One of the most over-rated and mystery shrouded activities on board a tanker, product, crude or chemical, is tank cleaning. And now we have supercargoes who are making money by putting in expertise of all kinds in this field, when all that they do is simple logic.
Another field that is making a lot of money in this is the Tank cleaning chemicals manufacturers, who have over-rated a simple tank cleaning also to heights, where every tank cleaning will require use of their chemicals.
I've sailed on all the three types, been a 46 months Chief Mate, apart from all the other ranks, upto Master, and trust me, I've mostly avoided a tank cleaning chemical, even to prepare the vessel for a wall wash cargo spec, for Rohm & Haas as the cargo suppliers. And never once did i have tanks failing either.
So what did I do differently?
Use logic and trial method!
How? Very simple. Understand simple reasoning, the environment, the exposure and the result.
To elaborate, let's take a simple example.
Epoxy coated tanks. Cleaning to be done.
Environment : Sea water temperature, air temperature, gases in the tank, humidity, tank coating.
Exposure : cargo physical and chemical properties, in direct context of the last cargo, upto the 10th last cargo, the next cargo and the tank coating.
Result : Water White or Wall wash, specs differ.
So how do coated tanks make any difference ?
Coated tanks - this is paint. Paint requires a solvent and a binder. These in the simplest layman term are what constitutes the binding property and are more often organic in nature. Else, the paint would not dry up. That implies there is something in paint that can evaporate, leaving a dry film behind. What all causes evaportation? Temperature and the ability of the solvent to evaporate.
So what happens. A cargo is loaded, if it is solvent based or solvent type of cargo, or a Hydrocarbon rich cargo, it will always be absorbed in the coating.
What would tank cleaning chemicals do in such case? They soften the coating, open the pores and remove the absorbed last cargoes.
So, is their any other way to do same, without a chemical. Yes, raise the tank temperature. You could do live steaming (beware of LEL, if a constraint) or you could run steam through the heating coils (or thermal oil, as applicable) at minimum pressure. This will raise the tank temperature. However, doing steaming is the better solution, as it does three things -
1) It raises the tank temperature, thus releasing absorbed cargo or HC.
2) It is mostly pure water, next best to DI water, so you do not need too much Fresh water wash.
3) IT removes odour of last cargoes.
An ideal tank cleaning, when chemicals are not used is as follows :
1) Check for drying or non-drying oil and accordingly decide on a pre-wash, and SW temp as required. Wash the tank for 30 min immediately or soonest after discharge, if drying or semi-drying.
2) Ambient Sea Water. Ambient is the temperature, at which you get it. Now in winters, in North Sea you would not get water at 20 Deg C. And anything less is not helping. So heat the water to about 30-35DegC, or at least 10-15DegC above the melting point or pour point of the cargo.
What this will do, is it will only work as a force to push through the remnants of the cargo, which mostly, I assume is insoluble in water. So, basically, the cargo ROB, is pushed with water force, down through the tank bulkheads and then through the pipelines, out. If the cargo is not a heated cargo, and the cleaning specifications are not big, the process ends here. Purge and / or gas-free. Mop, may require some local cleaning and removal of collected water.
3) Hot Sea Water. If the cargo is a heated cargo, rest assured, your attempt at using ambient Sea Water or warm water has not made much of effect to the process. There is a lot of solidified clingage on the bulkheads. In such case, this is the largest part of cleaning using machines. 3 hours to 4 hours. Use hot water, the more you use, the more machines you use, including portable, the more helpful it is. And sea water is plentiful in supply. Don't worry about slops either, if the cargo is Annex-I. first, its the result that matters, as to how much you need to clean, and you can mostly always decant it. The ROB oil will not increase just because you used more water.
Hot water does the heating the tank part too. So, you can be assured that it is taking care of a lot of absorbed cargo too. Don't worry for chlorides at this stage. Sea water has roughly 19000 ppm of chlorides. Whether you use, 10 ltrs or 1000 m3, it will not change. Hot water helps in evaportation too. Make sure you manage the tank atmosphere, if required, controlling rising LEL or HC concentration.
4) Fresh water rinsing. Yes. do no more then mere rinsing. Normal FW supplied to the ships is at about 200 ppm Chlorides. So, use it only as much, so that you could bring down the Chlorides, accumulated during Sea water wash, from 19000ppm to 200 ppm. And, after doing hot sea water, you can only make one error more. Use ambient or cold Fresh water. If you use FW rinsing at the same or similar temperature as the Sea water wash in the last stage, you'll possibly need 10m3 in each tank for bringing down chlorides to 200ppm. If you use cold, you'll possibly need 30m3.
5) Now the interesting part. Your tank is mostly ready. If you're loading wall wash cargo, carry out live steaming of tank (make sure the tank is gas-free) and don't even think of using any solvents or chemicals (they are mostly banned for a reason). Do the live steaming for about 2 hours. Around this time, also do live steaming of all pipelines and pumps too. Let condensed water accumulate in the tank. Keep stripping out once in a while, if you wish. But if you leave it there, it is no harm either. This would, in an ideal case, bring down your Chloride ppm to less than 10. If need be, do another 1 hour (depends on tank size).
Now the important thing. You need to let the tank cool down. Gas free, enter, strip, mop, dry. Once dried, check wall wash sample. If the result is bad or the required spec is not met, give a DI water rinse. No more hot water, or steaming, once the tank has cooled down.
You'll find that once the tank has cooled down and dry, the wall wash will show excellent result. No HC, close to 0 Chlorides. Why? Because the coating has now stopped releasing anymore absorbed cargo.
Here, it is important to point out that sometimes tank cleaning chemicals are necessary -
1) In case of stains - use Bleach
2) In case of rust - use rust remover
3) In case of crude palm stearin carried at 65DegC, an alkaline cleaner.
4) In case, the last few tank cleanings have been a hog wash only, then possibly a HC remover too, if any of the last 10 cargoes has been HC rich.
5) Oh and yes, if odour is so much an issue and you can't live with it, then a deodorizer.
6) Special cargoes (chemicals like TDI, MDI) require a prewash by chemicals, as this is reactive to water.
And most of these chemicals are to be used in Fresh water at a high temp about 60-65DegC or sometimes even higher.When you take bath and use soap, the soap does not leave your body easily, if the water you are bathing with is cold, or putting it other way round, it leaves faster, when the water is warm or hot.
LOGIC : try cleaning utensils at home, or cleaning the floor, our Indian housewives are better cleaning expert then all of these super cargoes put together. Highly under-rated, house wives, who are actually not working mothers, wives, are more practical and logical thinkers and with common sense, more than the working ones.
CAREFUL, LOGICAL AND COMMON SENSE. Think in the box sometimes. What would actually be happening. If you cannot, just make a container, painted with the same tank coating, fill it up with cargo, leave it for few hours. Then try cleaning it. Trust me, you'll be happy to think, you can do it too!
Another field that is making a lot of money in this is the Tank cleaning chemicals manufacturers, who have over-rated a simple tank cleaning also to heights, where every tank cleaning will require use of their chemicals.
I've sailed on all the three types, been a 46 months Chief Mate, apart from all the other ranks, upto Master, and trust me, I've mostly avoided a tank cleaning chemical, even to prepare the vessel for a wall wash cargo spec, for Rohm & Haas as the cargo suppliers. And never once did i have tanks failing either.
So what did I do differently?
Use logic and trial method!
How? Very simple. Understand simple reasoning, the environment, the exposure and the result.
To elaborate, let's take a simple example.
Epoxy coated tanks. Cleaning to be done.
Environment : Sea water temperature, air temperature, gases in the tank, humidity, tank coating.
Exposure : cargo physical and chemical properties, in direct context of the last cargo, upto the 10th last cargo, the next cargo and the tank coating.
Result : Water White or Wall wash, specs differ.
So how do coated tanks make any difference ?
Coated tanks - this is paint. Paint requires a solvent and a binder. These in the simplest layman term are what constitutes the binding property and are more often organic in nature. Else, the paint would not dry up. That implies there is something in paint that can evaporate, leaving a dry film behind. What all causes evaportation? Temperature and the ability of the solvent to evaporate.
So what happens. A cargo is loaded, if it is solvent based or solvent type of cargo, or a Hydrocarbon rich cargo, it will always be absorbed in the coating.
What would tank cleaning chemicals do in such case? They soften the coating, open the pores and remove the absorbed last cargoes.
So, is their any other way to do same, without a chemical. Yes, raise the tank temperature. You could do live steaming (beware of LEL, if a constraint) or you could run steam through the heating coils (or thermal oil, as applicable) at minimum pressure. This will raise the tank temperature. However, doing steaming is the better solution, as it does three things -
1) It raises the tank temperature, thus releasing absorbed cargo or HC.
2) It is mostly pure water, next best to DI water, so you do not need too much Fresh water wash.
3) IT removes odour of last cargoes.
An ideal tank cleaning, when chemicals are not used is as follows :
1) Check for drying or non-drying oil and accordingly decide on a pre-wash, and SW temp as required. Wash the tank for 30 min immediately or soonest after discharge, if drying or semi-drying.
2) Ambient Sea Water. Ambient is the temperature, at which you get it. Now in winters, in North Sea you would not get water at 20 Deg C. And anything less is not helping. So heat the water to about 30-35DegC, or at least 10-15DegC above the melting point or pour point of the cargo.
What this will do, is it will only work as a force to push through the remnants of the cargo, which mostly, I assume is insoluble in water. So, basically, the cargo ROB, is pushed with water force, down through the tank bulkheads and then through the pipelines, out. If the cargo is not a heated cargo, and the cleaning specifications are not big, the process ends here. Purge and / or gas-free. Mop, may require some local cleaning and removal of collected water.
3) Hot Sea Water. If the cargo is a heated cargo, rest assured, your attempt at using ambient Sea Water or warm water has not made much of effect to the process. There is a lot of solidified clingage on the bulkheads. In such case, this is the largest part of cleaning using machines. 3 hours to 4 hours. Use hot water, the more you use, the more machines you use, including portable, the more helpful it is. And sea water is plentiful in supply. Don't worry about slops either, if the cargo is Annex-I. first, its the result that matters, as to how much you need to clean, and you can mostly always decant it. The ROB oil will not increase just because you used more water.
Hot water does the heating the tank part too. So, you can be assured that it is taking care of a lot of absorbed cargo too. Don't worry for chlorides at this stage. Sea water has roughly 19000 ppm of chlorides. Whether you use, 10 ltrs or 1000 m3, it will not change. Hot water helps in evaportation too. Make sure you manage the tank atmosphere, if required, controlling rising LEL or HC concentration.
4) Fresh water rinsing. Yes. do no more then mere rinsing. Normal FW supplied to the ships is at about 200 ppm Chlorides. So, use it only as much, so that you could bring down the Chlorides, accumulated during Sea water wash, from 19000ppm to 200 ppm. And, after doing hot sea water, you can only make one error more. Use ambient or cold Fresh water. If you use FW rinsing at the same or similar temperature as the Sea water wash in the last stage, you'll possibly need 10m3 in each tank for bringing down chlorides to 200ppm. If you use cold, you'll possibly need 30m3.
5) Now the interesting part. Your tank is mostly ready. If you're loading wall wash cargo, carry out live steaming of tank (make sure the tank is gas-free) and don't even think of using any solvents or chemicals (they are mostly banned for a reason). Do the live steaming for about 2 hours. Around this time, also do live steaming of all pipelines and pumps too. Let condensed water accumulate in the tank. Keep stripping out once in a while, if you wish. But if you leave it there, it is no harm either. This would, in an ideal case, bring down your Chloride ppm to less than 10. If need be, do another 1 hour (depends on tank size).
Now the important thing. You need to let the tank cool down. Gas free, enter, strip, mop, dry. Once dried, check wall wash sample. If the result is bad or the required spec is not met, give a DI water rinse. No more hot water, or steaming, once the tank has cooled down.
You'll find that once the tank has cooled down and dry, the wall wash will show excellent result. No HC, close to 0 Chlorides. Why? Because the coating has now stopped releasing anymore absorbed cargo.
Here, it is important to point out that sometimes tank cleaning chemicals are necessary -
1) In case of stains - use Bleach
2) In case of rust - use rust remover
3) In case of crude palm stearin carried at 65DegC, an alkaline cleaner.
4) In case, the last few tank cleanings have been a hog wash only, then possibly a HC remover too, if any of the last 10 cargoes has been HC rich.
5) Oh and yes, if odour is so much an issue and you can't live with it, then a deodorizer.
6) Special cargoes (chemicals like TDI, MDI) require a prewash by chemicals, as this is reactive to water.
And most of these chemicals are to be used in Fresh water at a high temp about 60-65DegC or sometimes even higher.When you take bath and use soap, the soap does not leave your body easily, if the water you are bathing with is cold, or putting it other way round, it leaves faster, when the water is warm or hot.
LOGIC : try cleaning utensils at home, or cleaning the floor, our Indian housewives are better cleaning expert then all of these super cargoes put together. Highly under-rated, house wives, who are actually not working mothers, wives, are more practical and logical thinkers and with common sense, more than the working ones.
CAREFUL, LOGICAL AND COMMON SENSE. Think in the box sometimes. What would actually be happening. If you cannot, just make a container, painted with the same tank coating, fill it up with cargo, leave it for few hours. Then try cleaning it. Trust me, you'll be happy to think, you can do it too!
