Stress Relieving for Pressure Vessel Head with Clad material

[azmirosman]

Dear All,

Good Day.

I need your guidance on the require testing and precaution when dealing with clad material normalizing.

Basically i'm dealing with one project which the head of the vessel need normalizing due to fiber elongation exceed the acceptable limit.

I'm requesting from contractor and vendor on the heat treatment procedure and the procedure was prepared as per clad plate mill certificate temperature and cooling rate.

My question:
Is there any guideline or precaution or any testing require after the heat treatment to check the condition of the bonding or clad material itself.

Edit:

Base Metal is Sa 516 Gr.70 (30mm) with SS316L clad.Fiber elongation calculated is 7%.

I don't have any experience on this.

Appreciate your response

 

[SJones]

1. Bonding: A263/264/265 Class 1
2. Material condition: Dependent upon the cladding alloy, normalising might not be the correct heat treatment. Dependent upon the function of the cladding alloy, some form of quality control corrosion testing could be required. For example, an N06625 cladding for corrosive service in oil and gas might require an ASTM G28 Method A test with an acceptance criterion of maximum corrosion rate 0.91 mm/year.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[david339933]

Fiber elongation does not require normalizing.

 

[azmirosman]

Hi Steve,

The material is SA 516 Gr.70 with SS316 Clad.
Actually i'm looking for any NDT that i should request to fabricator to conduct after stress relieve.Plate mill advice to heat until 950 degree for 30minutes and cool with air naturally.

There is concern from end user on the integrity of the SS316 part (crack,sensitization etc.) as well as to check any defect on the bonding area after stress relieve.

Thank You

 

[EdStainless]

The two big issues here are metallurgical damage to the 316L (usually sensitization) and problems related to the 2x difference in thermal expansion causing bond strain.
The most straightforward test for the 316L is A262, and it is typical to require the Practice E immersion test.
Controlled and slow heating and cooling are needed, rapid cooling will cause higher stresses than you have now.

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P.E. Metallurgy, consulting work welcomed

 

[david339933]

950 degrees? You are either too cold or way too hot, depending on F or C. Are you confusing stress relief with normalizing?

 

[azmirosman]

Hi David

It is degree celcius.

It is stress relief.Not normalizing.

Wrong title.

Thanks

 

[david339933]

Then you have to follow UCS-56. Normal temp is 595C. There are restrictions on heating and cooling as well. Mill gave you normalizing temp. and cooling.

 

[weldstan]

As david stated above, the required stress relief of a cold formed head that exceeds 5% strain is per UCS-56. How was the cladding applied? Explosion? Rolled? Weld overlayed? Clad vessels are often subject to PWHT.

 

[azmirosman]

Hi Weldstan.

This head is cold formed and EFE is more than 5%.

Head thickness after form is 28mm.

Clad is explosion bonded type.

And this vessel not subject to PWHT (Not by thicknes and service)

Only need PFHT due to EFE exceeded 5%.

Actually,i'm going to challenge my vendor and main contractor that their proposed temperature (900 degc to 950 degc for 30minutes holding time) is too high.

I'm going to suggest to them the temperature for stress relieve will be 600degc to 700 degc.My basis is UCS 56 given min temperature around 600 degc.And to avoid sensitizarion for clad part ,not to exceed 800 degc.Still studying.

Any comment much appreciated

Thanks

 

[david339933]

Holding time is 1 hr/inch, basemetal.

 

[SJones]

Whatever you sort out, still run the QC corrosion test

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

A max of 700-725C should minimize the sensitization.

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P.E. Metallurgy, consulting work welcomed

 

[weldstan]

This is not so uncommon. Do UT check for disbondment before and after SR.