Hydrostatic test on tanks during the section stage of a ship: The case study of the PSV 5000

Abstract

The main topic discussed in the thesis, is the “Hydrostatic test on tanks during the section stage of a ship” and it is particularly focused on the existing project of the vessel PSV5000. The hydrostatic test is framed from the international rules (IACS S.14; Lloyd's Register; etc...) as a structural test carried out to demonstrate the tightness of the tanks and the structural adequacy of the design of the vessel. The test is required for all the types of tanks present on board in consideration of the different types of structure and location. Only after this test the Class Society assigns the usability of the tank and it is accepted by the client. So the hydrostatic test that could appear simply as secondary activity in the whole complexity of the shipbuilding construction, it is a condicio sine qua non for the final delivery. In the actual organization of the ship production process at DAMEN Shipyard Galati the hydrostatic test is performed after the launching of the ship, during the commissioning, using the pump systems installed on board for the displacement of the masses of water from one tank to another one and for the discharge. The main concern about this strategy is in the event if the tank fails the test. The problem will affect the engineering department that must redesign the tank and inevitably the production chain will stop and be compromised. If a huge structural modification is required, it becomes a difficult task to solve in advanced state of construction. It must be considered also that in normal conditions this test is performed in a period very crowed of activities and few time available, with the high risk of overlapping, bottleneck issues and delays. Therefore, the thesis was oriented to identify the possibility to perform the hydrostatic test at the earlier building stage of the ship, preferably at the section stage of the fabrication process of the vessel. It could have a positive impact on all the production chain if shortening of expenditures and of delivery time are obtained. So the main goal is to find the point of construction stage where technically it is possible to carry out the test and to verify that this constitutes an advantage for the shipyard. The tanks that must be tested are individuate on the structural test plan of the PSV 5000, this plan is already prepared at the shipyard and approved from the class society. Knowing the position and distribution of the tanks, it is analyzed the building strategy of the vessel PSV 5000 in construction in the dry dock. The analysis returns eligible stage points where the test could be performed, they are chosen on the base of the stage of completion of the structure, presence of critical equipment that must be insert as well as weights that load over the tank. At this point it is necessary to check whether the total load on each support below the ship does not exceed the limit of 50 tons. With this purpose the software CVSL_64 was used, in which the project for the vessel PSV 5000 was uploaded and where it is possible to insert the weight estimation with all the loads and their positions. The study indicates the necessity of placing 4 four additional supports below the ship to sustain the weight of the structure, foundations, piping, equipment and the mass of water added during the test. The dates of start and finish of testing for each single tank are elaborated on the base of the actual planning, taking into consideration all the activities that affect the completion of the tank. In conclusion, it is possible to perform the hydrostatic test before the launch and to insert it in the planning of the activities, but it must be take into account that the systems on board are not operative yet. Thus must be used external pumps and special devices that they have to be available in time for the test. Moreover an economic analysis returns a total cost of 6800€ for perform all the package of activities of testing on the vessel. It is emerged that the main cost item is the man-hour. In addition with the plan proposed for the test in the earlier stage, it is possible to save money without using fresh water in the tanks that are designated to contain fuel, oil, or fresh water. This is possible because the tests are performed before the painting. The amount of saving for the fresh water is of 1200€ (included in the previous cost). In last analysis were advanced two proposals regarding investments in new equipments, that could save man-hours, reduce the total time necessary for the test execution and consequently provide more days of advantage on the final delivery day. The first investment gives the possibility to introduce inflatable plugs that could reduce the time consumption of the 50% for the preparation piping operations with a saving of 1300€ (to subtract to the total cost). To this saving it is added the cost for the special equipments unnecessary that will not be prepared. Some other savings come from the absence of welding and consequently the missing of paint/coating damaged by heat. Thus the total cost it is reduced till 5200€. In addition to this investment it is possible to buy 4 four more pumps. This allows the possibility to test till four tanks at the same time, With these solutions it is possible to finish with a total advance of four working days on the previous schedule.