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What happens when malleable iron pipe fitting fail full of water?

What happens when malleable iron pipe fitting fail full of water?

What happens when malleable iron pipe fitting fail full of water?

(OP)
I was wondering what malleable iron pipe fittings do when they fail full of water... like 1/2 or 3/4" size fittings with no air

Do they burst and then leak everywhere? or is it more normal for the fitting to deform at the threads and leak there or spring a small leak? just wonder if there is a way that they fail that would be more likely.

It would not seam to me that there would be any danger if it is filled completely with water

Does anyone know the factor of safety design into fittings like these? so when you buy 150psi max fitting what it will most likely hold before fail?  

RE: What happens when malleable iron pipe fitting fail full of water?

Think about your energy source:  A water-filled pressure vessel (yeah - this case is about a failed single fitting in a pipe, but it acts like a PV) suddenly failing at some location.

So your energy is going to be dumped out through the failure point -> the pressure differential decreases proportional to the loss of water (if you assume you are not pumping up the pressure through temperature increase in the system or a positive-displacement pump!), the flow rate decreases (since the fitting hole will "probably" not continue to tear out metal from the sides of the hole), and eventually the pipe will still be filled but the pressure differential will approach zero between inside and outside pressure.

In nuclear systems under maintenance, we occasionally had to maintain pressure by running PD pumps (pushing water into a solid system to raise pressure at night when temperatures decreased) or draining water to lower pressure (taking chemistry samples, opening the drain valve, lowering room temperature, etc.)  Pressure loss - almost regardless of the size of the fluid system - is very quick if you're losing water when solid!   

Now - think of a pressurized gas system: The initial excessive high pressure doesn't go down quickly as soon the leak/crack occurs because an ideal gas expands to replace the little bit of lost fluid.   The leak rate stays constant, and the erosion or expansion of the crack is much more likely.  Catastrophic failure - deadly failure! - is thus more likely when a pressure test is done with gas rather than water.  

Malleable iron is just that - it will tend to stretch and tear rather than be brittly exploding under over-pressure (over-tension) forces.   

RE: What happens when malleable iron pipe fitting fail full of water?

From experience during hydrotests, they simply start leaking and won't stop, and the leakage rate is greater than our hydrotest pump has a hope of keeping up with.

I've seen them split by an overly ambitious pipefitter with too large of a pipewrench, but never seen one split due to overpressure.

RE: What happens when malleable iron pipe fitting fail full of water?

Yes - Unless there is a some kind of goofy failure right through a fitting (a casting failure and then forging and then machining failure and then inspection failure), real-world leaks are through a mechanical joint: valve cover, body-to-bonnet leak, valve stem, valve leak, piping flange, instrument connection .....   

RE: What happens when malleable iron pipe fitting fail full of water?

By the way, using our typical materials and methods around here, I can hydraulically turn an ordinary nipple into a good approximation of a swage nipple before the threads start to leak so bad that the hydro pump can't keep up.  The fittings generally shrug off the whole thing without noticeable effect.  Then again, we haven't tested thousands of them to this ridiculous extent.

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