SS316Ti Vs 321

[Aodwan]

We are designing one vessel whose material is CS + Clad 316Ti, now we do not have 316Ti material available, Can we propose the 321 instead. (Client do not want to change material since they are happy with old equipemnt or don't want to do engineering) I found all the chemical requirement of both are almost same as per section II Part A.This Vesssel is subject to H2S service.

 

[metengr]

I will put this in as simple terms as I can; you need to convince the client regarding alternative cladding material, nothing we say here will alter this approach.

"Almost the same"... does not mean equivalent. Look for alternative weld/cladding overlay materials that are equivalent in terms of service performance and provide that in writing. You may need to subcontract a pressure vessel firm that has the material/corrosion expertise to provide alternative material options with necessary calculations to ensure similar long life. If this is too much to do, follow the client’s requirements.

 

[stanweld]

The resistance to pitting corrosion and other specific types of corrosion of 316Ti is significantly greater than that of 321. One should assume that the Owner or Owner's Engineer originally selected the material for the corrosive service.

 

[blacksmith37]

The Mo in the 316Ti makes a significant improvement in corrosion resistance over 321 in some service. In general you can think of 321 equal to 304Ti (or 304 Nb/Cb). 317Ti would be an upgrade to 316Ti - but even less available. Have you tried European sources for 316-stabilized? It was more common there .

 

[lganga]

Aodwan

321 is for medium temperature service (some cracking furnace use it but no more than 600ºC).
Then,321 is a different service than 316Ti
In both you have to be aware when you weld them. Is very hard to retain titanium in the bath, so it has to welded with addition of another stabilizer than Ti (that is the case of 321 welded witn 347 cnsumable) so a WPS with its PQR is the first to do.

Sandvik-Avesta have good handbooks about corrosion for different Service- For consumable also Metrode is an option.

Regards
Luis