Diesel leak

[AlanH]

I have just noticed a very small leak in my diesel tank. Perhaps a thimble full a day. The leak is coming from behind a rubbing strake on the stern of the boat. The obvious answer is to empty the tank, fill it with water, grind off the offending bit of rubbing strake and weld up the leak. This would be very expensive and time consuming. Any suggestions? I'm tempted to just leave it. It has probably been there since the boat was new in 1993.

Edited November 18, 2009 by AlanH

[PhilR]

I have just noticed a very small leak in my diesel tank. Perhaps a thimble full a day. The leak is coming from behind a rubbing strake on the stern of the boat. The obvious answer is to empty the tank, fill it with water, grind off the offending bit of rubbing strake and weld up the leak. This would be very expensive and time consuming. Any suggestions? I'm tempted to just leave it. It has probably been there since the boat was new in 1993.

 

Milliput might seal it.

[Liam]

I thought all diesel tanks should be pressure tested?

[Nickhlx]

I thought all diesel tanks should be pressure tested?

 

My guy has to weld something onto my tank and was just going to drain it, weld it, and re-fill it... seemed to be un-fussed about welding a diesel tank !

 

It's insured I suppose....

 

Nick

[Timleech]

My guy has to weld something onto my tank and was just going to drain it, weld it, and re-fill it... seemed to be un-fussed about welding a diesel tank !

 

Nick

 

Better full than empty, IMO.

There shouldn't be a need to drain & fill with water, it's not petrol. Just avoid getting too much heat into it, especially if welding above the level of the fuel.

 

Leaks behind guard irons can be a pain. Somtimes the welds on the guard are part of the tank, sometimes the tank is fully welded & the guard added afterwards. You can seal one leak and find it then leaks from somewhere else, etc etc., sometimes fuel appears halfway down the boat!

 

Tim

[RobinJ]

I have just noticed a very small leak in my diesel tank. Perhaps a thimble full a day. The leak is coming from behind a rubbing strake on the stern of the boat. The obvious answer is to empty the tank, fill it with water, grind off the offending bit of rubbing strake and weld up the leak. This would be very expensive and time consuming. Any suggestions? I'm tempted to just leave it. It has probably been there since the boat was new in 1993.

As a temporary solution?

If you can find the hole (rubbing strakes are prone to long runs from the point of leak), screw a self tapper in and grind off!

[nb Innisfree]

I thought all diesel tanks should be pressure tested?

 

A builder may say "All our tanks are pressure tested" but that doesn't mean it passes!

[WotEver]

A builder may say "All our tanks are pressure tested" but that doesn't mean it passes!

 

Boss builder: Have you pressure tested that tank yet?

Jnr builder: Yep!

Boss builder: How bad are the leaks?

Jnr builder: Oh, a little less than the last boat.

Boss builder: Great - get it in the water.

[casper ghost]

I'm afraid I would grind off strake and repair properly.. I've heard you can weld diesel tanks as long as it's below the diesel level.

[furnessvale]

Better full than empty, IMO.

There shouldn't be a need to drain & fill with water, it's not petrol. Just avoid getting too much heat into it, especially if welding above the level of the fuel.

 

Tim

 

*NOT RECOMMENDED*

A friend of mine used to weld petrol tanks without flushing them out. He would simply drain them and leave the filler cap off so that the subsequent explosion had somewhere to go! It used to scare the S**t out of me but he was still alive the last time I heard of him a few years ago.

 

George ex nb Alton retired

[Sir Nibble]

*NOT RECOMMENDED*

A friend of mine used to weld petrol tanks without flushing them out. He would simply drain them and leave the filler cap off so that the subsequent explosion had somewhere to go! It used to scare the S**t out of me but he was still alive the last time I heard of him a few years ago.

 

George ex nb Alton retired

World of difference between petrol and diesel. I have seen a fire put out by chucking a bucket of diesel over it!

[Big COL]

*NOT RECOMMENDED*

A friend of mine used to weld petrol tanks without flushing them out. He would simply drain them and leave the filler cap off so that the subsequent explosion had somewhere to go! It used to scare the S**t out of me but he was still alive the last time I heard of him a few years ago.

 

George ex nb Alton retired

 

I knew a repairer who would weld motorbike tanks without neutralising them first. He used to empty them of petrol leave them to vent overnight fill them with water the next day and the weld the hole up.

No problem did loads of them until he sent one through the workshop across the street and into the lounge of the house opposite took the door and frame out with it as the tank passed through needless to say last tank he ever welded.

He survived the blast with just singeing of hair and eyebrows what went wrong this time was due to the shape of the tank it left a small air gap and unfortunately it was just where the hole was.

[AlanH]

Better full than empty, IMO.

There shouldn't be a need to drain & fill with water, it's not petrol. Just avoid getting too much heat into it, especially if welding above the level of the fuel.

 

Leaks behind guard irons can be a pain. Somtimes the welds on the guard are part of the tank, sometimes the tank is fully welded & the guard added afterwards. You can seal one leak and find it then leaks from somewhere else, etc etc., sometimes fuel appears halfway down the boat!

 

Tim

Hmm... I thought that this might be the case. I'm pretty sure that the tank was welded and the rubbing strake added after as the strake appears to be not continuously welded. I can see me chasing the leak around. As it is so small and I can't see any reason for it to get larger I think I'll have a go with milliput and if that fails I'll leave it alone.

[Proper Job]

I'm afraid I would grind off strake and repair properly.. I've heard you can weld diesel tanks as long as it's below the diesel level.

I can't see how you can weld a full tank if the tank is leaking. The diesel coming out of the hole will instantly vapourise and catch fire from the arc/flame and blow any filler rod out of the hole/crack that you are trying to weld?

 

I've welded both petrol and diesel tanks in the past. The method that I've always used:

• empty the tank to below the leak level (if its petrol empty it out completely)
  
• purge 'air space' with Nitrogen/CO2/Argon or other inert gas
  
• continue to feed inert gas into the tank throughout the welding process
  

As long as you don't let air (oxygen) in to the tank during the welding process you should be fine. No oxygen - no bang.

 

Oh........ and diesel doesn't really go bang - it just burns very quickly when vapourised.

[WotEver]

Oh........ and diesel doesn't really go bang...

How does my engine work then?

 

okay, got me coat....

[Timleech]

I can't see how you can weld a full tank if the tank is leaking. The diesel coming out of the hole will instantly vapourise and catch fire from the arc/flame and blow any filler rod out of the hole/crack that you are trying to weld?

 

Depends how big the leak is (same with welding leaky boats from inside!)

Any leak which has not been noticed until after handover is going to be tiny, in terms of actual volume of diesel.

Yes it can be done, I've done it several times & I'm not alone in that.

 

Tim

[RLWP]

Depends how big the leak is (same with welding leaky boats from inside!)

Any leak which has not been noticed until after handover is going to be tiny, in terms of actual volume of diesel.

Yes it can be done, I've done it several times & I'm not alone in that.

 

Tim

 

For me, I would be concerned that this leak has now appeared after sixteen years. I'd want to know that it wasn't a rust hole behind a strake.

 

Richard

[Timleech]

For me, I would be concerned that this leak has now appeared after sixteen years. I'd want to know that it wasn't a rust hole behind a strake.

 

Richard

 

Highly improbable after 'only' 16 years.

The OP did say it might have been there all the time, chances are a bit of welding slag has been dislodged allowing it to increase a bit.

 

Tim

[nb Innisfree]

True diesel doesn't go bang but burns quickly, same as petrol but a bit slower, but both will cause a similar nasty explosion in the right conditions, though diesel is a lot less likely to.

[AlanH]

Highly improbable after 'only' 16 years.

The OP did say it might have been there all the time, chances are a bit of welding slag has been dislodged allowing it to increase a bit.

 

Tim

I'm with you there. There is no sign of any rust around the area. As I said, I suspect it has always been there. Just a very slow dribble from under the strake. If I clean it off it takes several hours to reach the water again - about a foot. Perhaps I'll have a go at it next year when the boat comes out of the water. The resident welder at our boat club reckons some kind of sealer would do the job.

[Timleech]

Please note I'm not advocating that it's OK to weld on diesel tanks in any circumstance.

Anyone planning to do it needs to carefully assess the risks for that particular case before starting, and take suitable precautions.

 

Tim

Edited November 19, 2009 by Timleech

[casper ghost]

You can buy diesel filler, like putty. Only any use if you can find the hole though.. Diesel is a very good rust inhibitor, which is why you don't have to worry about rusty inside of tanks.

[AlanH]

You can buy diesel filler, like putty. Only any use if you can find the hole though.. Diesel is a very good rust inhibitor, which is why you don't have to worry about rusty inside of tanks.

Any idea what it is called and where I can get some from?

[AlanH]

OK. Found it at Midland Chandlers. I've ordered some and will give it a go.