Stainless steel bolts in carbon steel plates
Stainless steel bolts in carbon steel plates
(OP)
Hello everybody:
The Hydroelectric Power Plants have, among their auxiliaries, the hydro mechanical equipments such as: trash racks, inlet gates, draft tube gates, bulkheads and stoplogs.
In a general manner, the gates (skin plate, girders, trunnions girders, wear plates, struts, end frames) are manufactured with structural steel ASTM A36 or ASTM A572.
For seal plates and bolts, the material is 304 stainless steel.
In this context, with stainless steel bolts and nuts it exist a small cathode area relative to a large anode area (the structural plates) and a bimetallic corrosion should be a minor issue in the absence of an electrolytic; but, in the environment of hydropower plants, besides the occasional immersion, the rain water or the humidity of the air acts like an electrolyte.
From the document "Design of Spillway Tainter Gates", page 8-1
(U S Army Corps of Engineers. Engineering and Design. EM 1110-2-2702 1 January 2000) it can be read:
"......Where dissimilar metals are in contact, rubber gaskets or equivalent insulators should separate them. Generally, this is not necessary for stainless steel bolts, because the area of contact between the bolt and structural steel is very small".
Is it or is it not necessary any insulation (paint, polymer, etc.) to avoid the direct contact between the threads of these materials?
Thanks in advance for your comments.
The Hydroelectric Power Plants have, among their auxiliaries, the hydro mechanical equipments such as: trash racks, inlet gates, draft tube gates, bulkheads and stoplogs.
In a general manner, the gates (skin plate, girders, trunnions girders, wear plates, struts, end frames) are manufactured with structural steel ASTM A36 or ASTM A572.
For seal plates and bolts, the material is 304 stainless steel.
In this context, with stainless steel bolts and nuts it exist a small cathode area relative to a large anode area (the structural plates) and a bimetallic corrosion should be a minor issue in the absence of an electrolytic; but, in the environment of hydropower plants, besides the occasional immersion, the rain water or the humidity of the air acts like an electrolyte.
From the document "Design of Spillway Tainter Gates", page 8-1
(U S Army Corps of Engineers. Engineering and Design. EM 1110-2-2702 1 January 2000) it can be read:
"......Where dissimilar metals are in contact, rubber gaskets or equivalent insulators should separate them. Generally, this is not necessary for stainless steel bolts, because the area of contact between the bolt and structural steel is very small".
Is it or is it not necessary any insulation (paint, polymer, etc.) to avoid the direct contact between the threads of these materials?
Thanks in advance for your comments.
El que no puede andar, se sienta.





RE: Stainless steel bolts in carbon steel plates
RE: Stainless steel bolts in carbon steel plates
If you have locations that only get wet occasionally then you can have a situation where all of the steel corroding is under the bold heads resulting in loose connections. In those cases coating the SS bolts would be a good practice.
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Plymouth Tube
RE: Stainless steel bolts in carbon steel plates
The organic carrier and metal dust therein may affect the real outcome associated with your theoretical considerations.
Mike Halloran
Pembroke Pines, FL, USA
RE: Stainless steel bolts in carbon steel plates
The wording in the COE document is deceptive and should be studied very carefully - the words "equivalent insulators" is the catch phrase. Even if you have a gasket, if you have a noble and sacrificial metal in close proximity and the ability for an electrical circuit to complete between them, the ions will flow through the electrolyte.
So unless you are able to completely isolate the two from each other electrically, gaskets, etc are band-aids not solutions. Where this is absolutely necessary, there is specialized equipment to accomplish this. Trust me, you don't want to go there for your application.
rmw
RE: Stainless steel bolts in carbon steel plates
As always, the cavalry of the forum to the rescue.
Once again, I very much appreciate the kindness of all of you by giving your opportune comments. Thanks.
El que no puede andar, se sienta.