ceramic coating of CS heat exchanger bonnet internals

[alwayslearning]

Dear All,

Sorry for laziness - I didnt do due diligence on researching this subject. I hope members would be forgiving and kind enough to provide useful tips.

We are going to apply ceramic coating for internals of CS bonnets of our sea water exchangers. I want to know if any special precaution/ care needs to be taken for this.

1) Is there any standard/ specification which governs such a coating. If there is one then I surely wont have it, so I would appreciate if you could give a summary of it in this post

2) ARe there different grades of ceramics coatings? WHich is the best?

3) What test/ inspection to be done to ensure cermic coating is good.

4) We plan to operate these exchangers, uninterrupted, for 5 years. After this duration, is it recommended to re-coat the ceramic? How to ascertain whether any partial damage has occured or not?

5) Is there any external non-invasive NDT test that can be carried out by our plant maintenance people (say once every 1 year) to ensure that the ceramic coating is "intact" and has not flaked/ peeled/ eroded?



Regards

 

[alwayslearning]

Well, I guess the weekend has got our cermic forum members to take some rest. In the meantime I did some research and came to learn about HVOF (high vel oxy fuel) coated ceramics.

Anyone having experience with HVOF ceramics in industrial environment (Refiner, petrochemicals, etc). Is it cost effective to do it.

I received some quotations for the bonnets. The vendors are proposing the following coating method:

grit blast to SA2-1/2, and apply two coats of 250 microns each of EPIGEN 806BR; ie a total of 500 microns.

Is this a reliable coating? Compared to HVOF ceramic coating how does this coating stand?

Regards

 

[kenvlach]

EPIGEN 806BR is actually a composite: a ceramic powder-filled epoxy.
For most liquid applications, it may be better (less porous) than HVOF-applied ceramics. However, it is limited temperature-wise:

"Maximum exposure temperature, 125^oC.
Heat deflection temperature ASTM D648, 80^oC."

from Tech data available at

http://www.epigen.com.au/

I suggest contacting their technical support with your application specifics.

I am unaware of any standard for ceramic-coated seawater HXers. HVOF ceramics are rougher & (I expect) will generally foul more rapidly than metals or plastic coatings. There are very slick plasma-applied ceramics,

http://www.sub-one.com/breakthrough.html,

but I have no first-hand experience.

I suggest a titanium or Ni-based alloy HXer for best chance at operating 5 years uninterrupted. Is abrasion resistance (due to sandy conditions) required? What maintenance will you be doing (periodic dosing with acids, biocides, etc.)?

 

[bobstak]

You can test the thickness and correct application of the ceramics using a new microwave technique. Mechanical Integrity (in Houston) offers this service.

 

[alwayslearning]

Hi Bobstak. Can you plesae elaborate more on the micorwave technique. Is it applicable for paint based ceramic coating too? I have to take the exchangers half way across the globe to reach Houston - for checking

Regards

 

[bobstak]

Actually, the inspection can be performed in the field, or any location. Yes, it is completely applicable to any application of a dielectric material. The inspection can detecet holidays, coating adhesion (or lack thereof), and coating thickness in one inspection. The delivery system is similar to a UT system but no couplant is required. Access to one side only is required. It cannot do the inspection through metal, but detecting coating thickness, adhesion, and holidays on a metal substrate provides exceptional results.

 

[EdStainless]

The EPIGEN is not a ceramic, it is an epoxy that is ceramic filled. There are dozens of similar coatings on the market (Belzona, Duromar, 3M, ......).
There are rules on cleaning and blasting profiles. One source is NACE.
With epoxy coatings only three things matter, surface prep, surface prep, and surface prep. The selection of the epoxy, its application and curing are important, but nothing will make up for poor surface prep.

= = = = = = = = = = = = = = = = = = = =
Corrosion, every where, all the time.
Manage it or it will manage you.

http://www.trent-tube.com/contact/Tech_Assist.cfm