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Heat exchanger descaling

Scale dissolves readily in acid, which is the easy part. Choosing an acid that will not also dissolve the exchanger is the part that needs getting right. Send the unit details and the material, and a specialist will come back to you.

  • RemovesCarbonate scale, milkstone, beerstone, struvite
  • Chosen againstThe metal, not the deposit
  • Followed byNeutralisation and passivation

Submit a cleaning request

Four steps: unit, deposit, postcode, contact details.

  1. 01Unit
  2. 02Situation
  3. 03Site
  4. 04Contact
What needs cleaning?

01The method

The metal chooses the acid, and the inhibitor is what makes it survivable

Heat exchanger descaling dissolves mineral deposit using an inhibited acid, circulated through the unit or applied in an immersion tank. Of all the cleaning methods it is the one where the deposit is least of a problem. Carbonate scale dissolves readily. The difficulty is entirely in the selection: an acid that removes the scale efficiently may also attack the tube material, the gaskets, the brazing or the connected pipework.

01

Inhibited acid attacks the scale and leaves the metal, up to a point

Descaling chemistry is acid plus a corrosion inhibitor, and the inhibitor is what makes it viable. It adsorbs onto exposed metal and slows attack on it while the acid continues to dissolve the deposit. That protection is not unlimited. It depends on the inhibitor being right for that metal, on temperature staying within range, and on the acid not being left in far longer than intended. Uninhibited acid, or the wrong inhibitor, removes scale and tube wall at similar rates.

Works by
Inhibitor adsorbing onto metal while acid dissolves the deposit
Depends on
Correct inhibitor for the metal, temperature in range, controlled duration
Fails when
Left in too long, run too hot, or matched to the deposit alone
02

Material compatibility rules out chemistry before the deposit narrows it down

Stainless is attacked by chloride, so hydrochloric acid is generally avoided on stainless plate packs however well it works on the scale. Copper alloys, aluminium and galvanised surfaces each have their own incompatibilities. Brazed plate exchangers add the braze alloy as a separate material with its own limits, and it is frequently the braze and not the plate that sets the constraint. Establishing what the unit is made of comes before selecting anything.

Stainless
Chloride attacks it. Hydrochloric acid is generally avoided
Copper and aluminium
Each with their own incompatibilities and inhibitor requirements
Brazed units
The braze alloy is a separate material and often the limiting one
03

Neutralisation and passivation are part of the job, not an optional finish

Acid left in a system continues working, so the cycle finishes with neutralisation and a thorough flush, verified rather than assumed. On stainless the acid has also stripped the passive chromium oxide layer along with the deposit, and a surface returned to service without passivation corrodes faster and refouls faster than before it was cleaned. Skipping passivation is a false economy that shows up within months.

Neutralise
Then flush, and verify, not assume it has gone
Passivate
On stainless, always. The acid removed the passive layer with the scale
Dispose
Spent acid carrying dissolved metals, consigned under duty of care

02When it is the right call

Descaling suits mineral deposit and nothing else

It is precise about what it removes, which is a strength. Applied to the wrong deposit it achieves very little at considerable cost.

  • Right whenThe deposit is mineral. Carbonate scale, milkstone, beerstone, struvite.
  • Right whenThe unit cannot be opened, so mechanical cleaning is not available at all.
  • Right whenGeometry is complex and chemistry will reach where a tool cannot.
  • Wrong whenThe deposit is organic, fibrous or particulate. It was never dissolved and will not dissolve.
  • Wrong whenThe deposit is interlocked with protein. Acid alone stalls; it needs the caustic stage first.
  • Wrong whenThe site has no route to dispose of spent acid carrying dissolved metals.

03What happens next

Four steps take a fouled unit from enquiry to a tested return

The enquiry goes straight to a contractor who cleans that unit type. There is no qualifying call in between.

  1. You send the unit details, the deposit and the postcode.

  2. The enquiry goes to a specialist set up for that unit type and that fouling.

  3. They come back with method, timescale and price.

  4. The clean is carried out in place or off site, and the unit is tested before it goes back.

04Questions

Material, deposit type and disposal route decide whether descaling is the right method

Which acid is used?

It depends on the metal first and the deposit second. Sulphamic, citric and phosphoric acids are commonly used on stainless because they avoid chloride; hydrochloric is effective on carbonate scale and is generally kept away from stainless for that reason.

The inhibitor package matters as much as the acid. A correctly inhibited formulation appropriate to the metal is what makes descaling safe, and it is the part that distinguishes a specialist product from a drum of acid.

Will descaling damage the unit?

Not when the chemistry, the temperature and the duration are right. Correctly inhibited acid removes deposit at a far higher rate than it removes metal, and controlled descaling is routine across every sector.

It damages units when it is left in too long, run too hot, or selected against the deposit without checking the material. Those three are the failure modes, and all of them are avoidable by establishing what the unit is made of before starting.

Why did descaling not remove our deposit?

Almost certainly because the deposit is not mineral, or not only mineral. Acid dissolves carbonate readily; it does very little to protein, oil, fibre or coke.

Where the deposit is interlocked, beerstone grown into a protein layer, milkstone with denatured protein, acid alone stalls because the organic material shields the mineral. That needs a caustic stage first, then a rinse, then the acid.

Is passivation really necessary?

On stainless, after any acid cleaning, yes. The acid strips the passive chromium oxide film along with the scale, and that film is what makes stainless corrosion resistant. A unit returned without it will pit and refoul faster than it did before cleaning.

It is a short additional step and it protects the work just done. Treating it as optional is one of the commoner ways a successful clean turns into a shorter interval before the next one.

What happens to the spent acid?

It is neutralised and consigned under duty of care. Spent descaling solution carries dissolved metals from whatever it removed, so it is not neutral water once the pH is corrected.

Establish the disposal route before the work instead of after. Some sites can take it through their own effluent treatment and many cannot, and on occasion the disposal difficulty is enough to make mechanical cleaning the better choice.

How do we stop the scale coming back?

By addressing why it formed. Scale means hardness is precipitating faster than the treatment is controlling it, so the answer lies in softening, dosing, bleed rate or cycles of concentration and not in a shorter cleaning interval.

Descaling on a cycle without correcting the water treatment is a recurring cost with no end. Reviewing the treatment at the same visit is usually inexpensive and is what turns a repeat job into a one-off.

A specialist who cleans that unit type answers the request

Unit, deposit and postcode are enough to start. Your details go to a specialist who cleans that unit type. No obligation.

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