Scale cleaning on condensers with iron-calcium-magnesium-aluminum silicate

[cavbilly]

Very complicated scale analysis, but the analysis reminds me of montmorillonite clay, also portland cement.
I tried about every sort of acidic cleaner in the known universe (short of hydrofluoric acid, which I refuse to deal with), then realized we had a quantity of concrete tool cleaner. I tried it on a section of stainless steel tubing 5/8" OD that was heavily scaled with this material. In fifteen minutes, the scale was sloughing off the tube and dropping to the bottom of the graduated cylinder.

We have purchased some concrete remover, and had other samples sent. All of them perform moderately well in the cleanings we have undertaken thus far on oil coolers both for steam turbine oil cooling, and one that was badly scaled with small 1/4" or less diameter tubes that was the scavenge oil cooler for an LM6000 gas turbine. No complaints thus far.

 

[EdStainless]

Is it acidic? What is in the cleaner? Specifically any chlorides at all? If so then you have initiated pits and destroyed any stainless involved.
Yes, often chemical cleaning is needed. Some of the foaming cleaners are nice because they lift debris from the surface. Chemical cleaning in a mixed metallurgy system often comes down to doing the least harm.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

A weak hot solution of either citric or acetic acid in a recirculation loop may also be possible.

 

[cavbilly]

EdStainless: (1) Our water already has up to 1000 ppm chloride in it, and even with the heat of gas turbine scavenge oil cooling, no issues on the type of stainless present in the tubes mentioned. The cleaner has had no deleterious effect. (2)We were out of options, due to some engineer genius (not me) setting this oil cooler up with hard, silica laden cooling water, with minimal flow velocity, as by the time cleaning took place, the tubes were at 60% blockage (a lot more loss of cooling).
I have had experience in the past where sample coolers on boilers were set up by an instrument tech at a customers facility, where the coolant applied was untreated city potable water (high chloride content in the local water), and within a week the boiler sample cooling coils had fractured. Those were all 316 stainless steel.

Things that were tried before with NO effect on the scale: (1)citric acid, (2)hydrochloric acid, (3) acetic acid, (4)glycolic acid alone.

These concrete removers have a mysterious something else in them (perhaps a zwitterion?) that is extremely effective in peptizing concretions.

 

[cavbilly]

Are any of you familiar with carbon dioxide bead blasting to clean metals post machining?
I have tried over and over to get one of the OEM's of that equipment to make a tool that will allow the same on oil cooler and condenser tubes. I am pretty sure that sudden chilling of the deposits (with the sudden shrinkage in dimensions) will result in powderization of the concrete-like scale deposits, along with any metal oxides, and clean the tubes down to bare metal, no corrosion. The tubes would be air blown to dryness first, as is about typical in most outage inspections.

I should probably take this idea to one of the tube cleaner companies out there. The problem getting a big slot in the market is the vested interest these companies have in cleaning the way they are now, and convincing their customers that is a good cleaning, and the vast majority of sites where the only type of scale that forms is calcium carbonate scale that is paper thin, and very easily removed. The stuff I have been referring to is difficult to even sample with a knife edge scraper bent 90 degree to its length to reach in and scrape the inside of a tube.

 

[georgeverghese]

Have you tried a solution with a chelate with say EDTA as the anion ( ethylene di amine tetra acetic acid)? - there are other similar chelates too - EDTA should be readily avaialable though.

 

[cavbilly]

Yes, EDTA was tried, from concentrated, to fairly dilute, with negative effect.
There is something in the concrete remover product (or the overall formulation) that seems to destabilize ionic attraction between local crystalline zones.

 

[georgeverghese]

Some derivative of phosphonic acid seems to be an antiscale agent for chelating and dissoliving out calcium scales - see ATMP - amino tris(methylenephosphonic acid).

 

[EdStainless]

Since you didn't bother to say what alloy was involved you left us guessing.
Variation of phosphoric acid derivatives mixed with chelating agents is what makes these work.

Either move to treated water, or lower the pH with sulfuric acid.

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P.E. Metallurgy, Plymouth Tube

 

[cavbilly]

Most of our heat exchangers are Admiralty Brass, one condenser was 90/10 copper alloy (unit retired at 40 years).
The scavenge oil cooler mentioned is stainless steel 316. No cracks in the metal (yet).
I already told management a long time ago we would have problems on this cooler if we did not put in on secondary loop (i.e. a closed loop) with either air cooling, or secondary heat exchange with plant cooling water from cooling tower (once the temperature is lower it is not nearly as big a deal).

 

[georgeverghese]

These phosphonic acid derivatives may be okay with SS316 in dilute solutions only.
Agree better to transfer these oil coolers to some closed loop treated water cooling system with low TDS since these are in critical service.

 

[cavbilly]

The real challenge is get people at GE (and other turbine OEM's) to get on board with the need to introduce secondary coolant loops in plants where the water is simply not in specification levels of chloride, hardness ions, and silica. The next hurdle after that, is to convince the "wrench twisters" posing as engineers to comply with manufacturer specifications on water quality required.

 

[georgeverghese]

Most, if not all, the oil coolers in turbine and compressor service I've come across were air cooled.

 

[georgeverghese]

Design case exit cooling water temp from heat exchangers in open loop cooling water is typically limited to 45-50degC. What was the design spec for these units for exit CW temp when completely unfouled ?

 

[cavbilly]

The design point was 115 °F, 46.1 °C...no brainer for wanting to have fin-fan cooler on this. I prefer water loop, and keep the heat exchangers existing, with air cooled water loop, simply from the stand point of containment of the oil is more secure.

 

[georgeverghese]

Would this work in this application ?

https://www.youtube.com/watch?v=_eGUMRCm-Xg

 

[cavbilly]

That was an impressive demonstration on a large heat exchanger scaled badly with iron carbonate. We have a silicate based scale, but I suppose that even with smaller tubes, the concrete remover product combined with ultrasound could have a seriously powerful impact on breaking up scale from the metal surfaces. Unfortunately, there does not appear to be a way to do this without removal of the tube bundles. We clean in place, typically. I suspect that if we were planning the substitution of some new tube bundles, we could take the old ones out and send them off for a serious ultrasonic attempt or two, and understand the results. I would still recommend the use of the concrete remover type products, as this does have a positive effect on reducing scale (where the solution can get in contact with the scale), except on totally blocked tubes, which have to be bored back open.