GMAW in Nuclear Applications

By Stephan (***)

Date 05-31-2008 18:37 Edited 05-31-2008 18:42

Friends,

I'm hoping to ignite a broad discussion about the topic mentioned above.

I have asked myself "Might Gas Shielded Metal Arc Welding (GMAW) ever be a competitive Joining Process vs Gas Shielded Tungsten Arc Welding (GTAW) as being used in the Nuclear Power Station erecting Industry?"

In particular I am considering tube welds carried out by using orbital welding equipment or being performed by manual GTA Welding.

You know, I am pursuing the history of the welding processes within this sector since many years with a great interest. And I hope you may agree with me when I say that GTAW was or is yet unbeatable as being the most reliable and stable welding process, followed by SMAW. I have read lots of papers over the years dealing with trials to implement GMAW within Nuclear Welding Applications but even though the laboratory results were very impressive and sound, GMAW has - at least to my best knowledge - never adequately been used in this highest technology level sector.

Since there are efforts or a rebirth observable in Europe but as well in the USA and even globally to increase - in relation to the current CO2 emission discussions - the nuclear power generation and on the other hand there is a considerable sophistication in the GMAW technology observable as well, I am curious if now - as new nuclear power plants are planned to be built, advanced GMAW might have a chance to eventually replace GTAW from its leading position as the #1 welding process in this field.

And where may a question as mine be better placed as here in the worlds best welding forum, where all the best welders, experts, NDT specialists, engineers,..., are meeting periodically?? Nowhere!

So any kind of opinion, idea, assumption or even general feedback on this topic is greatly appreciated!

Thanks and best regards,
Stephan

By MBSims

Date 06-01-2008 01:39

GMAW does have a history of use here in the US in nuclear power construction. It is primarily used for ductwork fabrication and light gauge structural work. It has also been used for corrosion resistant weld overlays in reactor vessels, steam generators, pressurizers, valves and other pressure vessels such as feedwater heaters. In the spray transfer mode it is also used for piping fabrication. It has not found widespread acceptance in short circuiting transfer or pulsed transfer for butt welds in piping or other pressure retaining welds due to the tendency for welders to drift into the short circuiting mode and leave incomplete fusion defects. Unless the application is constantly monitored for compliance to procedures, it is difficult to use on a general basis. Most fabricators and constructors rely on more "forgiving" processes, such as FCAW, SMAW or GTAW. Most installation welding of nuclear system piping is done with one or more of these processes. There are a number of "balance of plant" piping systems in nuclear plants that are built to non-nuclear codes, such as service water , extraction steam, circulating water, etc. Some of these occasionally use GMAW root passes with FCAW or SMAW fill.

By Stephan (***)

Date 06-01-2008 08:54

Marty,

thank you very much for this precise explanation!

I appreciate it very much and I guess that no further discussion is necessary now by even your descriptions on history and status of GMAW in the US Nuclear Power Industry.

Hmmm, it would be interesting how the "new", or better, sophisticated GMAW processes (STT,...) may influence these reasonable facts - described by you - in the forthcoming projects.

Once again thanks for your great reply and best regards,
Stephan

By js55

Date 06-02-2008 13:32

Stephen,
In my opinion when the problem is fusion defects I do not believe STT (and the similar technologies) is of much help. They suffer essentially from the same phenomena that pulsing does. The shut down of arc energy. I know much has been promoted of the 'plasma boost' (speaking predominantly of Lincoln though all these technologies are pretty much the same), but it has been my expereince (and we ran STT's up the wazoo) that a reduction in arc energy is a reduction in arc energy. The very thing that allows a reduction in spatter, and greater all position control, is the very thing that reduces energy for fusion. Just as with pulsing. Prohibitions against short circuit for fill and caps are, in my opinion valid. For spray I think concerns are invalid, but then FCAW is almost always more productive.

By Stephan (***)

Date 06-02-2008 20:17

Most excellent Jeff!

Great post - as always - and most comprehensible!

Thank you Sir!