Normalized Material Vs. PWHT 2

[keens]

Hello,

I have a Pressure Vessel that I am working on for another Customer, that has specified SA516-70N & it also needs to be PWHT. I would like to know if anybody knows wheather I can get rid of the Normalized requirement, if I PWHT to the Temperature required to Normalize the Material. The thing that is driving this question is cost. Normalized Material is about 0.30$ more than Non-Normalized Material. Thanks...

 

[metengr]

As long as the PWHT temperature is BELOW the original tempering temperature of the pressure vessel plate, the bulk properties of the pressure vessel plate established by the original N&T heat treatment will not change.

Typically, you should remain about 50 deg F below the original tempering temperature to avoid affecting bulk properties.

If you decide to PWHT at the normalizing temperature, you will need to temper the plate to achieve a N&T heat treatment per the orginal plate specification.

 

[keens]

Metengr,

What is the original N&T heat treatment? Does this mean if we keep the PWHT Temperature below the N&T Heat Treatment Temperature, the Normalizing does not need to be performed? Thanks...

 

[metengr]

keens;
SA-516 plate can be purchased as N&T, which is a separate heat treatment step, depending on service requirements. The N&T heat treatment that I had mentioned was that performed by the mill and is listed on the mill test report (MTR).

Now, if you perform a PWHT below the stated tempering temperature on the mill test report, the bulk properties of the plate established by the N&T heat treatment will not change.

 

[keens]

Metengr,

Thank you for your help. This will help out. Have a good Day

 

[keens]

Metengr,

I am not sure I explained everything clearly, I apologize. Let me start over. Say the customer specifies the want the Material to be Normalized and PWHT is required. So, I should order Normalized Material and PWHT the Vessel after Fabrication. Now, what if I ordered the Material as Non-Normalized and still performed the PWHT after Fabrication. The question now is, is it possible or allowed by ASME Code to PWHT at the Temperature required to Normalize the Material and the Material to be considered as Normalized?

 

[metengr]

keens;
Ah, a definite twist to the plot. You can re-heat treat the plate after welding using a normalize and temper heat treatment, following the requirements in SA-516 for normalize and temper heat treatment.

Keep in mind that the importance of this heat treatment either before or after welding is to assure adequate low temperature toughness. If you decide to perform a normalize and temper as part of post weld heat treatment, your weld procedure needs to be qualified using this heat treatment method.

 

[keens]

Metengr,

Thanks again for the help. I appreciate it. Have a good Day....

 

[JStephen]

Would you run into any problems with distortion or with material weakening during the operation? Just a thought...

Also, do you have facilities that CAN normalize? I know of some different facilities for stress relief, but don't know how high they can run stuff.

And lastly, you might find that the extra to normalize after fabrication isn't any more than the extra to normalize before.

 

[vesselguy]

Good answers by all the metallurgist. But I think his original question is not answered.

He is asking can he use non-normalized 516-70. What he needs to know is why SA-516-70N is specified. It must be due to low temperature (MDMT) limitation on impact testing. Confirm if this is so. If the idea is to be able to use Curve D in UCS-66 for impact test exemption on thickness then that's why.

PWHT is specified probably due to sour service or other process reason, if PWHT is not required by Code for the thickness.

 

[keens]

vesselguy,

Thanks. The customer has alraedy specified Normalized Material and PWHT. So, the question of why it was not specified does not matter, or is not what is concerning me. What I would like to find out is, can I order Material Non-normalized and then PWHT to the Normalizing Temperature. Would this Procedure result in a Normalized and PWHT Vessel? This is a question posed to the Engineering department by the Estimating department. I think Non-Normalized Material is quite a bit cheaper than Normalized Material. So, if we could buy Non-Normalized Material and then PWHT and Normalize after Fabrication, we would save a lot of money. I geuss the other question is, will PWHT at Normalizing Temperatures produce Normalized properties in the Material?

 

[metengr]

keens;
Heat treatment of pressure vessel steels should be performed by a professional heat treatment shop that deals with this stuff day in and day out. Furnace requirements for normalizing and tempering require specific temperature controls for handling plate steels during heating and are not like applying PWHT with electric resistance contact heaters in a small furnace or enclosure or with rosebud torches. Rapid cooling of the plate after normalizing (1650 deg F) can be tricky to achieve a uniform structure.

N&T heat treatments for pressure vessel plates that are specified by the customer require some form of certification or documentation that the heat treatment was performed in accordance with SA-516. I hope this answers your question.

 

[SJones]

Ask the customer and see if they will accept a post weld normalising heat treatment. If I was in their position, I would not accept it for all the reasons alluded to above unless your company could demonstrate that it was a routine operation completed satisfactorily at all times.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[GenB]

keens( I geuss the other question is, will PWHT at Normalizing Temperatures produce Normalized properties in the Material?)
I will research it further. My guess is that the material will be normalized if PWHT at normalizing temps, it will be actually PWHT with normalizing properties,
one catch: you may have to test the material afterwards to check certify the normalizing properties.
genb

 

[keens]

Metengr,

Our intention is to purchase the material as SA516-70, and fabricate the vessel. After fabrication we will send it to a company that will stick the whole vessel into a big Furnace and perform the PWHT. We were thinking of having them perform the Normalizing also. So, we were thinking that the PWHT and Normalizing could be performed at the Normalizing Temperature. It sounds like the only catch would be to make sure my weld procedures are qualified to the Normalizing Temps. Does this sound correct, or am I still not catching everything you have explained to me? Thanks...

 

[metengr]

Keens;
You need to be very careful with this approach because of concerns related to distortion of the pressure vessel. I don't know what your vessel size is but you need to make sure that you have adequate support during the elevated temperature normalizing heat treatment. Although I generally support a re-heat treatment after welding for certain alloys, the risk of distortion is too great for carbon steel plate material.

If it was me, I would stick with the sub critical PWHT versus normalization heat treatment.

 

[keens]

Metengr,

So, have you ever heard of anyone trying to do this? It sound s like it would be best to just let the Mill supply the Material as SA516-70N, and perform the PWHT after Fabrication. The Estmating Department was trying to think of a way to save some money.....Thanks again...

 

[metengr]

Yes, I have heard and seen poor results.

 

[keens]

Metengr,

Thank you for the valuable advice. I will talk to my supervisor and the estimating department. Have a nice day...

 

[GenB]

I would stick to standard procedures, means spend the xtra Dlls and purchase N material then PWHT at std rate,
too risky to deal with distorsion.
genb