The fire water network of all the buildings associated with the Liquefied Natural Gas Import (LNGI) facility had experienced several leaks due to corrosion. During visual inspection, it was noticed that the leaks were from the pipes/fittings through isolated pinholes in the base metal and adjacent to welds. Detailed analysis was conducted to determine the root cause of the failures. The entire piping was both shop and field fabricated using SS 304 piping materials. Desalinated water was used for the fire water lines. After the analysis, it was concluded that Microbiologically Influenced Corrosion (MIC) was the reason for the severe corrosion & leaks. It was observed that Hydrotest waster was not treated and not drained from the system.
In this paper, a case study of the failure that occurred in the Desalinated Fire (DF) water line is presented. A brief description of water quality, material of construction, existing site conditions and the failure analysis are included in this paper. The mitigating options which were implemented is also covered in this paper.
Utility water and fire water which is desalinated is supplied by Ministry of Electricity & Water (MEW) and stored in utility/fire water tank (70-T-0002). The process areas and the tanks are protected by desalinated water as fire water backed up by sea water and the buildings are protected completely by desalinated water. Buildings to be protected by desalinated fire water are fire station, maintenance & operation building, warehouse, workshop, laboratory, and administration building. DF water system used in buildings are stagnant and for the fire water in tanks are used frequently. This fire water system comprises of two fire water jockey pumps (70-P-0006A/B) and two fire water pumps (70-P-0007A/B). The piping of the fire water network was both shop and site fabricated. After completion of fabrication all lines were satisfactorily hydrotested.
After 4 months of completion of hydrostatic tests, service leak test was carried out for the fire water system as a part of pre-commissioning requirements. Several leaks were noticed from pin holes adjacent to the weld joints of 304/304L SS pipes/fittings. The locations of leak were suction and discharge pipes of fire water pumps and fire water sprinkler lines inside the buildings (6 Nos.). SS piping network includes various piping sizes ranging from ¾" Sch40 up to 12" Sch10S.
