4 replies to this topic

[process En]

Dear all:
please be informed that we using three air compressor (centrifugal,three stage)with 7000 NM3/h capacity which including 3 air cooler for each to provide instrument air for gas plant.

the weather is humid (normally 70%) here and air cooler material (including tube + header of air cooler and interconnection between stages) is Carbon steel.

the problem is that we have some deformation on blade of third stage of compressor.
we think the problem comes from rusted material which resulting from carbon steel and humid air.

My question question :
1) what would be the results if air cooler tube material change from cc to stainless steel?
from point of required surface area for air cooler to have same heat exchange capacity?
from point of pressure drop?
(we changed the material of interconnections between stages.)

2) what is your idea about our problem?


your actions are highly appreciated

[Art Montemayor]

Process:

I am confused by your statement that “the problem is that we have some deformation on blade of third stage of compressor” and then you go on to ask if you can change the material of the air cooled after cooler. I presume that you mean the post aftercooler found on all compressors and used to remove the heat of compression in the LAST stage – unlike intercoolers. If that is so, then how can the corrosion problem in the aftercooler have any effect on the upstream compressor blades? The two do not seem to be related.

There is no heat transfer problem created, in my opinion, if you change your carbon steel tubes to stainless material. It will be costly, however. If you check your properties of carbon steel and stainless, you will find that stainless has a higher thermal conductivity value – so it will conduct heat faster. But you won’t be able to measure the difference. I know because I’ve done it in the past many times on other exchangers. Your pressure drop will also practically be the same.

Your basic compressor impeller problem is, in my opinion, unrelated to the potential corrosion by condensed water. Without any background, mechanical details, operating history, and detailed basic data, there is nothing much that I can offer as to why your 3rd stage impeller deformed.

[process En]

Dear Montemayou:
I mean:third stage of compressor damaged, we think it is the result of corrosion product which is the result of CS with condensed water ( second after cooler + interconnection lines which is carbon steel(CS))..
so recommendation is to change air cooler tubes material from CS to SS.

Dear all:
what is normal practice for air cooler tubes material in the high humid air (>70%)ambient ?
is there any practice which using stainless steel(SS) apart from cost?

[srfish]

Normally most of the moisture would be removed in the first intercooer. Then less moisture would be removed in the second intercooler,just before the third stage compressor. If there was to be corrosion, it would be before the third stage compression.

[Art Montemayor]

Process:

I have operated many multi-stage compressors - most of them air compresors. Most, if not all of them employed copper or bass tubes in the inter- and aftercoolers. I have also used carbon steel and stainless as well in special cases, but not in air service. I have never experienced or witnessed any corrosion caused by water condensed from atmospheric air. Perhaps what you believe is atmospheric air is really air contaminated with acidic gases.

If you have damaged impeller vanes in your third stage, this could be because of inadecuacies in your water removal and/or drainage from the 2nd stage intercooler. You should have working level alarms in your interstage condensate traps.