Ship RO Maintenance — Pretreatment, CIP & Troubleshooting

Ship RO maintenance keeps a seawater reverse osmosis (SWRO) plant reliable at sea. This guide covers daily/weekly checks, pretreatment hygiene, cartridge & chemical dosing, when and how to run CIP, and a practical troubleshooting table plus spares planning for 3–6 months.

Why ship RO maintenance matters

At sea, uptime depends more on pretreatment and routine care than on the RO stack. Stable intake, clean strainers, healthy dosing and timely cartridge changes prevent most shutdowns and extend membrane life.

Daily & weekly checks

• Pressures & flows: feed, concentrate, permeate; record ΔP across cartridges and vessels.
• Quality: permeate conductivity/TDS, temperature, pH (post-treatment).
• Dosing: antiscalant/SMBS tank levels, pump stroke/Hz, leak inspection.
• Visuals: sea chest level, strainers, leaks, vibration/noise, electrical panels.
• Weekly: pull/clean basket strainers; change 5-µm cartridges per ΔP trend; inspect UV lamp status.

Pretreatment hygiene (intake → cartridge)

• Sea chest & lift pump: keep grates clear; verify NPSH margin (no cavitation).
• Strainers: clean routinely; spare gaskets ready.
• Cartridge housing: monitor ΔP rise; avoid letting ΔP exceed vendor limits.
• Chemical dosing:
  • Antiscalant: steady dose per feed flow and chemistry; avoid starvation during tank change.
  • SMBS (if dechlorinating): verify no free chlorine at membranes; overdosing can depress pH.

Performance normalization (know when to act)

Raw flow varies with temperature and salinity. Normalize before you judge performance:

• Normalized permeate flow (NPF): correct measured flow with a temperature correction factor (TCF) and pressure term to compare vs. baseline.
• Salt passage (or rejection): track % change relative to baseline acceptance test.
• ΔP normalized: compare vessel/cartridge ΔP over time to flag fouling.

Typical action thresholds (guideline): NPF ↓ 10–15%, ΔP ↑ ~15%, or salt passage ↑ 10–20% → plan cleaning (CIP) after verifying pretreatment.

When to run CIP

• Sustained NPF drop after temperature correction.
• ΔP rise not explained by new cartridges/flow changes.
• Permeate quality drift (salt passage up) not fixed by operating tweaks.

CIP sequence (field-tested routine)

1. Diagnose: identify likely foulant (bio/organic → alkaline; scale/metal → acid; colloids → surfactant/alkaline).
2. Isolate: switch to CIP loop; bypass product to drain; protect instruments.
3. Mix: prepare solution with permeate or DI; control temperature (often 20–30 °C unless vendor states otherwise).
4. Recirculate: low pressure/low crossflow to avoid compaction; alternate recirc and soak (e.g., 20 min recirc + 30 min soak).
5. Rinse: with permeate to neutral pH/low conductivity.
6. Second step: if needed, run the complementary cleaner (acid then alkaline, or vice-versa) with rinse in between.
7. Post-CIP test: restart, normalize, and compare to baseline. If recovery < 90% of baseline, review pretreatment and consider vendor advice.

Typical chem windows (confirm with your membrane vendor): alkaline pH 10–12 for organics/biofilm; acid pH 2–3 for scale/iron; keep temperatures within membrane limits.

Troubleshooting (quick table)

Symptom	Likely causes	Checks	Actions
Permeate flow low	Fouled cartridges/membranes; low feed pressure; cold water	ΔP trend, pump curve, temperature	Change cartridges; verify pump/VFD; plan CIP; adjust setpoints for temperature
ΔP high	Plugged strainers/cartridges; colloids/biofouling	Strainer debris, cartridge weight/color	Clean strainers; replace cartridges; alkaline clean; check dosing
Product conductivity high	Membrane damage; O-ring leaks; excessive recovery	Salt passage calc; vessel inspection	Lower recovery; inspect interconnectors; vendor assessment
Pump noise/vibration	Cavitation (NPSH), misalignment, air ingress	NPSH margin, suction line, seals	Improve suction head; align pump; fix leaks

Spares for 3–6 months (starter list)

• 5-µm cartridges (weekly change baseline; adjust by fouling rate)
• Antiscalant & SMBS (per dosing rate), pH adjusters
• HP pump seal kit; pressure-vessel O-rings; instrument spares (conductivity/pressure)
• One spare membrane element per train (optional, for rapid swap)
• UV lamp & ballast (if used)

Logs, safety & compliance

• Daily log: flows/pressures/ΔP/quality/temperature/dosing.
• Safety: chemical handling, eyewash, confined-space awareness around tanks.
• Zgodność: reject/brine discharge rules; potable water standards; keep records for inspections.

References & further reading

• WHO – Guidelines for Drinking-water Quality · CDC – Vessel Sanitation Program (Potable Water) · DNV – Rules & Standards (marine potable water)

Helpful internal links

Free RO sizing calculator · RO accessories & spare parts · Stainless-steel tanks

Ship RO maintenance summary & next steps

This ship RO maintenance guide summarized routines, normalization, CIP and troubleshooting. Start by tightening your daily log, setting CIP triggers, and aligning spares with your route and seawater seasonality. When performance drifts, normalize first—then clean deliberately, not reactively.

FAQs

How often should we change 5-µm cartridges?
Use ΔP and trend, not calendar alone: replace when ΔP rises rapidly or reaches vendor limits.

When do we run CIP?
Typically when normalized flow drops 10–15%, ΔP rises ~15%, or salt passage rises 10–20% and pretreatment is confirmed stable.

Do we need energy recovery on small skids?
Often not; smaller units see limited gains vs. added complexity. On larger SWRO, ERDs can materially cut kWh/m³.

What records should inspectors see?
Daily logs (pressures/flows/quality), chemical usage, CIP reports, calibration records, and potable water test results.