Mars Report 2012 – Experience Feedback
The Nautical Institute has issued Mars Report No. 63 regarding dangers of pressure testing tanks/ vessels/ compartments as follows:
Minor repairs had just been completed on the shell plate of the fresh water generator (evaporator) by a shore workshop while in port. As an original spare was not available, the damaged sight glass was substituted with a disc cut from a 5 mm thick acrylic sheet.
Upon restarting the plant after sailing, it was observed that the drum chamber was not developing sufficient vacuum. The ship’s engineers decided to carry out a pressure test of the casing to locate any leaks. Without considering the hazards, the crew introduced compressed air into the vessel and raised the internal pressure to about 3 bar. Suddenly, the acrylic sight glass shattered, injuring the electrical officer, who was applying soap solution to the shell’s exterior.
Lessons learnt
1 It is very unsafe to subject vessels, tanks or containers to uncontrolled pneumatic pressure for testing purposes as there is great risk of permanent deformation or violent rupture;
2 A controlled hydrostatic test i.e. filling up the container with water to a permissible head (preferably under Class supervision) is the most appropriate and safe method for leak testing on board;
3 When a pneumatic test is considered the only practicable method, compressed air must be admitted through a suitable reducing arrangement and pressure must be closely monitored by a manometer/water column gauge, ensuring safe limits are never exceeded;
4 Fresh water generators should ideally be tested by creating an internal vacuum and applying a liquid dye externally on suspected areas.
Source: Mars/ The Nautical Institute
