Bolting 316L to inconel 625 ?

[Henderson17]

Just want to pick the collective brains.

We are currently in design phase for some internals to be installed into a Inconel 625 weld overlayed vessel (gas scrubber service). Our intenals are typically 316l, bolted with A4 grade 316 bolting.

Are we ok to use the A4 bolting direct to the Inconel lugs on the vessel from a corrosion point of view?

Many thanks,
Scott

 

[strider6]

Galvanic corrosion is the only issue i can see, but Alloy 625 and 316L, in passive state, are very close in the galvanic series so in my opinion this should not be a problem. It also depends on the fluid inside the vessel, if is not possbile that a water phase, or another electrolyte, will be present that i don't see any possibility of corrosion.

hope this help

S.

http://www.corrosionist.com

 

[Henderson17]

Thanks S,

That is what I was hoping to hear.

The vessel will be seeing very little fluid and by this point of the process train it really should be oil as opposed to water.

many thanks.
Scott.

 

[EdStainless]

I have always felt better using fasteners of the more corrosion resistant grade.
If your system stays dry then you should be fine, but any moisture in these connections and the 316 bolts could fail fast.
Would it kill you to use 625 hardware?

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Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[Henderson17]

Thanks Ed,

Its not really my call.

We sold based on 316 and therefore all I can do is make the technical case for a change and see if the project will suffer the subsequent financial impact.

Our kit most definitely shall not be changed to Inconel 625 (too much to ask cost wise) so I would hasten to guess that the risk would simply move further up the chain from bolting/lug to bolting/internal.

Scott.

 

[mshimko]

I do not recommend SS fasteners.

From work I had done a decade ago (seawater immersion, mind you), I found the "closeness of two materials" on a galvanic series to be very misleading to many, especially when two passivating materials are involved (it didn't take much for one material to depassivate locally).

I recommend seeking a more noble fastener, maybe titanium, but I think the cost may force you to say with the CCRES.

 

[unclesyd]

If the 316 SS internals hold up bolting shouldn't be a problem.

As stated above you shouldn't have any trouble with 625 with 316 fasteners. We used a similar combination, 600 and 316 for many years without any problems in a extremely corrosive service. This process required that the equipment be steam cleaned about every 72 hrs, so the fasteners would see a different corrosive environment for about 8 hours. There was never any corrosion noted in the system over many years operation.

We use both 304SS and 316SS fasteners by the ton in contact
with our process.

 

[SJones]

Who has actually specified the vessel materials and on what basis? If the owner wants a 625 clad vessel, why do they, or anyone else, want to put less corrosion resistant material into the system? Is 316L being offered because it is a 'typical material'?

Steve Jones
Materials & Corrosion Engineer

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

 

[Henderson17]

Hi all- thanks for all your replies.

Steve

The Client specified the material for the vessel and the internals.

The internals are designed to be removable and therefore replacable.

There life span is considered to be less than that of a vessel regardless of material, as they will most probably be optimised during the lifetime of the well to accomodate changes in production.

For this reason clients tend to opt for them to be made from a less resistant material than they would accept for the vessel.

Thanks Scott.

 

[strider6]

is not so unusual to have SS316L internals inside a vessel cladded with 625 Alloy.
I've seen it in many of our vessel in oil & gas production.

S.

http://www.corrosionist.com

 

[macmet]

Could you coat the bolts? We had a guy stop by and he was pushing a new coating technology for bolts to replace the need of stainless and other high grade materials.

I have no experience with it myself.