SS Piping

It's a lot easier to thread the joints. Welding SS pipe is a pain in the azz. If you decide to thread, remember to tighten joints, wait 3-5 minutes, and re-tighten before next section. SS pipe has a way of breaking seal due to the difference in wall thickness between fittings and pipe. Think thermal expansion/contraction.

Thank you for the information, yea welding seems difficult. So better to go with threading. But these lines are mainly for hot and cold water conveying , so whether the expansion / contraction is an issue..?

What is it conveying? Are you sure this does not have to be sanitary piping? Threaded 304 SS has a definite tendency to gall. How is similar piping in the plant installed?

Mainly water & air. Three lines are for water ( hot, cold and normal water) & one line is for compressed air. Yes for sure it is nothing related to sanitary purpose. It is a new plant and so no other lines are there at present.

My experience with threaded 304SS hasn't been good - leaks at the joints and then you can't disassemble the joints because they have galled. And unions are very difficult to get leak tight. I visited eng-tips.com and the experience there seems to be similar. Their recommendations:

1) Use an anaerobic joint compound such as Loctite 567 instead of teflon tape.

2) Consider flanges instead of unions.

3) Use welding instead of threads above 2", and maybe on 2"

4) Consider tubing for the 1/2" and maybe 3/4".

I know this sounds extreme, but you may want to make a few test joints and pressure them up before you go too far, with the largest size you intend to thread. Even threading SS is different from iron pipe. Maybe pennpiper will jump in with his wisdom.

Good advice. Flanges add more cost, but are probably worth it overall.

Loctite may not be allowed, depending on the purity levels required.

Ya, Loctite 567 not suitable for potable water.

This sounds like it might be your first time dealing with SS piping. Chances are good that your client may have done this before and may have a preference of one joining method over the other.

Welded joints are more reliable. Threaded joints are cheaper to produce. But more unions should be used to assist in repairing the leaks that will come later.

Ask your client what he prefers.

This should have been resolved before the quote was completed. It will affect the piping costs.

If the piping carries foods or ingredients, it probably needs to be welded and joined with "3A" type sanitary sittings; most likely it would be tube rather than pipe, relatively thin-walled and suitable for TIG welding.

If the piping is for utilities such as air, threading may be fine, with the caveats already mentioned.

You will find there are 2 specific problems with threaded ss pipe- galling & leakage.

I did a bunch of runs in our plant & welded as much as possible (1" & 1-1/2") because it was carrying surfactants etc. that leak even worse than water. If there is any sort of wetting agent in the material being conveyed it's a real pain. If you do thread it I advise making sure the dies have SS specific cutters in them. Another thing that makes a difference is to step up from the regular 150lb fittings- I've had success with forged fittings where the other ones leak all the time. The 5 minute relax/ retighten sequence mentioned in a previous post can also help.

You don't have enough information.

Talk to your customer, you have to realize its may not only be about costs. If you put in thread the delta P increases, affecting pump Size, as cape pared to a flange or welded joints.

Since you have taken on this without even knowing, best you discuss this with the customer. Because will affect the system load balance.

You may want to check out Victaulic fittings.

Very good grooved pipe fittings.

Leak proof. Rugged.

https://www.google.com/search?q=victaulic+fittings+fro+sanitary+use&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a

Another product line to consider is the "Pro-Press" line of fittings by Viega. The expense of the product might be offset by the speed of assembly. It was originally promoted for copper, but has expanded to black iron and SS piping.

Since the welding is for Food Processing Industry, I suggest you go for Orbital Welding an extremely elegant and neat joining process.

Process : Modern orbital welding is computer controlled process with the skills of the certified welders built in and enables welding of enormous number and varieties of identical welds with very little room for errors. It has mechanism to rotate a weld arc from tungsten electrode around a tube weld joint, regulated weld current with control system automating the entire process.

Advantages: Especially suited for joining Stainless Steels 300 tubes used in food and beverage industries where consistent weld with smooth surface is a prerequisite to avoid pits crevices and cracks which can harbor bacteria.

This welding though high technology is commonly available nowadays and can be easily outsourced.

Thanks a lot for your valuable suggestions & advice !! Indeed it helps me a lot. I had a discussion with the contractor yesterday and they suggested us to go with threaded joints up to 2" diameter pipes. We would cross check these points with them before going further ahead.

In order to meet sanitary standards, the pipe joints are usually clamped sanitary flanges with Teflon gaskets. The flanges are welded to the tubing and then polished.

McMaster -Carr has a selection in their catalog and I used to buy in bulk from Andron.

Not necessarily. Depends on which sanitary standards you require. USDA, 3A, FDA. Which depends on the type of process and the inspector.

I worked with a USDA inspector in California, when I designed and built a HTST pasteurizer. Followed USDA-3A specification. And he discounted it. Said he uses FDA specs. :/ and that i should have known that, wtf.

Hi

We do a lot of this, Depending on the pressure up to 10 bar for up to 4" we use Tube purged tig welded not hard very clean and simple and use BSM fittings (could use other unions eg RJT) for any unions/ joints that are needed. For air any take offs come out of the top of the pipe line and dont forget water drain off points at the low points in the line. Place a valve at every branch so as maintenace can be preformed while the main line is still live. This will be far far cheaper than any threaded pipe a lot cleaner and will look like a million dollars when completed. Dont forget to label with the drection of flow and the international colour code for the product being conveyed

That sounds good. So what about the joint sealant that is to be used..? Any suggestions for food processing plant..?

With BSM unions or RJT they use an o-ring type gasket usually EPDM but as most are made for the dairy industry the gasket compound has to be approved for food, so unless your product has a reaction with EPDM (need to check, you will be ok).

Unions are welded direct to tube so no threads there, But if you have any threads eg depending on your choice of valves, plumbers thread tape OK for potable water, just check your product is OK no reaction with the thread tape

To have a food processing operation without having associated piping standards for Engineering to follow is a bit like having a road network without a Highway Code.

So, obtain a copy of the Client's piping standards, and follow them.

Some customer that I have worked with would not have piping standards, while others have standards that are 2 inches thick.

The biggest is to conform to the governing agencies that specify the standards that need to be held.