galvanised bolts with ss flange

Yes,you can use provided

1 Flanges are raised face flanges

2 Fluid flowing through is not highly corrosive as in case a leakage which can not be noticed easily may errode the bolt causing a bigger leakage due to bolt failure

I'll try and answer yours if you try and answer mine. Okay? Here we go.

Can I cut a material using carbide? The material weighs 7 kilos. Please tell why or why not.

So you go first.........

Yes CR3, you CAN cut a material using carbide. But only if you cut it lengthwise and use a speed that isn't too fast. Also ... and this is extremely important ... be sure to start your cut on the first edge, and work toward the third. Never the reverse. That could result in losing a finger or even an eye. The weight is also very important. Your material must be light weight. Otherwise, once again ... finger or eye.

Follow those rules, and you're good to go. Cut away!

I hope this clears things up for you!

Can we? Yes.

Should we? no.

Reason, Galvanic series. This is taught in chemistry, metallurgy, and materials science courses.

MAy be a very long time to failure in dry atmosphere, but it is a known failure method.

Just cause something is cheaper doesn't make it a best practice.

milo

Maybe you have anticipated what guest 1 already had in mind?

If there is a reason to use SS as the flange material, then the same reason exists to use SS bolts. If SS flanges are not critical, but were merely "on-hand", then you run less of a risk (but still a risk) if you use galv bolts. As Milo said, galvanic reaction. This is a subject that is not cut and dry. Galvanic reactions are a fact. But they are also rather slow in occurring (usually). So it depends on your application. Will a long term failure rate be a critical failure in your situation? Or will slowly corroding bolts not be an issue in what you're doing?

It's all relative. And all speculation at this point, from this end... as you've not provided all of the information needed for us to give you a more definitive answer.

It depends on what is flowing through the pipe.

You can use even cs slip on flanges with SS stub for economy.Design engineer's decision?

Ratnagiri

You can add fiber, nylon or plastic washers to the bolts to reduce the surface contact between the ss and galvanized bolts. Also a sleeve on the bolt through the ss flange to keep the galvanized bolt from coming in contact wiith the ss.

Yes you can, taking into consideration to isolate the galvanized stud bolts ( bolt with 2 nuts) with nonmetallic material, not only to avoid corrosion due to leakage, but also to prevent contacting of dissimilar metals and establishing a corrosion cell in presence of moisture.

if corrosive fluids are handled then you should not use galvanised bolts.

Sure you could; but why would you? You used the word "flange" which is singular-is one (1) mating flange constructed of stainless-steel and the other mating flange of normal steel or iron? Are both mating flanges constructed of stainless-steel? I presume if they are it is because they are involved in the transport of a corrosive liquid or gas.

If both flanges are constructed of stainless-steel, there must be a reason for this and why would you damage the integrity of a stainless-steel flanged joint by using anything but stainless-steel fasteners? I mean; why be a cheapskate at this point? The fasteners used to assemble a flanged joint are very much a part of it, and play a vital role in its success.

Regards,

Ing. Robert Forbus

Hi

can use. But, it depends on your client's spec: and requirement.

You can use galvanised bolts with SS flanges but:

1. The bolt must have the same capacity (high strength for instance if required)

2. What is inside the pipe is not as important as the outside conditions. If you have an aggressive environment rather use SS bolts. If you have a humid condition you could have galvanic corrosion between the bolt and the flange.

Please remember that bolts need lubrication to torque to a specified torque!!

Lubrication also prevents ingress of moisture into the threads.

Who?... What?... Lubrication?

When bolting together I'm relying on deformation and friction to keep my fasteners tight. When trying to maintain a specific torque, I don't apply lubrication. On the contrary...

Who among you ........... applies lube?

I apply lube. But we are definitely talking of different applications.

Lubrication is essential. What is important is the elastic tension in the bolt and not the friction. To keep two items together or to seal a surface you require a specified force. If you torque against friction you have no idea what the tension is that you are applying.

It is good practice to use lubrication when tightening bolts. An anti scuffing or copperlube type is usually preferred but if nothing else use grease.

With the correct torque enough friction still exist to prevent loosening of the bolts.

Without lubrication chances of the thread picking up is great and probably you will not be able to loosen the bolts after a while due to corrosion in the thread.

A vibration resistant fastener uses increased frictional forces to prevent nut loosening where a vibration proof (positive-locking) fastener actually uses a physical stop or barrier to prevent nut loosening. Google "positive-locking fastener" to learn more.

I am troubled by the different answers here.

I would have answered you can, but should not (different potentials of metals), but I do not know what the different potentials are.

Before reading this thread I tried to find the materials on a listed series, but no luck.

SS was listed about 20 different times in different locations based on the composition, but I never found galvanized steel (which is what I imagine is what is meant with the mention of galvanized bolts).

Does anyone know what the potential difference is, and where I can find a good reference for this series?

Thanks!

You should look up Zinc not galvanised steel as the steel is coated with zinc.

The potential is thus between ss and zinc.

Galvanising is being done with zinc, tin and cadmium of which zinc is the most common.

Galvanising can be done either by hot dip process into molten zinc or by electroplating.

Cadmium and tin is mostly electroplated.

You can also get silver plated SS bolts, which prevent galling. I also use lube when torquing non-permanent flanges such as temperature of pressure vessels. This also helps to prevent galling.

Zinc is the metal in the galvanize, that would be the pair, Zinc and Stainless.

milo

In the short term, pending the arrival of the correct <...SS...> bolts and nuts, maybe.

Woe will ensue if the process fluid, the nature of which, the temperature of which and the pressure of which have been withheld from the forum, should leak from that joint in that period. A satisfactory and safe method of changing the bolts must be available at the due time.