It has been reported several times that overpressure and structural damage to cargo tank occurred in chemical tankers during loading operation, and alleged to be caused by malfunction of the High Velocity Vents manufactured by Niikura Kogyo Co., Ltd.

A prime reason was considered that the viscous substance derived from cargo vapour clogged the valve seat and caused malfunction resulted in an overpressure condition exceeding allowable structural strength of the cargo tanks.

While assuming that you have done the maintenance and inspection work for High Velocity Vents installed on board your ships in accordance with the Instruction Manual of the manufacturer, we sincerely recommend in view of the above to inspect High Velocity Vents and to ensure no foreign materials on the valve seats, prior to each loading operation.

For any questions about the above, please contact:

NIPPON KAIJI KYOKAI (ClassNK)
Survey Department, Administration Center, Head Office
Address: 4-7 Kioi-cho, Chiyoda-ku, Tokyo 102-8567, Japan
Tel.: +81-3-5226-2027 / 2028
Fax: +81-3-5226-2029
E-mail: svd@classnk.or.jp