Maintenance, cleaning and service life of plate heat exchangers

Plate heat exchangers are regarded as low-maintenance units. That is true for clean media and regular operational monitoring. Without any attention, however, fouling, gasket ageing and slowly progressing leaks accumulate unchecked. Knowing maintenance intervals and cleaning correctly preserves the unit’s performance and significantly extends its service life.

How does fouling develop in operation?

What is fouling and how does it arise

Fouling describes the deposition of substances on the heat transfer surface. This deposit layer acts as thermal insulation: it increases thermal resistance and reduces the k value. As fouling progresses, heat duty falls at a constant flow rate - or the operator must raise the supply temperature to maintain output.

Typical fouling types:

• Scale (calcium carbonate deposits): with hard water and high temperatures (> 60 °C) dissolved calcium precipitates and forms a hard crust. Particularly critical in domestic hot water stations and steam condensers.
• Biological fouling: cooling water circuits can promote algae, biofilms and Legionella if the minimum operating temperature is not maintained.
• Corrosion products: rust from unalloyed steel components in the pipework deposits in the channels. Magnetite sludge in heating circuits is a common case.
• Particle deposits: sand, suspended solids and particles from poorly filtered systems become lodged in the narrow plate channels and can block them.

Fouling indicators in operation

Fouling manifests as: falling outlet temperature on the cold side under constant operating conditions, rising pressure drop (channel constriction due to deposits), or increased pump energy demand. Regular performance logging allows fouling onset to be detected early and cleaning to be carried out in good time.

How does CIP cleaning (cleaning in place) work?

What is CIP

CIP (cleaning in place) refers to chemical flushing of the unit without dismantling. The cleaning medium is pumped through the channels, dissolves deposits, and is then flushed out. CIP is the only cleaning option for welded plate heat exchangers; for gasketed units it complements mechanical cleaning.

CIP procedure

1. Pre-rinse with water to flush out loose particles.
2. Main cleaning with a suitable cleaning medium. The choice of cleaning agent depends on the type of deposit:
   • Scale deposits: dilute acid solution (e.g. 2 - 5 % citric acid or nitric acid solution, max. 2 % HNO3).
   • Biological fouling / fats: alkaline cleaning solution (e.g. 1 - 2 % NaOH).
   • Combination: alternate acid and alkaline phases.
3. Final rinse until the effluent reaches neutral pH.

Note: chlorine-bearing cleaning agents can also attack stainless steel surfaces (pitting corrosion). Always verify the material compatibility of the cleaning agent with the manufacturer. Do not exceed acid concentration and contact time - excessively aggressive CIP also damages high-alloy steel surfaces.

CIP frequency

Heating applications with filtered, chemically conditioned heating water: CIP every 3 - 5 years as a routine measure. Cooling water circuits: depending on water quality and fouling monitoring. Domestic hot water stations: annual inspection recommended, CIP when performance drops.

How does mechanical cleaning of gasketed designs work?

For gasketed plate heat exchangers the unit can be opened on site. The clamping bolts are released according to the manufacturer’s specification (even de-tensioning in a defined sequence), the moveable pressure plate is pushed back, and the individual plates are removed.

Mechanical cleaning of plates:

• High-pressure water cleaning (max. 100 bar, keep nozzle perpendicular to the plate)
• Soft plastic brush (no metal brushes - scratches promote corrosion)
• For hard scale: brief soaking in dilute acid (citric acid solution), then rinse thoroughly

After cleaning, inspect plates and gaskets for damage: cracks, deformations, harder or more brittle material in gaskets are signs of ageing.

When are gasket replacement and spare parts due?

When must gaskets be replaced

The service life of elastomer gaskets depends on temperature, medium and operating hours. EPDM gaskets typically last 5 - 10 years in normal heating applications (<= 90 °C). At continuous operation close to the temperature limit (130 - 150 °C) service life may fall to 3 - 5 years.

Signs that gasket replacement is needed:

• Visible external leakage on the unit
• Harder, more brittle gasket texture when opening the unit
• Cracks or deformations on individual gaskets
• Permanent pressure drop increase despite cleaning (channel constriction due to swollen gaskets)

Obtaining spare parts

The plate count, plate type and gasket material must be specified exactly when ordering spares. Always use original spare parts or equivalents approved by the manufacturer. Incompatible gaskets from alternative sources can impair surface coverage and sealing function.

Gasket replacement procedure

1. Isolate the unit and depressurise.
2. Record the existing installation length (distance between the pressure plates).
3. Evenly release the bolts in the defined sequence and open the unit.
4. Remove old gaskets (depending on gasket type: clip-on or adhesive-bonded).
5. Clean and inspect the plate surface.
6. Fit new gaskets (for adhesive gaskets: use a suitable contact adhesive, observe curing time).
7. Close the unit and tighten to the installation length per the manufacturer’s specification.
8. Pressure test with water at 1.5× working pressure before returning to service.

How long does a plate heat exchanger last?

The technical service life of a plate heat exchanger depends on the material, operating conditions and maintenance quality:

Design	Typical service life	Key factors
Gasketed	10 - 20 years	Gasket intervals, fouling management
Welded	15 - 25 years	Media suitability, CIP quality

The plate pack itself can theoretically outlast the frame in gasketed units if fouling and corrosion are controlled. The gasket material in practice determines the maintenance intervals.

Summary

Plate heat exchangers require no intensive servicing, but benefit significantly from regular inspection, timely CIP cleaning and professional gasket replacement. Operators who log performance and pressure drop detect fouling onset early and can avoid unplanned shutdowns. With good maintenance management, gasketed units readily achieve service lives of 15 - 20 years.