Super duplex stainless steel 1

[Indy]

Hello,
I have a( maybe silly) question about duplex stainless steel. If we have a psv valve spec and the body is SA995 Gr6A/ UNS JN99380 and the nozzle is super duplex. Are these the same material ie both nozzle and body are the same,super duplex stainless steel?

Thanks

 

[bobjustbob]

We refer to SA995 6A as superduplex, however, without a certification on the nozzle you cannot be sure of the actual material.

Bob

 

[Indy]

Thanks for this. So to confirm the material is super duplex, it would need to have a positive material identification (PMI) test?

Thanks

 

[EdStainless]

You need to get your UNS correct, one letter and 5 numbers.
And I hope that you have requirements for testing the metallurgy, these alloys can be made wrong in multiple ways.

Super duplex is a 'common term' without a firm technical definition. It is usually take as a duplex SS with a PREn >40 (usually Cr + 3.3xMo + 14xN)

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P.E. Metallurgy, consulting work welcomed

 

[Indy]

Thanks. So we need to confirm the nozzle is UNS relating to duplex stainless steel?

Thanks again

 

[bobjustbob]

PMI is not going to tell you the whole story on a superduplex. If it is critical that the part be 6A then you need a material test report from the supplier certifying the part to 6A. PMI is just going to tell you that the major elements match to the specification. It will not give you carbon and nitrogen. Carbon and nitrogen are important elements in 6A.

Bob

 

[EdStainless]

C and N are important in all duplex grades.
You will need the MTR for the chemistry as well as confirmation that the HT produced the correct balance of austenite and ferrite, and that the structure is free from intermetallics (by corrosion test or low temp impact test).

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P.E. Metallurgy, consulting work welcomed

 

[chrysa1975]

Dear EdStainless, the requirements are included in the SA995? Or they are from your experience?

 

[bobjustbob]

Basic SA995 6A does not require a ferrite point count or corrosion test. It does not even require an estimated ferrite by A800 but we supplied that at minimum. Rarely did I ever see a valve made to 6A not have a corrosion test and point count included in the requirements.

Bob

 

[EdStainless]

All of the major oil/chemical/refining companies that use these alloys would have those requirements (A923 for example).
Besides, if you can make a good product then it is just the costs of the tests. I can't see a high quality producer not doing these as internal controls.
And if you make crap you would try to hide it.

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P.E. Metallurgy, consulting work welcomed

 

[Indy]

Thanks for the replies. Can I also ask what the difference between A182 s32760 and Sa479 UNS 32760? In relation to valve internals?
Thanks

 

[EdStainless]

Other than Code coverage?
They could be the same material, but they could also be made by different working processes.
I am unsure if the NDT requirements are any different.
they do have the same chemistry and strength.

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P.E. Metallurgy, consulting work welcomed

 

[Indy]

Thanks,
What is the difference between A182 and A479?

Thanks again

 

[XL83NL]

@I de, do you own a copy of said standards?

Huub
- You never get what you expect, you only get what you inspect.

 

[chrysa1975]

Dear Indy, with a common search in internet you will see that ASTM A182 is forged while ASTM A479 is a bar material. Furthermore SA prefix denotes materials listed in ASME II for vessels. If we would want to correlate with valve internals, then a simple approach is that the forgings are usually the ball/disc/gate and seats, and the bar material is for the stem.

 

[EdStainless]

While we think of A182 as forgings and A479 as rolled material, they could both be met using hot rolled material. This largely depends on product form required for each part. We supply hot extrusions to both specs for example.

ASTM A182 / A182M - 20
Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service

Abstract

This specification covers forged or rolled alloy and stainless steel pipe flanges, forged fittings, and valves and parts for high-temperature service. After hot working, forgings shall be cooled to a specific temperature prior to heat treatment, which shall be performed in accordance with certain requirements such as heat treatment type, austenitizing/solution temperature, cooling media, and quenching. The materials shall conform to the required chemical composition for carbon, manganese, phosphorus, silicon, nickel, chromium, molybdenum, columbium, titanium. The material shall conform to the requirements as to mechanical properties for the grade ordered such as tensile strength, yield strength, elongation, Brinell hardness. All H grades and grade F 63 shall be tested for average grain size.


ASTM A479 / A479M - 20
Standard Specification for Stainless Steel Bars and Shapes for Use in Boilers and Other Pressure Vessels

Abstract

This specification covers hot- and cold-finished bars of stainless steel, including rounds, squares, and hexagons, and hot-rolled or extruded shapes such as angles, tees, and channels for use in boiler and pressure vessel construction. Four grades of the stainless steel are available which includes austenitic, austenitic-ferritic, ferritic, and martensitic grades. Mechanical properties such as tensile strength, yield strength, elongation, and hardness shall be determined for the specimens subjected to normalized, tempered, annealed, and quenched conditions. The austenitic stainless steels shall be subjected to heat treatment and shall undergo corrosion test.

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P.E. Metallurgy, consulting work welcomed

 

So to confirm the material is super duplex, it would need to have a positive material identification (PMI) test?

PMI is at best a screening test that can discover that your composition is incorrect. PMI is NOT equivalent to proper chemical analysis and therefore it does NOT confirm that the composition conforms to the material spec.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

If you have material that is marked properly (all of the info) and the MTR that goes with it then you can use PMI confirm that you have the right piece. But if for any reason you have questions then real chemical analysis is needed because you will need C and N, and precision matters.

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P.E. Metallurgy, consulting work welcomed

 

[MJCronin]

Did you have a competent Valve engineer review the vendor print before purchasing the valve ?

Did he accept a vague material description such as "Super Duplex" in the material description column ???

I have reviewed many, many vendor drawings and would never accept general phrases such as "SS" "Steel" or "Carbon steel" in the material description box for the component.

The vendor knows what he is buying and most often, has hired a lazy drafter who doesn't like to print out the complete ASTM or UNS Material description ....

Do the Job Right !!!!

MJCronin
Sr. Process Engineer

 

I have reviewed many, many vendor drawings and would never accept general phrases such as "SS" "Steel" or "Carbon steel" in the material description box for the component.

Reading 'stainless steel' in a tech spec or on a drawing has been the bane of my work existence. (Well, that and dysfunctional management.)

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."