stainless water tank

[davehull]

Our water tank has developed a leak, the tank is stainless steel and fully integrated into the bow of the boat. The only part accessible is the back of the tank with the take off pipe. I am asuming one of the welds has split because the tank had emptied itself into the boat in the space of 5 days.

Without filling the tank to try to trace the leak and it then empting into the boat again I was thinking about silicon sealing all the joints from inside the tank while it was empty.

I would appreciate option/ideas on this course of action and other ideas to sort this.

Dave

[ditchcrawler]

You can't normally get inside a stainless tank, well I have never seen one. The only way is to get it out and welded, bad news probably

[davehull]

I have a big access hatch on the top of the tank which I can just get in.

 

The top of the tank is welded into this hatch so removing the tank would mean cutting the top of the bow off, so not really an option.

[ditchcrawler]

I have a big access hatch on the top of the tank which I can just get in.

 

The top of the tank is welded into this hatch so removing the tank would mean cutting the top of the bow off, so not really an option.

Are you sure its stainless, it sounds a very strange arrangement to weld stainless to mild steel, what make of boat is it, someone else may be able to throw light on it as its something I have never come across.

[davehull]

I had the shell made for me about 10 years ago by the company I work for. The tank is quite large and shaped to fit the front of the boat.

 

We often weld stainless and mild steel at work so it was not usual for us to do the tank this way.

 

The large hatch was for cleaning purposes.

 

Dave

[the barnacle]

i also weld steel to stainless for the odd customer - i dont think flexable sealant will be any good long term - you could get a flexable water tank to insert into yous stainless one - some companies make the size and shape to order.

[Murflynn]

i also weld steel to stainless for the odd customer - i dont think flexable sealant will be any good long term - you could get a flexable water tank to insert into yous stainless one - some companies make the size and shape to order.

but you will need to cut a hole in the s/s tank for the outlet from the flexible tank liner.

[ditchcrawler]

but you will need to cut a hole in the s/s tank for the outlet from the flexible tank liner.

 

 

i also weld steel to stainless for the odd customer - i dont think flexable sealant will be any good long term - you could get a flexable water tank to insert into yous stainless one - some companies make the size and shape to order.

I think that will be the best bet

[Señor Chris]

Find the leak is the only option. You could just end up with a bigger hole if you don't find and rectify the cause.

[Robbo]

Another solution would be too get a flexible tank made and use the current tank as support for it.

 

Edit, just seen already suggested. I'll have to read threads before replying!

Edited May 20, 2016 by Robbo

[ditchcrawler]

If you can get inside then can't you get it welded up from the inside.

[gazza]

The full SP on welding dissimilar metals.

 

Copy and paste from here saves a load of typing.

 

http://www.bssa.org.uk/topics.php?article=101

 

Welding stainless steels to other steels

 

Introduction

 

Welding austenitic stainless steels to carbon and low alloy steels are established methods in the process and construction industries.

Dissimilar metal welds involving stainless steels can be done using most full fusion weld methods, including TIG (Tungsten Inert Gas) and MIG (Metal Inert Gas).

Weld procedures using filler (consumable) enable better control of joint corrosion resistance and mechanical properties. In selecting the weld filler, the joint is considered as being stainless, rather than the carbon steel. Over-alloyed fillers are used to avoid dilution of the alloying elements in the fusion zone of the parent stainless steel.

 

Dissimilar metal combinations

 

The most common combinations of dissimilar steels involving stainless steel are plain carbon or low alloy structural grades and austenitic stainless steel grades such as 1.4301 (304) or 1.4401 (316).

 

Welding conditions

 

Carbon and alloy steels containing less than 0.20%C do not normally need any preheat when being welded to austenitic stainless steels. Carbon and alloy steels with carbon levels over 0.20% may require preheat. High restraint joints, where material thickness is over 30mm, should also be preheated. Temperatures of 150 C are usually adequate.

 

Carbon steels may be more prone to hydrogen associated defects than austenitic stainless steels and so careful drying of welding consumables is advisable.

 

When welding stainless steels to galvanised steel, the zinc coating around the area to be joined should be removed before welding. Molten zinc if present in the weld fusion zone can result in embrittlement or reduced corrosion resistance of the finished weld.

 

Selection of welding consumables (filler)

 

Ambient service temperatures

Although a standard 308 type filler can be used for joining a 304 type stainless steel to carbon steel, more highly alloyed fillers, such as the 309 type (23 12L to BS EN 12072) are preferable.

This is should help avoid cracking in the weld dilution zone that can be a problem if a 308 type (19 9L to BS EN 12072) filler is used, where there can be too low a ferrite level and martensite may also be formed on cooling.

 

Elevated temperature services temperatures (over 425�C)

If the welded parts are for higher temperature service, then the differences in thermal expansion rates of the steels and filler can lead to thermal fatigue cracking. Long exposure times at these temperatures of welds with enhanced ferrite levels can result in embrittlement due to sigma phase formation.

Nickel based fillers (Inconel) produce welds with lower thermal expansion rates than the stainless steel fillers and so may be preferable.

 

Risk of bimetallic corrosion at welds between carbon and stainless steel

 

Unprotected welds subject to aggressive environments such as immersion in seawater could result in sacrificial corrosion to the less noble carbon steel part. However, post weld surface coating repair would normally be needed to the carbon steel to 'restore' the corrosion protection.

If this re-coating / painting is allowed to lap over onto the weld bead then the joint should not be at risk to bimetallic corrosion in any environment so long as the coating is sound. Ideally the weld bead should be covered so that only the 'parent' stainless steel is ultimately exposed. This ensures that galvanic corrosion cells cannot be set up across the joint, where there is a composition 'gradient'

 

Bummer you've sprung a leak. Access is always the issue for repair work.

 

As others have said, go for a liner if a torch can't be got at the leaking joint.

 

Snot will get you out of a pickle but it's not a long term answer.

[dmr]

As you can get into the tank, would it be possible to weld the split from the inside?

 

I have welded stainless, and stainless to mild, but am just an amateur when it comes to welding. I have been told that welding does weaken stainless unless suitable precautions are taken, which is why stainless tanks split so often.

 

...............Dave

The full SP on welding dissimilar metals.

.....

Snot will get you out of a pickle but it's not a long term answer.

 

Thanks, will sit down and read this a bit later.

 

...............Dave

[gazza]

A stainless tank will only split if it's been poorly welded.

 

Carlsberg in Northampton officially opened in 1974. There are lots of gert big tanks still in service from the day it opened.

 

 

We used to suffer some cracking in the Mash Tuns and Wort Kettles, mainly due to the constant extremes of temperature. Regular crack detection and repair keeps them in service.

 

Never had such issues with the Fermentation and Storage Vessels as the temperature changes are nowhere near as extreme.

 

A water tank in a boat should suffer no such problems.

[ditchcrawler]

A stainless tank will only split if it's been poorly welded.

 

Carlsberg in Northampton officially opened in 1974. There are lots of gert big tanks still in service from the day it opened.

 

 

We used to suffer some cracking in the Mash Tuns and Wort Kettles, mainly due to the constant extremes of temperature. Regular crack detection and repair keeps them in service.

 

Never had such issues with the Fermentation and Storage Vessels as the temperature changes are nowhere near as extreme.

 

A water tank in a boat should suffer no such problems.

Vibration maybe

[dmr]

When I used to do my amateur stainless welding (MIG) I noticed a quite porous type effect on the rear of the welds. I was told this was local oxidation and was also told that length of masking tape behind each weld (whilst welding) was a quick fix to exclude the air. I suspect this is not how the professionals do it but it did improve things quite significantly. I've also spoken to a tank repair welder who said he fills the tanks with Nitrogen whilst welding them.

Sold the VW when we moved onto the boat and have not welded since.

 

................Dave

[gazza]

Vibration maybe

Not likely.

 

They are bigger than some prefab garages!

 

I shut the steam boilers down after overenthusiastically opening the globe valves for the heating jacket on one of them.

 

The guys in the energy centre were not often seen outside their dingy confines except to bollock hapless young lads like me

 

You can see the brewhouse and energy centre from the river - it's the glass bit at the back.

When I used to do my amateur stainless welding (MIG) I noticed a quite porous type effect on the rear of the welds. I was told this was local oxidation and was also told that length of masking tape behind each weld (whilst welding) was a quick fix to exclude the air. I suspect this is not how the professionals do it but it did improve things quite significantly. I've also spoken to a tank repair welder who said he fills the tanks with Nitrogen whilst welding them.

Sold the VW when we moved onto the boat and have not welded since.

 

................Dave

Not nitrogen! Argon.

 

Ali backers help, but excluding air from the joint is the answer.

I had the job of chasing a seam in a big hose bath with an open ended tube flushing argon over the back of the seam, shit, hot, sweaty back aching job fit only for a young small of frame apprentice

Edited May 20, 2016 by gazza

[davehull]

Thanks for the replies

 

Getting someone to the middle of nowhere with welding gear and asking them to squeeze into a tank may prove difficult.

 

Finding the leak without filling the tank is my big problem at present.

 

Liner for the tank is an expensive option I was hoping to leave as a last option.

 

The tank was fully dye pen tested and then filled and left for 2 days before it was fitted in the shell, after 10 years I think vibration and the constant filling and empting has stressed a weak spot on a weld.

 

May have to silicon in short term and ask a friendly short thin welder to quote for rewelding from the inside.

 

Dave

[gazza]

Thanks for the replies

 

Getting someone to the middle of nowhere with welding gear and asking them to squeeze into a tank may prove difficult.

 

Finding the leak without filling the tank is my big problem at present.

 

Liner for the tank is an expensive option I was hoping to leave as a last option.

 

The tank was fully dye pen tested and then filled and left for 2 days before it was fitted in the shell, after 10 years I think vibration and the constant filling and empting has stressed a weak spot on a weld.

 

May have to silicon in short term and ask a friendly short thin welder to quote for rewelding from the inside.

 

Dave

I'm busy and too expensive

 

Good luck getting it sorted.

[Guest]

a bloke once told me (that a bloke had told him) that stainless welds should be pickled and something else with a certain acid before using with water. No idea if this is correct, but some welders have agreed in the past.

 

ps would araldite/epoxy not make a temp. repair if you can get inside? (I uses araldite for lots of things ) Perhaps reinforced with some glass fibre tape or similar?

Edited May 20, 2016 by Guest

[Joe the plumber]

Is there any way you can block up the access hatch and breather, and get a bit of air pressure inside it (possibly back down the tank outlet pipe) to try to find out if it is a split or something less drastic without re-filling it?

 

The other thing you could perhaps try is some of the slosh petrol tank sealants which seem to work okay with petrol so may be able to withstand water, eg:

 

http://www.rust.co.uk/0002-slosh-ethanol-resistant-petrol-tank-seal/p405062

 

You'd have to be careful not to block the outlet pipe with it of course.

[gazza]

a bloke once told me (that a bloke had told him) that stainless welds should be pickled and something else with a certain acid before using with water. No idea if this is correct, but some welders have agreed in the past.

 

ps would araldite/epoxy not make a temp. repair if you can get inside? (I uses araldite for lots of things ) Perhaps reinforced with some glass fibre tape or similar?

http://www.wellyweld.com/products/pickling-paste-antox-71e-2kg-45164.aspx

 

it's for removing oxide scale and tarnish, it doesn't alter the mechanical properties of the joint.

 

An MV Augusta motorbike exhaust i looked at still had the oxide at the joints, it looked unfinished to me

[Guest]

http://www.wellyweld.com/products/pickling-paste-antox-71e-2kg-45164.aspx

 

it's for removing oxide scale and tarnish, it doesn't alter the mechanical properties of the joint.

 

An MV Augusta motorbike exhaust i looked at still had the oxide at the joints, it looked unfinished to me

thanks for that. We live and learn.

[gazza]

thanks for that. We live and learn.

 

its also good for waging chemical warfare on cockroaches.....

[Guest]

 

its also good for waging chemical warfare on cockroaches.....

LOL. Horrible things they are