There are two major symptoms that we typically associate with membrane damage:

1. Increase in permeate conductivity coupled without a loss in productivity, or in extreme cases, with an increased productivity– this could indicate delamination or chemical damage.  Membrane probing can determine whether this increase permeate conductivity is simply due to leakage at the permeate tube interconnectors (damaged O-ring).

2. Increase in differential pressure (ΔP) in both stages without a loss in productivity – this typically indicates membrane “ballooning” or “pouching” that occurs during system shutdown as a result of excessive permeate backpressure.   This causes the membrane to stretch out of shape and the deformed membrane now intrudes into the feed channels, impeding flow and creating pressure losses.

If the ΔP increase is only in the second stage, and a membrane autopsy determines that the membrane pouching is only in the tail element, it is usually an indication that a permeate valve was closed during membrane cleaning.  In such a case, membrane deformation will be found to be most worse near the concentrate end.

A pressurized dye test of the membrane element followed by membrane autopsy can further determine the cause of damage by staining the permeate side in areas of the membrane where damage has occurred.  The location and pattern of the stains offer clues as to the nature and cause of the membrane damage.

For examples, please see the blog titled Membrane Autopsy: Damage from Permeate Backpressure at