Material for Instrument Tubing 3

[nickypaliwal]

The piping classes are Duplex SS and Super Duplex SS. Can we use SS316 tubing for instruments as DSS/SDSS tubing are not available in market and the next higher grade for tubing available in market is Inconel 625 which is not locally available and will cost heavily.

Service is water injection with high chlorides and also hydrocarbon with H2S and chlorides.

Note: Instrument tubing discussed are only used to drain the fluid when DBB valves are opened. These are connected to the flanges and are used with instruments suchas pressure gauges.

 

[EdStainless]

You are asking for the risk of chloride stress corrosion cracking if you use 316.
You are using SDSS for a reason, the instrument lines should be equal of better.
"C" (276 or 22) tubing is also generally produced.
Yes, it is expensive. But what will failure of these cost you?

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Many operating companies have switched out to grades other than 316 / 316L for instrumentation tubing due to low Mo content (<3-3.5%) / low pitting resistance. Recall some of these other grades are 6Mo SS, AL-6XN, tungum(UNS C69100). See which suits you and the service application. Tungum cannot be used in mercury bearing fluids.

 

[EdStainless]

goerge, actually 316 has a min Mo of 2%, and given the price of Mo you have to pay for a heat lot in order to get anything above 2%.
While 6% Mo tubing has been used it is all custom made and I don't know of anyone stocking it. That is why I suggested a "C" alloy.
Withing the next 5 years 316 will virtually vanish, with lean duplex alloys taking that slot in the $ vs corrosion resistance spectrum.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

I suspect that predictions of the demise of 316 for instrumentation tubing are very premature. Nobody is going to want to make the fittings and valves, which cost more than the tubing by far in any instrumentation system I've ever built, with duplexes lean or otherwise for the price they can be made from 316. And using the 316 fittings with duplex tubing is not likely to be a recipe for success.

 

[EdStainless]

The duplex fittings will cost 40% less than 316 (the tubing will be 30% less), the alloy is less expensive and it machines better.
It will take time, but I see it starting to happen.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

I've seen pitting on these "SS316" instrumentation tubing lines even before the facility was started up, with these facilities being constructed in fabrication yards right next to the sea.

 

[Corroneer]

316SS pits like crazy and fails in marine environment. The O&G industry is now moving to Inconel 625 and cuppornickels. A client used 316, then 904L and now Incoloy 825, all failed in a hot marine environment.

 

[XL83NL]

I've seen pitting on these "SS316" instrumentation tubing lines even before the facility was started up, with these facilities being constructed in fabrication yards right next to the sea.

and you find that strange?

The duplex fittings will cost 40% less than 316 (the tubing will be 30% less), the alloy is less expensive and it machines better.

not sure on what you base this.
last time I checked we paid a lot more for DSS compared to standard SS316 fittings (about a factor 10) and tubing (about 7-10 times). as for lean grades, I recently spoke to a guy from one of the bigger stainless suppliers out there who told me their trend is more towards super and hyper duplexes rather than lean ones. the lean ones are typically (only) used for vessel large enough where their price aspect is outweighted by the material weight savings. that aspect is not under consideration in tubing.

 

[moltenmetal]

The duplex and super duplex materials are apparently not so great to forge. So machining straight components from bar would be fine, but tees, elbows or anything that typically requires forging would be more difficult with duplexes than with 316. I've heard of the impending demise of 316 on and off for at least two decades and yet it's still the benchmark stainless material. Not one of the tube fitting manufacturers has a lean or 2205/31803 material in its standard stocked materials list yet, and none that I've talked to see a strong market pull to change that. Swagelok prices their super duplex stuff about where they price alloy C, around 10x 316, and C is an alloy superior in just about every way except raw material price.

 

[EdStainless]

Look at sheet, bar, or plate prices for 2101, 2201, 2202 and you will find that the delivered price is +/-10% of the 304L price, While today 316L is 30-40% above that.
I have been involved in a few machining trials and the lean duplex machined as well or better than Prodec and other enhanced machining grades of 3xx.
We have hot worked 2205 and lean duplex, they are no more difficult than 316, just different.
Hot working super duplex is a bear, the temp bands are narrow and the heat treat requirements are very difficult.
I know that Swagelok charges a premium, but we have made production runs of welded and drawn tubing in LDSS that was the same price as 304L.

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P.E. Metallurgy, Plymouth Tube

 

[moltenmetal]

Assuming the compression fittings work with the duplex's greater hardness, which shouldn't be a huge issue, then as soon as a mfg starts selling the fittings for less than 316 I will start buying and trialling them. Will keep my eye out for Plymouth to start offering duplex tubing for less than 316 much less 304 in the coming days- we don't buy whole mill runs Ed. Once the market tells me to buy duplexes, I will- but not before.

 

[EdStainless]

The catch today is having distributors build stock in a new grade, even if it saves money.
The tubing isn't the hang up, the valves and fittings are.
My hunch is that the next time we have an economic expansion you will see some of the guys doing it.
We are ready to make runs as soon as someone will place an order. We have done some isolated jobs with lean duplex, but I don't see people expanding inventory these days.

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P.E. Metallurgy, Plymouth Tube