Plate Heat Exchanger Leaking: Diagnosis & Repair

Types of Leaks

• External leak: Fluid leaks from between the plate pack to the atmosphere. Visible as drips or weeping from the plate edges. Usually caused by damaged gaskets, insufficient tightening, or plate corrosion.
• Internal leak (cross-contamination): The two fluids mix internally through a perforated plate or a failed gasket between adjacent plates. Harder to detect — the contamination may not be visible until product quality is affected.

Causes of External Leaks

• Gasket deterioration: The elastomer gaskets between plates age, harden, and lose their seal. Heat, chemical attack, and compression fatigue all contribute. Fix: replace all gaskets (never replace individual gaskets — always re-gasket the entire unit).
• Insufficient tightening: The plate pack must be compressed to a specific dimension (measured between the frame plates). If it loosens over time, leaks occur. Fix: re-tighten to the manufacturer's specified dimension.
• Plate corrosion or cracking: Corrosion pits or stress cracks in the plates create leak paths. Fix: replace the damaged plates.
• Over-tightening: Excessive tightening crushes the gaskets, causing them to extrude and fail. Always tighten to the specified dimension, not by feel.
• Thermal cycling: Rapid temperature changes cause differential expansion between plates and gaskets, breaking the seal. Fix: ramp temperatures gradually.

Detecting Internal Leaks

Internal leaks are dangerous because the two fluids mix — potentially contaminating a clean process fluid with a heating/cooling medium. Detection methods:

• Conductivity monitoring — if the two fluids have different conductivity, a sensor on the low-pressure side detects contamination
• Pressure test — isolate one side, pressurise the other, and monitor for pressure drop indicating cross-flow
• Dye test — add a fluorescent dye to one side and inspect the other side with a UV light
• Visual inspection during disassembly — look for perforations, pinholes, or cracks in the plates

Repair Procedure

1. Isolate and drain: Close both inlet and outlet valves on both sides. Drain all fluid from the unit.
2. Loosen the tie bolts: Release the compression on the plate pack following the manufacturer's procedure.
3. Remove plates: Slide the plates off the guide bars one at a time. Keep them in order — reassembly must be in the same sequence.
4. Inspect each plate: Use a dye penetrant test to detect cracks and pinholes. Look for corrosion, erosion, and gasket damage.
5. Replace damaged plates and all gaskets: Even if only one gasket is failed, replace all gaskets for consistent compression.
6. Reassemble in correct order: Follow the plate arrangement diagram — plates have specific orientations (A-plate, B-plate pattern). Getting this wrong creates internal leaks.
7. Tighten to specified dimension: Use a torque wrench or measure the gap between frame plates. Do not over-tighten.
8. Pressure test: Hydrostatic test both sides at 1.5× design pressure before returning to service.