Normalized elipse Head

[petroPV]

For fatigue service reason, we call out vessel material to be normalized SA 516-70, and elipse heads (min thickness 2") get to be hot formed. The vessel fabricator proposes to use normalized plates to hot form the elipse heads and normalize the heads after.
My concern is if the mechanical properties of SA 516-70 plates are impacted by twicw normalization. The plate MTR only shows simulation test results of two cycles PWHT. But I only feel confident if MTR shows normalization simulation test results.
Any contribution will be appreciated.

 

[jamesl]

If the test plates for MTR were cut out before forming, then MTR should show the test plates have gone through hot forming and normalizing process plus SPWHT.

 

[petroPV]

Jamesl,

The MTR actually is provided by mill without normalization simulation test, not by head former. As i said, I like to see normalization test results of two cycles simulation since head material actually experiences twice normalization.

 

[jamesl]

That is what I tried to say. The head manufacturer should have cut test plates before forming the head. The test plates should have gone through hot forming cycle and normalizing cycles and SPWHT (for vessel fabrication). Test results should be provided by head manufacturer.

 

[petroPV]

Thanks, James.
I expected MTR from mill includes normalization simulation test results (2 cycles min), not from head former. I know most mills provide PWHT simulation test results, but not sure if majority mills provide normalization simulation test.
My understanding is that multiple normalization (even PWHT) cycles may soften steel plate, decrease strength (or hardness).

Have a good night!

 

[jamesl]

I am not a metallurgist. Normalizing is a different kind of heat treatment from PWHT. If you bought a normalized plates, carried out a hot forming, then do a normalizing again just to restore the mechanical properties of normalized plates.

 

[r6155]

petroPV

Fatigue service or not, always plates over 1,5 in. in thickness shall be normalized: see SA-516

Regards

r6155

 

[petroPV]

r6155,

It's clear that elipse heads need to be normalized. Vessel fabricator is to use normalized plate to cold form the elipse head and thereafter normalize the head again. My concern is that if twice normalizations cause negative impacts to material mechanical properties. I will feel much comfortable if plate MTR from mill verifies the test results with two cycles normalization simulation test.

I am thinking to suggest veseel fabricator using non-normalized plate to cold form the head and following to normalize the head accordingly. Since EFE% is over 5%, I am wondering if vessel fabricator needs to heat treat the head after head normalization per UCS-79. I would think the normalization heat treatment can perform the stress relieving function. If this is true, then it's not necessary to heat treat the head again after head normalization. I am not sure if my thought is against code or acceptable in terms of metallurgy.

Regards,

 

[vesselfab]

i don't know why any fabricator would spend the extra money for normalized plate if they are going to normalize it again.

If it were me, i would use as rolled plate with mtrs base on simulated coupons in normalized condition

do it every day

 

[petroPV]

Vesselfab,
since they would have hard time to get non-normalized plate with 2" norminal thickness of SA 516-70.

 

[vesselfab]

hmmm

buy thick as rolled all the time.

 

[petroPV]

Vesselfab,
I was told plate over 1.5" shall be normalized per 5.2 of SA-516/SA-516M in Sec II-D.

 

[vesselfab]

yes it does, but not neccessarily at the mill

many fabricators buy it as rolled with normalized coupons for mtrs and then normalize during or after forming process.