Once more: Welding stainless to carbon steel
Once more: Welding stainless to carbon steel
(OP)
A co-worker is designing a 150' tapered, stainless steel flagpole that will be welded to a carbon steel baseplate.
He intends to connect the pole to the plate using a full pen weld from the inside of the pole; on the exterior circumference he's calling for a carbon steel backer bar fillet welded to a carbon steel base plate. The first three feet of the pole will be buried.
I have several concerns:
1. Although stainless can be welded to carbon steel is galvanic corrosion of the base plate a possibility because it will be buried?
2. Similarly, is the carbon steel backer bar a potential cause of galvanic corrosion?
3. Since the weld between the pole and the base plate will be a chrome steel is there a fatigue cracking concern since the weld will not be as ductile as one between two stainless steel or two carbon steel plates?
Any thoughts, or am I over-thinking the problem?
He intends to connect the pole to the plate using a full pen weld from the inside of the pole; on the exterior circumference he's calling for a carbon steel backer bar fillet welded to a carbon steel base plate. The first three feet of the pole will be buried.
I have several concerns:
1. Although stainless can be welded to carbon steel is galvanic corrosion of the base plate a possibility because it will be buried?
2. Similarly, is the carbon steel backer bar a potential cause of galvanic corrosion?
3. Since the weld between the pole and the base plate will be a chrome steel is there a fatigue cracking concern since the weld will not be as ductile as one between two stainless steel or two carbon steel plates?
Any thoughts, or am I over-thinking the problem?





RE: Once more: Welding stainless to carbon steel
The buried part of the structure will have to be coated to prevent corrosion unless there's a convenient cathodic protection system to hook into. The major problem will arise at pinholes in the coating on the carbon steel side should there be a significant amount of bare stainless steel exposed to the soil as well. A good coating on both, including the welds, should protect for a while (several years)before maintenance becomes necessary. Of course, if the structure is buried in concrete that would serve to protect the carbon steel for a period as well.
2.
Yes, as above.
3.
A corectly made dissimilar weld should not be more prone to fatigue problems from a purely mechanical view point. Correctly made = choice of joint design, consumable, fit up, correct welding parameters, attention to preheat and interpass temperature limitations, good workmanship and weld finishing.
Steve Jones
Materials & Corrosion Engineer
http://www.pdo.co.om/pdo/
RE: Once more: Welding stainless to carbon steel
RE: Once more: Welding stainless to carbon steel
RE: Once more: Welding stainless to carbon steel
Even if it is all SS I would still paint the underground portion.
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Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm
RE: Once more: Welding stainless to carbon steel
Thanks for your assistance.