CRITICAL OPERATIONS ON BOARD LPG TANKERS

By Capt. Victor Guinto. Jr.

The nature of it’s cargoes makes LPG Tankers one of the most hazardous vessels today. In spite of the fact, they are among the safest and cleanest vessels to be on. The idea is if we take a very close look at the critical operations and manage the risks properly, then safety can be maximized and risks minimized.

Among the critical operations are: Loading Operations, Discharging Operations, Ship-to-Ship Operations, Gas Freeing, and Gassing-up Operations. We will take a brief look at each of these.

Before loading operations start, the Ship/Shore Interface procedures must be done and the Ship/Shore Safety Checklist completed and signed. This will be the basis of how both the ship and terminal will conduct the operations according to an agreed plan. Standard and emergency communication will be agreed upon. Initial, normal, and final loading rates will be discussed. Allowable list and trim are also included. The idea is all items that are essential to be understood, clarified and agreed upon must be done at this point.

The loading plan is a critical tool for the success of the voyage. Changes in temperature during the voyage will greatly affect the volume of the cargo. On a refrigerated or semi-refrigerated gas tanker, temperatures can be controlled but on a fully-pressurized gas tanker temperatures are subject to the weather conditions. The maximum loadable quantity therefore must be subject to repeated checks. The most critical time is during topping-up of the tanks. Continuous monitoring is a key to safety during loading operations.

Discharging operations are similar to loading operations except that they are done in reverse. Ship/Shore Interface procedures as well as the other safety checks are standard. One difference is the use of pumps and compressors. They must be checked and tried out at least 24 hours before discharging to ensure that they are working properly. They are also run just before the discharging operations. It is normal to discharge the liquid part of the cargo with part of the vapour remaining.

Ship-to-ship operations are done when the infrastructure of terminals are insufficient for some tankers. This is one of the most critical and riskiest operations. Loading and discharging operations are basically similar. The number of mooring lines used is much more than in port and requires more frequent tending and care. Mooring lines can part due to abrasion.

Gas-freeing is a procedure usually done before dry docking, tank inspection, or tank cleaning. The goal is to replace the cargo gas inside the tanks with inert gas then with air to reduce the risk of having an explosive condition. This can be done by proper inerting

methods and continuous monitoring of the contents of the tanks during the process. An approved chemist is required to certify that a tank is gas-free.

Gassing-up is the reverse of gas-freeing. This procedure is done after inerting to prepare the tanks for loading. The objective is to replace the inert gas inside the tanks with cargo gas. The amount of inert gas left inside the tanks must be minimized. The tank atmosphere is closely monitored during inerting and gassing-up to reduce the risk of explosive conditions and quality of the tank atmosphere.

These critical operations on board LPG tankers are briefly described to give an overview. Each gas tanker has different equipment and must have its own detailed procedures clearly approved and listed.