White Rust in HVAC Ductwork, again

[PagoMitch]

All,

So last year I posted a question re: how to resolve white rust on interior sheet metal duct wall. That thread has been closed, but here is the link:

How to resolve white rust issues inside ductwork? - HVAC/R engineering

I am helping a client commission some medium sized (34,000 CFM) chilled water AHU's that were installed several years ago, but never started. This is in a hospital, on an island with lots of rain and high humidity. In cutting into a large (10 ft x 3ft) vertical SA plenum in order to get to some...

www.eng-tips.com

I recommended to the owner that the Contractor shall line the ductwork with new, un-blemished G90 sheetmetal. The owner supported us (our firm), and they completed that work on (1) of the AHU's end of last year. Fast forward several months, and the completion of this task (on the other AHU) has been a topic on our weekly task list discussion ever since. Until yesterday; when the Contractor advised that it was done. I asked them how they did it. Silence for several seconds. Then the Contractor Field Foreman (not the Project Manager, who was sitting next to him) said that one of their (the Contractor's) consultants (not an engineer, but more a Project Manager) advised that they could just paint it with spray galvanizing. So they did. I'm assuming they went to ACE hardware, bought a dozen cans of spray galvanizing, and applied over all the white rust. I was speechless. Photos from earlier thread below. I have requested the Contractor provide me with details of exactly what product they used.

from earlier thread for context:

So. Just to reiterate. This location is the Supply Air plenum, downstream of the final MERV 14 filters in a 30,000 CFM AHU, serving the core area of a hospital. My concern expressed in the earlier thread was that while spray galvanizing works fine - on a welded hitch or the underside of your car - I can find no references for the suitability of applying this to the inside of ductwork, let alone ductwork serving a Hospital.

My concerns are mainly:
1. Surface prep. Due to the difficulty of working within this plenum, I would hazard a guess that they just sprayed the galvanizing over the white rust. From my experience, spray galvanizing only works well when applied to bare metal. Will parts eventually flake off and be sent down the ductwork to be discharged out the Supply Air grilles into the breathable environment and deposited on horizontal surfaces? My guess would be yes, eventually. Next month? Next Year? Several years? No matter the timeline, it WILL happen; at which point the AHU will need to be turned off, apply new G90 steel, then ALSO clean the downstream ductwork to eliminate the contaminants... This would be weeks of work, at least...
2. The additional components being added to the spray-can to make it sprayable are...nasty. Will these eventually slough-off and be mixed with the airstream? My guess would also be yes. From the MSDS on an ACE Spray Galvanizing can:



Oddly enough, the MSDS on this can does not say anything about zinc purity or other compounds... ??? Not sure how that happens, but I have to assume it is close to the label at 92%...

At this point, I am waiting for them to get back to me with the exact spray galvanizing they used. Although I do not think the particulars of another brand will change the underlying problem. In my opinion, this stuff has no place inside an air duct; let alone for use inside a hospital, and downstream of the final filters. My recommendation to the owner is to require the Contractor to resolve this properly, which would entail another G90 layer of sheetmetal to cover and encapsulate this chemical soup, and prevent it from sloughing off into the downstream ductwork and entering what is supposed to be a reasonably sterile - or at least, uncontaminated-by-heavy-metals environment.

What a pita. If they push back (which I expect), my next move would be to get an industrial hygienist involved... I think.

Thoughts?

TIA.

 

[3DDave]

Looks to me like those listed components will evaporate in very short order. If they can stand the smell and the amount - which is the critical part of any chemical contamination - one spray can vented into a building is unlikely to be noticed, but 50 cans might be a short term intoxication problem.

Certainly other brands may have different components, so an evaluation must depend on which one. I am surprised that a roller application wasn't used from a paint can. Less volatiles and more direct amount deposited; less need for a dust mask to avoid zinc plating the lungs of the users.

I doubt that there is sufficient airspeed to maintain any big flakes in the air supply; the biggest contribution would be due to atomization of the liquid during the spraying. I don't see what binds the material in place. It does require contact via electrical conduction to provide sacrificial protection, so I think it cannot be encapsulated.

If flaking is a worry I suppose going over it with a transparent coating would bind the zinc particles in large clumps so that only if moisture penetrated the coating that the zinc would do it's job and inspection could see if there was such a problem, unlike using an opaque paint.

Zinc-oxide, the product of protection, is generally benign, though inhaling milligrams or such as nanoparticles such as from welding galvanized material, can make people feel ill. It's used in sunscreen for external application.

Over-layering with sheet metal leaves a place for mold to grow without being detected.

Replacing the duct with clean material would be the other option.

 

[SAK9]

Get the ducts replaced that is the only lasting solution. Moreover it is a healthcare facility and an air quality check may expose you to potential insurance claims. If the duct work is not very old you need to investigate what is causing this for eg saline air in a coastal area. If weather is causing it Aluminum duct work may be a better alternative

 

[MintJulep]

It's a fine mess.

I doubt that the applying new galvanized sheet over the existing rust would have worked. As 3DDave noted, it just becomes a place for mold to grow and other crap to accumulate.

Did whoever actually did the spraying wear any sort of respirator? Toxic nasty stuff in an enclosed space. Are there any occupational safety laws where you are?

Did you hire the contractor, or the hospital?

 

[dvd]

Are there other ducts that have been in-service while this system was not? What do the insides of those units look like?

This doesn't address your issue, but you may find it informative -

https://galvanizeit.org/uploads/publications/Wet_Storage_Stain_On_Galvanized_Steel.pdf

 

[PagoMitch]

All,
Thanks for the responses.
Unfortunately, I am thousands of miles from the site, and the owner only brings our firm to the island a few times a year. In between our visits, the local Contractors pretty much run rampant. Our firm does not hire the Contractors. They are hired by the Facility.

This entire process started by the Contractor storing their galvanized steel ductwork panels outside, for months - or maybe years - prior to actual fab into ductwork. This is a place where it rains appx. 200" a year. When it is not raining, the air has a very high saline content. It is always hot and humid; unless it is raining. Having lived and worked at the facility for 8 years, I can state that it is the worst place for exterior steel or aluminum longevity I have ever seen.

From TEAMS meeting several weeks ago, apparently they spray painted the inside of the plenum with the spray galvanizing. I have asked for data sheets of what they used; no response. Before recommending re-lining, I advised that issues with spray painting were) I have never seen it done, nor can I find anything online, and there are a lot of nasty chemicals in a standard spray galvanizing can, and 2) they would need a full-face suitable respirator as a minimum, and potentially a positive pressure respirator. I do not know what PP was used. Personally, I would not work for the hours it had to take in that closed environment without positive pressure air.

Monday this week I got a call from the Facility Manager, who got a call from the Operating Room staff, who had to shut down the OR because of paint smells coming from the HVAC Grilles. "Any idea what is going on?" Uh oh... After several hours of phone calls, it seems the Contractor decided to roll on 2-part epoxy paint over the previously spray painted galvanizing (in the supply plenum), as well as over some less severe white rust in the intake plenum. I had not indicated for them to do anything about the intake plenum, as 1) it was much less severe, and 2) the AHU Final Filters (HEPA) are downstream, so I was not too worried about any flaking off particulates.

The Contractor did not coordinate this with the hospital, nor provide anything to us (the A/E) in a submittal. As they did not isolate the AHU, it appears the epoxy smell was distributed throughout the hospital core. Sigh.

At this point... they finally turned on an Exhaust Fan for the area (another issue), and the smell is much reduced. I have asked the Contractor to provide an MSDS on the epoxy paint they used. Using the AI feature MS Edge keeps trying to force on me, it appears my concerns may be valid: See attached. Note: one of the few times I have ever seen AI useful...

Hopefully they can provide me with an MSDS that indicates the Epoxy Paint meets IMC flame and smoke requirements. If not... it would appear they have just created a massive amount of work for themselves.

DVD - Thanks for that link. Very informative.

Any other ideas?

 

[3DDave]

Unless you trace back the actual sources, be aware that Large Language Model (LLM) AIs are notorious for unreliable responses to the point of total falsehoods. More than once now a law firm has found that the AI they relied on made fictional cases up to support arguments and the lawyers using the software were met with hostility by the court.

As to the actual circumstance, why do they hire you if they ignore your work? Is this customer worth it?

 

[HVAC-Novice]

Since the owner lets the contractor do whatever they want, let them. This situation isn't salvageable if these conditions persist.

Applying the best material on flaky/rusty duct or paint won't work. In paint and adhesion, surface preparation and conditions are everything. Any product also will have a temperature and humidity range for application and curing time. Even if these yahoos had used the correct product (likely they didn't), it wouldn't matter if not applied properly.

Regarding toxicity/small/flammability/smoke dangers, you have to consider the scenario of application (solvents etc.) and after curing. A product that theoretically could be harmless after curing, still can be harmful during application.

AI has its place and isn't worse than a book, magazine, a human or any other source. You still have to think critically. According to one book, Earth was created 6000 years ago - also a questionable statement not worse than AI. To judge the product, you need to know what product. Whatever that contractor calls epoxy could be anything that has nothing to do with polyepoxides.

If the facility owner isn't helping to get that contractor under control or at least get you the information you requested, you shouldn't lose sleep over it.

 

[PagoMitch]

3DDave - good comment and question.

Re: The AI - hence my comment. Thanks for yours. Last year I spent a few hours with CHAT GPT in an attempt to quantify the distribution of motor heat (inside an AHU) to downstream air and ducts. The Engineering 101 and basic Physics mistakes it made were hilarious. "I apologize. You are correct that in that it is impossible for the sum of the downstream heat transfer to objects to be greater than the input heat source. Let me revise the calculations". Somewhere I have a printout of the exchanges. It was 10 pages... As an Engineer, it is perplexing to me that the AI programming allows for violations of basic physics and outright denial of truth to be presented as facts. What would you do if your calculator was only accurate 95% of the time? I'd bin it and go back to hand calcs if it was not 100% accurate every.single.time. Correct numbers matter.

Back on topic, I did not find many - but I did find a few Epoxies that discussed flame and smoke spread; but with oddities - like this one:

Fire Retardant Spray

Learn about our fire retardant spray products and their benefits.

flameoffcoatings.com

Tested on wood, fabrics, and leather. Nothing on galvanized steel, nor on application over earlier applied epoxy.
My other concern is that (unlike some in US politics these days) ... "I don't know what I don't know". If you are old enough, you may remember the snafu re: treating kids pajamas with flame retardant chemicals. Yep, it mostly worked. But years later we now know that the flame retardants used probably exposed 1000x - or 10,000x - or more - kids to cancer causing chemicals than were potentially saved from their parents dropping a lit cigarette on them. Even if an epoxy painted inside a duct can meet flame and smoke... I am not certain that there are not other more salient issues - that have yet to be identified - that would truly make this a bad idea. This is indeed a hot mess.

As to the why? I used to work at the facility for several years. It was challenging from a Mechanical Systems perspective, but rewarding. They have few technical or experienced mechanical systems personnel; yet they must also meet US criteria for all hospital systems. ASHRAE, Infection Control, UL, NFPA, CMS, FGI, and the I series Codes. This is difficult for their mostly local staff. They have also had major personnel changes in management; and I am literally their only "institutional memory" on almost all Mechanical infrastructure. Our firm (here in the CUS) has continued to provide A/E services for various expansion projects; and as part of that Construction Admin SOW I just try and assist their staff where I can. Sometimes they listen - sometimes not so much.

 

[MintJulep]

I just don't see any way to fix this.

There seem to be two options:

1. Leave it as is and hope for the best.
2. Rip all the ducts out and replace them.

Adding more layers of whatever over the top of the already applied stuff just makes the situation worse.

If mixed correctly (and that seems like a big if), then the epoxy will cure and probably stop off gassing.

 

[3DDave]

This seems like a way to continue responsibility for a situation over which there is no control.

 

[mfgenggear]

OP
Would be prudent to have hired a third party at the client's expense to obtain test sample of the corrosion?
Make the client aware?
This is a mess. Time to get a release.
Is this a possible chemical attack.
While in storage , sheets got contamination?
Never seen such physical corrosion.