Testing the welding integrity of an overplated boat

[TheBiscuits]

3 minutes ago, Mike the Boilerman said:

If water can get in, it takes oxygen in with it. 

Won't the new breather holes that @Bloomsberry has drilled in the original hull not do that on their own? 

[MtB]

16 minutes ago, TheBiscuits said:

Won't the new breather holes that @Bloomsberry has drilled in the original hull not do that on their own? 

 

Troublemaker!!

[roland elsdon]

All this talk about waiting until a hull rusts through and insurance companies being over carefull forgets sods law.

sods law says that indeed your 2mm bit of plate will be fine, as it is indeed maintaining integrity. As long as nothing changes.

However sods law also says that the bit that is 2mm thick will also be the bit hit by,

a scaffold pole sticking up from the canal bed, or

a large rock on the canal bed that the boat lands on when some idiot leaves the paddles open, or

that bit of sticking out iron that you hit running into the lock.

 

at this point your expensive batteries 42 cm tv laptop clothes and cat descend in a cloud of methane to the bottom of the canal.

 

you blame the scaffold pole ejit or crt lock repairs , your insurance company claim your hull wasnt fit for purpose.

they have the $$$$ you want the $$$$ the give you $ or even nothing.

 

 

[mark99]

10 hours ago, Captain Pegg said:

No. It's pushing in all directions. So you need to divide by infinity not by two. Then you'll find that logically there's no pressure on any surface at all.

 

 

I love bad Physics. You can prove anything you want.

 

JP

 

I wish I knew we had to divide by 2 the 1100 psig pressure test we did on 9.52mm steel pipe fabrication recently. Maybe the Lloyds inspector signing off should be told too.

 

Just imaging a sphere with infinite sides. You could pump it up to whatever pressure you want - no forces on the "sides".  

 

Edited November 22, 2018 by mark99

[Alan de Enfield]

19 minutes ago, mark99 said:

Just imaging a sphere with infinite sides.

Nope - that's beyond me.

I can only imagine 2-sides (inside and outside)

[mark99]

2 minutes ago, Alan de Enfield said:

Nope - that's beyond me.

I can only imagine 2-sides (inside and outside)

I want to see the how you work out of the divisor  for this new sciencific principle no one else has heard of as applied to spheres. 

Edited November 22, 2018 by mark99

[mark99]

You could expose the cavity (and external skin) to a max pressure/force per unit squared the same max as it experiences underwater to be "safe".

 

Assume the hull is < 3 foot below the surface. Water pressure @ 3 foot = 36" water gauge = 90 mbar = 1.3 psig.

 

Drill and tap a 1/4" hole on the inside plate and inflate to 1.3 psig and lock off pressure. Use digital pressure gauge/manometer. Allow to stabilise temperature wise and see if the pressure drops over 1/2 hour or so.

 

This won't give you a condition report as such but will tell you if it's leaking somewhere. Bear in mind it could be leaking on bad welding (cracked or porous) and the outer skin could still be ok so it's just a rough and ready collection of info. I suspose you could look for bubbles rising to surface too if the pressure dropped. The nifty thing about bubbles is that you will see not only if but where the outer skin is leaking if it is.

 

 

Edited November 22, 2018 by mark99

[MtB]

2 hours ago, mark99 said:

Just imaging a sphere with infinite sides. You could pump it up to whatever pressure you want - no forces on the "sides".  

 

Not sure buy that.

 

There will be a tensile stress on the material the sphere is made of, across any imaginary 'equator' line you might chose to draw on the surface of said sphere. The origin of this stress will be the gas pressure in the sphere. The total force will be pressure x cross sectional area of the sphere at the diameter. The stress will be the total force divided by the (length of the equator x the thickness of the steel). As any fule kno. 

 

 

 

Edited November 22, 2018 by Mike the Boilerman
Improve clarity

[mark99]

35 minutes ago, Mike the Boilerman said:

 

Not sure buy that.

 

There will be a tensile stress on the material the sphere is made of, across any imaginary 'equator' line you might chose to draw on the surface of said sphere. The origin of this stress will be the gas pressure in the sphere. The total force will be pressure x cross sectional area of the sphere at the diameter. The stress will be the total force divided by the (length of the equator x the thickness of the steel). As any fule kno. 

 

 

 

I was taking the pee out of this "divisor" bad physics above, surely that was obvious? mebbe not.

 

 

Edited November 22, 2018 by mark99

[MtB]

3 minutes ago, mark99 said:

I was taking the pee out of this "divisor" bad physics above, surely that was obvious? mebbe not.

 

 

 

Doh!!

 

 

[Captain Pegg]

1 hour ago, mark99 said:

I was taking the pee out of this "divisor" bad physics above, surely that was obvious? mebbe not.

 

 

I think you were only person who got the point I was making. I’m too obtuse for the literal folks.

 

A sphere is a polyhedron with an infinite number of faces. A circle is a polygon with an infinite number of sides. Similarly, a straight line is a curve of infinite radius. Pretty good basic mathematical models.

 

JP

Edited November 22, 2018 by Captain Pegg
Correct my own mathematical mistake.

[alan_fincher]

14 hours ago, Mike the Boilerman said:

 

Any time.

 

My 1887 boat survived until five years ago without overplating. 

 

 

(Then it sank, lol!!)

I think the evidence is that 1887 rivetted wrought iron lasts a lot longer in canal water than 1960s/1970s/1980s welded steel.

A 1890s BCN boat that we used to own has apparently had the steel bottom it had put in in the 1960s to replace composite wood replaced for a second time, whilst the wrought iron sides remain largely original.

(Just my luck that both of my 1930s Yarwoods boats are steel rather than iron built ones!).

[MtB]

3 minutes ago, Captain Pegg said:

I think you were only person who got the point I was making. I’m too obtuse for the literal folks.

 

A sphere is a polygon with an infinite number of sides. Similarly, a straight line is a curve of infinite radius. Pretty good basic mathematical models.

 

JP

 

I hadn't actually read the thread fully when I posted.... 

[Captain Pegg]

5 hours ago, alan_fincher said:

I think the evidence is that 1887 rivetted wrought iron lasts a lot longer in canal water than 1960s/1970s/1980s welded steel.

A 1890s BCN boat that we used to own has apparently had the steel bottom it had put in in the 1960s to replace composite wood replaced for a second time, whilst the wrought iron sides remain largely original.

(Just my luck that both of my 1930s Yarwoods boats are steel rather than iron built ones!).

Not sure I would worry about that. Steel from 1887 would probably have similar corrosion properties to wrought iron. Early Bessemer steels were close in chemical composition to wrought iron as the processes for making both required almost full decarburisation (removal of carbon). As steel making methods improved the levels of carbon increased and structurally there are benefits from steel over iron. Your 1930s steel will be softer and more coarsely grained than post war products which is probably why we get anecdotal evidence that it's easier to work with.

 

As for the original question I would absolutely not deploy a semi-destructive test to a problem that only exists in theory and for which there are no specific symptoms.

 

JP

[ditchcrawler]

10 hours ago, mark99 said:

 

I wish I knew we had to divide by 2 the 1100 psig pressure test we did on 9.52mm steel pipe fabrication recently. Maybe the Lloyds inspector signing off should be told too.

 

Just imaging a sphere with infinite sides. You could pump it up to whatever pressure you want - no forces on the "sides".  

 

We use to pressure test to 3 times that nearly 1500 psi working

 

[mark99]

37 minutes ago, ditchcrawler said:

We use to pressure test to 3 times that nearly 1500 psi working

 

Ours was a class 300 unit. We do go to class 600 too. That's over 2000 psig test. Hydro of course. 

 

Just done a 600  metre long high density plastic hppe pipe next to Banbury canal to 150 psig. The wall thickness is circa 20mm. The pipe elongates slightly under pressure.

 

At these pressures safety is a big feature. Potentially lethal.

Edited November 22, 2018 by mark99

[ditchcrawler]

18 minutes ago, mark99 said:

Ours was a class 300 unit. We do go to class 600 too. That's over 2000 psig test. Hydro of course. 

 

Just done a 600  metre long high density plastic hppe pipe next to Banbury canal to 150 psig. The wall thickness is circa 20mm. The pipe elongates slightly under pressure.

 

At these pressures safety is a big feature. Potentially lethal.

True, I wouldn't consider pumping between two plates with air. I only worked with steel not plastic. Some of out tests lasted for several hours to satisfy Lloyds inspectors

[jonesthenuke]

In the proposed application the objective is to check for leaks rather than the strength of the weld to the hull (water pressure is pushing the new plate onto the hull not away from it) thus apply a vacuum to the interspace and check for a pressure rise over time.

[ditchcrawler]

51 minutes ago, jonesthenuke said:

In the proposed application the objective is to check for leaks rather than the strength of the weld to the hull (water pressure is pushing the new plate onto the hull not away from it) thus apply a vacuum to the interspace and check for a pressure rise over time.

Or drill a hole on the inside , connect an air line and look for bubbles. What if whoever did the overplating cut holes on the inner skin to check for water ingress, how do you pressurise that?

 

[jonesthenuke]

7 hours ago, ditchcrawler said:

Or drill a hole on the inside , connect an air line and look for bubbles. What if whoever did the overplating cut holes on the inner skin to check for water ingress, how do you pressurise that?

 

Yes there is no complete solution to this, but applying a vacuum avoids pitfalls of pressurising the interspace due to the large forces developed acting to tear the plates apart. If there are holes in the original plating already then the only solution is careful inspection of the welds, visual and NDT (Dye Penetrant and Mag particle etc)

[cuthound]

On 21/11/2018 at 19:01, Trento said:

You can try "penetrant dye test" on the welds, or a Ultra sonic weld test. Either of which would confirm any weld defects.

the boat will need to be lifted out of the water to complete.

 

 

We used to use magnetic particle testing to prove the welds on the chilled water and heated water pipes when I was working in data centres.

 

https://en.m.wikipedia.org/wiki/Magnetic_particle_inspection

[mark99]

18 minutes ago, cuthound said:

 

We used to use magnetic particle testing to prove the welds on the chilled water and heated water pipes when I was working in data centres.

 

https://en.m.wikipedia.org/wiki/Magnetic_particle_inspection

 

Were they fillet welds only?

 

 

[cuthound]

1 hour ago, mark99 said:

 

Were they fillet welds only?

 

 

 

Not sure, they were joining flanges onto sections of 10 inch ID steel piping to carry chilled water or hot water. 

[mark99]

Sounds like slip on flanges via fillet weld not weld necked flanges via butt welding.

[ditchcrawler]

100% radiograph will tell you. this is critical structural welding we are talking about, aren't we.