What does TIG post-flow do?

TIG post-flow keeps shielding gas flowing after the arc stops so the hot tungsten, weld crater, and filler end can cool without oxygen contamination.

How do I know if TIG post-flow is too short?

Post-flow is too short if the tungsten turns black, blue, gray, or crusty after the weld, or if arc restarts become rough because the tungsten oxidized during cooling.

What is a good TIG post-flow starting point?

A common starting point is about 1 second of post-flow per 10 amps of welding current, then adjust based on tungsten color, torch heat, cup size, material, and gas coverage.

What are the signs of poor TIG shielding gas coverage?

Common signs include porosity, black soot, gray weld color, dirty tungsten, rough arc starts, sugaring on stainless, and rapid tungsten discoloration after arc stop.

Can too much argon cause TIG problems?

Yes. Excessive flow can create turbulence and pull air into the shielding envelope, causing oxidation, porosity, or dirty tungsten.

Why does my TIG tungsten turn black?

A black tungsten usually means the hot tungsten was exposed to air because of low flow, a gas leak, damaged cup or gas lens, poor torch angle, drafts, or too little post-flow.

Tag: argon flow

TIG Post-Flow Setting Troubleshooting: Black Tungsten, Porosity, Gas Waste, and Torch Cooling

TIG post-flow is the shielding gas that keeps flowing after the arc stops. If it is too short, the hot tungsten and cooling weld crater are exposed to air, causing black, blue, gray, or crusty tungsten, rough restarts, porosity, and contaminated weld starts. If post-flow is too long, weld quality may be fine, but argon usage goes up fast during tack welding or short beads.

Start by watching the tungsten after arc stop. If the tungsten is still glowing when argon shuts off, increase post-flow. If the tungsten stays clean but gas keeps flowing long after the torch cools, reduce post-flow in small steps. Do not fix black tungsten by only increasing flow rate; a cracked cup, leaking back cap O-ring, clogged gas lens, or loose torch fitting can still expose the electrode to oxygen.

Common Symptoms

Symptom	Likely Post-Flow Issue	First Check
Tungsten turns black after weld	Post-flow too short or gas leak	Increase post-flow and inspect gas path
Tungsten turns blue or gray	Hot tungsten exposed during cooling	Watch whether gas stops before glow is gone
Rough arc restart	Oxidized tungsten from previous stop	Regrind tungsten and extend post-flow
Porosity at crater or restart	Weld pool loses shielding while cooling	Hold torch over crater during post-flow
Argon bottle empties quickly	Post-flow too long for short welds	Reduce time gradually after tungsten stays clean

What Post-Flow Does

Post-flow protects three hot areas after the arc shuts off: the tungsten, the weld crater, and the end of the filler rod if it remains inside the gas envelope. Tungsten can oxidize after the bead looks finished because the electrode remains hot longer than many operators expect. The goal is enough shielding to let the tungsten cool without discoloration, not maximum gas flow for every weld.

Starting Point for Post-Flow

A common field rule is about 1 second of post-flow per 10 amps of welding current. Some Miller GTAW guidance also lists 10–15 seconds as a corrective range when inadequate post-flow is causing tungsten or arc problems. Use those as starting points, then tune by tungsten color, material, torch heat, tungsten size, and weld length.

Welding Current	Common Starting Range	What To Watch
50 amps	5 seconds	Tungsten should not color after gas stops
80 amps	8 seconds	Good range for many light TIG jobs
120 amps	12 seconds	Check torch heat and tungsten color
150 amps	15 seconds	Often needs longer protection on hot torch setups
200 amps	20 seconds	Verify torch rating and cooling; gas use increases quickly

Inspection Steps

Confirm the gas. Most TIG work uses 100% argon. Do not use MIG gas with CO2 or oxygen for TIG.
Watch tungsten color. Black, gray, blue, or crusted tungsten after arc stop points to oxygen exposure, contamination, or too little post-flow.
Hold the torch still. Keep the cup over the crater until post-flow ends. Moving away early defeats the setting.
Check flow at the cup. A regulator reading does not prove gas is reaching the tungsten.
Inspect the cup. Replace cracked, chipped, loose, or overheated cups.
Inspect the gas lens or collet body. Blocked screens or damaged gas passages can cause poor coverage even with long post-flow.
Check the back cap O-ring. A damaged O-ring can pull air into the torch and oxidize tungsten.
Check hoses and fittings. Use approved leak-check methods and repair leaks before welding.
Adjust gradually. Add or subtract a few seconds at a time, then retest on clean material.

Post-Flow Too Short vs Too Long

Condition	Result	Corrective Action
Too short	Black tungsten, rough restarts, crater oxidation	Increase time and hold torch over weld
Too long	High argon consumption with no quality gain	Reduce time after tungsten remains clean
Correct time but black tungsten	Leak, cracked cup, bad O-ring, dirty gas lens	Inspect torch and gas path
Correct time but porosity	Draft, contamination, wrong cup, no purge	Check shielding coverage and base-metal prep

Field Fix vs Proper Fix

Problem	Field Fix	Proper Fix
Tungsten blackens after stop	Add post-flow time	Set time by amps and repair leaks or worn torch parts
Gas wastes during tacks	Lower post-flow slightly	Use a repeatable tack schedule that still protects tungsten
Crater porosity	Hold torch over crater longer	Correct post-flow, torch angle, cup size, and cleanliness
Blue tungsten on aluminum	Add post-flow	Check AC heat, torch cooling, gas lens, and cup size
Soot remains after increasing post-flow	Clean cup and tungsten	Fix gas coverage, contaminated material, or wrong gas

Common Wrong-Part Mistakes

Replacing tungsten repeatedly while ignoring a leaking back cap O-ring.
Using a cracked cup and trying to compensate with longer post-flow.
Installing gas lens parts that do not match the torch series or cup setup.
Using a collet that does not match tungsten diameter, causing poor alignment and overheating.
Turning gas flow too high and creating turbulence instead of fixing post-flow time.

Compatibility Notes

Post-flow is a machine setting, but the correct result depends on torch family, cup size, gas lens or standard collet body, tungsten diameter, amperage, material, and torch cooling. Consumables for WP-9/20-style torches and WP-17/18/26-style torches are not automatically interchangeable. Verify torch series and tungsten diameter before replacing cups, collets, gas lenses, or back caps.

Related Failure Paths

Black tungsten from oxygen exposure after arc stop.
Rough arc starts from oxidized tungsten.
TIG porosity at crater or restart.
Sooty TIG welds caused by poor gas coverage.
Cracked cups or clogged gas lenses mistaken for bad post-flow.
High argon use from excessive post-flow during tack welding.

Safety Notes

Let tungsten, cups, and torch parts cool before handling.
Secure argon cylinders upright and protect regulators from impact.
Argon can displace oxygen in confined areas; use ventilation and confined-space controls where required.
Use eye protection when grinding tungsten.
Do not weld through suspected gas leaks or damaged hoses.

Sources Checked

Weld Support Parts TIG tungsten discoloration support page.
Weld Support Parts TIG porosity and soot troubleshooting pages.
Weld Support Parts TIG cup size and gas lens support page.
CK Worldwide TIG troubleshooting and gas shielding guidance.
Miller GTAW troubleshooting guidance.

May 18, 2026

TIG Shielding Gas Coverage Troubleshooting: Porosity, Soot, Tungsten Color, and Cup Setup

Poor TIG shielding gas coverage shows up as porosity, gray or black weld color, dirty tungsten, unstable arc starts, sugaring on stainless, and oxidation around the bead. The most common causes are low argon flow, excessive flow creating turbulence, torch angle pulling air into the puddle, drafts, a cracked cup, damaged gas lens, loose torch parts, gas leaks, or not enough post-flow after the weld.

Start with the gas path before changing amperage. Confirm 100% argon for most TIG work, verify flow at the torch, remove drafts, inspect the cup and gas lens, shorten tungsten stickout, and hold a tighter torch angle. If tungsten stays bright and the weld color improves after these checks, the problem was coverage—not the machine.

Related TIG support checks include TIG porosity troubleshooting, sooty TIG weld gas coverage fixes, and TIG cup size selection.

Common Symptoms

Symptom	Likely Coverage Cause	First Check
Pinholes or porosity	Air entering weld zone or contaminated gas path	Verify argon flow at torch and check leaks
Black soot on weld	Weak shielding, torch angle, dirty lens, draft	Inspect cup/lens and block air movement
Tungsten turns blue, black, or crusty	Hot tungsten exposed after arc stops	Increase post-flow and check torch angle
Stainless weld turns dark gray	Insufficient argon envelope or no back purge	Check cup size, gas lens, and backside shielding
Arc wanders or starts rough	Contaminated tungsten or loose collet parts	Regrind tungsten and inspect collet/collet body

What Shielding Gas Coverage Does

TIG shielding gas protects the tungsten, arc column, molten weld pool, and hot cooling metal from oxygen and nitrogen. When coverage breaks down, the puddle oxidizes before it solidifies. On stainless and titanium, poor shielding can damage corrosion resistance and weld quality. On carbon steel and aluminum, it can leave porosity, soot, rough starts, and contaminated tungsten.

Inspection Steps

Confirm the gas. Most TIG welding uses 100% argon. Unknown mixed gas is a common mistake when switching between MIG and TIG.
Verify flow at the torch. Do not rely only on the regulator. A kinked hose, loose fitting, blocked torch, or bad connector can reduce actual flow.
Start in the normal TIG range. Many shop setups start around 15–20 CFH. Larger cups, aluminum, or longer stickout may need more, but excessive flow can pull air into the shield.
Block drafts. Fans, open doors, outdoor work, and fume extraction too close to the arc can strip argon away.
Inspect the cup. Replace chipped, cracked, contaminated, or oversized/undersized cups that do not match the joint.
Inspect the gas lens or collet body. Look for plugged screens, cracks, discoloration, or damaged threads.
Check tungsten stickout. Too much stickout without a gas lens exposes the tungsten and puddle to air.
Correct torch angle. Keep the torch close to vertical. A steep push angle can pull air into the argon stream.
Check post-flow. Argon must continue long enough to protect the hot tungsten and weld crater after the arc stops.

Visual Wear Indicators

Cup: cracks, chips, metal dust, black deposits, or heat damage.
Gas lens: clogged screen, discoloration, blocked mesh, or loose fit.
Collet: poor tungsten grip, split end damage, wrong tungsten size.
Back cap O-ring: cracked, missing, flattened, or leaking.
Gas hose: cracked rubber, loose clamps, leaking fittings, or kinks.
Tungsten: blue/black color, crusted tip, split point, or contamination balling.

Test Procedures

Flow-at-cup test: Listen and feel for steady argon flow at the cup before welding. If the flow is weak, uneven, or silent, inspect the hose, torch connection, solenoid, regulator, and torch front end.

Draft test: Run a short bead with all fans and doors controlled. If the weld brightens and porosity drops, gas coverage was being stripped away.

Post-flow test: Watch the tungsten after arc stop. If it colors immediately, increase post-flow or find a gas leak. Tungsten should remain shielded while it cools.