MARPOL Annex II Reg 12: pumping, piping, stripping

MARPOL Annex II Regulation 12 is the engineering rule of the noxious-liquid-substance regime. Where Regulation 16 decides what a chemical tanker is built to carry and Regulation 13 decides how the residue is washed and discharged, Regulation 12 fixes the quantity of cargo that may be left behind in the first place. It sets a hard ceiling, in liters, on the residue a tank and its piping may retain after the cargo pump and stripper have done their work, and it ties that ceiling to a witnessed performance test. Every downstream Annex II duty inherits its starting point from this number. A tank that strips to 75 liters begins its prewash with one-quarter of the residue a tank that strips to 300 liters carries, and the discharge criteria of Regulation 13 only make environmental sense because Regulation 12 has already squeezed the tank near empty.

The consolidated number is Regulation 12, titled “Pumping, piping, unloading arrangements and slop tanks,” as renumbered by Resolution MEPC.118(52) when the revised Annex II entered force on 1 January 2007. In the original 1987 Annex II the same engineering content sat under different regulation numbers within the design-and-equipment block, but every current edition, every recognized-organization rule set, and every Procedures and Arrangements Manual approved since 2007 references it as Regulation 12. This matters because the older A-B-C-D category text numbered its provisions differently, and a small number of secondary sources still quote a stale number. The figures below are taken paragraph by paragraph from the consolidated Annex II text and verified against the residue ceilings recorded in approved P&A Manuals.

The efficient-stripping standard: residue ceilings by build date

The core of Regulation 12 is a single quantity: the maximum residue, in liters, that a cargo tank and its associated piping may retain after unloading and stripping. The regulation states this as three tiers keyed to the ship’s construction date, and the standard tightens at each tier. The tier that applies to a given ship is fixed for the life of that hull. A 1990-built chemical tanker is held to the 1986-to-2007 figures for its entire service, not retroactively pulled up to the 75-liter standard, because the requirement is a design-and-construction obligation discharged at the build survey, not an operational limit re-tested each voyage.

Read the table by build date first, then by category. The pre-1986 ship may leave up to 300 liters of a Category X or Y substance and up to 900 liters of a Category Z substance in each tank and its piping. The ship built in the long middle window, from 1 July 1986 to the end of 2006, is held to 100 liters for the two higher-hazard categories and 300 liters for Category Z. The modern ship, built on or after 1 January 2007 under the revised Annex II, is held to a single uniform figure of 75 liters for all three categories. The 2007 revision did not invent the 75-liter number out of nothing; it took the tightest figure the industry had already proven achievable and applied it across the board, removing the category-dependent slack that older tonnage still enjoys.

Two points on the table earn an asterisk in practice. First, the categories named here are the present X, Y and Z. The pre-1986 and 1986-to-2007 ships were certified under the old A, B, C, D system, and the figures map across when the substance is re-categorized under the present list maintained in IBC Code Chapter 17. Second, for a ship other than a dedicated chemical tanker, built before 1 January 2007 and unable to meet the Category Z figure, Annex II provides that no quantity requirement applies and the tank need only be emptied to the most practicable extent. That carve-out is narrow. It does not reach chemical tankers, and it does not reach any ship built from 2007 onward.

Why the piping counts, not just the tank

The phrase “in the tank and its associated piping” is doing real work. A cargo officer who measures only the bottom of the tank, ignoring the loop of cargo line, the manifold drop, the stripping line, and the deadleg behind the cargo pump, will undercount the residue and over-report compliance. The Annex II figure is a system figure. It captures the cargo trapped in horizontal pipe runs where the pump can no longer pull a head, the heel in the pump casing itself, and the slug standing in the riser between the deck manifold valve and the shore connection. On a large parcel tanker with twenty or more segregations, the piping volume associated with a single tank can rival the strippable tank heel, which is exactly why the regulation refuses to let the piping be ignored.

This is also why deep-well pumps and educator-based stripping systems dominate the modern fleet. A submerged hydraulic deep-well pump mounted at the tank bottom strips the tank to a thin film, and a separate educator or a small reciprocating stripping pump then clears the cargo line back to the manifold. The combination is what lets a 2007-built ship hit 75 liters tank-plus-piping where a 1970s centrifugal pump with a long suction line could not reliably beat 300 liters. The performance of that system is what the Appendix 5 test measures, and the residue figure recorded for each tank in the P&A Manual is the tank-by-tank result, not a fleet assumption.

The arithmetic of a stripping run is straightforward once the system geometry is fixed. The residual that remains is the tank film plus the unstrippable piping holdup, and the compliance test is a simple inequality.

The Appendix 5 performance test

Regulation 12 does not let an owner assert compliance on paper. Each of the three residue-tier paragraphs ends with the same sentence: a performance test shall be carried out in accordance with Appendix 5 of the Annex. Appendix 5 is the procedure that turns the liter ceiling into a measured number for the specific ship as built or as converted. The test is the gate the cargo system must pass before the flag administration, or the recognized classification society acting for it, will approve the Procedures and Arrangements Manual and let the certificate of fitness list the cargoes the ship intends to carry.

The test medium is water, not the cargo. Water is used because it is repeatable, cheap, non-hazardous, and viscous enough at the test temperature to give a conservative read on a system that will later handle a range of products. The Administration approves the test, and the result is the residual quantity left in the tank and its piping after the prescribed stripping operation is run to completion. That measured residual is compared against the build-date ceiling. A 2007-built tank that strips to a measured 60 liters passes the 75-liter standard with margin. A tank that strips to 90 liters fails, and the pumping or piping arrangement must be modified, retested, and re-measured before the manual is approved for that tank.

How the residual quantity is measured

The measurement is the practical heart of the test. After the stripping run, the residue standing in the tank and the cargo piping associated with that tank is collected and gauged. On a tank with a sump and a deep-well pump, the strippable volume is run down until the pump loses suction, the system is allowed to drain to the low point, and the residue is then measured by collecting it into a calibrated container or by sounding the sump against a calibrated table. The piping holdup is measured by draining the associated lines to a collection point. The figure recorded is the sum: tank residue plus piping residue, against the single ceiling.

The test is run at a defined condition of trim and, where relevant, list, because a tank’s strippability is sensitive to attitude. A tank that strips clean at even keel may hold a wedge of residue at the after bulkhead if the ship trims by the head, since the suction bellmouth sits forward of the low point. Appendix 5 conditions are chosen to represent the attitude the ship will realistically achieve at the end of a discharge, so the recorded figure is not an optimistic best-case taken at an artificial trim. The surveyor witnessing the test confirms the trim, the stripping sequence, and the collection method, then signs the figure into the manual. That signed figure is what a port state control officer can later cross-check against the tank’s as-built arrangement.

What the witnessed test certifies, and what it does not

The Appendix 5 test certifies the system’s design stripping capability under controlled conditions. It does not certify that every operational discharge will leave exactly that residue. Operational residue depends on cargo viscosity, temperature, the integrity of the stripping sequence the crew actually runs, and the condition of the pump and valves on the day. A cargo that is far more viscous than water, discharged cold, will strip worse than the Appendix 5 water test predicts. This is the reason Regulation 13 layers a prewash duty and a discharge-criteria check on top of the Regulation 12 design figure rather than treating the build-survey number as a guarantee. The build test sets the floor; the operational regime polices the gap between the floor and reality.

Pumping and piping arrangements

The hardware that delivers the stripping standard is the cargo pumping and piping arrangement, and Regulation 12 governs its layout because the layout determines how much cargo the system can recover. Three features carry the regulation’s intent: the dedicated cargo pump per segregation, the stripping arrangement that clears the lines, and the underwater discharge outlet through which any residue-and-water mixture leaves the ship below the waterline.

The modern chemical tanker runs a dedicated submerged pump in each cargo tank, typically a hydraulically driven deep-well pump with its bellmouth set at the low point of the tank bottom. Dedicated pumping matters for two reasons. It keeps segregations physically separate so a Category X cargo never shares a pump or a line with a different parcel, and it lets each tank be stripped independently to the Regulation 12 ceiling without contamination from a common manifold. A shared-pump arrangement, common on older product tankers retrofitted for NLS service, complicates compliance because the common suction header holds residue that belongs to no single tank yet counts against the tank being measured.

The stripping arrangement and the manifold

Stripping is the operation of clearing the last heel from the tank and the cargo from the piping after the main discharge is complete. The arrangement is usually a small reciprocating stripping pump or an educator driven by the cargo pump’s own discharge, plumbed to pull the low points of the tank and the cargo line back to the manifold or to a slop tank. The stripping rate is low and the head is high, the opposite duty to the main cargo pump, which is why a separate device handles it. The performance of that device, paired with the line geometry, is what determines whether the piping holdup falls inside the 75-liter or 300-liter budget. A reciprocating stripping pump sized for the cargo line volume can clear a deadleg that an educator with limited suction lift cannot.

The cargo manifold is the regulated boundary between ship and shore. The drop from the deck manifold valve to the shore arm is part of the associated piping for residue-accounting purposes when the cargo is being stripped back into the ship, and the manifold identification, the line sizes, and the valve arrangement are recorded in the P&A Manual so the surveyor and the PSC officer can trace each tank to its lines. A discrepancy between the manifold arrangement as built and the arrangement as drawn in the manual is a finding, because it means the residue accounting cannot be trusted.

Pump types and the physics of the residue heel

The residue figure is set by physics the cargo officer cannot wish away, so the pump choice is the design decision that fixes whether a tank can meet the ceiling. A centrifugal deep-well pump pulls a head proportional to the square of impeller speed, and as the liquid level drops to a thin film the suction starts to draw vapor, the head collapses, and the pump can no longer move what is left. That point, the loss of suction, is where stripping begins and where the centrifugal pump alone stops being useful. The residue heel standing at that moment is a function of the tank-bottom geometry, the bellmouth clearance, and the ship’s attitude, and it is typically far larger than the 75-liter ceiling on its own.

Positive-displacement stripping closes the gap. A reciprocating stripping pump moves a fixed volume per stroke regardless of head, so it keeps pulling the heel down to a film measured in millimeters and clears the cargo line of the slug a centrifugal pump leaves behind. An educator, driven by a portion of the main cargo pump’s discharge through a venturi throat, creates a low-pressure region that entrains the heel and the line contents, trading some of the main pump’s flow for suction lift it cannot otherwise reach. The choice between a reciprocating stripping pump and an educator turns on the cargo-line length and the required lift: an educator is simpler and has no moving parts in the cargo, but its suction lift is limited, so a ship with long horizontal line runs to the manifold often carries a dedicated reciprocating stripper to guarantee the piping holdup falls inside budget. The stripping rate of a reciprocating pump can be sized directly against the line volume to be cleared.

The geometry that the pump fights is the unstrippable holdup: the cargo trapped where no suction can reach. The deadleg behind a closed valve, the horizontal run that drains to a low point the bellmouth does not command, and the pump casing itself all hold cargo that counts against the tank. A well-designed system slopes every cargo line toward a strippable low point and minimizes deadlegs, because every liter of unstrippable holdup is a liter subtracted from the 75-liter budget before the tank film is even counted. This is why two ships with identical pumps can post different Appendix 5 figures: the one with the cleaner line layout strips closer to the film, and the one with deadlegs and badly drained horizontals carries a permanent piping penalty.

The underwater discharge outlet

Where a ship is certified to carry Category X, Y or Z substances, Regulation 12 requires an underwater discharge outlet, or more than one, through which a residue-and-water mixture authorized for discharge under Regulation 13 leaves the ship. The outlet is required to be below the waterline for a specific environmental reason: a sub-surface discharge mixes into the receiving water and dilutes far faster than a surface discharge, which would streak the residue along the hull and into the wake where it stays concentrated and visible. The regulation locates the outlet within the cargo area, in the vicinity of the turn of the bilge, and requires that it be arranged so the discharge does not re-enter the ship through the seawater intakes serving the cooling and ballast systems.

The outlet must also be sized and positioned so the discharged mixture does not pass back through the ship’s boundary layer, the thin sheath of slow-moving water dragged along with the hull. If the discharge re-enters the boundary layer it travels aft with the ship instead of mixing into open water, defeating the dilution the sub-surface outlet was meant to deliver. Annex II fixes the minimum outlet diameter through a relationship between the discharge rate and the outlet’s longitudinal position:

where $d$ is the minimum diameter of the discharge outlet in meters, $Q_d$ is the maximum rate, in cubic meters per hour, at which the ship is permitted to discharge the residue-and-water mixture through the outlet, and $L_d$ is the distance in meters from the forward perpendicular to the outlet. The formula ties a higher permitted discharge rate to a larger outlet, and an outlet placed further aft, with a larger $L_d$, to a smaller minimum diameter, because the boundary-layer thickness and the local flow change along the hull. Where the discharge is directed at an angle to the shell plating rather than normal to it, the regulation substitutes for $Q_d$ the component of $Q_d$ normal to the shell, since only the normal component must clear the boundary layer.

The $Q_d$ value chosen at design then becomes an operational ceiling. The crew cannot discharge faster than the rate the outlet was sized for, because exceeding it would push the plume into the boundary layer that the diameter equation was solved to avoid. The P&A Manual records the maximum discharge rate, the outlet diameter, and the outlet location, and the at-sea discharge under Regulation 13 must respect that rate alongside the speed, depth, and distance conditions.

The slop tank and its relationship to Regulation 12

Regulation 12’s title names slop tanks, and the regulation’s position on them is more permissive than crews sometimes assume. Annex II does not require a dedicated slop tank on every NLS ship. The text provides that slop tanks may be needed for certain washing procedures and that cargo tanks may be used as slop tanks. The driver for fitting a segregated slop tank is the IBC Code and the ship’s assigned Type, together with the trade the ship is built for, rather than a blanket Regulation 12 mandate.

In practice a sophisticated parcel tanker carries one or more dedicated slop tanks within the cargo area, segregated from the cargo tanks and the machinery spaces by cofferdams or an approved equivalent, because the trade demands somewhere to collect prewash effluent and contaminated water before it goes to a reception facility or, for qualifying Category Z residues, before a controlled discharge to sea. A simpler ship that nominates a cargo tank as its slop tank for a given voyage records that nomination in the P&A Manual and accepts that the nominated tank is out of cargo service for the voyage. Either way, the slop arrangement is one of the defined sections of the P&A Manual, and the manual must state which tanks serve as slop tanks and how the prewash effluent routes from the cargo tank to the slop tank and onward.

The slop tank sits at the junction between Regulation 12 and Regulation 13. Regulation 12 strips the cargo tank to the liter ceiling; Regulation 13 then prewashes the stripped tank where the category demands it, and the prewash effluent has to go somewhere. The slop tank is where it goes if it is not landed directly to the shore reception manifold. The capacity of the slop arrangement therefore has to match the prewash water volumes the P&A Manual prescribes for the cargoes the ship carries, a sizing question the Regulation 13 wash patterns drive and the stripping efficiency of Regulation 12 feeds.

How the stripping standard drives the Regulation 13 prewash and discharge criteria

The Regulation 12 residue figure is the input to every Regulation 13 decision, and the two regulations are best understood as a sequence. Strip first, to the Regulation 12 ceiling. Then decide, under Regulation 13, what to do with the residue and the wash water that follows. The lower the strip figure, the less work Regulation 13 has to do and the faster the tank reaches a lawful state.

For a Category X residue, Regulation 13.1 requires a prewash before the ship leaves the port of unloading, with the effluent landed to a reception facility until the concentration at the receiving-facility inlet is at or below 0.1 percent by volume and the tank is empty. A tank stripped to 75 liters under the modern standard carries one-quarter the residue of a tank stripped to 300 liters into that prewash, so it reaches the 0.1 percent end-point in fewer wash cycles and less wash water. The Regulation 12 standard is what makes the Regulation 13.1 end-point economically and physically achievable; without efficient stripping, the dilution math would demand impractical volumes of wash water to drag the concentration down.

For high-viscosity and solidifying Category Y residues, Regulation 13.2 imposes the same prewash-to-reception duty, and the stripping standard matters even more because viscous and solidifying cargoes strip worse than the Appendix 5 water test predicts. A solidifying cargo that congeals on the tank bottom can leave far more than the certified residue if the stripping run is not done hot and fast, which is why the P&A Manual specifies heated wash water and a defined cycle structure for those cargoes. For standard Category Y and most Category Z residues handled through the operational discharge regime, the residue left by Regulation 12 stripping is the quantity that the at-sea discharge criteria then have to render harmless by dilution.

The at-sea discharge criteria

When a residue-and-water mixture is discharged to sea rather than landed ashore, Annex II Regulation 13 imposes simultaneous operational conditions, and the underwater outlet sized under Regulation 12 is the only lawful path for that discharge. The ship must be proceeding en route at a speed of at least 7 knots if self-propelled, or at least 4 knots if under tow. The discharge point must be at least 12 nautical miles from the nearest land, in water at least 25 meters deep. The discharge must pass through the underwater outlet at no more than the maximum rate $Q_d$ the outlet was designed for. These conditions exist to guarantee dilution: speed and depth spread the plume, distance keeps it off the coast, and the boundary-layer-clearing outlet from Regulation 12 ensures the diluted mixture actually mixes into open water rather than clinging to the hull. Strip the tank well under Regulation 12, and the quantity entering this discharge is small; strip it poorly, and the discharge criteria are carrying a larger load they were never designed to neutralize.

The Cargo Record Book and the P&A Manual cross-check

The Regulation 12 figure is not a one-time build-survey artefact; it reappears every voyage in the operational paperwork. The Procedures and Arrangements Manual records the tested stripping quantity for each tank, the slop-tank arrangement, the underwater outlet diameter and location, and the maximum discharge rate, all approved by the flag administration or its recognized classification society. The manual is the single operational reference the cargo officer reads before each discharge, and it is the document the surveyor checks against the as-built pumping and stripping arrangement at each periodic survey.

The Cargo Record Book is where the operational reality is logged against the design figures. Each unloading, each stripping operation, each prewash, each transfer to a slop tank, each receipt at a reception facility, and each at-sea discharge is entered under the prescribed letter codes, signed by the officer in charge, and countersigned by the master. A port state control officer reading the Cargo Record Book against the P&A Manual is verifying that the residual quantities the crew claims to have achieved are consistent with the tested stripping capability the manual certifies. If the record book shows a discharge of a Category X residue to sea, or a quantity inconsistent with the tank’s certified stripping figure, the officer has a documentary trail to a deficiency. The Cargo Record Book retention period is three years from the date of the last entry, which gives the PSC regime a multi-voyage window to detect a pattern of non-compliance rather than a single bad discharge.

What a PSC officer checks on the stripping arrangement

A port state control officer cannot re-run the Appendix 5 test, so the inspection works by consistency. The officer reads the tested stripping figure for each tank from the P&A Manual, then walks the deck to confirm the pumping and piping arrangement matches the manual: the pump type, the stripping arrangement, the manifold layout, and the underwater outlet diameter and location. A mismatch between the as-built hardware and the manual breaks the residue accounting, because the tested figure was certified against an arrangement the ship no longer has. The officer then reads the Cargo Record Book for the recent voyages and asks whether the logged residual quantities and discharge entries are consistent with the certified stripping capability. A record book that shows residuals well above the tank’s tested figure, or an at-sea discharge of a residue the category does not permit, is the documentary trail to a deficiency.

The stripping arrangement is a recurring PSC focus on chemical tankers because it is the rule most directly tied to what reaches the sea. The officer’s only tool is not a fresh measurement but the three-way cross-check: certificate of fitness against P&A Manual against Cargo Record Book, plus a physical walk of the deck. A ship that strips well, keeps its manual current with its hardware, and logs honestly has nothing to fear from the cross-check; a ship that has let its arrangement drift from its manual, or that strips poorly and discharges the excess at sea, leaves a paper trail the inspection is built to find. The escalation runs from a recorded deficiency to a rectification requirement, and in a clear case to detention until the arrangement is corrected and re-approved.

This three-document chain, certificate of fitness, P&A Manual, and Cargo Record Book, is how Regulation 12 stays enforceable after the build survey. The certificate says what the ship may carry, the manual says how the ship strips and discharges it, and the record book says what the ship actually did. A break in the chain, a manual that lists a stripping figure the certificate’s tank assignment cannot support, or a record book entry the manual’s procedures cannot produce, is the signature of a Regulation 12 problem.

Worked example: compliant versus non-compliant stripping

Take a chemical tanker built in 2010, so the 75-liter Regulation 12 ceiling applies to all categories. Tank 4 starboard is certified for a Category Y substance and is fitted with a deep-well pump and a reciprocating stripping pump serving the cargo line back to the manifold. The Appendix 5 test recorded a residual of 58 liters for this tank. Two discharges follow, one run correctly and one run badly, to show how the same hardware produces a compliant and a non-compliant result.

In the compliant discharge, the cargo officer runs the main cargo pump down until it loses suction, then starts the stripping pump and works the low points of the tank and the cargo line in the sequence the P&A Manual prescribes, with the ship trimmed by the stern to bring the residue to the suction bellmouth. The tank film measures 34 liters and the cargo-line holdup measures 27 liters, for a total of 61 liters. Against the 75-liter ceiling the tank is compliant, with 14 liters of margin. The residual is logged, the prewash for the high-viscosity Category Y cargo proceeds from a low starting load, and the wash reaches the 0.1 percent end-point inside the cycle count the manual specifies.

In the non-compliant discharge, the officer stops at the main cargo pump and skips the line-stripping step, leaving the ship trimmed slightly by the head. The tank film now measures 52 liters because the residue has pooled against the forward bulkhead away from the bellmouth, and the cargo line holds its full 41 liters because the stripping pump never ran. The total is 93 liters, which exceeds the 75-liter ceiling by 18 liters.

The hardware was identical in both cases; the certified capability was 58 liters in both cases. The difference is entirely operational: the trim attitude and the decision to run or skip the line-stripping sequence. This is the gap between the Appendix 5 design figure and operational reality that Regulation 13’s prewash and discharge criteria exist to police. The 93-liter tank carries 53 percent more residue into its prewash than the 61-liter tank, demands more wash water and more cycles to reach the same end-point, and produces a larger volume of effluent that the slop tank and the reception facility have to absorb. A PSC officer who finds the Cargo Record Book showing residual quantities inconsistent with the tank’s 58-liter tested figure has grounds to inspect the discharge sequence the crew actually follows. The cost of poor stripping is not paid at the tank; it is paid downstream in wash water, slop capacity, reception charges, and inspection exposure. The residual-quantity arithmetic and the prewash-water demand it drives can be checked with the relevant stripping and discharge calculators below.

Interaction with the IBC Code and the certificate of fitness

Regulation 12 does not stand alone; it is read with the IBC Code, the mandatory construction-and-equipment standard for ships carrying dangerous chemicals in bulk. The IBC Code Chapter 5 cargo-transfer requirements and the Chapter 16 operational requirements work alongside Annex II Regulation 12 to define the pumping, piping, and stripping arrangement that the certificate of fitness then certifies. A ship’s IBC certificate of fitness cargo annex lists the tanks and the cargoes each may carry; the Regulation 12 stripping figure recorded in the P&A Manual is the evidence that each listed tank can be emptied to the Annex II ceiling for the cargoes assigned to it.

The two instruments share a boundary at the cargo system. The IBC Code governs the materials, the segregation, the venting, and the safety of the cargo handling; Annex II Regulation 12 governs the environmental performance of the same system, expressed as the residue ceiling. A tank that satisfies the IBC Code on materials and segregation but cannot strip to the Regulation 12 figure cannot carry the cargo lawfully, because the environmental obligation is independent of the safety obligation. The class society plan-approval process checks both, and the build survey witnesses the Appendix 5 stripping test as part of issuing the certificate of fitness alongside the Annex II certificate of fitness for NLS.

Limitations

The figures and procedures here describe the consolidated MARPOL Annex II as revised by MEPC.118(52) and in force from 1 January 2007, with the related Standard for Procedures and Arrangements Manual adopted as MEPC.119(52) at the same session. Annex II is amended periodically, and later resolutions, including those addressing high-viscosity and solidifying substances, change the operational rules around stripping and prewashing without altering the core Regulation 12 residue ceilings. A reader applying this to a specific ship must confirm the edition of Annex II in force at the ship’s build date and the current edition for operational duties, and must read the ship’s own P&A Manual and certificate of fitness, which carry the tank-specific tested figures that govern that ship.

This article does not reproduce the full text of Appendix 5 or the exact wording of any Regulation 12 paragraph; it summarizes the standard and the tested values. The underwater discharge outlet diameter equation is presented in its standard form, but the precise constant and the exact definition of the longitudinal reference can vary in presentation between editions and between flag-state and class-society guidance, and the authoritative form for a specific ship is the one in that ship’s approved P&A Manual. The worked example uses illustrative residual figures to show the compliant-versus-non-compliant contrast; it is not drawn from a specific ship’s survey record. The stripping and discharge calculators paired with this article model the residue and discharge arithmetic under stated assumptions and do not substitute for the witnessed Appendix 5 test or the flag-approved manual.

Regulation 12 is one regulation in a tightly coupled set. The numbering and content here are accurate for the consolidated text, but the regulation cannot be applied in isolation from the category-determination rules of Regulation 6, the cargo-tank arrangement of Regulation 16, the washing and discharge regime of Regulation 13, and the survey-and-certification provisions that bring the certificate of fitness into force. Practitioners should treat this as a reference to the stripping standard and its engineering, not as a standalone compliance procedure.

See also

• MARPOL Annex II: the noxious-liquid-substance regime and the X/Y/Z/OS category structure
• MARPOL Annex II Regulation 13: cargo tank washing: the prewash, ventilation, and discharge regime that follows stripping
• MARPOL Annex II Regulation 16: cargo tank arrangement: the structural rule and ship-Type assignment
• MARPOL Convention: the parent instrument and its six annexes
• IBC Code: the construction-and-equipment standard read with Annex II
• Chemical tanker: ship types, cargo systems, and the parcel trade
• Port state control: the inspection regime that cross-checks the Cargo Record Book against the P&A Manual
• MARPOL Annex I Regulation 38: reception facilities: the shore facilities that receive prewash effluent