SS threaded valves on CS piping 1

[scotty36]

We have specified SS treaded valves to be installed in CS systems on a large sugar project. Many of these are in aqueous service. We were trying to standardise our valves as much as possible. The pressures are minimal and the fluids are non-hazardous. The valves are all less than or equal to 2" size.

In specifying this, I spoke to all the people that I could and nobody objected. It seems that the sugar industry do all sorts of 'agricultural' things in thier piping systems.

However, now I cannot sleep at night thinking about how this will be recieved during construction - dissimilar metals and all.

Can anyone let me know if they have seen this in other process plants - particularly sugar?

 

[quark]

There won't be any problem and I have been doing that(non sugar industry). But threaded valves...I really hate them for those sizes.

 

[JStephen]

We have built water tanks where the consultants required stainless steel items to be welded to the carbon steel tank. Evidently, not as big an item as it's made out to be.

 

[TD2K]

The corrosion potential between SS and CS is not that large so I wouldn't see a problem for a service like this.

 

[Montemayor]

scotty:

I have joined stainless and carbon steel countless times in the field and for different reasons and fluids; I never witnessed nor heard of any corrosion or metallurgical problem in these applications.

However, I believe you have cause for some degree of worry when using screwed stainless steel valves. Stainless steel inherently galls - especially when combined with mating stainless threads. This is a well known "trade-off" characteristic of stainless - including stress corrosion.

My advice would be to make sure your pipefitters are well trained in applying Teflon paste (I wouldn't use the tape) correctly in order to alleviate the galling - this is assuming the paste is acceptable to the process and as a possible contaminant. Like Quark, this is what I hate about being forced to employ screwed fittings in today's era of high purity and quality expectations from produced and processed fluids. This is like asking to have your cake and eat it too. You are correct in expecting to have problems with screwed fittings when challenged to produce competitively in the 21st century.

It seems the Sugar Industry is still operating in the 19th century - much as I found it when I first had experiences in it in the 1960's. Good Luck.


Art Montemayor
Spring, TX