NX 25 Series

Common issues

• Gasket hardening or leakage over time, especially where compatibility with the process fluid has degraded
• Plate fouling and scaling on the raw seawater side, reducing heat transfer
• Galvanic or pitting corrosion on plates in raw seawater service if plate material is not matched to the water chemistry
• Inter-plate leakage causing fluid mixing between circuits, critical where one side is seawater and the other a closed fresh-water or oil circuit
• Frame bolt tension loss or uneven compression causing localized leaks
• Reduced flow and increased pressure drop from progressive fouling

Inspection checklist

• Check for external leakage at the gasket line and frame seals
• Measure pressure drop across the exchanger and compare to the baseline/design value
• Inspect plates for fouling, scaling or pitting during opening for cleaning
• Verify gasket condition and re-torque frame bolts to the plate manufacturer's sequence and value after any plate pack disturbance
• Pressure/leak test the plate pack after reassembly, checking for cross-contamination between circuits
• Check the raw water side for marine growth/biofouling ahead of the exchanger
• Verify instrumentation (temperature, pressure) used to trend performance

Service intervals

Critical spares

• Gasket sets matched to the specific plate type and fluid service
• Frame bolts and washers
• Plates for the affected duty, since raw water and closed-circuit plates may differ in material or coating
• Connection seals at the frame inlet/outlet ports

Safety

• Stored pressure in the plate pack must be relieved and the unit isolated before opening
• Frame bolts must be re-torqued to the correct sequence - uneven compression can cause a sudden gasket failure under pressure
• Where one circuit carries a hazardous or hot fluid, cross-contamination from a failed plate is a safety issue, not just a performance one

Class survey

Plate heat exchangers in seawater-cooled circuits supporting classed machinery are typically covered under the associated system's survey scope rather than surveyed as a standalone item; surveyors commonly look for a maintained cleaning/inspection record and evidence that the plate pack has been pressure-tested after reassembly.