What weld Process is suitable

[bmoorthy]

Hello All

The user's specification indicates that weld shall not be anodic with respect to the base material.

The material in question is API 5L X 65.

Welding is done with SAW and GMAW combination.

What flux (If SAW is used) will result in Cathodic Weld.

If GMAW is used fully, whether changing the gas composotion result in change in Cathodicity/Anodicity? If so what is the recommended Gas composition.

Suppose the potential measured of the pipe base material is "- 0.5" and the potential of the weld is "-0.4" (I persume it is the potential that will be determined as the measure of Anodicity or Cathodicity), is the Weld Anodic with respect to Pipe.

 

[metengr]

Anodic, I believe in reference to your specification, refers to the filler metal chemical composition in relation to the pipe base metal chemical composition. Flux is selected based on filler metal chemical composition. So, select the filler metal that matches as close as possible to the chemical composition of the pipe and provides similar mechanical properties.

 

[Goahead]

If the user's specification indicates that the weld shall not be anodic... it should also say how that is determined and what is the limiting acceptable result.
Otherwise it does not appear to be a meaningful requirement.
Fluxes for SAW are not designed to control anodic condition.

http://www.welding-advisers.com/

 

[vainala]

I have not heard about anodic. I presume the spec may be mentioning of job being anode while welding. Generally GTAW process requires straight polarity (Electrode negative and job positive).

Vainala

 

[weldtek]

metengr,
Your post makes perfect sense, I'm wondering if there also may be a concern over hardness?

 

[0707]

I suppose that whichever the welding process you use, if you chose the proper filler metal it has to match the base metal with the same composition or very similar, so the question of being cathodic or anodic doesn´t make sense.

 

[stanweld]

The Owner's specification may make sense depending on the process fluid's corrosivity. Deposited, matching chemistry, weld filler metals are often more susceptible to corrsion than the base metal, even in carbon steels. The Owner or its Engineer should also specify the filler metal(s) that will provide acceptable corrosion resistance. Filler metals with higher chromium, molybdenum or copper contents than the X65 pipe base material may provide better corrsion resistance and extended service life.

 

[SJones]

http://www.google.co.uk/search?hl=en&q="preferential+weld+corrosion"&btnG=Google+Search&meta=

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/