Correct material for heating coil
Correct material for heating coil
(OP)
Hi all!
I'm designing a heating coil for a pool filled with a water and a biodegradable degreaser. The degreaser solution need be heated and will be used to soften oil residues from heat exchanger bundles. The pool is near to the coast. Steam at 40 psig and 400°F will be used to heat the degreaser to 170°F. Sometimes the pool will be drained and the coil will be exposed to the atmosphere for weeks.
Select the correct material for the tubes has been a problem for me.
I first thought in carbon steel, but due the water and the proximity to the coast I consider that the corrosion will be agressive; then I thought in austenitic stainless steel, but again the proximity to the coast (chlorides from sea water in the air) when the coil is exposed to the atmosphere I think that it can cause corrosion. Maybe using a painted carbon steel (crazy idea?)...
Could someone please recommend me the correct material for these tubes?
Any help is well appreciated.
Best regards!!
I'm designing a heating coil for a pool filled with a water and a biodegradable degreaser. The degreaser solution need be heated and will be used to soften oil residues from heat exchanger bundles. The pool is near to the coast. Steam at 40 psig and 400°F will be used to heat the degreaser to 170°F. Sometimes the pool will be drained and the coil will be exposed to the atmosphere for weeks.
Select the correct material for the tubes has been a problem for me.
I first thought in carbon steel, but due the water and the proximity to the coast I consider that the corrosion will be agressive; then I thought in austenitic stainless steel, but again the proximity to the coast (chlorides from sea water in the air) when the coil is exposed to the atmosphere I think that it can cause corrosion. Maybe using a painted carbon steel (crazy idea?)...
Could someone please recommend me the correct material for these tubes?
Any help is well appreciated.
Best regards!!
RE: Correct material for heating coil
a painted carbon steel (crazy idea?), I think...
luis
RE: Correct material for heating coil
RE: Correct material for heating coil
If a bit of rust doesn't bother your process than CS may be the best bet.
I don't know of any coating that will hold up well in this service.
When you start looking at higher alloys you are in a bit of a bind.
If you can keep the Cl levels modest then 2205 may work, but since you don't know that you are going to be washing off I would hesitate.
Check your data, 40psig steam is only 267F.
A safer option would be Ti gr2. And in thin wall tubes it isn't outrageously expensive.
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P.E. Metallurgy, consulting work welcomed
RE: Correct material for heating coil
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P.E. Metallurgy, consulting work welcomed
RE: Correct material for heating coil
RE: Correct material for heating coil
MIC isn't an issue with copper as far as I'm aware.
RE: Correct material for heating coil
Monel might be a good option, but compare the cost to Ti (Monel is more expensive, but easier to work with).
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P.E. Metallurgy, consulting work welcomed
RE: Correct material for heating coil
Develop a max design pressure and temperature and get a quote for tubes mad from Monel and Ti
How long do you want this device to last ?
Is three, five or ten years a reasonable life for your purposes ?
MJCronin
Sr. Process Engineer
RE: Correct material for heating coil
The device is expected to have ten years of useful life but considering the CAPEX this parameter could be modified (downward).
One supplier recommends us to use a phenolic epoxy coating on a carbon steel pipe, but I am not sure about it, the film need to be thick (16-20 mils) and they do not have the conductive coefficient to estimate the lost in heat transfer efficiency. On the other hand, I am not sure if that coating resists sun exposure.
I'm going to look for quotes for Monel and Ti tubes, then compare these three alternatives. Four considering bare carbon steel that was the initial point.
RE: Correct material for heating coil
MJCronin
Sr. Process Engineer
RE: Correct material for heating coil
You really should look for an experienced fabricator that weld this for you using thin gage tubes.
For 40psi at 275F sch5 pipe is likely too heavy for the job.
And in expensive materials every pound matters.
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P.E. Metallurgy, consulting work welcomed
RE: Correct material for heating coil
RE: Correct material for heating coil
RE: Correct material for heating coil
I want to share the final decision.
Before, it is neccesary to tell that the client informed that the pool will not have continuos operation.
We look for experinced suppliers of 2205, CuNi or Ti heating coils but no one offers that materials in my location in the required dimensions, in each case they offers just austenitic stainless steel. As foreign suppliers would be required, we discard these options due the cost.
Considering that coating suppliers did not offer a paint that will withstand substrate temperature under immersion conditions, Finally it was selected bare CS, recommending the client to always keep the coil submerged, if it is necessary to drain the pool to replace the degreaser, dry the coil well and submerge it again as soon as possible. For longer periods of no operation to apply an anticorrosive paint. Due to comparative lower cost of CS, the client accepts the eventual replace of the tubes.
Thank you to all of you for your replies, they were a valuable input to handle the problem and to learn a bit more.
RE: Correct material for heating coil
RE: Correct material for heating coil
luis
RE: Correct material for heating coil
0707, the main component is fatty acid esters (i just have that information). The coil will be not painted for the operation, the anti corrosive film will be only necessary for "storage" while the pool is not in operation, before to operate again it will be removed.
RE: Correct material for heating coil
luis
RE: Correct material for heating coil
- Corrosion Allowance: to be considered per the corrosion rate expected by chemical analysis and velocity of the service. If the steam is condensed in the heat exchanger, the corrosion will be noticeably appeared.
- To avoid the dissimilar metal contact, such as stainless steel, Ni alloy, copper alloy, etc.
- The tube bundles should be easily replaceable.
- All water (internal and external) should be completely drained during suspension (idle) of the pool service. After drained, the relative humidity near the heat exchanger should be less than 65% (60% preferable); or VpCI/Desiccant should be treated; or nitrogen blanketing is to be used.
- After drained for suspension, if there are some scales on the coil surfaces, they should be removed by water jet or chemicals accordingly.
References: MTI 34 Mothballing/ NACE Corrosion Journal, p515-522, June 2004/ NACE Paper 98244, 10147, 14-4335, 15-5450, 20-15004, Others
Thomas Eun
https://www.springer.com/us/book/9783030364298?gcl...