TL;DR

External leaks from between plates are almost always a gasket issue: either the frame bolts backed off or the gaskets aged out. Re-torque first, then replace gaskets if leaking continues.

What you might see

liquid dripping from between plates on the frame edge
liquid trail running down the frame toward the floor
leakage increases at higher operating pressure
gasket visible extruding past the plate edge

Likely causes

Tap to mark as ruled out

Frame bolts backing off due to thermal cycling or vibration, reducing clamping force on the gasket
Gasket material age-hardening, losing elasticity and sealing ability
Gasket extruded during a previous over-tightening event
Operating temperature or pressure exceeding the gasket material rating

Required tools

Torque wrench sized to the frame bolts
Vernier caliper or depth gauge to measure tightening dimension A
Solvent wipe cloths
Replacement gaskets per Alfa Laval M-Series part numbers
LOTO kit

Safety first

Do not attempt to tighten frame bolts while the unit is at full operating pressure. Reduce or stop flow first.
Hot process fluids remain in the plates after shutdown. Verify cool and zero pressure before de-plating.

Procedure

9 steps · ~60 min

1
Reduce process flow to the minimum and reduce pressure if controllable, to limit the leak while preparing for repair.
2
Shut down and lock out both sides. Verify zero pressure before touching the frame.
Warning: Stored thermal energy and residual process fluid pressure remain after shutdown. Allow the unit to cool and verify zero pressure before opening.
3
Measure the current tightening dimension A of the frame (distance between the fixed and movable end plates) per the Alfa Laval instruction manual.[1]
4
Compare to the dimension stamped on the frame label. If A is larger than the stamped dimension, tighten the bolts evenly in a cross pattern in 2 mm increments until A matches.[1]
5
Restart the unit and observe the leak point for 15 minutes. If leakage stops, the re-torque resolved it.
6
If leakage continues after correct tightening, the gasket at that plate position has failed. De-plate and identify the leaking gasket by the wet plate edge.
7
Remove the damaged gasket. Clean the gasket groove with a solvent wipe and verify the groove is free of adhesive residue.
8
Install the new Alfa Laval-specified gasket for the M-Series model. Seat the gasket into the groove without adhesive unless the manual specifies otherwise.[1]
9
Reassemble and tighten to the correct A dimension. Perform a leak check at operating pressure before returning to full flow.

Sources

Alfa Laval M-Series Plate Heat Exchanger Instruction Manual, Alfa Laval
Alfa Laval M-Series PHE Instruction Manual, tightening dimension and gasket replacement procedure (general)
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