Pulsed mig vs 7018

[amron]

Hi
I would like to know which seam is better for a pressure tank that has to hold 30bar pressure, one that is made with a pulsed mig with 80/20 Ar co2 mixture or with 7018 electrodes? please let me know if there is a table or any other sort of data that provides qualified info / comparison about it? I've didn't mentioned that the material to be used is A516 - G70 steel.
Thanks.

 

[gordon stephenson]

At 30 bar it Sounds to me like a job that needs a proper weld spec before even starting.

 

[Delgado]

As above, not really an internet question, get a welding engineer in to write you a proper WPS.

 

[TechnicAl]

Gordon and Delgado are right, you need to have a written procedure, however, the choice of consumable is usually determined before that happens.
In terms of strength they are roughly equal, both 70 grade (70,000 psi tensile) so from that point of view it shouldnt matter.
In the hands of the inexperienced the MIG can be more susceptible to lack of fusion defects but the 7018 will be more prone to slag traps. What Im sayimng is that the best choice is what your happiest with.
Once youve decided, set up a mock joint, weld it, note the parameters used (everything) and have it tested. This is the basis for your Welding Procedure Spec (WPS).
If its a pressure vessel it may be suject to a code and you may need to meet certain criteria. If not probably the most relevant tests would be to have it x rayed and then do some cross weld bend tests. These will determine if it will be water tight.

 

[amron]

Thanks for your answers. I'm affraid that I wasn't clear enough. I do have a WPS and it is with a 7018 rod. I wanted to know if the pulsed mig can be a subsitute to arc welding for that purpose, because if it can be, I would like to suggest to pulse weld it ( after getting the authorization to carry out the change). that's why I've turned to your experience and expertise to ask if strengthwise the pulsed mig weld is equal or better than the 7018 rod weld?

 

[TechnicAl]

As I said its certainly capable. You cant just change the WPS. Its a definite material change so you would need a new WPS.

But yes you could do if you want to go to the bother

 

[asmeix6g]

good luck Amron, its usually a nightmare trying to beg for a wps to be changed! i.e sticking some brackets that just hold a spec plate on a tank, the design doesnt allow for the fcaw torch to fit in very well, only way was to have a real long stick out of wire! i ask our QC/QA inspector guy if i can just stick it on with a lo hy and i get back a "no, definatly not! the wps says fcaw so thats what you will use" :/

 

[aametalmaster]

Gas flux core wire and 75/25 or co2 would be a good wire choice also. I have been welding 3,000# tested pressure tanks for a few weeks now...Bob