Recently GC Energy Services was asked to provide a proposal for repairing a damaged Inert Gas Generator (IG Generator ) on a Products Tanker. The ship was half loaded with Gasoline and at the Bolivar Roads anchorage Galveston Texas, where it was waiting for it’s discharge berth to be available.
An IG Generator is a piece of equipment that is required on all products tankers. As the name suggests, the function of an IG Generator is to produce sufficient Inert Gas to place in to the atmosphere of the void space inside cargo tanks. When sufficient Inert Gas is placed into this space, there is insufficient oxygen to support ignition or explosion. This prevents the space from having an explosive atmosphere even when there is a cargo with a low flash point, or a cargo that generates explosive fumes under normal circumstances. There are many designs of IG Generators. Most of them have an air mover and a burner. The design must be able to support a large enough combustion to generate a volume of inert gas equal to, or greater than the volume of cargo be pumped out of the cargo tank when discharging. This will allow it to maintain the non explosive atmosphere at all times during the discharge period. This particular IG Generator design is by a Japanese Manufacturer Kashiwa, the Original Equipment Manufacturer (OEM). It is cylindrical with a burner and air inlet at one end, a water spray scrubber in the middle and outlet at the other end. The design is relatively compact. To cool the unit and the space around the burner, the cylinder has two walls. An inner wall, and an outer wall. Between the two walls there is seawater circulated by a dedicated circulating pump.
At some point recently, the ship had suffered problems with the dedicated seawater system for cooling the IG Generator. As a solution, the engineering staff decided to cross over a seawater source from the fire pump discharge. This would normally be an acceptable solution, however the discharge from a fire pump is normally at a much higher pressure than a seawater cooling/circulating system, and without correcting for this, it could be problematic. In this case there was not an adequate control of the water pressure and the much higher pressure on the relatively thin walls of the IG Generator resulted in severe deformation of the inner wall.
The ship had arrived at Houston to discharge Gasoline. By regulation the ship is required to notify the United States Coast Guard of any malfunctions or non operating equipment on board. Therefore there would be operational restrictions placed on the vessel unless she could repair or replace her IGG. Some of the restrictions placed on any solution to this problem;
1. By regulation, a ship is not allowed to discharge a cargo of gasoline without a means to maintain a non explosive atmosphere in the void space above the cargo of gasoline.
2. The size and location of the IG Generator made it impractical and cost prohibitive to bring the unit ashore for repair.
3. The United States Coast Guard placed some restrictions on the vessel. They would not allow any hot work outside of the machinery spaces, which ruled out cutting access holes in to the superstructure, which limited the size of replacement pieces that could be maneuvered to the location of the IG Generator inside the machinery spaces.
4. In addition, the space at either end of the unit was limited and the bulkheads and piping were such that access holes there were not possible.
5. The stainless steel used in the fabrication of the inner and outer walls of this IGG is YUS 254, which has a particularly high resistance to chlorides (seawater), and is sparsely stocked in the USA.
The extent of damage to the inner wall was significant, it was a complete failure to the inner wall. While the wall did not crack or break, the extreme distortion created unacceptable cooling and overheating of the outer wall. After some discussion with the Original Equipment Maker (OEM) Kashiwa Company Ltd., in Japan, and the vessel’s Classification Society DNV-GL, it was determined that a full replacement of the inner wall was the best acceptable solution. GC Energy Services made a proposal to change out the inner wall in-situ.
GC Energy Services proposed to roll five (5) cans of a length that would allow them to be to be maneuvered into the space and fit into the end opposite of the burner. The end of the unit opposite the burner would be removed for access to the inner wall. The water spray piping and nozzles would be removed. The inner wall would be removed except for about 10 inches closest to the burner. While this area of the inner wall was still distorted, it would be faired in to the new pieces using hydraulic jacks and wedge dogs. The pieces would be set in the end of the unit one at a time, sliding them in and welding them to each other as they go in. The final weld of the new to the old would be faired, fit and welded once the full inner wall was placed in to the unit. After preparing a 50 page repair procedure inclusive of; the written procedure, drawings of the cans, inspection test plan, welding procedures, steel mill certificates, GC Energy Service’s repair proposal received approval from the OEM, DNV-GL, and the owner’s representative.
A team of six (6) men were sent on board and organized into two shifts and carried out the repairs as per the repair plan. The final repair was approved by the owner representative, DNV-GL, and the USCG as a permanent repair to the Inert Gas Generator. The unit was function tested, then operated to allow the vessel to proceed to her discharge terminal and discharge her cargo of gasoline safely. Another challenge successfully completed by the team at GC Energy Services, a division of Gulf Copper & Manufacturing Inc.
GC Energy Services provides offshore and marine repair services for clients around the world. Providing low pressure and high pressure pipe fabrications and repairs, steel structure fabrication and repairs, electrical repairs and installations, scaffolding services, non-destructive testing, hull gauging, and environmental services. We can mobilize quickly from either of our locations in Galveston or Ciudad del Carmen, where we also have light fabrication facilities. GC Energy Services is a division of Gulf Copper & Manufacturing Corp supported by Gulf Copper fabrication facilities in Port Arthur and Galveston for larger fabrication projects.
Founded in 1948, Gulf Copper & Manufacturing Corporation is an employee-owned company that repairs and refurbishes marine vessels and offshore rigs and fabricates specialty components for the oil and gas market. The company operates strategically located shipyards, drydocks and fabrication facilities along the U.S. Gulf Coast. Gulf Copper serves the marine transportation, offshore construction and offshore drilling markets in addition to various United States government agencies.
Be safe in all that you do,
Leonard Hale