deisel leak

[mizpah2]

oops , I have a minute diesel leak from the weld underwater at the back of our boat .the fuel tank is made in part of the hull , usual narrow boat way , is there something I can put on the weld while it is underwater to seal it ? do not want to have to take it out !

[rusty69]

Guess you could try a product such as:-

http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802656583681&msdsLanguage=EN_GB&selectedTab=technica

lIf you can access it, but it would only be a temporary repair until welding can be done. 

Edited June 30, 2017 by rusty69

[PaulJ]

Probably wiser to empty the tank and then run off a temporary tank until you can get it repaired. Think even underwater epoxy may struggle sticking to diesel coated steel. 

[MtB]

I don't think you have any choice but to take the boat out and have it welded properly. 

[mross]

If you block the air vent and drain a bit of fuel off you can create a negative pressure in the tank.  Then apply some underwater epoxy.  It sticks like point to a blanket.  You can clean any diesel off with a wire brush or even a brush and soap or detergent.

https://www.google.co.uk/search?q=underwater+epoxy&client=ms-android-wileyfox&sa=X&biw=360&bih=512&tbs=vw:l,ss:44&tbm=shop&prmd=svin&srpd=9018669697564665590&prds=epd:5647729731973741013,cdl:1,cid:17492075444723704517&ved=0ahUKEwikioDKlebUAhUlCsAKHXN2ALEQgTYIiwQ

Edited June 30, 2017 by mross

[David Mack]

If this weld is below diesel level on the inside and below water level on the outside I think you are going to struggle to get anything to stick. 

Can you move ballast or tip the boat in some way to get the weld above water level? Then you might stand a chance of geting it clean and dry enough for something to stick.

[Bloomsberry]

If diesel is leaking out then surely canal water will be entering the fuel tank.

 

If this builds to a certain level then this is going to go to the engine (when running) which isn't going to do it much good.

 

It may be a good idea to syphon the tank bottom to make sure there isn't a build up of canal water in there.

8 minutes ago, David Mack said:

If this weld is below diesel level on the inside and below water level on the outside I think you are going to struggle to get anything to stick. 

Can you move ballast or tip the boat in some way to get the weld above water level? Then you might stand a chance of geting it clean and dry enough for something to stick.

If the water tank is at the bow then try filling this up to maximum which will raise the back end up, maybe enough to get to the leak

[mross]

If the leak is tiny, you might be able to stop it by peening it with a hammer and centre punch.  Peening puts the steel into compression.

[Jess--]

20 minutes ago, David Mack said:

If this weld is below diesel level on the inside and below water level on the outside I think you are going to struggle to get anything to stick. 

Can you move ballast or tip the boat in some way to get the weld above water level? Then you might stand a chance of geting it clean and dry enough for something to stick.

another option would be to deliberately ground yourself to make repairs, doesn't take much to get the whole counter out of the water on a narrowboat.

just have a friend ready to pull you back off as once your prop is pulling in air you probably won't get off under your own power. 

[MtB]

12 minutes ago, Bloomsberry said:

If diesel is leaking out then surely canal water will be entering the fuel tank.

 

 

No, the tank is a typical NB stern tank the OP says, so the diesel level in the tank is always above water level. So the diesel will be leaking OUT rather than water leaking IN.

I expect trails of rainbow water develop around the stern when moored up, which is how he knows about the leak.

This also means even if the boat is out of the water, diesel will continue to leak out unless the tank is totally and completely drained.

I've heard about diesel tanks being welded with deisel in, but I wouldn't want to be anywhere near at the time!

[Bloomsberry]

33 minutes ago, Mike the Boilerman said:

 

No, the tank is a typical NB stern tank the OP says, so the diesel level in the tank is always above water level. So the diesel will be leaking OUT rather than water leaking IN.

I expect trails of rainbow water develop around the stern when moored up, which is how he knows about the leak.

This also means even if the boat is out of the water, diesel will continue to leak out unless the tank is totally and completely drained.

I've heard about diesel tanks being welded with deisel in, but I wouldn't want to be anywhere near at the time!

"is always" above water level or "should be" above water level ?

Wouldn't the trim of the boat effect this also ie. if it's been overplated, water tank at the bow empty etc.  but then again probably not by that much more if the bottom of the tank is close to the waterline anyway.

But like you say , if the diesel level in the tank is always maintained above the water level then there should be no water leaking in.

[Sea Dog]

12 hours ago, Bloomsberry said:

 

But like you say , if the diesel level in the tank is always maintained above the water level then there should be no water leaking in.

But there will be diesel leaking out, which is damaging the environment... and the blacking on other folks boats. Also, if the weld is failing at that point, where else is it weak or rotted? Quite simply, this needs fixing urgently, and if that involves docking then that's the price that has to be paid.

[Neil Smith]

How would you be able to locate the pin hole under water to enable you to seal it, unless it's on the water line.

Neil

[rusty69]

3 minutes ago, Neil Smith said:

How would you be able to locate the pin hole under water to enable you to seal it, unless it's on the water line.

Neil

Empty tank, pump in air, watch for bubbles. 

[mross]

1 hour ago, Sea Dog said:

Also, if the weld is failing at that point, where else is it weak or rotted?

It's likely that a pinhole leak is due to a minor weld defect.  There is no reason to extrapolate this into a rotten hull.

[MtB]

On 01/07/2017 at 09:54, mross said:

It's likely that a pinhole leak is due to a minor weld defect.  There is no reason to extrapolate this into a rotten hull.

Yes there is.

We LURVE escalating minor problems like this into major disasters on here!

[mross]

If you decide to pressure test with air, please be very careful and use a pressure regulator if taking compressed air from a tank or compressor.  15psi could cause a lot of damage.  Much safer to use a hand pump, foot pump or low pressure pump.

https://www.google.co.uk/imgres?imgurl=http%3A%2F%2Fwww.alltranstek.com%2Fuploads%2F4%2F5%2F1%2F7%2F45171167%2F1363732_orig.jpg&imgrefurl=http%3A%2F%2Fwww.alltranstek.com%2Fmythbusters.html&docid=c3ueCcJYQF5udM&tbnid=FbvDJIKIyBqdDM%3A&vet=10ahUKEwj02Jia3ufUAhUILlAKHT_7ASkQMwhDKBcwFw..i&w=1100&h=733&bih=660&biw=1368&q=" tank" vacuum collapsed damage&ved=0ahUKEwj02Jia3ufUAhUILlAKHT_7ASkQMwhDKBcwFw&iact=mrc&uact=8

[rusty69]

5 minutes ago, mross said:

If you decide to pressure test with air, please be very careful and use a pressure regulator if taking compressed air from a tank or compressor.  15psi could cause a lot of damage.  Much safer to use a hand pump, foot pump or low pressure pump.

https://www.google.co.uk/imgres?imgurl=http%3A%2F%2Fwww.alltranstek.com%2Fuploads%2F4%2F5%2F1%2F7%2F45171167%2F1363732_orig.jpg&imgrefurl=http%3A%2F%2Fwww.alltranstek.com%2Fmythbusters.html&docid=c3ueCcJYQF5udM&tbnid=FbvDJIKIyBqdDM%3A&vet=10ahUKEwj02Jia3ufUAhUILlAKHT_7ASkQMwhDKBcwFw..i&w=1100&h=733&bih=660&biw=1368&q=" tank" vacuum collapsed damage&ved=0ahUKEwj02Jia3ufUAhUILlAKHT_7ASkQMwhDKBcwFw&iact=mrc&uact=8

Wow, impressive. I wonder if CRT could use this method to "crush"  boats of non paying owners

Edited July 1, 2017 by rusty69

[mross]

It happened once, on an oil tanker when they forgot to remove a ballast tank air vent blank that had been fitted whilst men worked in the tank.  The centrifugal ballast pumps created enough vacuum to buckle the side of the ship.  I tried to find photos but it was before the internet.

[MtB]

But we are talking about pressurising a tank, not creating a vacuum.

15psi should be easily held by a the typical welded steel tank formed in the stern of a narrowboat. There will only be about five of six tons of outward force on the structure. 

The biggest risk will be bowing out the flat plate that forms the front face of such a tank.

[mross]

I cited a vacuum as it must have been 15psi or less.  There are dozens of photos where very strong, cylindrical tanks have collapsed under vacuum.  Also, turning your tank into an air receiver is dangerous should a weld fail.  It could explode.  Shore supplies come at 100psi and that is definitely enough to rupture any tank not designed as a pressure vessel.  I'm just urging caution and pointing out potential hazards.  15psi might be enough to bow out the flat side of the fuel tank, much like inflating a balloon.  Quite a few people have been killed inflating vehicle tyres.

[MtB]

I think you are overinflating the risk

A weld is far more likely to crack and just let the air out with a big "psssssffftttttt" noise. 

Yes it is possible for the tank to explode but vanishingly unlikely.

[cuthound]

When I was working it was common practice to test welded steel bulk diesel tanks and chilled water pipework by pressurising them to 5 psi, marking the gauge and leaving them for an hour. If the pressure remained then the test was passed.

I think 15psi might damage the tank, particularly as it will not have any internal bracing to add extra strength.

[mross]

In industry, pressure testing is normally hydraulic, often with water.  This eliminates the risk of an explosive failure.  Certain pressure regulators need a constant, small flow to work correctly.  If connected to a tank and set at, say, 5psi, the pressure continues to rise until it matches the supply pressure.  This is the risk that most concerns me.

A tank seven foot wide and two foot long would experience a force of 13.6 tonnes under 15psi on the top (and bottom).  that's surely enough to cause something to bend or crack.

 

 

[bizzard]