TIG is an arc welding method using inert gas Ar as protection medium. Argon gas spray out from the nozzle, forming inert gas protection layer, isolating the air invasion, so as to protect the arc & molten pool.

The advantage of TIG includes: good protection performance, high welding quality, no welding splash, beautiful welding seam, small welding deformation,able to realize single side welding and double side shaping,  able to ensure root pass penetration, suitable for kinds of welding position, able to weld all kinds of metal & alloy, stable welding arc, open arc welding, no welding slag, easy to realize automation. 

Therefore, it is widely used in lots of industries. Nevetheless, TIG welding is weak on anti-wind capability, sensitive to the rust, water, grease. It has strictly requirement of the gas purity, beveling edge clearance, welding parameters and so on. Due of above feature, gas pore is a usual welding defect in TIG welding.  Based on actual production experience, we herein analyse the reason & propose some method with attention matters.

TIG welding gas pore active factor analyze

1. Impurity argon gas.
By carbon steel welding, Ar purity no less than 99.7%. By Al welding, purity no less than 99.9%. By Ti or Ti alloy, purity should no less than 99.99%.

Method to measure Ar gas purity:
(1). Welding without wire filling on clean milled metal plate or pipe. Multi re-melting on the weld bead. If gas pore appeared, the argon gas is impurity.  

(2). Tiny spark around the arc, the gas is impurity.

(3). Sometimes when the purity approaching the required purity, it could not be detected by above methods. But by weld the job with clearance, there would be intermittent gas pore at root of the weld seam. By cosmetic welding, there would be gas pore at surface of the welding seam, or an oxide coating at surface of the welding seam.  

(4). Spot welding on Ni plate.  The weld spot appear silver white color, mirror surface, the purity is no problem.

2. Ar gas flow rate
Small flow rate decrease the anti wind capability. Big flow rate would thin the laminar sublayer when through nozzle. Gas flow would be disordered after spray out, and easy to involve air, worse the protection of molten pool. Therefore, the gas flow rate should be fit for welding condition to have stable gas flow.  

3. Air hose leakage
Air hose or air hose coupling leakage would make the flow rate small, air sucking into the air hose, worse the protection performance.

4. Wind
Wind would make the Ar protection layer forming eddy flow, worse the gas protection. So when wind speed >2m/s, there should be measure for wind proof. By welding pipes, pipe ends should be blocked, avoid draught through the pipe.

5. Weld Nozzle
If the nozzle diameter too small, the effective protection range of Ar around the arc could not cover the whole molten pool surface. There would be air pore due to the worse protection. Especially for field working / big pipe welding, bigger diameter nozzle is good, to effectively protect the arc & molten pool.  

6. distance between nozzle & job.
Small distance smaller the sensitive to side wind. Big distance would decrease the ability of anti wind interference.

7.small gas cylinder pressure
It should be changed when gas cylinder pressure small than 1Mpa.

8.weld torch angle too big
If the weld torch angle too big, on one hand, it would bring the air into molten pool, on the other hand, it would worse the Ar flow protection of arc & molten pool by the longer arc side.

9.flow meter influence
Unstable gas spray of flow meter would influence the protection.

10. Operation
Using TIG weld torch with control button, it should be deflating before weld to avoid high pressure in the air hose, which would produce momentary big air flow when arc starting & produce air pore.

11. improper welding torch accessories
Improper collet would block the gas path. Gas is flowing from one side of the nozzle, could not forming integrated protection circle.

Welding material influence

1.welding wire
SAW wire could not be used for TIG welding. Or else, there would be imtermittent or uninterrupted air pore.

2.impure weld wire
Rust,oil grease,water at surface of the wire would directly lead to air pore producing inside the weld seam.

Base metal material

1. Plate or pipe material
Impurity in the interlayer of base material would lead to air pore defect.

2.Steel grade
Effervescing steel (big oxygen content, lot impurity) could not use TIG welding method.

Electrode

1. Electrode tip
Unpointed electrode tip would make the arc drift, broke the protection zone, make the molten pool oxidize with air pore.

2. worse protection due to arc run-up when arc starting
By high frequency art start equipment, Tungsten electrode tip temperature is low when arc starting, lack of sufficient thermal electron. The electron is easy emission from place with oxide skin, running up along the electrode to the place with oxide skin,  the arc is prolonged. Ar flow protection to the molten pool is worse. When Tungsten electrode temperature rising up, electron is emitting from the top, arc length would shorten. It could be solved by remove the oxide skin at surface of the Tungsten electrode.  

Welding procedure

1.Beveling edge clearance
Beveling edge & range within 10mm at both side of the edge should grind clearly, avoid the nearby rust sucked into molten pool by the magnetism of arc during welding.

2.Welding speed
Under quick welding speed, the air resistance would curve the Ar gas flow, make it deviate from the electrode center & molten pool, worse the protection effect.

3.Arc extinguish method
Using weaken current / filling wire to take the arc to bevel edge side & low down arc to extinguish the arc, do not stop the arc suddenly, the high temperature molten pool out of protection of Ar gas flow, avoid arc pit appear air pore or shrinkage cavity.

4.Weld current
Small weld current, the arc is not stable, arc drift irregular at top of the electrode, destroy the protection zone. Big weld current, arc disturb the gas flow, worse the protection effect.

5.Tungsten electrode protend length
Too much protend length, Ar flow protection effect would be worse.

Though there are lots of factors producing the air pore during TIG welding, with knowing the feature of TIG welding, as per actual situation to investigate the influence factor, take care of all factors which may produce air pore, it could be solved & the welding quality could be guaranteed in the actual production.