Mariners Library ⚓️

Dear colleagues and friends, The attached survey form is part of a research project conducted by our colleagues at a reputable company, aimed at exploring the use of new technologies in the maritime industry. Your participation in this survey can help make the research results more accurate and practical, leading to a clearer understanding of ideal working conditions. Regards

⚙️ 3️⃣ Practical Guidance Default conservative value (older and common designs): ➤ ≤ 350 cSt at washing temperature. Modern or heavy crude–optimized vessels: ➤ ≤ 600 cSt at washing temperature (if specifically approved and noted in the COW Manual). Always follow: The limit stated in your vessel’s COW Manual, since it reflects the manufacturer’s nozzle design, pump capacity, and heating system. 🧾 Example (from an actual COW Manual entry) “The crude oil used for washing shall have a viscosity not exceeding 600 cSt at the washing temperature, and the temperature shall be maintained at least 10 °C above the pour point.” ✅ In short: MARPOL = no fixed number. OCIMF (typical design) = 350 cSt. Some modern systems (flag/class approved) = up to 600 cSt. Your COW Manual = final authority.

⚙️ 2️⃣ What These Actually Say About Viscosity Here’s the key part: Neither MARPOL nor MEPC.81(43) specifies an exact numerical limit for viscosity such as 350 cSt or 600 cSt. Instead, they say: “Crude oils with a viscosity, pour point or wax content that would adversely affect the efficiency of the crude oil washing system shall not be used for washing.” This means: The specific limit depends on the design capability of the vessel’s COW system, as documented in the ship’s approved COW Manual. ⚙️ 2️⃣ What These Actually Say About Viscosity Here’s the key part: Neither MARPOL nor MEPC.81(43) specifies an exact numerical limit for viscosity such as 350 cSt or 600 cSt. Instead, they say: “Crude oils with a viscosity, pour point or wax content that would adversely affect the efficiency of the crude oil washing system shall not be used for washing.” This means: The specific limit depends on the design capability of the vessel’s COW system, as documented in the ship’s approved COW Manual.

⁉️ Viscosity Limit is 350 or 600 cSt ? this is an area where confusion often arises because different documents and eras have quoted different viscosity limits for crude oil washing (COW). Let’s clear it up carefully and trace the official reference sources. ⚙️ 1️⃣ The Official Framework COW operations are governed mainly by: MARPOL Annex I, Regulation 35 (requirements for crude oil washing) IMO Resolution MEPC.81(43) — “Revised Specifications for the Design, Operation and Control of Crude Oil Washing Systems” The ship’s approved Crude Oil Washing Operations and Equipment Manual (COW Manual) — prepared according to MEPC.81(43) OCIMF/ICS “Crude Oil Washing (COW) – Systems and Operations” (industry best practice)

⚠️ Key Operational Check: Before washing, you must confirm from: Cargo analysis report (viscosity at known temperature), and COW Manual (temperature/viscosity limits specified for your vessel). If viscosity > 350 cSt at washing temperature → COW must not be carried out.

⚙️ Viscosity Limit for Crude Oil Washing According to MARPOL Annex I, the ship’s approved COW Manual, and OCIMF/ICS guidelines, the viscosity of the crude oil should generally not exceed: 350 centistokes (cSt) at the washing temperature. 🧭 Explanation: Crude oil washing relies on the kinetic energy of the crude oil jets to dislodge clingage (residues) from tank surfaces. If the crude is too viscous, the jet loses energy quickly and cannot effectively clean the surfaces. High-viscosity crude also causes: Poor atomization from the washing machines. Blockage in the lines and strainers. Inadequate stripping and drainage. Increased sludge formation. 💡 Temperature adjustment Since viscosity decreases with heat, you can still use a heavier crude for washing if it is heated sufficiently. Recommended rule of thumb: Maintain washing temperature at least 10°C above the crude’s pour point, and Ensure the viscosity at that temperature does not exceed 350 cSt.

3- Instability or tendency to form emulsions Some crude oils form stable emulsions when agitated, making the washing ineffective and recovery of oil difficult. 4- Toxic, volatile, or hazardous crude cargoes If the crude has unusually high levels of H₂S or toxic vapors, COW may be unsafe due to the potential release of harmful gases. 5-When cargo is not crude oil COW is only for crude oil cargoes. It cannot be used if the ship is carrying: Refined products (e.g., diesel, gasoline, naphtha) Fuel oils, lubricating oils, or other non-crude products. 6- Temperature limitation If the cargo temperature falls too low for effective washing (below pour point +10°C), COW should not be carried out.