Short term 316SS pipe at 10000ppm Cl- and 30 deg C 2

[Spikeyi]

Hi,
I'm a chemist turned process engineer.
I am looking at using a 316ss pipe in a water treatment plant as a temporary substitute for a better duplex pipe that wont arrive for 4 months. There is about 10000ppm Cl- and the temperature of the water is at ambient temperature (20 - 30 deg C). pH = 8 - 10, not sure about dissolved oxygen, aside from this the water has low (<100 ppm) of pretty much everything. P = 7 bar and the flow is continuous (I think)

Whats the bet on 18 weeks?

Looking around the internet most sources say pitting and SCC kick in at around 50 deg C although others predict temperatures much lower. I am fairly sure its OK but have been asked to justify it.

 

[Metalguy]

*IF* the water flows continuously, pitting probably won't happen. What is the carbon content of the pipe--assuming it is as-welded?

What is the downside if it does leak via SCC?

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[moltenmetal]

My bet is you'll do the 18 weeks no problem, provided the water is not acidic or stagnant, the pipe is L grade and properly fabricated and passivated prior to use, and it is not locally heated anywhere above your 30 C stated case.

At 7 bar, liquid full, it sounds like the consequences of a failure aren't life-threatening- but of course I'm safe to say this from behind my computer here- that pipe is nowhere near me! YOU need to think carefully about that, because you know where the pipe is going.

Is it a long term solution? No way. You were right to order the duplex.

 

[moltenmetal]

Actually, if it is really just nice clean brine at 30 C and only 7 bar, why the heck aren't you using PVC as your temporary solution?

 

[EdStainless]

With pH over 8 and continuous flow you should make your time.
If you shut off flow and let it sit partially full I would expect pitting to start overnight.
I don't think that SCC will be the issue.
At 30C and 7 bar why not use fiberglass pipe for this installation?

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[rustbuster]

I agree with Ed, Fibreglass as a permenant solution. I used to have water injection lines 120,000 chloride at 2000 psig with no issues.

 

[Duwe6]

Thru-wall Chloride SCC will take years at 30°C. However, anticipate your s/s pipe to be ruined at the end of your 4-month run.

Use CPVC or PVC for temporary service, and tell the boss that you have saved the company a large ammount of $$$.

 

[racookpe1978]

Hide the pvc pipe inside the outside stainless steel pipe? 8<)

 

[unclesyd]

I see no problem with using 316 SS in theis service as long as you have a good flow nd clean runs of pipe.

We use underground 304L SS process waste collection system which carries all the process waste to an injection well. The front end of the line carries mainly acidic waste, HNO# and at the half point on the trunk line to the well we pickup HCL neutralized wash water that has passed through a limestone bed. The chloride concentration is usually around 2-3% with pH at 6-7 with a flow rate of 200 gpm. The pressure in the line is no more that the 10 ' is 10 pounds and the temperature is around 80C. The PH at the injection pumps never gets above 5. There has never been any problem with SCC in this line. About 200" was removed in 2000 to replace a chase under the railroad tracks, another set of tracks were installed.
This section of line had been in service for around 25 years.
When it was proposed to add the HCl stream there was lot concern that we would get SCC MD or corrosion due to the mixture could approach the Aqua-Regia thresh-hold. Lab test of 6+ months duration revealed no problems with the SS even a low PH and as pointed out above not letting the stream becomes stagnant.
Our waste line has to be SS due to mixture of chemicals it contains and the possibility of some local reactions causing very high temperatures,
I don't think that passivisation of the ;line is necessary as I found that when Cl's are involved it doesn't help
One other thing not mentioned above is in the OP's process solids do drop out MIC is very good possibility.

 

[Duwe6]

unclesyd, you are basically certain th have 'spider-cracking' on the ID with those conditions, especially the 2% Chloride! However, it takes decades at your temp & pressure for anything to make it thru-wall. Wish you were in Indiana, I'd drop by and UT it with an ID Creeping Wave probe; they were developed to find Chlorine- Induced Intergranular Stress Corrosion Cracking. Happens a LOT at Nuke plants, but much lower chlorides [1 ppm], and much, much higher temp's -- 250°C.

 

[EdStainless]

And that is one of the reasons why so many people are moving to lean duplex SS grades. (and it is less expensive and you get better pitting resistance)

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[Metalguy]

>they were developed to find Chlorine- Induced Intergranular Stress Corrosion Cracking. Happens a LOT at Nuke plants, but much lower chlorides [1 ppm], and much, much higher temp's -- 250°C.<

Chlorides usually cause transgranular SCC, not inter. Nuke plant primary water SCC (PWSCC) is usually intergranular, and CERT tests (constant extension rate testing) at 288 C revealed some interesting results.

At very low extension rates, IGSCC formed. If the rate was increased, at some point it switched to TGSCC.

"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein

 

[unclesyd]

Dume6,
Rest assured that there was no SCC in the pipe that was removed. We examined about half of the pipe by splitting with and abrasive saw and after a thorough cleaning using PT there was no cracking. Three areas of discoloration were sectioned and mount and examined microscopically, no problems. Not finding any sign of cracking or pitting was a surprise to us as we know Chloride SCC as it has cost us several million dollars and caused us to do a lot of equipment and material modifications. Mitigation of SCC and MIC was a major Tour De Force at our site.

I am not familiar with your NDT method but from your statement I certainly would liked to have had it when we were having SCC on our SS storage tank bottoms.
Is this equipment available commercially?
Is it applicable for thin sections?

Aside from the tanks I've fought the wet insulation, closed tubsheet vents, process cracking due to Nitrosyl Chloride, cleaning with toilet bowel cleaner, and every other battle. You name it I've been there.

One interesting observation I've made over the years is where there is measurable(100+ ppm)) quantities of Chlorides people tend to take precautions as to design and materials, it is the low concentrations where the SCC will bite you.

 

[Duwe6]

unclesyd, Toilet Bowl Cleaner! I'm rather glad it was you and not me; sorry.

The ut probe I use is from GE-Krautkramer and is a WSY-70, and is not in their catalog, but very available. It looks identical the VSY-70 that is cataloged. VSY is shearwave, WSY is compression wave, IIRC. Both generate 'creeping waves', but the WSY is the better choice.

There are several excellent discussions of WSY and Creeping Waves on the NDT.org Forum, in the archives. Anything J.Mark Davis or Ed Ginzel say is to be heeded. Both are world-class experts.