corrosion coatings for cooling coil tube

[ginsoakedboy]

We have a hyperbaric chamber rated to 5,000 psi. We are currently testing some equipment in a 30% glycol + water solution. The chamber is pressurized to 4500 psi and is required to be maintained below 38°F. The chamber is allowed to stabilize in temperature prior to pressuring it. This is done by circulating chamber fluid for about 8 hours.

But, once we pressurize the chamber ... We are not able to cool the chamber fluid to below 38°F on a hot day (80°F). The test ran just fine on a cold day (60°F). We are located in Houston, Texas.

The sides and the bottom of the chamber are well insulated. Only the top is exposed. The fluid within the chamber is cooled using a simple finned tube shaped into U-loop. Chilled water + glycol solution is circulated at about 30 Gpm from a pump/chiller unit. The chiller is rated at 5 tons. The tube and fins is made out of carbon steel. We found them to be rusted quite a bit on the outside. I am sure the inside is rusted as well. I am looking at different concurrent solutions:

1. Remove rust from tubing
2. Coat tubing
3. Add insulation to top

I know I can get the tubing sand blasted for the OD. What kind of process will be used to remove the rust from the inside?

What kind of corrosion coatings are best (and cheap) for heat transfer applications? Can these be performed on the insides of the tubing as well?

I am also trying to model this system mathematically. Will natural convection be a large factor? Chamber ID and length: 42" and 130".

 

[unclesyd]

I would look at TSA (Thermally Sprayed Aluminum) for your cooling coil.

You should have no rust on the inside of your pipe if you have an inhibitor package in the water/glycol system.

Yes, I would insulate the top.

If there is no means for internal medium circulation you could very easily develop a stagnant condition.

I would also look at changing the materials of coiling coil.

Someone to talk to in your area.

http://www.centurycorrosion.com/contactInfo.htm

 

[ginsoakedboy]

Thank you for the response.

There is no inhibitor in the system per se. I don't know if glycol itself is effective enough.

I should have more thermocouple data for top and bottom of the top cover. Then I can compute the heat flux and see if the coolant is really transferring enough heat to offset the exposure to atmosphere.

While changing the material is a last resort, we are open to coating the coil. Incidentally, the thermal conductivity of stainless steel is less than half that of carbon steel.

How effective would be simply phosphate coating the part? How expensive is the TSA process? A sketch of the tubing is at the following URL:

http://files.engineering.com/downlo...-f017-49b3-a6c2-31b9baa1a231&file=figures.png

 

[coatingengineer]

Hi.

Epoxy- or phenolic-based coatings, when limited to 0.003 to 0.005 inch, can be excellent protective means from corrosion in heat exchangers. Glycols, you'll find, do not affect them.

For coating help, check out Heresite. Here's their link:

http://www.heresite.com.

Good luck!








William Gunnar

http://www.IndustrialCoatingsWorld.com