1.The ship just departed from the port of newyork around midnight. Temperature outside were subzero. The very next day I was asked to provide deck service air for deck maintanance jobs. As usual all I have to do was open a valve. But this time as soon as I opened the valve the pressure of service air bottle started dropping rapidly. The service air compressor was not able to meet the required air demand. At first I thought that they might have opened to many air connections for use. So i called to bridge and asked if they are using too many connections. But I was told that only one connection was in use and they are not receiving the required pressure. The first thing came to my mind is that there might be some air connections opened in e/r also or there is some leak somewhere. So I went to look for service air leaks in e/r and I found none. I now decided to first ensure that my compressor is ok. To ensure this I just closed the outlet v/v of service air bottle. After closing the valve the pressure inside tank started rising and the time taken to reach the pressure was also normal. The compressor cut out at set pressure. Now I opened the service air bottle discharge vlave and the story was same. Pressure rapidly dropped. I came to the conclusion that there must be some leak in service air line. Luckily there were separate valves for deck and engine room service air lines. The pressure was dropping after opening the deck service valve only.
I informed chief engineer regarding the situation. After discussing with chief officer, deck crew were sent to lookout for any air leaks on deck. After an hour we were informed that there are no leaks. But chief engineer was sure regarding any major leak in deck service air line. Any major leak can be clearly identified by its hissing sound. So we came to conclusion that air must be leaking at some space which was not visitedvthat day and provided that we just came out of subzero temperatures, there was always a possibility that any condensed water in service air line might have freezed-expanded and ruptured the line, and this water must have collected to the lowest point or any trapped section of line. So we took the line diagram and started to check the service line one by one paying special attention to the lowest service air points. After some time in bosun store we found a ruptured service air line. The ruptured section was removed, a new line was fabricted and fitted in place. Now the deck service valve was opened and all was working fine.
2. The ship was sailing in indian ocean in the month of may. The service air compressor discharge air temperature high alarm was coming. I had just joined the ship and was told that all attempts have been made to rectify the problem including air-oil cooler cleaning and was found that in hot regions it usually gives this alarm. I found the enclosing cabinet of service air compressor was opened and air was directly blowing to the cooler with a seperater blower duct and an electric blower. I was told that there is some problem with the location of cooling air intake of service air compressor, that’s why a separate blower and trunking was arranged to blow directly cool air to the cooler. Well with this arrangement the compreesor was running just ok. With limited air use it was ok but after opening even two-three connections the high temp. Alarm was coming. However after one week we enetered the colder region and the ship was now heading towards usa. The service air compressor was running ok without the separate blower arrangement. I was convieneced with the separate blower trunking arrangement.
After one month we were back sailing towards india and while crossing suez canal the same alarm started coming. We instaleed the same arrangement and this time somehow compressor managed with just one air connection opened. Two days later compressor was now giving continuously high discharge air temperature alarm.
I decided to open the air-oil cooler for inspection and cleaning. I put the air-oil cooler in chemical and after cleaning put back in use, but the problem was not solved. Including this a total of three times the cooler was cleaned within a month which generally is cleaned yearly. I changed the oil filters , oil seperators and even system lub oil but the result was same.
Later I took an infrared gun to monitor the heat exchange process in cooler( there were no thermometers in line of oil and air). I found that oil was not getting cooled at all and the same hot oil was injected back to air compressor. I suspected this might be the problem. But the cooler was already cleaned. So I decided to open the cooler one more time and have a close inspection. All was found well. But still I decided to clean it one more time. This time instead of just dipping it into the chemical I decided to clean it with circulating the chemical to get an idea of inside passeways which were not visible. The arrangement was made and cleaning was started. At first the chemical solution coming out of cooler was clear but after an hour of circulation I noticed a lot of mud coming out . It took almost 8 hours of continous circulation to get a clear mud free appearance of outcoming chemical solution.
After that a fresh water circulation was carried out to remove any residual chemical from inside, the cooler was dried and put in place inside the system. The compressor was now tried out and found running ok irrespective of the number of air connections in use and engine room temperature.
3. The very next contract on an another vessel I found the same problem of air discharge high temperature alarm. Being overconfident without investigating the cause I decided to open the air-oil cooler and clean it by chemical circulation. The same was cleaned and fitted back in place, but the problem still persisted.
Now I had no other option but to check temperature of each piping system with an infrared gun. I opened one of engine room service air valves just enough to keep air compressor running but not to get tripped on high discharge temperature. While monitoring the temperature I found that the oil line going to cooler after thermostatic valve was cold and the thermostatic valve return line going back to the air compressor very hot. It means that the thermostatic valve was malfunctioning and instead of sending hot oil to cooler it was directly sending it back to compressor. The thermostatic valve was changed and compressor was tried out. It run smoothly during my tenure onboard.