Demister Maintenance Checklist

Demisters are often ignored until differential pressure spikes or product quality drops. A short turnaround checklist prevents repeat failures.

Establish the clean baseline

After commissioning or a verified clean restart, record gas rate, operating pressure and temperature, differential pressure across the same instrument span, downstream carryover indicator, wash settings and any relevant liquid or solids load. This baseline makes later trends interpretable.

Keep the demister tag, drawing, material set, section map, installation photos and PI-defined QA records together. Without identity and baseline data, maintenance teams may compare different operating conditions or reorder an unknown construction.

During operation (remote signals)

• Rising ΔP across the pad zone
• Increased liquid carryover downstream
• Unexpected corrosion in ducts or compressors after the vessel
• Spray / wash system faults (if installed)

Trend these signals against throughput, pressure, temperature, liquid rate, foaming or level events and process-chemistry changes. A raw pressure-drop value without flow context is weak evidence. Confirm instrument health and impulse-line condition before attributing a change to the pad.

Define an owner-approved response for abnormal trends: verify instrumentation, inspect wash or drains, reduce load if required by the operating procedure, and schedule internal inspection. This guide does not set alarm or shutdown limits; those belong to the site’s process-safety and equipment basis.

At open inspection

1. Shape — crushed, dished or shifted sections
2. Bypass gaps — light gaps at the vessel wall or between sections
3. Fouling — type of deposit (gypsum, polymer, coke, salts)
4. Corrosion — pitting vs uniform loss on wires and grids
5. Hardware — missing tie wires, bent grids, wrong materials mixed in
6. Drainage — blocked drain paths that cause re-entrainment

Photograph the upstream and downstream faces before cleaning. Use section labels and a scale, and map each condition to the drawing. Record support ring, hold-downs, wall seals, section joints and wash nozzles as well as the media. A clean pad can still fail through bypass or mechanical displacement.

Cleaning decision

Cleaning is suitable only when the media and supports remain sound and the proposed method is compatible with the material and deposit. High-pressure water can stretch fine mesh or damage polymer vanes; steam and chemicals can exceed material limits. The vessel owner should approve the method, waste handling and safety controls.

After cleaning, re-inspect wire breakage, vane spacing, grid flatness, section thickness and material condition. A pad that looks open but has lost structural integrity should not be returned to service solely because deposits were removed.

Reinstallation discipline

• Follow section numbering
• Verify hold-downs torque / locking method per site practice
• Do not over-compress mesh beyond the design density envelope
• Photograph as-built conditions for the next RFQ

Also verify flow direction, joint staggering where shown, wall-seal continuity, support contact, drainage clearance and absence of loose tools or temporary material. Use only the site-approved fasteners and locking method. The supplier should not invent torque values for site hardware without a controlled basis.

Close the maintenance record

Record the decision, work performed, removed and installed part identity, dimensions checked, material evidence, deviations, photographs, cleaning method and the new operating baseline. If sections were replaced selectively, map old and new construction so the next inspection does not assume a uniform pad.

If the pad is replaced every short run, treat it as a design problem—style, material, velocity, liquid load, upstream distribution, washing or drainage—not only a purchasing problem. Compare actual run length with the site’s required maintenance interval and investigate the recurring mechanism before copying the part.

Use the inspection checklist for field evidence and the fouling guide when deposits control the run length.

Safety and responsibility boundary

Internal work requires the vessel owner’s isolation, entry, residue, lifting and rescue procedures. For U.S. workplaces, OSHA’s permit-required confined-space rule is one authoritative example; local law and site controls govern elsewhere. This maintenance checklist neither authorizes entry nor replaces pressure-vessel inspection.