ASME IX - Contact Tube to Work Distance

[beh188]

Does the variable "contact tube to work distance" apply to GTAW welding, or is this only applicable to GMAW or other processes?

Is there a place on a GTAW WPS that you specify the distance of the tungsten tip to the work surface?

 

[stanweld]

Does not apply to GTAW.

 

[WeldAppEng]

Stanweld..that actually surprises me that there is not. Wont the same principals apply with a GTAW torch as with stick and mig.?? pull back and amps drop off - volts go up. That has to have some effect although I can see that because it is a process where the arc itself is not part of the deposit process. Wire is fed independantly either manually or through a separate wire (hot/cold) feeder and not connected per se to the Tig torch.

Where as in GMAW/SMAW there is. Ok answered my own query.!

cheers,

 

[weldgooch]

With GTAW, Arc Voltage is directly related to the arc gap. Neither are Essential Variables, but Voltage is related to Heat Input which is a "Supplementary Essential Variable". That means that it only becomes an essential variable when other sections of code specify notch-toughness tests.

Simplified. Arc Gap in GTAW is not required to be controlled by ASME Section IX.

It is good practice to include the arc gap as a reference variable on the WPS in a supplementary notes section, particularly with Automated or Semi-automatic welding. For manual welding, it all comes down to the skill of the operator.

 

[stanweld]

Please note that by definition of contact tube, the GTAW process does not have a contact tube. The contact tube distance affects preheating of the wire electrode amongst other effects.

 

[Mr168]

Just to stir the pot a bit...

Definition of contact tube per ASME IX:

contact tube: a device which transfers current to a continuous
electrode.


One can argue that since the collet body meets this definition in transferring current to the tungsten, that it would indeed be considered a "contact tube."


QW-256 disagrees however, and is quite clear in that regard. And, since the filler wire isn't considered the electrode, it can't even apply to a hot-wire GTAW setup.