London: The DNV Effective Tank Cleaning (ETC) notation is increasingly being used for product and chemical tankers. This standard will now be even better in that it now requires an improved surface coverage in the cargo tanks and the use of tank cleaning machines with DNV-certified performance.

DNV has for more than 10 years now had the voluntary class notation Effective Tank Cleaning (ETC) to ensure efficient tank cleaning on board oil products and chemical tankers, initially in order to be able to change between black and white products.

So far, 93 oil and chemical tankers in operation have been built according to this standard, and an impressive additional 80 newbuildings have been ordered to DNV Class with this notation.

The cleanliness of cargo tanks is mainly a commercial issue. Except for the IMO Crude Oil Washing basic standard, there are only safety requirements related to cleaning standards in cargo tanks on oil tankers and chemical tankers. For chemical tankers and compliance with MARPOL Annex II, there are requirements for pre-wash and stripping performance that will be modified from the beginning of 2007.

From a technical point of view, cleaning cargo tanks on product and chemical tankers is often a time- and labour-consuming process due to the internal structures, lack of hot water capacity, low number and/or capacity of fixed tank cleaning machines, and in general too many shadows in cargo tanks.

Additionally, coated cargo piping systems have shown to be a source of cargo contamination when the coating is deteriorating.

DNV’s optional class notation ETC takes care of these issues by requiring:

• Cargo tanks to be stainless steel or coated, in general without internal structures (corrugated bulkheads).
• Cargo piping and heating coils to be of stainless steel or equivalent materials.
• Cargo tanks to be served by individual in-tank cargo pumps and have suction wells placed so as to ensure optimum drainage results.
• Cargo tank washing with hot water of min. 85°C with a capacity sufficient for washing at least the largest cargo tank.
• Tank cleaning machines:
• (Revised) Permanently installed tank washing machines giving minimum coverage of 96% based on DNV Certified Jet Length at normal operating pressure and minimum 10 degrees jet hit angle. Shadows caused by the pumps stacks are to be included in the shadow area.
• In addition, portable washing equipment and necessary access openings enabling complete washing of shadow areas are to be provided.