Normalizing of Sa 516 Gr 70 plates

[Merzi]

We ae fabricating a vessel where in the shell and the head material is to be SA 516 Gr 70 N 1/2" thk. The heads are to be hot formed . The head manufacturer does not have SA 516 Gr 70 plate in Normalized condition. What he proposes is thta if the heads are hot formed in the normalizing range that should suffice.

We are having same problem with the vendor from where we are buying the shell. He is proposing to normalize the plate before forming and carrying out the mechanical test.

Is this acceptable as per code

Merzi

 

[metengr]

Per the ASME SA-516 Specification, plates under 1.5" in thickness can be supplied in the hot rolled or hot worked condition. For plates 1.5" and over, the plates must be supplied in the normalized condition unless specified by the Purchaser. So, your supplier would not have normalized plates at 1/2" thickness.

If the plates are ordered with notch toughness testing requirements, then the plates shall be normalized. This would apply to your 1/2" thick plates, as well.

If your application requires notch toughness testing, the plates need to be re-heat treated after forming to be in the normalized condition per the Specification unless you specify otherwise. Plates that are hot worked and air cooled after hot working are not considered to be normalized. This is a separate heat treatment step.

 

[metengr]

One minor correction to my post above is that plates 1.5" AND under can be supplied in the hot rolled or hot worked condition. Plates over 1.5" must be supplied in the normalized condition after hot working.

 

[weldtek]

However, I think metengr will agree that it's perfectly acceptable for the head manufacturer to normalize the heads and state so on the documentation he supplies you. These days it's becoming more the norm to purchase 'green' plate and heve it normalized by a sub processor due to the extreme shortage of materials and backlogs at the mill furnaces. We have a situation right now where we're buying 3" SA 516-70 as rolled and having it normalized by a local heat treater for just that reason.

 

[metengr]

weldtek;
Yes, I totally agree with you.

 

[robsalv]

We've had the same question crop up in Australia.

Due to compressed schedules on one job, the head pressing subcontractor proposed to hot form at normalizing temperature. I was doubtful that it complied and doubtful about the control of temperature.

But, they were able to demonstrate enough temperature control and accuracy and the right soak time to satisfy the requirements. We also took a coupon from where the nozzle was going to be installed and had full mechs done to prove that the plate had normalised properties.

One issue with re-heat treating already pressed heads/rolled plate is distortion. On another job we experienced some significant warpage and the heads were barely salvagable... luckily we had a fair bit of green trim length to allow us to deal with the warping.

Thinking a bit more outside the box, could you weld up a vessel with the as rolled/pressed steel and then heat treat the whole vessel at normalising temperature??

 

[JoeTank]

robsalv,
One thing that comes to mind is that normalizing temperatures are usually above the upper transformation temps, so that would be an essential variable for the WPS/PQR in ASME IX. Perhaps a materials guru could comment further.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[metengr]

Two answers to the above posts;
1. Normalizing is a separate operation to assure uniform mechanical properties. If hot working is performed, and the piece is held immediately placed back in the furnace after hot working in the normalizing temperature range (without cool down that typically occurs during hot working) this would be appropriate. The concern that I have is that during hot working, the temperature may dip below that for a proper normalization heat treatment, and as such, one might not get the desired mechanical properties (including impact testing).

2. The problem with welding the vessel on as-hot worked material is that someone has to assume responsibility that the shell and head components were supplied in accordance with the appropriate ASME material specification for heat treatment. If the fab shop that supplies the material components and fabs the vessel has ASME qualified welding procedures (including those that would be qualified with a normalization heat treatment), this could work within code requirements. However, I see no reason why anyone would want to fabricate a vessel out of as-rolled material and risk significant distortion during a normalization heat treatment to meet the ASME material specification requirements.

 

[JoeTank]

Merzi,
I don't think anyone addressed your question about the shell being fomed with plate that has already been normalized. Since shell rolling (in the range of 1/2 inch)is usually done cold, I see no Code issue involved. It is acceptable to roll and weld such a shell w/o further heat treatment.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[kesjay]

As per ASME code,what is the time of normalising per inch thickness of plates.

 

[metengr]

The Code does not specifically get into that kind of process detail. For most applications, 1 hour per inch of material thickness, with 15 minutes as the minimum for conventional heating methods. Material heat treatments like normalizing or annealing tend to follow the same time/material thickness as with PWHT requirements in the Code.

 

[GenB]

I believe normalizing falls into the ASTM specification,
so if it is not listed in Sec II-A SA516 and SA20, you have to find mats spec in ASTM
When the head mfr normalizes the mat to form it and if certifies with statement: per UCS___
"the material has been normalized" you are okay.
I will follow up with Code par.

ER

 

[metengr]

GenB;
Most ASTM/ASME ferrous material specifications do not specify a normalization time at temperature, only a minimum normalization temperature.

 

[JoeTank]

GenB... it's UCS-79

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[weldtek]

If you need documentation from the head manufacturer that the heads were normalized, as part of, or subsequent to the forming operation, reference to UCS 79 is not sufficient.
The head manufacturer must describe any heat treatments the material undergoes. Typically their documentation includes a statement detailing the applicable heat treatment.