PWHT for CS equipment fully clad with SS316 in Amine Service

[SurajTinani]

API RP945 does not cover SS equipment/piping in amine service. Hence the question is whether PWHT is required for CS equipment/piping which is fully clad with SS316L and handling Rich amine service or would the velocity restrictions (less than 3 m/s or 10 f/s) suffice?

Maximum operating temperature ranges from 80-100°C and chloride is restricted below 50 ppm by use of wash water. Thanks.

 

[CoCoE]

Of course not needed. No meaning of doing PWHT on the material which is not coming under contact.

 

[EdStainless]

The CS fabrications are PWHT as needed, and then you overlay.
Any PWHT after overlay will sensitize the 316 and greatly reduce its corrosion resistance.

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P.E. Metallurgy, Plymouth Tube

 

[metengr]

First, the article below demonstrates the need for PWHT of carbon steel weldments exposed to amine service.

https://books.google.com/books?id=q...or carbon steel pipe in amine service&f=false

Why bother to clad when you can perform PWHT of butt welds and eliminate the risk of SCC? Seems like a much simpler approach than going to the expense of adding a corrosion resistant overlay (CRO) to avoid PWHT.

If you need to use a CRO, I would suggest you deposit a butter layer of 309, PWHT and add two layers of 316 SS to achieve a CRO.

 

[sk10009]

PWHT is not necessary because Carbon Steel doesn't contact with an amine service. However you should consider using 316ss lining in chloride SCC environment.

 

[Guest102023]

I concur with metengr's proposal for SS overlay, and I want to underscore that THREE and not two layers are needed to achieve full alloying in the top layer. Lots of folks (including some welding engineers I have butted heads with) wrongly believe it can be done in two.


"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[SurajTinani]

Thanks for your posts!

EdStainless - We're probably going with Hot Roll Bonded SS 316L plates (3 mm) and then weld them together so PWHT cannot be done beforehand. Besides PWHT is inevitable if required by code so we're ensuring that IGC testing is done for corrosion resistance.

Metengr - I would agree on using CS with corrosion allowance in lean amine service with pwht. But what about rich amine containing high H2S (but below the pH2S limits of ISO 15156) & CO2 in vapor phase? The Client requirement is SS cladding and we as a Contractor are obliged to do it.

Regards,

Suraj Tinani

 

[EdStainless]

When you use SS clad plate you need to use CS that does not require PWHT.
Or you chose to not do it since it is not the wetted surface.
You have a lot of weld qualification to do to show that you can get full corrosion resistance on the inside.
You also will be doing some UT after fab to verify that you didn't get any disbond, right?

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P.E. Metallurgy, Plymouth Tube

 

[CoCoE]

SurajTinani,

How have you made up your mind finally??
Considering high H2S and CO2 concentration in Rich amine service, 316 cladding will definitely be the cheapest selection since your chloride concenration in amine recovery is below 50 ppm. For using CS, the velocity of your rich amine service is above limit and not seems to be prudent in using that.

CoCoCa

 

[EdStainless]

What is the temperature of the service? Under 600F?
Has anyone looked at building this entirely out of a lean duplex alloy?
The strength is high, the walls would be much thinner, there would be less metal, faster welding, and no overlay or PWHT.
Just a thought.

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P.E. Metallurgy, Plymouth Tube

 

[SurajTinani]

Thanks for the follow up posts CoCoCa and EdStainless! Yes SS316L is considered for the service and since this is just a single clad equipment below 38mm thickness, we're doing PWHT. EdStainless - Lean Duplex was being considered but has fallen out of contention due to lower pH2S limits per Client Specification.

Regards,

Suraj Tinani