Class societies issue guidelines for preventing liquefaction sinkingsJun 14, 2012 04:00 PM
In response to bulk carrier sinkings linked to liquefaction of cargoes of nickel ore, the Japanese classification society ClassNK has released new guidelines to measure the structural strength of cargo holds and the stability of new vessels specifically built to carry this ore.
Major marine casualties related to the carriage of nickel ore have been reported, according to the second edition of the “Guidelines for the Safe Carriage of Nickel Ore” released by Nippon Kaiji Kyokai (ClassNK) in February. Four vessels carrying nickel ore — Jian Fu Star, Nasco Diamond, Hong Wei and Vinalines Queen — sank between the end of 2010 to 2011, leading to the deaths of 66 mariners.
All four vessels loaded cargo in Indonesia.
“We supported the newbuilding of a specially constructed cargo ship for the first time certified by Panama Maritime Authority on Oct. 17, 2011, whose findings later became the basis of the revised guidelines,” said Yasushi Nakamura, ClassNK executive vice president. “The revised guidelines have already been introduced to the governments of Liberia, the Marshall Islands and Japan, and we have had a positive reaction from these flag states.”
In July 2011, the Italian class society Registro Italiano Navale (RINA) released its own rules for design standards for newbuilds transporting all bulk cargoes that are at risk to liquefy, not just nickel ore.
The installation of longitudinal bulkheads to subdivide the hold and reduce the area where a cargo could move is one of the main design requirements to help prevent losses resulting from liquefaction.
When liquefaction occurs, cargo can flow, compromising stability and leading to a severe list or even to the capsizing of the ship, according to Clay Maitland, managing partner of International Registries Inc.
Liquefaction is caused by the presence of too much moisture in cargoes of bulk mineral ore. The danger of sinking due to liquefaction can be determined by calculating a cargo’s transportable moisture limit (TML) — a measure of the maximum safe moisture content in a cargo.
The rules governing the carriage of bulk cargoes — the International Maritime Solid Bulk Cargoes (IMSBC) Code — allows existing vessels to carry cargoes prone to liquefy, as long as the moisture content is below the TML and the cargo is properly loaded, stowed and trimmed, according to David McKie, partner at the international legal practice Norton Rose LLP.
But a vessel can safely transport a cargo that exceeds the TML, as long as the ship has been specially constructed to carry the cargo, according to the IMSBC Code. This code does not address the technical requirements needed to build this type of ship, hence the new rules.
The revised ClassNK’s guidelines aim to specify construction standards for cargo ships that could safely carry nickel ore that exceeds the TML, according to Nakamura.
ClassNK has already received a number of inquiries about specially constructed ships. “Several shipyards have already entered the design phase and have been in touch inquiring after specific calculation methods,” said Nakamura.
However, advocates working to stop sinkings resulting from liquefaction maintain that the vessel itself should not be the focus.
“The real issue is the cargo, not the structure of the ships,” Maitland wrote in an e-mail.
The central problem with shipping bulk cargoes prone to liquefaction is accurately measuring the moisture content before the cargo is loaded. These cargoes are made up of fine particles, containing air and moisture, according to Maitland.
“If moisture levels are low, the frictional forces between the grains will be enough to maintain the cargo in a solid state,” he wrote. “However, if the moisture level in the cargo is in excess of a specific level, known as flow moisture point (FMP), the frictional forces limiting movement are very weak, causing the cargo to shift and move, very like Jell-O in a tipped bowl.”
Bulk ores are often extracted from open-air mines and stored in the open in regions where there are frequent downpours. These factors can increase the moisture in cargoes to dangerous levels, Maitland wrote.
Problems with vessel stability can arise when cargoes are mistakenly thought to have moisture content below the limit. This occurs because of inaccurate sampling, incorrect testing, improper loading and trimming, lack of training of the master and crew, failure to spot an obviously wet cargo, commercial pressures or occasionally running a deliberate risk, according to McKie.
The installation of longitudinal bulkheads is the major design change to prevent movement of cargo and maintain stability of the vessel. The steel used in these bulkheads and other supporting structures in the hold has to meet specific criteria, according to the RINA guidelines.
Stability requirements for bulkers are also part of the rules that both ClassNK and RINA have released.
Using RINA’s rules, ships would be safe even if liquefaction occurred, said a July 28, 2011, press release from the classification society.
Establishing the TML is difficult and is easily impacted by other factors, according to Paolo Salza, senior manager for RINA’s technical department. “It is much safer to design or convert the ship to withstand liquefaction of the cargo,” he said. “That is what our new notation permits.”
These rules took effect Aug. 1, 2011. However, they are not compulsory for a ship to be classified by RINA, said Dino Cervetto, technical services manager for RINA.
The Italian classification society is working with STX Offshore & Shipbuilding Co. in Korea on a newbuild, which would use the new rules, according to Cervetto. RINA also completed a design for an existing vessel for the Chinese company Shanghai Tian Zheng Marine Technical Services Co. he said. The design is for a supramax vessel. RINA estimates it would cost about $3 million for retrofitting a supramax carrier.
Maitland is skeptical about changes to bulker design. The problem, he argues, has to do with the description, inspection and loading of cargo. To prevent losses, he suggests:
• criminal penalties for shippers who knowingly misdescribe cargo;
• declaring as unsafe terminals that lack proper covered areas for cargo;
• requiring independent surveys during loading;
• advising operators not to rely on local regulation to control exposure;
• instructing masters to get independent documentation of the cargo’s moisture content.