Ferrite Count for overlay for pressure vessel clad.

[azmirosman]

Dear All,

Good Day.

I would like to request your opinion regarding the ferrite count on the weld overlay.
Currently, I am involved in fabrication of3 units of pressure vessels made of SA516 Gr. 70 clad with SS316L.
As per my company's requirement, the ferrite content shall be as below:

The ferrite content of the weld overlay of the production welds at a depth
of 2 mm shall be determined to the following extent:
- One analysis per course; one analysis per each head and one analysis
for each nozzle.
The ferrite content shall be between 3% and 8%.

The overlay area are at all area that having CS to CS weldment such as nozzle flange face, nozzle to shell joint and shell to shell joint (capping)with 3.5mm thick.

As per current inspection result, many of the ferrite content reading is exceed 8% (Ranges from 8.5% to 11.5%).

Because this vessel's design temperature is only 120 °C and it is only 27 mm thick plus 3 mm of cladding (no PWHT or impact test), our fabricator requests that all points with reading areas less than 12% be accepted.

I need to convince my technical authority to accept the reading, but I need a basis to explain it to them.

Really appreciate if anybody can advice if this situation can be accepted.

Thank You

 

[SJones]

No 309LMo first layer? You need to find out the specific thinking behind the ferrite restriction: is it for cracking resistance, corrosion resistance, both.

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]

With one pass overlay 3-8% is way too tight. I would expect to hit that with a two-pass system.
Heck, I see flat rolled 316L product in on the market that is over 8%, 10% isn't too uncommon.
But it does lead me to ask, didn't the weld overlay qualification tests include this test?
How did they pass?
I am not sure what lower F gains you in these conditions.
I can't think of what harm a 12% cutoff would have.
Now if the service was at all acidic (even slightly) then 3% would be too high.

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P.E. Metallurgy, consulting work welcomed

 

[Dhurjati Sen]

Following are your options:

1. Take a Deviation. Of course, the client may not approve it.

2. Remove the welding and re-weld. Use mock-ups to ensure that ferrite content is within limits.

3 Perform localised solution annealing followed by quenching to set right the ferrite.

If I were you, I would have gone for No 2.

DHURJATI SEN
Kolkata, India

 

[azmirosman]

No 309LMo first layer? You need to find out the specific thinking behind the ferrite restriction: is it for cracking resistance, corrosion resistance, both.
Yes .There is 309LMo at 1st layer and this is for corrosion resistance.

But it does lead me to ask, didn't the weld overlay qualification tests include this test?
Yes,they pass the qualification with 7.2% which was within the range.

2. Remove the welding and re-weld. Use mock-ups to ensure that ferrite content is within limits.
Since the layer of overlay is 3 mm which very thin,any precaution that i need to aware during repair work.I afraid that grinding work will affect the CS welding underneath the overlay.And any Re-RT is require for the repair joint?.

Appreciate your advice.

Thank you.

 

[SJones]

For what specific purpose is the ferrite restriction being detailed?

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.

 

[Dhurjati Sen]

Use pencil grinder.

DHURJATI SEN
Kolkata, India