstep” welding. This distributes heat and limits localised buildup.
- Copper backing bars & heat sinks: Clamping copper bars adjacent to the weld zone conducts heat away rapidly. Critical on thin sheet and tube.
- Wet rags or compressed air: Cooling adjacent metal between passes using wet cloths (avoiding the weld itself) is acceptable for non-critical work. Do not quench the weld bead directly.
- Pulse TIG: Pulsed GTAW reduces average heat input by 30–50% compared to continuous arc, while maintaining adequate fusion. Strongly recommended for thin wall tube and sheet in pharmaceutical applications.
8) Post-Weld Treatment
The passive chromium oxide layer that protects stainless steel is partially disrupted in the HAZ and by surface contamination (spatter, scale, heat tint) during welding. Post-weld treatment restores and enhances this protection. This is a mandatory step for any component going into corrosive service.
Passivation
Passivation dissolves free iron and other contaminants from the surface, allowing the natural chromium oxide film to reform uniformly. For Stainless Steel 316/316L, passivation is typically performed using citric acid (5–10% solution at 50–60°C) or nitric acid (20–40% solution at ambient temperature). Citric acid is preferred in food, pharmaceutical, and environmentally sensitive applications. ASTM A967 covers standard passivation procedures.
Pickling (Acid Pickling / Pickling Paste)
Pickling removes heat tint, weld scale, and a shallow surface layer of chromium-depleted metal. It is more aggressive than passivation and is required wherever visible oxidation or discolouration has occurred in the HAZ. Pickling paste (typically a mixture of hydrofluoric and nitric acids) is applied, left for the specified dwell time, then thoroughly water-rinsed. Always follow safety protocols — pickling agents are highly corrosive to skin and eyes.
Post-Weld Solution Annealing (for heavy-section Stainless Steel 316)
Where heavy sections of standard Stainless Steel 316 (not 316L) have been multi-pass welded and sensitisation is suspected, post-weld solution annealing can fully restore corrosion resistance. The process involves heating to 1010–1121°C, holding for sufficient time to dissolve carbides, then rapidly water quenching. This must be followed by re-passivation. This treatment is not practical for large fabrications and is one of the strongest arguments for specifying 316L in the first place.
9) Common Defects & How to Fix Them
| Defect | Root Cause | Prevention / Fix |
|---|---|---|
| Hot Cracking (solidification cracking) | High heat input, high restraint, incorrect filler (low ferrite content). Most common in fully austenitic weld deposits with high S and P levels. | Use ER316L filler with a Ferrite Number (FN) of 3–8. Reduce heat input. Avoid crater cracking by using run-off tabs or the crater-fill function on your power source. |
| Porosity | Contamination (oil, moisture, zinc from galvanised steel nearby), inadequate shielding gas coverage, gas leaks in hose or torch, wind disturbing shielding during outdoor welding. | Thorough pre-weld degreasing. Check all gas connections. Use wind screens outdoors. Increase gas flow rate (typically 12–15 L/min for TIG, 14–18 L/min for MIG on stainless). |
| Lack of Fusion | Travel speed too fast, current too low, joint gap too tight, incorrect torch angle, excessive oxidation on faying surfaces. | Increase current / reduce travel speed. Ensure clean, correctly prepared joint faces. Maintain correct torch angle (15–20° drag for TIG). |
| Weld Root Sugaring (oxidation) | Inadequate or absent argon back purge. Residual oxygen above 0.5% during root pass. | Purge to below 0.1% O₂ before striking arc. Maintain purge until root cools below 300°C. Use oxygen analyser. Sugared roots must be ground back to clean metal and re-welded — no amount of pickling will restore them. |
| Sensitisation / Intergranular Corrosion | Using standard 316 (not 316L) in welded joints without post-weld anneal. Slow cooling through sensitisation range. Oxyacetylene welding. | Specify 316L base metal and ER316L filler. Limit heat input and interpass temperature. Post-weld solution anneal for heavy-section 316. Never use oxyacetylene on stainless steel. |
| Distortion | Unbalanced weld sequence, high heat input, thin section material, inadequate fixturing or clamping. | See Section 10. Pre-set the joint to anticipate distortion direction. Alternate weld passes. Use strongbacks and fixtures. |
10) Distortion Control
Because Stainless Steel 316/316L expands roughly 1.5× more than carbon steel under heat, distortion management requires more attention — particularly on thin-section sheet, tube, and fabricated frames.
- Pre-setting: Angle or offset the joint in the direction opposite to expected distortion before welding begins. After welding and cooling, the component returns to (or near) the correct position.
- Balanced welding: For butt welds in plate, alternate between face and root sides (where access allows) to balance shrinkage forces.
- Backstep welding: Deposit short incremental runs in the direction opposite to overall weld progression. Each increment shrinks away from the next, distributing distortion forces.
- Strongbacks and fixtures: Clamp the component securely to a rigid backing fixture during welding. Remove restraints only after the joint has cooled to ambient temperature.
- Sequence symmetry: On symmetrical structures (frames, vessels), weld in a sequence that applies heat symmetrically — alternate between opposite seams.
- Cold correction: Minor distortion in thin sections can be corrected by controlled cold pressing or rolling. Avoid flame straightening — heating stainless with an open flame risks re-sensitisation and carbon pickup.
Frequently Asked Questions
Q1. What filler wire should I use to weld Stainless Steel 316 and 316L?
Use ER316L for GTAW/TIG and ER316LSi for GMAW/MIG welding. The low carbon content of both fillers prevents sensitisation in the weld deposit and HAZ. Never use ER308L on SS 316/316L base metal — it lacks molybdenum and will produce a weld deposit with significantly lower pitting corrosion resistance than the parent material. For stick welding, use E316L-16 or E316L-17 electrodes.
Q2. What is sensitisation and why does it matter?
Sensitisation occurs when stainless steel is held in the 425–860°C temperature range, causing chromium carbides to form at grain boundaries. This depletes chromium from the surrounding zones and destroys their corrosion resistance. The result is intergranular corrosion — the weld joint corrodes along grain boundaries even though the bulk of the material remains intact. Using 316L instead of 316, and keeping heat input and interpass temperature under control, are the primary defences against sensitisation.
Q3. Does SS 316L require post-weld heat treatment?
For the vast majority of fabrications, Stainless Steel 316L does not require post-weld annealing. Its low carbon content prevents sensitisation during normal welding. However, all welded SS 316L components destined for corrosive service should receive post-weld passivation (citric or nitric acid treatment per ASTM A967) and, where heat tint is present, acid pickling. Standard Stainless Steel 316 in heavy multi-pass welded sections may require solution annealing — another reason to specify 316L wherever welding is involved.
Q4. What shielding gas is best for TIG welding Stainless Steel 316?
Pure argon (99.99%) is the standard shielding gas for GTAW/TIG welding of Stainless Steel 316 and 316L. For increased penetration on thicker sections, argon-helium blends (Ar/He 70/30 or 50/50) work well. For pipe welding, use the same pure argon as the root-side purge gas to prevent oxidation of the weld root. Never use CO₂-rich shielding gases or oxyacetylene — both introduce carbon into the weld deposit.
Q5. What is the maximum interpass temperature for Stainless Steel 316L?
The maximum recommended interpass temperature for Stainless Steel 316 and 316L is 150°C (300°F). Between passes on multi-run welds, allow the joint to cool to this temperature before depositing the next run. Use a contact thermometer or tempilstick — never estimate by colour. Lower interpass temperatures (100°C or below) are preferred for thin sections and pharmaceutical/food-grade fabrications where surface quality and corrosion resistance must be maximised.
Q6. Why is oxyacetylene welding not recommended for Stainless Steel 316?
Oxyacetylene welding of austenitic stainless steels — including Stainless Steel 316 and 316L — is explicitly not recommended because the combustion flame introduces carbon directly into the weld pool. This dramatically increases local carbon content, causes severe carbide precipitation (sensitisation), and permanently damages corrosion resistance in the weld zone. All recognised welding procedure standards (AWS D1.6, ASME IX, EN ISO 15614) exclude oxyacetylene for stainless steel welding in structural and process applications.
Q7. Where can I source ER316L TIG wire and ER316LSi MIG wire in India?
Ambica Steels supplies SS 316L TIG (GTAW) wire and SS 316LSi MIG (GMAW) wire from New Delhi, India, with mill certification and full traceability. Contact Ambica Steels at ambicasteels.com/contact-us to request specifications or a quotation.
