L7 bolting on A182F51 flange

[mariolucas75]

Dear All,

There are bolts installed on duplex SS flange A182F51, which started corroding...
Bolts are having marking L7 which as I found out is A320 material... what material is that (different resources say different thing - Alloy and SS)?

And the main question - Are these two compatible in terms of dissimilar metal corrosion .... or where i can find a reference what "family" bolts are compatible for such and such flange for example .. ?

Thank you so much

 

[akpipelineengr]

L7's are alloy. A320 covers some stainless grades as well.

[URL unfurl="true"]https://www.portlandbolt.com/technical/specifications/astm-a320/[/url]

You could be getting galvanic corrosion if this flange/bolting is exposed to the elements. Isolation kits would disrupt the galvanic circuit, or you could try a more compatible grade.

 

[The Obturator]

A320 L7 - A low temperature service, charpy impact tested alloy, was often used as the fastener material for duplex stainless steel valves. However, it was nearly always specified to be hot dip galvanised. The alternative was to use comparable duplex bolting, but the cost was much higher.


*** Per ISO-4126, the generic term
'Safety Valve' is used regardless of application or design ***

*** 'Pressure-relief Valve' is the equivalent ASME/API term ***

 

[r6155]

Any photo?
Regards

 

[mfgenggear]

Op
Any history of clean, passivate
Maybe contamination

 

[GD2]

OP,
Why don't you use the duplex bolts - ASTM A1082? It has decent corrosion resistance and can match Duplex 2205 and Super duplex 2507.
A320 L7 is a low alloy steel bolt and obviously can't stand the corrosion resistivity of Duplex steel.

GDD
Canada

 

[EdStainless]

Thanks GD2, there is no reason not to use duplex bolts/studs/nuts/washers.
The cost of these parts is trivial compared to a shut down in order to do it over again.

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P.E. Metallurgy, consulting work welcomed