Will ferrous contamination of Titanium accelerate corrosion? 1

[stanweld]

A Condenser manufacturer has delivered Titanium tube bundles that exhibit gross rust staining on the Ti tubesheets, some due to damage and weld spatter most due to rust bleed from iron contaminants left in the tubes. The manufacturer contends that the Fe contamination need not be removed from the tubesheets as accelerated pitting corrosion will not be incurred in the seawater service at the relatively low (< 125 F) sevice temperatures. Is his comment valid?

 

[unclesyd]

The jest of our specifications for Ti Hx's is that Ti should look like Ti not iron.

Our cleanliness specification specificially calls out that any type of surface contamination is prohibited. The big question arises where did the iron come from.

I would have serious doubts about this fabricators experience with Ti or he knows too much and is pushing the limit on Ti welding.

I would definitely ask him for a good peer reviewed reference as to the validity of his statement.

 

[stanweld]

unclesyd,
These are my concerns and experiences as well. All of the Ti vessels, piping equipment and rocket equipment with which I have been directly involved would never be less than pristeen. It is my contention that any contamination that could affect the ti-oxide passive layer must be removed and I have so stated to our Engineering/Procurement partner Contamination of the tubes was from grit blast media, which the manufacturer left in the tubes thinking that the the tubesheets were adequately shielded during grit blasting for painting of the carbon steel shell; they were sadly mistaken. The manufacturer's cleaning procedure requires thorough cleaning of the tubes only.

 

[metengr]

stanweld, your concerns are well founded. Iron contamination is strictly prohibited in Ti heat exchangers and vessels.

 

[TVP]

stanweld,

The following is an excerpt from the abstract of "Hydrogen embrittlement of commercial purity titanium", Corrosion Science 44 (2002) 1875–1888, by C.L. Briant, et al:

the reason why this material was more susceptible to hydride formation and hydrogen embrittlement was because of the higher iron content of the grade 3 titanium. © 2002 Elsevier Science Ltd. All rights reserved.

Their reference [11] contends that iron contamination of the surface led to enhanced hydrogen embrittlement potential: [11] L.C. Convington, R.W. Schutz, ASTM-STP 728 (1981) 163–180.

And this is not even addressing any of the other concerns with reduced passivity in various corrosive environments. I would strongly adhere to your requirements for clean surfaces that are free from iron contamination. ASTM B 600 addresses iron contamination, how to eliminate it, etc. Your supplier is gravely misinformed/ignorant with respect to iron contamination and titanium.

 

[stanweld]

TVP,
Thanks for the valuable reference.

 

[EdStainless]

If we are tallking about rust stains and superficial Fe conamination:
Could it cause a problem, yes.
Will it cause a problem, no. Not in low temp seawater.

Weld spaltter and imbedded Fe are a different issue. They can easily cause serious problems. And the rust stains hide the surface condition. If you had seen the equipment clean, and knew that it was fine, and now had some superficial Fe stains I wouldn't worry.
In your case I would worry.


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