Hot forming in normalising range (carbon steel) 3

[CaedmonH]

Hi folks,

I read in some topics in this forum that "hot forming in normalising range" is considered a separate production step and needs to be followed by a normalising (plus additional steps like annealing, quenching and so on depending on the material) to regain optimum mech. properties. I'd like to know if that is really a code requirement (mainly ASME) or just an individual approach to be on the safe side?

My company is operating in the hot forming of vessel heads since many many decades and has a lot of experience and knowledge about the mechanical values after hot forming in normalising range (forming operation to be finished above Ac3), so we are usually marketing to our customers that a subsequent normalising is not necessary and can even prove that, as said, by our experience and thousand of orders processed without an additional normalising. Of course, many customers and many specifications require an additional normalising, but I'd like to be sure that we are really marketing the truth saying that this is acceptable by ASME.

Thanks for comments.

Regards
Caedmon

 

[metengr]

Here is what is factual - hot working can be performed in the normalization temperature range. However, it is not a normalization heat treatment, this is a separate step.

What you can take credit for is after hot working is completed instead of cooling and reheating, hold the component within the normalization temperature range and air cool.

 

[CaedmonH]

Thanks metengr!

I got the point, but

1) would you expect to have a difference between the mechanical values with hot working in normalising range followed by a normalization compared to hot working without normalization?
2) what is the condition of the material after the hot working without subsequent normalising, is it "normalised" or is there any phrase to correctly describe it? So, if a specification requests "heads in normalised condition", is it necessary to perform a normalising after the hot working in normalising temperature?

If the specification requests a subsequent normalising, we usually transfer the formed part directly back to the furnace to complete the normalising incl. the appropiate holding time.

 

[metengr]

1) would you expect to have a difference between the mechanical values with hot working in normalising range followed by a normalization compared to hot working without normalization?

Yes, very possible. The problem is if the temperature during hot working falls below the austenitizing temperature range and now you have other phases that form, this results in variable mechanical properties. It is all about keeping the component within a temperature range that results in uniform mechanical properties.

2) what is the condition of the material after the hot working without subsequent normalising, is it "normalised" or is there any phrase to correctly describe it? So, if a specification requests "heads in normalised condition", is it necessary to perform a normalising after the hot working in normalising temperature?

Yes, normalization means the component was held above a certain miniimum temperature to ensure the proper elevated temperature phase forms and is uniform through-out before air or liquid cooling.

 

[jtseng123]

metengr, a little bit confused here,
1. Even CaedmonH can prove that there is no difference in microstructure and mechanical properties, it seems to me that you are not accepting hot forming in normalization temperature without holding additional period above Ac3 after forming, or without subsequent normalization after cooling, right ?
2. A dummy question: why only requiring base metal to be normalized, but not welding seams ? I did not see any vessels put to furnace for normalization after welding for vessels that require normalized materials such as in wet sour service, hydrogen service, or to avoid impact test.

 

[metengr]

1. Even CaedmonH can prove that there is no difference in microstructure and mechanical properties, it seems to me that you are not accepting hot forming in normalization temperature without holding additional period above Ac3 after forming, or without subsequent normalization after cooling, right ?

Right.

2. A dummy question: why only requiring base metal to be normalized, but not welding seams ? I did not see any vessels put to furnace for normalization after welding for vessels that require normalized materials such as in wet sour service, hydrogen service, or to avoid impact test.

It depends on the design engineer and prior experience in service. I have seen headers fabricated under Section I that a relong seam welded normalized and tempered because this was an internal requirement or customer requirement. Other times, not. The Code does not provide specific guidance for requiring normalized and tempered versus subcritical post weld heat treatment after welding. Only that the proper heat treatment method is followed if either option is selected.

 

[CaedmonH]

Coming back to the original intention of my request:

My company is producing hemi-heads and elliptical heads sometimes up to 170mm thickness, the normalising of such an item is a very costly thing (sometimes above 1000 USD per piece) if required after the forming and already considering the elevated temperature in the material. We are frequently supplying materials to power generation and oil&gas projects with requirements for extensive testing and sPWHT with 3 cycles at critical temperatures, and nevertheless, our control of the process is that good that we are confident to pass all testings without subsequent normalising if only the mill guaranteed the testing in N+sPWHT condition, without any requirement to simulate the hot forming procedure. Based on this confidence and the experience in this sector, we strongly market to our customers that it is not necessary to perform the subsequent normalising.

My impression is, although I understand the doubts, it is still metengr's personal attitude to better do a normalization after the hot forming, but the essential question for me is: Does ASME require this?

 

[jamesl]

I have seen many company specs requiring additional normalizing after hot forming. However, my understanding is the Code does not require subsequent normalizing if the forming process is carried out above lower transformation temperature. Here is part of Code Case VIII-1-89-69. The implication is normalized plates are still cosidered as normalized after hot forming in terms of the Code.

Question (1): If plates that have been normalized, and qualified on the basis of test specimens taken from the plates after normalizing, are subsequently heated to equivalent temperatures above the lower transformation temperature during hot forming, are additional test specimens representative of the second thermal cycle required by UCS-85?

Reply (1): No, provided all other requirements of UCS-85 are met.

 

[CaedmonH]

jamesl, that was a very helpful answer. Thanks for mentioning the code case

 

[metengr]

What you can take credit for is after hot working is completed instead of cooling and reheating, hold the component within the normalization temperature range and air cool.

This is what I said above. You don't need to re-normalize as a separate step.

 

[rhg]

CaedmonH

As you said "....many customers and many specifications require an additional normalising...", please consult your customer ¿why?

Regards

rhg

 

[CaedmonH]

@metengr: sorry, I misunderstood your answer in the first reading.

@rhg: if I ask my customers why, the answer will mostly be "Because it is in the specification". And the reason why it is in the specification is because some head forming companies have no idea about heat treatment and why it is necessary to finish the forming operation above ac3. And just to be on the safe side, some EPC added the clause "with subsequent normalising".

However, you proved that you didn't get the point of this discussion.
I'm dealing on a daily basis with vessel fabricators in India, SouthEastAsia, Brazil and so on which really don't have any idea of materials, consulting them regarding this topic is like talking to a parrot: "the specification says so", "the specification say so"..."...". Our know-how about hot forming and heat treatment is clearly above this level and it was my intention to confirm my understanding of this matter, and thanks to metengr and jamesl this worked well.
As mentioned above, we have successfully formed heads in that way several thousand times with no issues in mech. testing (with third party inspections as a standard), so my daily work is to teach people not to accept the wording of specifications without thinking about the sense behind.

Regards
Caedmon

 

[EngAddict]

If for example your client in SouthEastAsia is supplying vessels to Australia, that must meet the Australian pressure vessel standards, then AS4458 requires the following for material groups A1 & A2:

1. Any heads formed in the temperature range 850-950°C from material that requires impact testing must be normalized after cooling to room temperature.

2. Any heads formed in the temperature range 950-1050°C must be normalized after hot forming.

Is your company qualified to provide engineering advice to recommend what does and does not need normalizing, under any conditions? If your client has asked for it there is usually a reason, why not just supply what they ask for and charge them to do so? Do your clients always advise you of all process conditions that might also require normalising, like in sour service to protect against HIC and SSC?

"so my daily work is to teach people not to accept the wording of specifications without thinking about the sense behind"
Sounds like a dangerous job. While quite often the product may be of equivalent quality and not required further heat treatment, it is not in your purview to advise people to disregard project specifications, data sheets or code requirements. Legally speaking we are not allowed to 'read between the lines' so to speak, I would be wary of offering this type of advice.

Just my 2c

 

[CaedmonH]

@EngAddict

Thanks for your comment.

First of all, this is not a discussion about all specifications being scrap and their wording questionable. We are working acc. to most specifications fulfilling the requirements without any questioning and our general approach is, of course, to accept what is in the specification and to follow these rules.
However, when you are dealing, for example, in Oil&Gas projects, several fabricators from different countries are involved, and if you learn that some fabricators have the understanding and the technical background to waive this requirement (subsequent normalising) during a discussion with the EPC and some don't, then you also learn something about the know-how of the fabricators and their way to deal with EPCs.
I do agree, might be the word "teaching" was a bit too heavy, but somehow it is from time to time the way I feel when talking to designing people in the above mentioned areas, not at all saying that all designing people there are of the same quality. I know fabricators in Malaysia, for instance, with good engineering and material know-how and can remember very fruitful discussions there.
There's nothing "dangerous" in my job and my advice is never to disregard any requirements, and I think nowhere in my posts there was any indication that I'm doing this, my advice is to go the EPC, discuss why subsequent normalising (or any other requirement) is in the specification, and if the outcome is, that there are reasons beyond the fabricator's or my/our horizon, it is accepted and will be done, of course. Long-term customers of ours appreciate this way of working as we are supporting them with our knowledge and experience, and many engineering companies appreciate the feedback because some of their specifications are not up-to-date anymore and need some refreshment from time to time. We waived this requirement already in many cases and convinced the fabricator and the EPC to skip the subsequent normalising, so it's not nonsense I'm talking about here.
The reason for us to work like this is to be in a unique position in the market, not only selling our products but also sharing our know-how with our customers. I can tell you, this is a great way to establish long-term relationships and it works well for my company. Of course, sometimes our approach also is "just supply what they ask for and charge them to do so". But that's another story

Regards
Caedmon

 

[EngAddict]

You're welcome.

Good to see you are trying to find the best outcome for your clients, both for quality and cost savings, instead of charging for unnecessary heat treatment. Sounds like the relationship we have with our manufacturers and suppliers, which is a good knowledge sharing situation both ways.

I was just adding the other code requirements and replying to a few specific comments. I am always reluctant to make recommendations because if the outcome is not what the end user wanted then the client seem to think it is my fault, even though it was their decision. Make suggestions but get them to check with the specification, the code and the end user - which it seems like you are doing anyway. Specifications are not optional and the only ability to waive requirements is with a written dispensation from the operator. For things like heat treatment there is usually little room to move but there are always exceptions to the rule.

I have read some poor specifications that are clearly written by project engineers with little or no vessel design and manufacturing experience. However, like it or not we either comply with it or gain their written approval to deviate from the specification.

 

[rhg]

See BS EN 13445:
"A subsequent heat treatment may be waived, if the forming process of the last operation has been completed at a temperature above 750 °C or above 700 °C where the degree of deformation does not exceed 5 %."

Regards

rhg

 

[CaedmonH]

@rhg

This passage is often used for calibration works on EN dished & flanged heads for the final shape and diameter to avoid another heat treatment in the end.

Regards
Caedmon