How to Weld Stainless Steel: TIG, MIG, Stick, Pipe and Tube

How to weld stainless steel comes down to four controls: a joint cleaned with stainless-only tools, a filler matched to the grade, low heat input, and inert gas protecting both sides of the weld until it cools, and Paul Industries applies those controls to stainless pipe, tube and tank welding in plants across all 50 states.

How to weld stainless steel, step by step

Welding stainless steel uses the same arc fundamentals as carbon steel, with tighter control of cleanliness, heat and shielding at every step.

How to weld stainless steel: stick, MIG or TIG?

Process choice for stainless follows thickness, position and joint length: TIG suits thin material and roots, MIG suits long joints and production work, and stick suits heavy sections and repairs where gas and wire feeders are impractical. All of them count as arc welding stainless steel, and each is qualified under a written procedure.

Is stainless steel hard to weld?

Austenitic stainless steel such as 304L and 316L is readily welded by every arc process and needs no preheat, so the added difficulty lies in cleanliness and heat control rather than in striking and holding the arc. Can you weld to stainless steel with the machines used on carbon steel? Usually, with a change of filler, gas and tools. Is it hard to weld stainless steel to a code standard? The harder part is that the metal holds heat: thermal conductivity is about 16 W/m per degree C against about 47 for carbon steel, and expansion runs about 50 percent higher, so the part moves. Ferritic and martensitic grades ask for more care, as the table shows.

What is needed to weld stainless steel?

Welding stainless steel needs a power source matched to the process, inert gas for the shield and the purge, low-carbon filler, and a set of hand tools kept only for stainless. The right welding machine for stainless steel depends on the process: TIG needs a DC constant-current source with high-frequency arc starting, so the tungsten never touches the work; MIG needs a constant-voltage source, and short-circuit work benefits from slope, voltage and inductance control; stick runs on the same power sources as carbon steel electrodes.

Wire brushes, grinding wheels and files stay on stainless only, because iron or zinc carried over from other work causes rust or cracking. A MIG setup gets its own gun liner and drive rolls.

TIG welding stainless steel: settings and technique

TIG welding stainless steel runs on direct current, electrode negative, with argon shielding and a thoriated, ceriated or lanthanated tungsten, at a current set by thickness. The table gives published starting points for settings for TIG welding stainless steel across butt, corner, tee and lap joints.

How many amps for TIG welding stainless steel depends mostly on thickness, and stainless steel welding settings like these only start a procedure test, because they move with hand speed. For vertical-up and overhead welds, drop current 10 to 20 percent. A welder on a foot pedal travels slower and can run well below the table on thin sheet.

How to TIG weld stainless

Learning how to weld tig stainless steel starts with a short arc and a clean start, because the bead shows every lapse. Use high-frequency starting, and never strike on a carbon block, which adds carbon to the joint. Add cold filler at the front edge of the puddle, keep the hot rod end inside the gas envelope, and taper off at the end of the bead so the crater fills. Hold the torch through post-flow. When working out how to weld stainless steel with TIG on heavy wall, an argon-helium blend gives a hotter arc.

What gas do you need to weld stainless steel?

Stainless welding gas depends on the process: argon for TIG, a helium tri-mix or an argon mix with a small oxygen or CO2 addition for MIG, and CO2 or 75/25 only for flux-cored wire made for those gases. For TIG welding stainless steel, shielding gas is usually pure argon, whose stable arc and lower voltage help avoid burn-through on sheet.

The TIG gas for stainless steel is welding-grade argon, and stainless TIG welding gas only protects the bead if hoses and fittings are leak free, because a pinhole draws in air. TIG welding gas for stainless steel flows at 10 to 25 cfh in the settings table, and more through larger cups. What gas to MIG weld stainless steel comes down to transfer mode and carbon: MIG welding stainless steel shielding gas stays under about 5 percent CO2 on solid wire, since carbon pickup lowers the corrosion resistance of multipass welds. Argon welding for stainless steel is a shop name for TIG, and welding stainless steel with argon on the torch alone leaves an open root unprotected.

How to weld stainless steel with a MIG welder

How to MIG weld stainless comes down to a DCEP constant-voltage machine, low-carbon silicon-bearing wire such as ER308LSi, and a low-CO2 gas, with the gun pushed rather than dragged. Stainless wire welding covers solid, metal-cored and flux-cored wire, and stainless steel wire feed welding keeps deposition high because there is no stopping to change electrodes. Crews learning how to weld stainless steel with MIG should start with the short-circuit values below.

MIG welding stainless steel settings

Those MIG welding settings for stainless steel assume short-circuit transfer with helium tri-mix at 15 to 20 cfh. Spray transfer needs far more current: about 220 amps on 0.045 in wire and 300 to 350 amps on 1/16 in wire, at 22 to 30 volts. Argon-rich gases run the short-circuit arc up to 6 volts lower, and the colder arc invites lack of fusion. Sections up to 1/16 in need a backup strip, as does 1/4 in and thicker plate welded from one side, with inert gas on the underside.

Flux-cored wire opens up plate work: E308LT1-1 and -4 wires take CO2 and 75/25 because the slag shields the metal, and self-shielded -3 wires run without gas.

How to stick weld stainless steel

Stick welding for stainless steel uses low-carbon coated electrodes such as E308L-16 on DCEP, at lower current than an equal-diameter carbon steel rod, with a short arc that keeps the coating out of the puddle. The right electrode for stainless steel follows the grade, and anyone working out how to weld stainless steel with stick welder settings carried over from carbon steel finds that they run too hot.

For stainless steel electrodes, welding current in the flat position sits about 10 percent below the maximum. Choose coating by position: lime-coated -15 electrodes run DC only and suit vertical, overhead, pipe and root work; titania -16 electrodes suit flat work and run best on DC; silica-titania -17 suits flat and horizontal work with minimal cleanup. Keep to 5/32 in or smaller out of position, limit any weave to 2-1/2 times the electrode diameter, and remove all slag between passes.

Coated stainless electrodes can need reconditioning after only four hours in open air, and damp coatings cause porosity at arc starts. Store opened electrodes in a holding oven at 200 to 300 degrees F, and re-dry at 500 to 600 degrees F for about an hour, per the manufacturer.

Stainless steel filler rod: what to use on 304, 316 and other grades

A stainless steel filler rod for austenitic grades should match or exceed the alloy content of the base metal, so 304L takes ER308L and 316L takes ER316L. Anyone planning to weld 304 stainless steel will notice that no 304 filler exists: 308 runs slightly higher in chromium and nickel so the deposit keeps a little ferrite, which resists hot cracking. Welding 316 stainless steel needs molybdenum in the filler as well, which is why 316L base metal takes a 316L deposit.

The TIG welding stainless steel rod is a cut length of the same classification as MIG wire, so a filler rod for TIG welding stainless steel reads ER308L or ER316L on its tag, and a TIG stainless steel filler rod stays wiped clean and capped between uses. Rod choice is therefore a grade decision, governed by AWS A5.4 for coated electrodes, A5.9 for solid wire and rod, and A5.22 for cored wire. The low-carbon choice matters most when you weld 316 stainless or 304 for corrosive duty: the L grades hold carbon to 0.03 percent against 0.08 percent for standard grades, which limits chromium carbide formation between about 800 and 1,600 degrees F. Welding cast stainless steel follows the table through its cast designations, with a check of the casting specification for repair limits. Welding 304 stainless steel for severe corrosive duty means 304L and E308L, or a stabilized grade, and TIG welding 304 stainless steel normally uses ER308L rod.

Can stainless steel be welded to carbon steel?

Stainless steel can be welded to carbon steel by using an over-alloyed 309-type filler, which absorbs dilution from the carbon steel and still freezes with some ferrite and no brittle martensite. Can stainless steel be welded to regular steel in a pressure system? A qualified procedure with that filler covers it. That choice answers how to weld stainless steel to carbon steel for most plant tie-ins, by any process: MIG welding stainless steel to carbon steel uses ER309LSi with a low-CO2 gas, TIG welding stainless to carbon steel uses ER309L rod, and stick work uses E309L.

Can you weld steel to stainless steel with whatever wire is on the machine? The arc will run, yet the deposit loses corrosion resistance and can crack as it picks up alloy. The mild steel to stainless steel welding rod is E309L or ER309L in every process. Welding mild steel to stainless steel on a heavy or highly restrained joint starts by buttering the carbon steel face with E309, then finishing with stainless filler; keep penetration shallow, because less melted carbon steel means less dilution. TIG welding stainless steel to mild steel gives close control of dilution. Type 309 suits service below about 800 degrees F, and nickel-based fillers take over at higher temperatures. Strip any zinc coating first, since molten zinc penetrates stainless grain boundaries and causes cracking.

How to weld stainless steel pipe

Stainless steel pipe welding starts with a bevel and land set by the wall thickness, an inside purge verified before the arc starts, and a TIG root, followed by TIG, stick or MIG fill passes under a qualified procedure. AWS D10.4 gives recommended practice for austenitic piping, with a typical 37-1/2 degree bevel and a land of about 1/16 in. Welded stainless pipe and seamless pipe of the same grade sit in the same P-8 material grouping, so the welding procedure for stainless steel pipe stays the same for both within its qualified range. Welded stainless steel pipe fittings get the same fit-up check as pipe, because wall and ovality mismatch appears as a step at the root. See stainless steel piping for material selection and pipe fabrication for shop spools.

Stainless steel pipe TIG welding and the root pass

For TIG welding stainless steel pipe, root pass control comes from gap, land and gas. An open root relies on an even gap and steady filler; a consumable insert to AWS A5.30 gives a more repeatable bead where the specification allows it. Permanent backing rings are avoided in corrosive service, because they leave a crevice. TIG welding stainless pipe in a fixed position usually means a 6G welder test, and tight racks often come down to mirror work and torch angle.

Stainless steel pipe welding purging

In stainless steel pipe welding, purging is what protects the root, and back purging stainless steel keeps air off the inside of the joint until it cools. To set up the purge, plug or dam each side of the joint, tape the gap, feed argon low and vent high, and confirm oxygen with an analyzer before striking the arc. Keep the purge running through the root and hot pass, or until the root falls below about 250 degrees C.

MIG and stick on stainless pipe

Welding stainless steel pipe with MIG is mostly fill and cap work after a TIG root. Multiple MIG passes on pipe call for low CO2, because repeated reheating compounds carbon pickup. Welding stainless steel pipe with stick favors lime-coated -15 electrodes in all positions, with slag removed carefully between passes. A stainless steel pipe welding machine ranges from a constant-current inverter with upslope and downslope controls to orbital welding heads; see orbital versus manual welding for how that choice is made.

Stainless steel tubing welding, thin sheet and exhaust

Stainless steel tubing welding is usually done by TIG at low current with an inside purge, often with no filler on thin wall, and square, burr-free ends decide whether the joint fuses evenly. Stainless tube welding for process lines also means matching wall from tube to tube. Welding sanitary stainless raises the acceptance standard to the inside surface; sanitary welding covers those criteria, and what orbital welding is explains the automated method used on most of those joints. TIG welding stainless steel tubing by hand remains normal at tie-ins where a weld head will not fit.

Learning how to weld thin stainless steel is mostly learning to remove heat. Use a clamped backing bar or nickel-plated copper chill, a tight gap, just enough current to fuse, and short skip sequences. Welding stainless steel sheet in long seams depends on fixturing, because a free edge buckles. Stainless exhaust welding on generator and engine systems follows the same rules: thin wall, back purge or a flux-backing product where gas cannot reach, and filler matched to the tube. To weld stainless steel exhaust that is 409, use ER409 or a 309-type filler for a dissimilar joint.

Stainless steel tank welding

Stainless steel tank welding joins shell courses, heads and nozzles with low-distortion joint designs and a planned weld sequence, because long seams in thin plate move easily. Limit weld metal volume: on thick plate a U groove takes less metal than a V, and welding from both sides with a double-U or double-V balances the shrinkage. Submerged arc suits long flat seams on heavy shells, with multiple passes to bring its 40 to 60 percent single-pass dilution down. Welded stainless steel tanks in corrosive service get full-penetration seams and cleaning before the first fill. Pressure-retaining work moves to pressure vessel fabrication, and repairs on a used tank start with industrial tank cleaning.

How to spot weld stainless steel

Resistance spot welding joins stainless sheet by passing current through clamped electrodes, and the higher electrical resistivity of stainless lets a nugget form at lower current than carbon steel of the same gauge. To spot weld stainless steel well, keep the sheets clean, use dressed electrodes, and set a short weld time counted in cycles to limit heat in the sensitizing range. Qualify the schedule on coupons with peel or tensile tests, because published values vary with sheet thickness and machine.

Sugaring and heat tint on stainless welds

Sugaring on stainless steel is the grey, crusted oxide that forms on the back of a stainless weld when air reaches the hot root, and heat tint is the thinner colored oxide beside a weld, and both lower corrosion resistance. Published testing found that heat tint dropped the critical pitting temperature of a type 316 weld from 60 to 40 degrees C in a dilute chloride solution. A sugared root is normally cut out and rewelded in process service. Lighter tint can be cleaned; see heat tint removal for methods and color limits, and weld passivation for the treatment that follows.

How to control distortion and heat input on stainless

Distortion on austenitic stainless is controlled by depositing less metal, at lower heat, in a planned order, because the alloy expands about 50 percent more than carbon steel and holds its heat close to the joint. Tack welding stainless steel without a fixture calls for tacks every couple of inches, and light peening of each tack relieves its shrinkage. Fixtures should be rigid, with chill bars beside the weld and backing bars under it. Rapid cooling helps austenitic grades, so a chill also limits carbide precipitation. Copper chills must be nickel plated, since melted copper can penetrate stainless grain boundaries and crack them.

Skip welding and back-step sequences spread the heat on light gauge, and excess reinforcement adds shrinkage without useful strength.

Stainless steel welding tips

Stainless steel welding tips that hold across all three processes are to use dedicated tools, keep the arc short, run stringer beads and fill every crater, because most failures start with contamination or excess heat. These apply on every job:

• Tips for TIG welding stainless steel: sharpen the tungsten on a dedicated wheel, keep the filler end inside the gas, and taper down at the end of the bead.
• For MIG: push the gun, avoid long weaves, raise inductance if the bead looks ropey, and hold the gun over the end of the weld for a half second to three seconds of post-flow.
• Exhaust the fume at the arc, since stainless fume carries hexavalent chromium.

Stainless steel weld defects and how to fix them

Stainless weld defects usually trace back to one of four causes: contamination, moisture, too much heat, or poor gas coverage.

How stainless welds are inspected

Stainless weld inspection starts with visual examination and moves to dye penetrant, radiography, ultrasonic testing, borescope or ferrite measurement as the code and service require. On process piping, ASME B31.3 requires random radiographic or ultrasonic examination of at least 5 percent of circumferential butt and miter groove welds in normal fluid service. Procedures and welders are qualified to ASME Section IX, structural stainless work to AWS D1.6, and hygienic tube to AWS D18.1. Ferrite readings come from a magnetic gauge calibrated to AWS A4.2. Austenitic grades are non-magnetic, so dye penetrant takes the place of magnetic particle testing.

Stainless steel welding services from Paul Industries

Paul Industries provides stainless steel welding services for plants in all 50 states, including stainless pipe, tube, spool, tank and vessel welding, with same-day emergency response. Purge verification, inspection, tint removal, passivation and weld records sit in one scope, and code work follows the procedure and welder qualification rules of the governing code. Paul designs, fabricates, supplies, installs, repairs and maintains the systems around the weld too, from turnkey process systems to shutdown and turnaround work and emergency repairs. For hygienic lines, see sanitary welding. Request a quote with your grade, wall, joint count and governing code.

Standards referenced: ASME B31.3 · ASME BPVC Section IX · AWS D1.6 · AWS D10.4 · AWS D18.1 · AWS A4.2 · AWS A5.4 · AWS A5.9 · AWS A5.22 · AWS A5.30 · ASTM A380 · ASTM A967 · OSHA 29 CFR 1910.1026

Frequently asked questions

Can a MIG welder weld stainless steel?

A standard MIG welder handles stainless once it has stainless wire, a low-CO2 gas, and a dedicated liner and drive rolls. Short-circuit work on thin sheet also benefits from inductance control, and many shops use pulsed machines for out-of-position welds.

How to weld stainless with MIG on a machine set up for mild steel?

Swap the wire to ER308LSi or the matching grade, change the gas from 75/25 to tri-mix or 98/2, fit a clean liner and rolls, and reduce wire feed to the lower melt-off current.

Can you stick weld stainless steel?

Stick welding works well on stainless, from thin sheet of about 0.05 in up to several inches, and it is a practical choice for field repairs and outdoor work where wind would strip shielding gas. E308L-16 and E316L-16 cover much plant work, with lime-coated electrodes preferred for all-position pipe.

Which electrodes run on AC, and can you arc weld stainless steel that way?

Titania and silica-titania electrodes run on AC as well as DC, with the AC current range about 10 percent higher. DC gives a better result and remains the first choice whenever the machine offers it, and lime-coated -15 electrodes run only on DC.

What polarity for TIG welding stainless steel, AC or DC?

Direct current, electrode negative, sometimes called straight polarity, is the standard setup because it puts most of the heat into the work and gives a deep, narrow bead. AC is reserved for special cases such as aluminum-bearing precipitation-hardening grades, where its cleaning action helps.

What tungsten for TIG welding stainless steel?

For TIG welding stainless steel, tungsten choice comes down to thoriated, ceriated or lanthanated electrodes, all preferred over pure tungsten because they give a more stable arc and carry more current. Diameter is sized to current, as the settings table shows.

Can you weld stainless steel with 75/25 gas?

75/25 belongs with flux-cored stainless wires classified -4, where the slag protects the deposit from carbon. On solid MIG wire, its 25 percent CO2 far exceeds the usual limit of about 5 percent, so carbon pickup and chromium loss lower corrosion resistance.

How to weld stainless steel without gas?

Stick electrodes and self-shielded -3 flux-cored wires both weld stainless with no external gas, because the coating or core produces its own shield. Gasless processes still leave an unprotected root on open joints, so a process line carrying product or treated water needs a purged TIG root first.

Can you weld stainless steel with mild steel wire?

An arc will run, but the result is a carbon steel weld diluted with chromium and nickel, which rusts in service and can harden and crack. A 7018 stick rod behaves the same way. Use either only on a joint with no corrosion or strength duty; everything else takes a 308, 316 or 309 type filler.

What TIG welding stainless steel filler rod goes on 304?

ER308L suits 304L and dual-certified 304/304L, and ER308 suits standard 304 where low carbon is unnecessary. Rod diameter follows thickness, and the higher-silicon ER308LSi rod wets out more easily.

Is 308 filler acceptable, or can I weld stainless steel to mild steel only with 309?

Type 309 is the right choice, because 308 lacks the alloy margin for dilution from both base metals and the mixed deposit can form brittle martensite. A 309 deposit stays crack resistant at normal dilution, and a filler of that type is widely available in stick, wire and rod form.

What rod to weld stainless to mild steel?

E309L-16 is the usual stick electrode, and ER309L is the TIG rod. Both carry about 24 percent chromium and 12 to 13 percent nickel, enough to tolerate carbon steel dilution. Choose nickel-based filler when the joint will run hot, above about 800 degrees F, or cycle thermally.

What stops cracking when stainless steel is welded to carbon steel?

Bevel for low dilution, keep heat input low, and use a 309-type filler, buttering the carbon steel face first on thick or restrained joints. Remove all paint, scale and zinc beforehand, and coat the finished carbon steel side, because it remains the corrosion-prone half of the joint.

Can you weld mild steel to stainless steel with TIG?

TIG is a good match for this joint at thin to moderate wall, because it gives close control of dilution. Use ER309L rod, keep heat low to limit melted carbon steel, and purge the back when the stainless face will see a corrosive fluid.

Can you weld stainless steel to galvanized steel?

The joint can be made once all zinc is removed from the weld area. Grinding alone can leave zinc particles behind, so acid stripping and thorough rinsing are recommended, followed by 309-type filler as on any stainless to carbon steel joint.

Can stainless steel be welded to aluminum?

Stainless and aluminum join reliably through a bimetallic transition insert, with each end welded to its matching metal, because direct fusion forms brittle intermetallic phases. Weld the aluminum side first, so that its larger mass acts as a heat sink when the steel side is welded.

What gas for TIG welding stainless steel gives the cleanest bead?

Pure argon covers almost all manual work, on the torch and as backing gas. Bead color depends more on heat input, gas coverage and post-flow than on the gas blend, so a dull or grey bead usually points to technique or a leak.

Which type of stainless steel is the most weldable?

Austenitic grades such as 304L and 316L are generally regarded as the readily weldable family, since they do not harden and need no preheat or post-weld heat treatment. Low-carbon ferritic grades on thin sections also weld well, while high-carbon martensitic and free-machining grades are the difficult ones.

Is welding stainless steel toxic?

Stainless fume contains hexavalent chromium, which OSHA regulates under 29 CFR 1910.1026 with an exposure limit of 5 micrograms per cubic meter as an 8-hour average and an action level of 2.5. High exposure can cause lung cancer and damage the respiratory tract, eyes and skin, so stainless welding needs local exhaust, exposure assessment and respirators where controls fall short.

How does oxy acetylene welding stainless steel compare with TIG?

Oxy acetylene welding stainless steel needs a strictly neutral flame, because an acetylene-rich flame adds carbon and an oxygen-rich flame oxidizes the pool. TIG supplies an inert shield and a more concentrated heat source, so procedures for corrosion-resistant plant service are written around TIG and the other arc processes.

Welding stainless steel vs carbon steel: what changes on the job?

Current drops, because stainless holds heat near the joint, and preheat disappears on austenitic grades. Tools become dedicated, gas selection tightens, the back of the joint needs shielding, and post-weld cleaning restores the passive surface. Fit-up tolerances also get tighter because the material moves more.

How much does it cost to weld stainless steel?

Cost is set by weld count and joint complexity more than by footage, along with alloy and wall thickness, filler and argon use, purge setup time, access, inspection level, and passivation and paperwork. Field welds in a running plant cost more per joint than shop spools, so sending Paul Industries a joint count and code lets the price reflect the actual scope.

Related: Sanitary Welding · Orbital Welding Services for Sanitary Pipe · What Is Orbital Welding? · Orbital Welding vs. Manual TIG Welding: Which for Sanitary Piping? · Heat Tint Removal on Stainless Steel: Color Chart and Methods · Stainless Steel Piping · Request a quote