Steel Tank Condemned: Cracks in Threads?

[Southside]

So if these indeed are cracks, what is the worst that could happen to such tanks if used. Obviously leak but anything more serious?

Cyclical loading and unloading from filling and draining causes a crack to propagate. Eventually it will grow large enough that it will fail catastrophically. Lots of math and fatigue analysis will give you a ballpark of crack propagation rate but you have to make a lot of assumptions so not the most accurate.

 

[BoltSnap]

So if these indeed are cracks, what is the worst that could happen to such tanks if used. Obviously leak but anything more serious?

Eventually the tiny crack develops into a major rupture and then kaboom and lights are off for those that are close by.

 

[chris kippax]

Or it could turn the valve into a projectile

 

[BoltSnap]

Or it could turn the valve into a projectile

Or both...

 

[uncfnp]

But would not a leak of air be obvious before a catastrophic failure?

 

[chris kippax]

Maybe... Maybe not. I wouldn't wanna find out.
Filling a known to be cracked scuba tank could be instant nomination to the Darwin awards.

 

[GJC]

All the tank ruptures that I have heard about have either been during a fill or when a tank fell or was dropped on the valve.

 

[johndiver999]

But would not a leak of air be obvious before a catastrophic failure?

I've seen an aluminum tank crack near the neck and begin to leak pretty fast as the tank reached full pressure while filling. We stopped filling and kinda ran away and when we came back the pressure was lower and the crack had (IIRC) stopped leaking.

 

[Lostdiver71]

I have seen the threads fail on a tank while filling. The valve ripped the fill whip hose out of the fitting, went through the ceiling and the roof of the shop! Fortunately the owners son who was filling the tanks had just stepped a few feet away to grab something when it blew or he may have been hit by the valve!

 

[rjack321]

But would not a leak of air be obvious before a catastrophic failure?

yes but sometimes the leak is only obvious for a tiny tiny fraction of a second before something catastrophic happens