Thermal spray coating in Process Industries

[Chakraborty_P]

Dear Members,

I work in a petroleum refinery.

We had a corrosion problem in one of the distillations column, Due to very high H2S concentration, lot of corrosion products (scales) were generated. To combat the problem, we had applied SS410 coating (HVOF process) on CS parent metal with a top organic sealant.

After two years, the top sealant was found damaged - and rusting of SS410 layer has started. As the operating temp. is above 300 C (570-600 F), we had enough doubt about the longevity of sealant. However, the contractor had given assurance that the sealant will withstand the temperature & service (hydrocarbon - diesel + H2S).

Now in another column, we have been asked to apply SS316 on carbon steel substrate. And we have been asked to look at the possibility of "No sealant top coat" for that application.

As I understand, due to different levels of porosity, a sealant top coat is very helpful. In net surfing, found some literature which suggests that for such corrosion-resistant application using SS 316, sealant is required. Otherwise I need to apply Al thermal spray.

It will be helpful if you can guide me on these two counts -

1) For SS316 coating - can I do away with top sealant coat ?
2) Would like to know your experience in using Al-thermal spray in such application - please note that operating temp. in this case will be approx 150 C ( 300 F) - operating in hydrocarbon (naphtha+diesel) and very high level of H2S+NH4HS.

with regards

Chakraborty

[loriolo]

I would recommend you to apply TSA only, sealed with a high temperature sealant (for example a ceramic high temperature sealant from Aremco or high temperature silicon/Al sealant by Ameron coatings, which you must choose one that can resist the media, I mind that is dangerous to apply a cathodic coating like SS316 because it is enough to have a little hole in the surface, and the coating fault is immediate, I had a similar case in a chemical industry and the best solution was the application of TSA coating with arc spray system

[PurePulse]

If you have any interest in using a waterjet system to remove your HVOF hard coatings, check out our
website. We can remove hard coatings such as Chrome or HVOF using just 15K PSI.
No additives either. Just normal tap water.

[Chakraborty_P]

Dear Luis,

Thank you for the prompt reply. As a newbie in this field, I would like to understand what is meant by TSA - is it "Thermal spray Application" or Thermal Al spray - or something similar ?

By any chance, were/are you a member in Houston Oil forum under the same user name (Luis) ? If not, please ignore this part of the message.

regards
___________________________

Dear Purepulse,

Pl note that I am based in India - and hence irrespective of the supposed benefits of your system, we may not be able to utilize your system.

Anyway, I will go through the connection for upgrading my knowledge.

regards

Chakraborty

[loriolo]

I mean Thermal spray Alluminium, using pure alluminum or alloy alluminum/magnesium as coating material, if you use an arc spray system, you can reach a high bond, with flame spray could be necesary a steel flash in order to encrease bonding.

[wrjordan]

I mean Thermal spray Alluminium, using pure alluminum or alloy alluminum/magnesium as coating material, if you use an arc spray system, you can reach a high bond, with flame spray could be necesary a steel flash in order to encrease bonding.

Flame spray you can also get a high bond strength (comparable to Arc Spray) with correct surface preparation / application etc. We are getting 20MPa plus with Flame Spray TSA on existing Steel columns in a refinery.

[Chakraborty_P]

Dear Sirs,

Thanks for the info. It really helped me.

regards

Chakraborty

[Chakraborty_P]

Dear Gordon & other members,

In last few days, I have searched thru net about different thermal spray processes. It appears that for better quality (less porosity & less oxidation), I may use HVOF or HVAF methods. To me, cost factor is secondary. Only priority is getting a very good quality coating which will give at least 15 yrs protection & the job is to be completed reasonably fast. One question remains is - whether with HVOF or HVAF coating, a top coating is still necessary ? Some of the manufacturers claim that Sealant coat is not needed or difficult to apply due to very less porosity/smoother surface.

_________________________________

Hopefully, some of the Indian members in this forum can guide me to some good HVOF or HVAF coating providers in India. We are based in Mathura, approx 150 km/100 miles away from New Delhi, My e-mail id (hope this is not forbidden here) is chakrabortyp2@indianoil.in.

regards

Chakraborty

[ehasan]

Dear Mr. Chakrbarty,

We have carried out similar coating in DCU with SS316 with Sealant. Coating thickness of 1.5mm. After two year it was observed that except where the coating deposition was not proper the rest of coating was perfect. As you are in IOCL the first problem is not providing adequate time for carrying out the job. For any coating to function the Bonding is essential for which Surface preparation has to be perfect. From our experience on used Tanks the problem lies in surface preparation. We faced a similar situation where we had to depend on Grinding to remove the top layer (impreganted with Hydrocarbon). Where the Cleaning could be done perfectly the coating was intact.