heat treatment of pressure vessels

[sree60]

We have a query on simulated heat treatment of test coupons, As per one of project specification for pressure vessels, vendor has to perform 3 cycles of simulated heat treatment of test coupons.( one for actual PWHT,one for Normalising and one for site repair)

The material is carbon steel SA 516 Gr.65(Normalised). The design code is ASME SEC VIII DIV-2.

The equipment is production separator and thickness of shell is 135mm and hemispherical head is 68mm

Vendor is insisting that he will carry out simulated heat treatment of test coupon in once cycle with 3 times the holding time specified in table AF-402.1.

Vendor is also referring clause AT-113( Heat treating of sample test
coupons), wherein the last paragraph states that "The total time at
temperature shall be 80% of the total time at temperature during actual
heat treatment of the product and may be performed in single cycle"

You can also refer AF-402.1 where code allows holding temoeratures and
times to be exceeded for certain P and G numbers.

Whether vendor's proposal is acceptable?

Regards
sree60

 

[metengr]

sree60;
Yes, for the stated material and per the requirements in ASME Section VIII, Div 2.

 

[metengr]

sree60;
Just one additional comment on several options to possibly save you some money; if you can eliminate the normalize heat treatment during fabrication, and just use PWHT in the shop and in the field, and the PWHT does not exceed the lower critical transformation temperature you can avoid having any test coupons per the requirements of AT-112 and AT-113, see AT-115.2 (Exemptions from Requirement of Sample Test Coupons) for P-No 1 Materials.

If you absolutely need to normalize, you can take credit for any thermal treatments before the normalizing heat treatment provided the austenitizing temperature that is performed as part of normalizing is at least as high as the original normalizing temperature performed per the material specification - see AT-115.4

Last, if you normalize per AT-115.4, and perform a subsequent PWHT, you can take credit for this under AT-115.2 for P-No 1 materials, and not have any sample test coupons.

I hope this helps.

 

[SJones]

Why is normalising being simulated? Surely, the plate is being purchased in the normalised condition leaving only two cycles of PWHT to simulate. Also, check with the engineer responsible for the specification as there may have been a conscious requirement to override ASME and require a multi cycle simulation. It's good of people to chip in with their code interpretations but it's your company's quality assurance at stake and if you deviate from the specification without authorisation the consequences might not be pleasant.

Steve Jones
Materials & Corrosion Engineer

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