A scrubber washwater monitoring instrument that is not correctly maintained in service will drift from its calibrated baseline, produce unreliable readings and eventually fail. The compliance record it generates during that decline is also unreliable — and an unreliable compliance record is a liability during a port state control inspection even if the underlying washwater actually met the required parameter limits.
Under MEPC.340(77), maintenance and servicing records for the washwater monitoring system must be kept in the EGCS Record Book. This makes maintenance not just a technical matter but a documented compliance obligation. This article sets out the full maintenance programme for a scrubber washwater monitor in service: what tasks are required, how often, how to detect calibration drift early and what must be recorded in the EGCS Record Book. For the full records framework, see What Records Does a Ship Need to Prove Scrubber Washwater Compliance?.
| Key thing to remember Under MEPC.340(77), maintenance and servicing records for the washwater monitoring system are a mandatory part of the EGCS Record Book. Maintenance that is not recorded did not happen as far as a port state control inspector is concerned. Every cleaning event, filter replacement, sensor replacement, calibration verification and service engineer visit must be entered in the EGCS Record Book with the date, details and name of the person responsible. |
Why Does a Washwater Monitor Need Regular Maintenance?
A scrubber washwater monitoring instrument operates in one of the most demanding environments of any analytical instrument at sea. The washwater stream passing through the measurement cell contains dissolved sulphur compounds, PAH, heavy metals, particulate matter, residual oil and biological material. Over time, this combination of contaminants fouls the optical surfaces of the measurement cell, degrades consumable components in the sample conditioning system and causes the sensor to drift from its calibrated baseline.
The consequences of inadequate maintenance are:
- Calibration drift producing readings that do not accurately reflect the actual PAH, turbidity or pH of the washwater — with the risk that genuinely non-compliant discharge passes undetected or that compliant discharge triggers false alarms
- Optical path fouling producing elevated readings that trigger unnecessary alarms, leading crew to dismiss alarm events and undermining the integrity of the alarm response procedure
- Premature sensor failure requiring unscheduled replacement in port rather than planned replacement on schedule
- Gaps in the maintenance record that create compliance questions during port state control inspection regardless of whether the monitor was actually performing correctly
Correct preventive maintenance minimises all four risks simultaneously. It keeps the monitor accurate, keeps the alarm system credible, extends equipment life and keeps the EGCS Record Book clean.
What Is the Recommended Maintenance Schedule for a Washwater Monitor?
The table below sets out the recommended maintenance programme covering daily, weekly, monthly and scheduled interval tasks. Where the manufacturer’s O&M manual specifies different frequencies for any task, the manufacturer’s guidance takes precedence over this general schedule.
| Frequency | Task | What to do and check | Who carries it out |
| Daily | Visual inspection | Check monitor display for active alarms, error codes or unusual readings. Confirm data logging is active and recording. Note any anomalies in the watch log. | Officer of the watch |
| Daily | Sample line check | Confirm sample flow to the monitor is within the specified range. Check for leaks at sample line connections. | Officer of the watch or engineer |
| Weekly | Optical path inspection | Inspect the measurement cell optical surfaces for signs of fouling. Clean if fouling is visible or if readings appear elevated without process change. | Engineer |
| Weekly | Sample conditioning check | Check pressure regulator, flow control valve and filter condition. Replace filter elements if differential pressure indicates they are approaching end of life. | Engineer |
| Weekly | Alarm function test | Test the high-parameter alarm for at least one parameter to confirm the alarm activates correctly and that the alarm signal reaches the control room. | Engineer |
| Monthly | Full optical path clean | Clean all optical surfaces in the measurement cell using the manufacturer’s recommended procedure. Record the cleaning event in the EGCS Record Book. | Engineer |
| Monthly | Grab sample correlation | Take a grab sample from the same point as the monitor sample tap and send for independent laboratory analysis. Compare the laboratory result with the concurrent monitor reading to detect calibration drift. | Chief engineer |
| Monthly | Sample conditioning service | Replace filter elements on schedule regardless of differential pressure reading. Inspect pump and valve seals for signs of wear. Lubricate or replace as required. | Engineer |
| Monthly | Data logging verification | Confirm that the data log is recording continuously at the required frequency and that data can be exported correctly. Verify timestamps are accurate against vessel clock. | Engineer |
| At manufacturer interval | Sensor replacement | Replace the measurement sensor at the interval specified in the manufacturer’s O&M manual. Record replacement in the EGCS Record Book with component batch number and date. | Service engineer or trained crew |
| At manufacturer interval | Full calibration verification | Carry out a full calibration verification using a certified reference sample. Where calibration adjustment is needed, adjust and record the calibration event in the EGCS Record Book. | Service engineer |
| Annually or at drydock | Service engineer visit | Arrange a service engineer visit for full system inspection, sensor replacement if due, calibration verification and EGCS Record Book review. Obtain updated service certificate. | Rivertrace service engineer |
The SMART ESM from Rivertrace is designed to support this maintenance programme with modular components that allow optical path cleaning and sensor replacement to be carried out by trained crew without requiring specialist tools. Rivertrace provides planned maintenance agreements that schedule sensor replacement and calibration verification visits aligned with the vessel’s dry-docking and port call schedule.
How Do You Clean the Optical Path of a Washwater Monitor?
Optical path cleaning is the most frequent active maintenance task for a washwater monitoring instrument and the one that has the greatest impact on sustained measurement accuracy. The optical path covers all surfaces through which the light beam passes in the measurement cell, including the light source window, the sample flow path and the detector window.
The cleaning procedure for the SMART ESM and most similar instruments follows these steps:
- Isolate the sample flow to the measurement cell using the isolation valve on the sample line
- Allow the sample conditioning system to drain or flush through before opening the measurement cell
- Open the measurement cell according to the procedure in the manufacturer’s O&M manual — do not use tools or abrasives on optical surfaces
- Clean the optical windows using the manufacturer’s approved cleaning materials and procedure. Typically a soft, lint-free cloth or cotton swab with a recommended optical cleaning solution.
- Inspect the optical surfaces for damage, scratching or contamination that cannot be removed by cleaning. Note any damage in the EGCS Record Book.
- Reassemble the measurement cell and restore sample flow
- Allow the instrument to return to normal operation and verify that readings return to the expected baseline before resuming discharge monitoring
- Record the cleaning event in the EGCS Record Book with the date, condition of the surfaces and name of the person carrying out the work
| Never use abrasives or solvents not approved by the manufacturer The optical windows of a washwater monitoring instrument are precision optical components. Using unapproved cleaning materials, abrasive cloths or strong solvents can permanently damage the optical surfaces and affect measurement accuracy. Always use only the cleaning materials and procedures specified in the manufacturer’s O&M manual. Damage caused by incorrect cleaning is not covered by instrument warranty and may require cell replacement. |
How Do You Carry Out Grab Sample Correlation?
Grab sample correlation is the most effective method for detecting calibration drift in service between formal calibration verification events. It compares the reading produced by the monitoring instrument with an independent laboratory analysis of a sample taken from the same point at the same time.
The grab sample correlation procedure is:
- Take a representative grab sample from the monitoring sample tap at the discharge point, at the same time as the monitor is producing a steady reading
- Record the concurrent monitor reading for each parameter at the time of sampling — PAH, turbidity and pH
- Send the grab sample to an independent accredited laboratory for analysis of the same parameters
- When the laboratory result is received, compare it with the recorded concurrent monitor reading
- If the laboratory result and the monitor reading are within the acceptable correlation tolerance specified by the manufacturer or flag Administration, no calibration adjustment is required
- If the laboratory result and the monitor reading differ beyond the acceptable tolerance, calibration drift is indicated and a calibration verification and adjustment should be arranged
- Record the grab sample correlation result in the EGCS Record Book regardless of the outcome
Monthly grab sample correlation is recommended as a minimum. In conditions that increase the risk of calibration drift — high washwater solids loading, changing fuel types, recent maintenance events — more frequent correlation provides earlier warning of drift.
How Do You Detect Calibration Drift Early?
Calibration drift in a washwater monitor typically develops gradually rather than suddenly. The patterns in the monitoring data and the maintenance record that indicate developing drift are recognisable if the crew and technical superintendent know what to look for. The table below maps observable patterns to their likely causes and recommended actions.
| Observation | What it suggests | Recommended action |
| Consistent offset between monitor readings and grab sample results | The monitor reads consistently higher or lower than independent laboratory analysis of samples taken at the same point | Calibration drift is the most likely cause. Arrange a calibration verification and adjustment. Record in the EGCS Record Book. |
| Readings that are stable but implausible given process conditions | The monitor reading does not change in response to known process changes such as load variations or fuel changes that should affect PAH output | Sensor fouling or a blocked sample line may be causing the monitor to measure clean sample conditioning water rather than process washwater. Check sample line and clean optical path. |
| Erratic or spiking readings not explained by process events | Readings spike unpredictably without corresponding process events | Gas bubble interference from dissolved gas in the sample or sample conditioning system pressure problems. Check sample conditioning system pressure and degassing arrangements. |
| Readings that increase progressively over weeks | Gradual upward drift in baseline readings over a period of weeks | Progressive optical path fouling. Increase cleaning frequency. Check sample conditioning filtration. |
| Readings that fall to zero or near-zero implausibly | Monitor reads zero or near-zero even during normal EGCS operation | Sample line blockage or loss of sample flow. Check sample line and pump. Confirm sample is reaching the measurement cell. |
The most reliable early indicator of calibration drift is a consistent offset between the monitor reading and the grab sample correlation result. A single grab sample that differs from the monitor reading may reflect sampling variability. A consistent pattern across multiple monthly correlations in the same direction indicates drift and should trigger a calibration verification.
When Should the Monitoring Sensor Be Replaced?
The measurement sensor is the primary consumable component of a washwater monitoring instrument. Unlike filters and seals, which are replaced on a condition or interval basis, the sensor must be replaced at the interval specified by the manufacturer to maintain calibration validity and type approval compliance.
The sensor replacement obligation under MEPC.340(77) is more explicit than under MEPC.259(68). Where MEPC.340(77) applies, the monitoring system must be maintained in accordance with the manufacturer’s specifications and the maintenance records must be kept in the EGCS Record Book. An out-of-interval sensor is a maintenance deficiency that undermines the compliance status of the monitoring data produced after the replacement date.
Triggers for early sensor replacement before the scheduled interval include:
- Grab sample correlation results that consistently differ from the monitor reading beyond the acceptable tolerance despite cleaning and sample conditioning checks
- Progressive baseline drift that does not respond to optical path cleaning
- Physical damage to the sensor observed during a maintenance inspection
- Self-diagnostic error codes from the monitoring system indicating sensor performance below specification
Every sensor replacement must be recorded in the EGCS Record Book with the replacement date, the part number and batch number of the new sensor, the reason for replacement and the name of the person or service engineer carrying out the work.
What Calibration Verification Is Required and How Is It Carried Out?
Calibration verification confirms that the monitoring instrument is producing readings that accurately reflect the actual parameter values in the washwater sample. Under MEPC.340(77), the monitoring system must be approved by the flag state Administration, and maintaining it in calibration is part of that approval obligation. For the full context of MEPC.340(77) requirements, see What Is MEPC.340(77) and How Does It Differ From MEPC.259(68)?.
A formal calibration verification is carried out by a trained service engineer using certified reference standards. The procedure involves:
- Presenting a certified reference standard of known PAH concentration, turbidity or pH value to the monitoring instrument in controlled conditions
- Recording the instrument reading and comparing it with the certified reference value
- Adjusting the instrument calibration if the reading falls outside the acceptable tolerance specified by the manufacturer or flag Administration
- Repeating the verification after any adjustment to confirm the corrected reading is within tolerance
- Issuing an updated calibration certificate recording the verification date, reference standards used, result before and after any adjustment, and the name and credentials of the service engineer
The calibration certificate must be retained onboard and the calibration verification must be entered in the EGCS Record Book. Port state control inspectors and flag state surveyors will check whether the calibration is current when reviewing EGCS compliance documentation.
What Must Be Recorded in the EGCS Record Book for Each Maintenance Task?
Under MEPC.340(77), all maintenance and servicing records for the washwater monitoring system must be kept in the EGCS Record Book. The table below sets out the specific content required for each type of maintenance entry. For the complete records framework, see What Records Does a Ship Need to Prove Scrubber Washwater Compliance?.
| Maintenance event | Required EGCS Record Book entry content |
| Optical path cleaning | Date and time of cleaning; method used; condition of optical surfaces before and after cleaning; name of person carrying out the work |
| Filter element replacement | Date of replacement; filter element batch number or part number; reason for replacement (scheduled or early replacement due to high differential pressure); name of person carrying out the work |
| Sensor replacement | Date of replacement; sensor part number and batch number; reason for replacement (scheduled replacement or early replacement due to performance); name of person or service engineer carrying out the work |
| Grab sample correlation | Date and time of sample; concurrent monitor reading; laboratory result; correlation assessment; any action taken as a result |
| Calibration verification and adjustment | Date of verification; method used; reference standard used; result before and after adjustment; name of service engineer or person carrying out the verification; updated calibration certificate reference |
| Alarm function test | Date of test; parameter tested; test result (alarm activated or did not activate); any corrective action taken |
| Service engineer visit | Date of visit; name and organisation of service engineer; work carried out; components replaced; calibration status; service report reference number |
The discipline of making complete and timely EGCS Record Book entries for every maintenance event is the single most important habit for maintaining a clean compliance record. An inspector who sees consistent, detailed entries for every maintenance task sees a vessel that is managing its EGCS compliance actively. An inspector who sees blank pages, incomplete entries or entries made in retrospect sees a vessel that is not.
How Does the Rivertrace Service Programme Support In-Service Maintenance?
Rivertrace provides a planned maintenance and service programme for the SMART ESM that is designed to keep the instrument in calibrated, compliant operation across the vessel’s operating schedule.
The programme covers:
- Planned sensor replacement visits scheduled in advance to coincide with port calls or dry-docking, eliminating unscheduled downtime
- Calibration verification at manufacturer-specified intervals, with updated calibration certificates and EGCS Record Book documentation issued after each visit
- Technical support by phone and email for in-service troubleshooting and guidance on maintenance procedures
- Spares packages holding the key consumable and replacement components required for crew-maintained tasks between service engineer visits
- EGCS Record Book review at each service visit to confirm that the maintenance record is complete and consistent
For marine vessel operators seeking to establish or review a maintenance programme for the SMART ESM, contact the Rivertrace service team. For guidance on what to do if the monitoring instrument fails during operation, see What Happens if a Scrubber Washwater Monitoring Instrument Fails?.
Frequently Asked Questions
How often should a scrubber washwater monitor be maintained?
A scrubber washwater monitoring instrument requires daily visual checks and sample line verification, weekly optical inspection and alarm testing, monthly full optical path cleaning, monthly grab sample correlation and monthly sample conditioning service. At manufacturer-specified intervals, the measurement sensor must be replaced and a formal calibration verification must be carried out by a trained service engineer. All maintenance events must be recorded in the EGCS Record Book.
How do you clean the optical path of a washwater monitor?
Isolate sample flow to the measurement cell, allow the conditioning system to drain, open the cell according to the manufacturer’s procedure, clean the optical windows with manufacturer-approved materials and a soft lint-free cloth or cotton swab, inspect for damage, reassemble, restore sample flow and verify that readings return to the expected baseline. Use only cleaning materials and procedures specified in the O&M manual. Record the cleaning event in the EGCS Record Book.
What is grab sample correlation and why is it important?
Grab sample correlation involves taking a manual sample from the same point as the monitor sample tap at the same time the monitor is producing a steady reading, and sending it to an independent accredited laboratory for analysis of the same parameters. Comparing the laboratory result with the concurrent monitor reading is the most effective method of detecting calibration drift between formal calibration verification events. Monthly correlation is recommended as a minimum.
How do you know if the washwater monitor has drifted out of calibration?
The clearest indicator is a consistent offset between the monitor reading and the grab sample correlation result across multiple monthly correlations. Other indicators include readings that are stable but implausible given process conditions, progressive upward baseline drift that does not respond to optical path cleaning, and erratic readings not explained by process events. Any of these patterns should trigger a formal calibration verification.
When does the measurement sensor need to be replaced?
The sensor must be replaced at the interval specified in the manufacturer’s O&M manual. Early replacement is triggered by consistent calibration drift beyond acceptable tolerance despite cleaning, progressive baseline drift that does not respond to cleaning, physical damage to the sensor, or self-diagnostic error codes indicating sensor performance below specification. Every replacement must be recorded in the EGCS Record Book with the part number, batch number and name of the person carrying out the work.
Does MEPC.340(77) require washwater monitor maintenance to be recorded?
Yes. Under MEPC.340(77), the EGCS Record Book must contain maintenance and servicing records for the washwater monitoring system. Every cleaning event, filter replacement, sensor replacement, calibration verification and service engineer visit must be entered with the date, details of the work and the name of the responsible person. Maintenance that is not recorded in the EGCS Record Book will not be recognised as having been carried out during a port state control inspection.
What is included in the Rivertrace SMART ESM service programme?
The Rivertrace service programme for the SMART ESM includes planned sensor replacement visits scheduled around port calls or dry-docking, calibration verification at manufacturer-specified intervals with updated certificates and EGCS Record Book documentation, technical support for in-service troubleshooting, spares packages for crew-maintained tasks and EGCS Record Book review at each service visit. Contact Rivertrace for details of the programme and scheduling.