Learning Center | Welding | Troubleshooting
A weld can look clean while it is being made and still reveal a serious problem once the slag is removed or the weld is inspected: small holes scattered across the surface, clusters of pinholes, or internal voids discovered during testing.
That defect is porosity.
Porosity occurs when gas becomes trapped in the weld metal as it solidifies. For an industrial welder, simply recognizing porosity isn’t enough. The real skill is determining where the gas came from and why it became trapped.
In refineries, pipelines, power plants, fabrication shops, and industrial construction, the cause can range from contaminated base metal to shielding-gas problems, moisture, wind, incorrect technique, or equipment issues.
1. What Is Weld Porosity?
During welding, a molten weld pool is created between the base material and filler metal. While that metal is liquid, gases may enter or form within the weld pool.
Normally, the welding process and proper technique allow the weld to solidify without unacceptable gas pockets.
When gas becomes trapped before it can escape, it can leave cavities in the solidified weld metal.
These cavities are called porosity.
Depending on the situation, porosity may appear as isolated pores, scattered pores, clusters, linear patterns, or internal discontinuities that cannot be seen from the surface.
2. What Does Porosity Look Like?
Surface porosity often looks like tiny round holes or pits in the weld.
Sometimes there may only be one visible pore. In other cases, an entire section of weld can resemble a sponge or contain groups of small pinholes.
The visible surface does not always tell the entire story.
Porosity can also exist below the weld surface and may be discovered through inspection methods specified for the work.
This is why weld acceptance should be based on the applicable welding code, project specification, welding procedure, and inspection requirements—not simply whether the weld “looks good.”
3. Contamination Is a Major Cause
One of the first things to investigate is contamination.
The weld area may contain oil, grease, moisture, paint, rust, scale, dirt, coatings, cutting residue, or other foreign material.
When these materials are exposed to welding temperatures, they can produce gases that enter the molten weld pool.
If those gases become trapped during solidification, porosity can result.
Proper material preparation is therefore part of welding—not something separate from welding.
A few extra minutes preparing the joint can prevent much more time spent removing and repairing defective weld metal.
4. Moisture Can Create Problems
Moisture deserves special attention.
Water may be present on the base material, consumables, welding equipment, or surrounding work area.
Certain welding consumables require controlled storage and handling specifically because moisture exposure can affect weld quality.
The requirements depend on the welding process, electrode or filler classification, applicable welding procedure, and project specifications.
A welder should never assume that a consumable is acceptable simply because the package looks normal.
Follow the required storage, conditioning, exposure, and handling procedures for the specific consumable being used.
5. Shielding Gas Problems
Processes such as GMAW, GTAW, and FCAW-G rely on shielding gas to protect the molten weld pool from the surrounding atmosphere.
If that protective gas coverage is disturbed, atmospheric gases can contaminate the weld pool.
Possible causes include incorrect gas flow, an empty or restricted gas supply, leaks, damaged hoses, loose connections, clogged components, excessive gun-to-work distance, contaminated nozzles, or problems with the gas-delivery system.
The correct shielding gas and flow requirements must come from the approved welding procedure and equipment requirements.
More gas is not automatically better.
Excessive flow can sometimes create turbulence and pull surrounding air into the shielding zone.
6. Wind Can Destroy Gas Coverage
This is especially important in outdoor industrial work.
A welder may have the machine correctly set, the correct gas, and clean material—and still develop porosity because air movement is blowing the shielding gas away from the weld pool.
Wind doesn’t have to feel extreme to interfere with a gas-shielded welding process.
Fans, ventilation systems, open structures, cooling equipment, and air movement through a plant can also affect shielding.
The solution isn’t automatically increasing gas flow.
The work may require properly designed wind protection or another control permitted by the welding procedure and site requirements.
7. Check the Welding Gun and Torch
When porosity suddenly appears during production, inspect the equipment.
For a gas-shielded process, look at the complete shielding-gas path.
That can include the cylinder or supply, regulator or flowmeter, hoses, fittings, connections, gun or torch, diffuser, nozzle, O-rings, and other components.
A small leak or restriction can produce an inconsistent shielding environment.
This is why experienced welders often troubleshoot the entire system rather than immediately changing machine settings.
8. Gun or Torch Position Matters
Shielding gas needs to cover the molten weld pool effectively.
Improper torch angle or excessive distance between the gas nozzle and workpiece can reduce that protection.
Technique can therefore contribute to porosity even when the equipment itself is functioning correctly.
The appropriate position depends on the welding process, joint configuration, position, consumable, procedure, and other variables.
The goal isn’t to memorize one universal angle.
The goal is to understand why shielding coverage matters.
9. Arc Length Can Matter
An excessively long arc can create problems in several welding processes.
Among other effects, it can reduce control of the molten weld pool and influence shielding effectiveness.
This is another reason welders should understand what the arc is doing instead of concentrating only on travel speed.
Arc length, travel speed, electrode manipulation, work angle, travel angle, voltage, amperage, wire-feed speed, and other variables work together.
Changing one variable can affect several others.
10. Don’t Forget the Filler Metal
Contamination doesn’t have to come from the base material.
Filler wire or electrodes can also become contaminated.
Dirty wire, damaged consumables, improper storage, oil, moisture, rust, or handling problems can introduce contaminants directly into the weld.
When troubleshooting porosity, ask:
Is the base metal clean?
Is the filler material in acceptable condition?
Is the shielding system functioning correctly?
Is the technique appropriate?
That simple sequence can narrow down the problem quickly.
11. Porosity Appearing Suddenly Is a Clue
Imagine a welder has completed several acceptable joints using the same procedure.
Suddenly, porosity begins appearing.
Instead of immediately changing voltage, amperage, or wire-feed speed, consider what changed.
Did the shielding-gas supply run low?
Did a hose become damaged?
Did wind increase?
Was the material contaminated?
Was a new spool of wire installed?
Did the nozzle become obstructed?
Did the work move into a different environment?
Good troubleshooting starts by identifying what changed immediately before the problem appeared.
12. Porosity in Different Welding Processes
The exact troubleshooting process depends on the welding method.
With GTAW, shielding-gas coverage, torch condition, tungsten condition, filler cleanliness, joint cleanliness, purge conditions where required, and technique can all matter.
With GMAW, shielding gas, wire condition, nozzle condition, gas delivery, gun position, material cleanliness, and welding parameters are among the factors to investigate.
With FCAW-G, shielding-gas issues can also contribute, while the flux system introduces additional process-specific considerations.
With SMAW, external shielding gas isn’t normally supplied from a cylinder, so troubleshooting focuses more heavily on electrode condition and handling, base-material preparation, arc technique, parameters, and other process variables.
The lesson is simple:
Don’t troubleshoot every welding process the same way.
13. Repairing Porosity
Finding porosity does not mean a welder should simply weld over it.
Repair requirements depend on the applicable code, project specification, approved welding procedure, inspection requirements, and authorization for the work.
Where repair is permitted, defective material generally must be addressed using the approved repair process before the weld is restored and reinspected as required.
On code work, the welder does not personally redefine what is acceptable.
The governing requirements do.
Common Mistakes
One of the biggest mistakes is responding to porosity by immediately turning knobs on the welding machine. Parameters may be involved, but changing settings randomly can hide the actual cause rather than correct it.
Other mistakes include welding over contaminated material, ignoring wind, assuming shielding gas is flowing simply because the valve is open, using questionable consumables, allowing the nozzle to become heavily contaminated, and welding over visible defects without following the approved repair procedure.
Good welders don’t just know how to deposit metal.
They know how to diagnose the process.
Field Rule
When a weld suddenly changes, find out what else changed.
Material.
Consumables.
Gas.
Environment.
Equipment.
Technique.
Parameters.
Work through those variables systematically rather than randomly adjusting the machine.
That troubleshooting habit becomes increasingly valuable as a welder progresses from apprentice to journeyman.
Knowledge Check
1. What is weld porosity?
Gas pockets trapped in weld metal during solidification.
2. Can porosity exist without being visible on the weld surface?
Yes. Porosity can occur internally.
3. Why can wind cause porosity during gas-shielded welding?
It can disturb or remove the shielding-gas coverage protecting the molten weld pool.
4. Does increasing shielding-gas flow always solve the problem?
No. Excessive flow can create turbulence and may worsen shielding conditions.
5. What should you investigate when porosity suddenly appears after several acceptable welds?
Determine what changed in the material, consumables, shielding gas, environment, equipment, technique, or welding parameters.
Practical Exercise
You’re welding outdoors using a gas-shielded process. Your first several welds are acceptable.
Later in the afternoon, small pores begin appearing across the weld surface.
The machine settings haven’t changed.
Before touching the controls, identify what else may have changed.
A strong troubleshooting sequence would examine wind and air movement, shielding-gas flow and supply, hoses and connections, nozzle condition, material cleanliness, filler condition, and welding technique.
The objective isn’t to guess.
It’s to eliminate possible causes systematically until the source of the problem is identified.
Continue Learning
Porosity is only one weld discontinuity an industrial welder needs to understand. Future Næxon Learning Center lessons can break down undercut, lack of fusion, incomplete penetration, slag inclusions, cracks, overlap, burn-through, tungsten inclusions, arc strikes, weld profiles, and visual weld inspection.
Continue through the Næxon Learning Center for practical multi-craft training covering welding, millwright work, electrical, instrumentation, rigging, ironwork, scaffolding, operations, maintenance, and the other crafts that keep industrial facilities running.
