Gas Metal Arc Welding

[iskandar13]

I am making a steam header(12mm thick 12BarG operating pressure) from rolled plates A516 gr.70 and plan to weld all the joints using GMAW process with CO2 shielding gas. Can anyone give input if there will/may be a problem on the welding when the header is put on service.

iskandar13

 

[subhas123]

GMAW is a well recogonised process, whichis being widely used in Pressure Vessel Industry. Refto ASME Sec VIII Div 1 UW for approve method of welding. GMAW is permitted. SEC IX gives the PQR and WPS requirements. SEC II c would provide you with required wire. ER70S2 /ER 70 S6 are generally used.

Use good Joint preparation and preheat to 70 C, Co2 purity (Lack of it)also can cause havok with radiography, be sure to use proper co2. You may also try Argon if the job is critical.

 

[stanweld]

Lack of fusion problems are foreseen if you use "short cicuiting transfer" mode. Spatter will pose a problem with globular transfer. Suggest 175 Amps at 23-24 Volts as a starting point for welding with 100% CO2.

 

[Koz]

iskandar13,
I'm with stanweld. I think the short circuiting transfer GMAW welding mode that you will get with 100% CO2 will give you big lack of fusion problems unless you are a really talented welder. And the globular transfer you get with the 23-24 volts will cause you so much spatter, you will go broke cleaning the job up. But if you have proven your procedure by mechanical testing per ASME, go for it! ASME restricts your thickness ranges for this process mode.

If you are wild for wire feed, use a "dual shield" type flux cored arc welding process. E71T1 will give you RT quality welds and is great for out of position work. I recommend Argon rich gas to reduce spatter and cleanup. And I assume you are back gouging your welds to get full penetration. Going cheap on the shielding gas is false economy.

You might want to run any long seams you have using GMAW in the spray mode. You'll need at least 80% Argon to kick the process into spray. The pipe saddles at the header can be run using GTAW more economically than GMAW if the diameters are 6-in or less. I have actually let the welders weld out 12-in diameter just to save on set-up costs. If these are open root, one sided welds, GTAW roots with FCAW fills are very effective. I stay away from GMAW short circuit on material thicker than 1/4". I may GMAW-SC to seal the root of the weld and fill with a higher deposition open arc process.

I hope this adds to your information.
Koz