the deoxidizing of titanium tubes surfaces 1

[mombu]

Dear all,

can anybody helps me solving the following doubts?

Our client requested, for titanium tubes, the deoxidizing of the external surfaces , at both ends of each tube.

I suppose that this is somehow concerning the subsequent welding of the same tubes to the tubesheet (I am talking about shell and tube heat exchangers). Is my assumption correct?

Is this a usual or unusual requirement?

Do you know if the tubes suppliers normally include this treatment in their production schedule?

How does this treatment work?

Thanks in advance for helping me.

Kind regards

Mombu

 

[EdStainless]

Very unusual.
Years ago Kobe sold Ti HX tubes that had a distinct gold tint as a result of their process. They charged extra for this. I never saw anyone remove it before seal welding.

To do this would require the use of pickling and not only be expensive but add some risk due to additional handling and cleaning.

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Plymouth Tube

 

[metengr]

I would suggest you talk to the technical folks below. They are very helpful and know Ti tube products;

http://www.valtimet.com/

 

[unclesyd]

Polishing tubes for Hx's is not unusual and is part of our specification on new and reworked tube bundles. I know of two other large chemical companies that have similar requirements.

For titanium we polish back tubesheet thickness + 1" and clean with laboratory grade ethanol using virgin rags.

Here is the apparatus from Sugino that will do the job.

http://www.sugino.com/products/db/e_yotoprod_a.asp?seq_no=11741

http://www.sugino.com/e_menu/menu_index/idx_distributor.html

 

[MikeMet]

I have seen this requirement before but only in the most unusual caes and it is typically not required or does cleaning oxide necessarily increase the potential for getting a good weld. It is very common and good practice for the ends of the tubes to be thoroughly cleaned ID and OD with an appropriate solvent to remove any traces of dirt, grease or hydrocarbon contamination. The welder technique and experience has much more to do with getting a good weld. But as they say, the customer knows best, even if he isn't right.

 

[EdStainless]

We also use alcohol to clean before welding. Our rule is that an operator must dump and replace the solvent every two hours. Otherwise is absorbs so much moisture from the air that you leave surfaces wet after cleaning them.

A mechanical polish does not remove the surface oxides, it just moves them around.
If this was a hot finished product I could understand.

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Plymouth Tube

 

[TVP]

When I first read this question, I was assuming that the tubes were hot finished, and therefore needed to be deoxidized (descaled is the usual English term used by industry). This is obviously much different than the typical cleaning process performed on any weld.

mombu,

Can you clarify the process used to manufacture the tubes?