SS321 Versus SS304

1. You can not over-rule customner specification (what-ever we may say)

2. yes SS321 is not as freely available as 304 or 304L (or as cheap).

3. SS321 is a low carbon SS with added Ti for further carbide stabilisation which is extremely important for the high temperature properties of the SS. Which obviously 304 lacks. Nearest contender will be 347 may be (which is even costlier and more difficult to get)

The only person who can answer your question is your customer.

It's silly of you to ask us for ways to circumvent the customer specifications.

They want SS321, they are willing to pay for SS321, so give them SS321, or get a deviation authorization FROM YOUR CUSTOMER!

I agree with Lyn. Yes, it is impossible (or at least unwise) to use ss304 if the customers' datasheet specifies ss321. But it is very easy to ask the customer why they have specified ss321 in the first place. They could have a very good reason, in which case you'll have to stick with it. Or it could have been specified very haphazardly, with little understanding of actual requirements and ramifications (this is not so unusual), in which case you should be able to justifiably, and with the customers' approval, change to ss304. Furthermore, we cannot advise on the suitability of ss304 without full specs and application data.

"Customer specification says that SS321 is required for all carbon materials with cladding and overlay as well as stainless steel as per manufacturing heat exchanger."

This statement is challengeable as to meaning regarding the relationship to carbon materials. You should consult your project engineer.

Unless your ISO scope includes design responsibility, you should leave the designin and material sppecification issues up to folks that have that Scope and responsibility.

Milo

I have to agree with the other responses in this thread - you cannot deviate from a customer spec without incurring serious issues. If you deviate without consultation and written permission from the customer, you have violated the terms of the contract and that will precipitate serious problems. The best you can expect is a very unhappy customer and at worst they could cancel the contract and subject your company to legal action.

Now if the problem is availablity of 321 in suitable shapes or sizes for specific design applications, you may have to look at alternatives such as cladding or material substitution. These things can be discussed with your customer in business-like fashion and shows you are a competent company to work with. No one expects you to use "unobtanium" and they will certainly consider well-thought-out solutions.

Without knowing more specifics about your problems areas, I can't offer more specific solutions.

Agree with all above responses but with one addition. If you are so incompetent as to not understand this already, then I question the wisdom of your customer giving you the job. You have come on here and asked a lot of what I feel to be really dumb questions for someone who is in the heat exchanger manufacturing business. You should know this stuff already. If you don't you are not qualified to do the job. It is one thing to ask these things to expand your knowledge, but it is quite another to come on here and look for excuses to not do the job you were contracted to do.

Yes I agree to other replies. Customers's spec should be followed.

There is a case study in this regard. In our plant in convection zone of reformer furnace, steam super heater coils were of material SS 321(Tube OD 101mm, Thick. 10.4mm, Tube length 12000mm), which were installed in yr 1996. Within one year of operation, these tube assemblies failed due to brakage of intermediate tube sheets and tubes sagged badely touching each other. Replacement of this bundle was planned and the same licensor suggested to change the material of construction of tubes from SS 321 to SS 304H. As per lincensor, SS 321 is good for high temperature but the creep strength is poor as compared to SS 304H. In higher creep, extra loading on the ligaments of intermediate tube sheet give way to failure. Now after replacement of those tubes in 1998 with SS 304H material, equipment is performing satisfactorily without any sag or failure.

In this regards it may be noted that in newer projects later on licensor has used only SS 304H and have changed their specs.