We're still working with just one cargo pump here on the HQ. Haven't had time to visit the local Honey Wagon and get our ducks in a row to have the tank cleaning and blow down done, marine chemist hired, and engineer& mechanic team available for a tank dive, all steps necessary for human entry into a tank vessel's cargo tanks. So while we were trying to get through a few last cargoes, the radiator on our one good pump engine started to go. It held up for 2 more days, so we lost half a day swapping it out with a new one, but this cost us our window to get a cleanout.
On board a ship, the chief mate is trained to oversee and issue permits for tank entry and cleaning procedures. I am not, as 1) we do not inert our cargo tanks and 2), my company does not want to pay me to be certified for this. Oh, and also 3) we do not carry the necessary testing and support equipment necessary, seeing as we usually stick close to home so the company doesn't have to buy 8 million Coppus blowers, air horns and testing kits. We do carry oxygen meters, explosimeters and crickets (personal gas sampling alarms that get pinned to your clothes), which is what we need to stay safe under normal circumstances.
Tank cleaning is a pretty neat process- well, it's supposed to be, anyhow. On a ship, tank cleaning can make an absolutely pristine clean job. You can go from carrying black oil to jet fuel with a day's work (jet fuel being required to be *aboslutely pristine* in every way, crystal clear, no color, no contamination. On a ship with a well-designed tank cleaning system you can eat off the tank bottoms after a good douching.
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|the gold color is paint that has had the tint bleached out so it can't tint any liquids|
The HQ does not have built in tank cleaners. We use high pressure hoses and a Butterworth sprayer.
A Butterworth sprayer is a pressure washer that rotates slowly on two axis (axes?). By opening a cleaning hatch (called a Butterworth hatch, originally enough) and sticking a hose down a fixed distance and running high pressure water through it, the machine rotates and spins slowly while sending a very high pressure stream to scour any contaminants off the bulkheads, overhead and bottoms of the tank. Basically you set the machine to a certain depth, tie off the hose, turn it on and a little while later (15 minutes to an hour), you drop it some more, and repeat. Generally I like doing 3 drops.
Oh, you heat the hell out of the water. 180 degrees is good. It cuts the oil, and you pump the oil/water emulsion out of the tanks as you go. I like using 2-3 machines per tank if I can. It reduces 'shadow areas,' spots the machines can't clean.
After the machines are done, the tank should be clean but damp. Properly speaking, a tank should be inerted (filled with gas with minimal oxygen in it so nothing can combust- those Butterworth machines can cause a real lightning show from all the static they can generate), but you can get around that in several ways if you happen not to have an inert gas system. The tank can then be Blown Down by force ventilating it with massive volumes of air. We use Air Horns and Coppus blowers for that. Air horns are just simple venturi cones that use small air jets to suck large volumes of air into the cone. A coppus blower is an air- or steam powered air turbine.
Forced air is then blasted into the tank to ventilate it. A marine chemist (a licensed safety consultant) will then test the air in the tank and issue a permit for people to enter the tank if the air tests as safe for entry. The criteria for safe entry is strict. A tank can be entered if it is marginally safe, using certain PPE if required- respirators, OBA's (basically a fireman's oxygen kit), certain clothing and such) under VERY strict circumstances, although this is best avoided and I have never had to do a hazardous entry tank dive with my current employer. I actually didn't mind doing it back in the day, if I trust my gear, my spotters up top and the guy who issues the permit to enter I'm cool.
Well, at any rate, I'm hoping we can actually get all this done before I go home next week. I don't like passing off major projects to my relief, but the work is just stacking up and we'd need a solid day and a half free to do what needed to be done, so I don't think we'll have time. Have to see.