Næxon Learning Center | Welding Fundamentals
Porosity is one of the most recognizable welding defects. Those small holes or cavities in a weld are evidence that gas became trapped in the molten weld metal before it could escape.
Finding porosity is easy. Finding why it happened is where a welder’s troubleshooting skills matter.
Instead of immediately changing amperage, wire speed, or technique, experienced welders look at the pattern of the porosity and work backward through the possible causes: contamination, moisture, shielding gas problems, wind, electrode condition, joint preparation, and welding technique.
What Is Weld Porosity?
During welding, the weld puddle is molten metal. If gas enters or forms inside that puddle and doesn’t escape before the metal solidifies, it can leave cavities behind.
Some porosity appears directly on the surface. Other porosity can be trapped beneath the surface and may only be discovered through inspection or testing.
The important lesson is:
Porosity is the symptom. Your job is to find the source.
1. Start With Contamination
Before changing machine settings, inspect the material.
Oil, grease, paint, rust, mill scale, cutting fluids, dirt, coatings, and other contaminants can introduce gases into the weld puddle.
Pay particular attention to the joint itself.
A pipe may look clean from the outside while contamination remains around the bevel, root face, or inside diameter.
If porosity suddenly appears after several good welds, ask what changed.
Did you move to another piece of material?
Was the joint handled with oily gloves?
Was something recently ground, cut, painted, cleaned, or exposed to process contamination?
Sometimes the problem isn’t the welding machine at all.
2. Check for Moisture
Water and welding don’t mix well.
Material stored outdoors can collect rain, condensation, frost, or humidity. A pipe brought from a cold environment into a warmer area may develop condensation even though nobody actually got it wet.
Consumables can also be affected by moisture.
Certain electrodes require controlled storage and handling according to their classification, manufacturer requirements, WPS, and site procedures.
If moisture is suspected, don’t simply strike an arc and hope the heat burns everything away.
Correct the condition first.
3. Check Shielding Gas
For processes that depend on external shielding gas, gas coverage should be one of your first troubleshooting areas.
Check the complete shielding system rather than only looking at the flowmeter.
Depending on the setup, investigate the gas supply, regulator or flowmeter, hoses, fittings, gun, connections, diffuser, O-rings, and nozzle.
A system can show gas flow and still have poor shielding at the weld.
A damaged hose can create problems. A loose connection can create problems. A dirty or obstructed nozzle can disrupt coverage.
Don’t assume:
“The bottle isn’t empty, so the gas is fine.”
Verify the entire path.
4. Too Much Gas Can Also Cause Problems
When welders suspect inadequate shielding, the instinct can be to keep increasing gas flow.
More isn’t automatically better.
Excessive flow can create turbulence around the shielding envelope and may draw surrounding atmosphere into the protected area.
Use the gas type and flow requirements specified by the applicable procedure and equipment setup rather than treating the flow control like a volume knob.
5. Look for Wind and Air Movement
You can have perfectly functioning equipment and still lose shielding because the atmosphere around the weld is moving.
Outdoor wind is obvious.
Indoor airflow isn’t always.
Fans, ventilation equipment, open doors, compressed air, exhaust systems, and nearby operations can disturb shielding gas.
If porosity appears only when welding in a certain location, investigate the environment.
Ask:
What is moving the air around this weld?
Correct shielding measures must follow the welding procedure and site safety requirements. Never defeat required ventilation to protect shielding gas.
6. Inspect the Nozzle
For GMAW and FCAW processes using external shielding, inspect the nozzle and surrounding components.
Spatter buildup can interfere with shielding-gas distribution.
Clean the nozzle using the appropriate method and inspect the gas-diffusion components.
A welder who carefully cleans the joint but ignores a heavily obstructed nozzle may keep chasing the wrong problem.
7. Check Your Arc Length and Technique
Technique can contribute to porosity.
Excessive arc length may reduce effective shielding or expose the molten puddle to the atmosphere, depending on the process.
Incorrect gun or electrode positioning can also contribute to inconsistent protection.
Watch your puddle.
Maintain the appropriate arc length, work angle, travel angle, and travel speed for the procedure you’re using.
Don’t try to compensate for a mechanical gas problem with unusual welding technique.
Fix the actual problem.
8. Look at Where the Porosity Appears
The location and pattern of porosity can provide useful troubleshooting clues.
If porosity occurs throughout a weld, investigate conditions affecting the entire operation, such as contamination, consumables, shielding, or technique.
If it suddenly begins halfway through a weld, ask what changed at that moment.
Did the shielding become disturbed?
Did you cross a contaminated area?
Did your arc length change?
Did the nozzle become obstructed?
If the porosity repeatedly appears in one particular location on multiple attempts, investigate that location carefully.
The pattern doesn’t automatically prove the cause, but it gives you somewhere to start.
9. Don’t Just Grind the Hole
A visible pore can tempt someone to grind the surface until the hole disappears and immediately weld over it.
The problem is that the visible opening may not represent the full extent of the discontinuity.
Follow the applicable repair procedure and inspection requirements. Defective material may need to be removed to sound metal before repair.
More importantly, determine why the porosity occurred before rewelding.
Otherwise, you may simply put the same defect back into the joint.
A Practical Troubleshooting Sequence
When porosity appears, avoid randomly changing five things at once.
Start with the obvious conditions.
Material → Moisture → Consumables → Shielding Gas → Air Movement → Equipment → Technique → Parameters
Check the joint for contamination. Check whether the material or consumables were exposed to moisture. Verify shielding-gas supply and delivery where applicable. Look for wind or ventilation effects. Inspect the gun, nozzle, hoses, connections, and related equipment. Then evaluate arc length, angles, travel speed, and welding parameters against the WPS.
Changing one variable at a time makes it much easier to identify the actual cause.
Example: Porosity Appears Suddenly
Imagine you’re making a series of welds.
The first five are clean.
The sixth suddenly develops porosity.
Before changing your machine settings, think about what that tells you.
If the same machine, settings, welder, and process produced five acceptable welds immediately beforehand, something may have changed.
Inspect the sixth joint.
Check contamination.
Check the shielding system.
Check the nozzle.
Check the environment.
Check whether airflow changed.
Troubleshooting starts by asking:
What changed between the good weld and the bad weld?
That question can save a lot of wasted time.
Common Mistakes
One of the biggest mistakes is immediately blaming the welding machine. Another is automatically increasing shielding-gas flow.
Welders can also overlook contaminated base material, moisture, damaged gas hoses, loose fittings, obstructed nozzles, excessive arc length, environmental airflow, or improperly handled consumables.
And one of the worst habits is repairing porosity without investigating what caused it.
The defect may disappear temporarily.
The cause hasn’t.
Field Rule
DON’T CHASE THE HOLE. CHASE WHAT CREATED IT.
Porosity troubleshooting becomes much easier when you stop treating every pore as an isolated defect and start looking at the complete welding environment.
Knowledge Check
1. What creates porosity?
Gas becomes trapped in the weld metal as it solidifies.
2. Can excessive shielding-gas flow contribute to problems?
Yes. Excessive flow can create turbulence and disturb effective shielding.
3. Why can welding outdoors cause porosity?
Wind can disrupt shielding gas and expose the molten weld pool to the atmosphere.
4. If five welds are good and the sixth suddenly develops porosity, what should you ask first?
What changed?
5. Should you simply grind away a visible pore and weld over it?
No. Follow the applicable repair requirements, remove defective material as required, and identify the cause before rewelding.
Practical Exercise
Imagine you’re welding carbon steel with a gas-shielded process and suddenly discover porosity.
Before touching the machine settings, identify at least five things you would inspect.
Start with:
Joint cleanliness.
Moisture.
Shielding-gas supply and delivery.
Nozzle condition.
Air movement around the weld.
Then inspect your welding technique and compare the operating parameters with the approved WPS.
The goal isn’t simply to make the next weld look better.
The goal is to understand why the first weld developed porosity so you don’t create the same defect again.
