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1st yr welding apprentice project

What welding projects are you working on? Are you proud of something you built?
How about posting some pics so other welders can get some ideas?

Re: 1st yr welding apprentice project

Postby Sftyvlv » Sun May 07, 2017 6:53 pm

That's why water is used. Unlike a gas (compressed air, nitrogen etc) you can't compress water. Inside a vessel the water will act as a solid and when released to the atmosphere it sprays harmlessly for a split second and drops to atmospheric pressure. If the same was done with a gas...........well you saw Mythbusters.
Enuf said.
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Re: 1st yr welding apprentice project

Postby exnailpounder » Sun May 07, 2017 9:12 pm

Farmwelding wrote:
electrode wrote:
exnailpounder wrote: I always wondered that when I worked in a dive shop when I was alive.


You mean you are actually dead now? :lol:

I guess Jeff died and now his ghost has taken over him. Endless alcohol and can weld without gloves and a helmet and in any position with no problems. His wife is actually not happy though because Jeff has decided to use his ghost abilities to scare the living hell out of her all the time bu sneaking around unnoticed and then using a haunting voice. From now on he is phantom Jeff.

Gosh you guys are some serious thread-jackers ain't ya? :lol:
Ifyoucantellmewhatthissaysiwillbuyyouabeer.
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Re: 1st yr welding apprentice project

Postby Farmwelding » Sun May 07, 2017 9:43 pm

Shut up Jeff, remember you're dead :lol:

On a more serious note-when you pressure test a vessel with water-how do you find the failure point? Does a small pinhole happen or is it a reading somewhere in the tubing.
A student now but really want to weld everyday. Want to learn everything about everything.
warning!! Bad English may be in post. It's off a phone/autocorrect. I've had teachers with worse spelling!
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Re: 1st yr welding apprentice project

Postby exnailpounder » Sun May 07, 2017 10:50 pm

Farmwelding wrote:Shut up Jeff, remember you're dead :lol:

On a more serious note-when you pressure test a vessel with water-how do you find the failure point? Does a small pinhole happen or is it a reading somewhere in the tubing.

https://en.wikipedia.org/wiki/Hydrostatic_test
Very interesting science.
Ifyoucantellmewhatthissaysiwillbuyyouabeer.
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Re: 1st yr welding apprentice project

Postby Sftyvlv » Mon May 08, 2017 8:59 am

An engineer will decide the test pressure. He bases his calculations on code requirements from ASME (American Society of Mechanical Engineers). They are the regulatory body responsible for pressure vessel and piping (boilers, air receivers and the like as well as piping for steam, air, nitrogen, acidic fluids etc).
The results of an engineers calcs decide a given pressure test (max allowable, and service pressure and temp). The usual spec for testing is 1 1/2 times the working pressure held for a specific period of time. A failure is deemed if any part of the vessel/pipe including the weld leaks.
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Re: 1st yr welding apprentice project

Postby Otto Nobedder » Mon May 08, 2017 8:40 pm

Sftyvlv wrote:An engineer will decide the test pressure. He bases his calculations on code requirements from ASME (American Society of Mechanical Engineers). They are the regulatory body responsible for pressure vessel and piping (boilers, air receivers and the like as well as piping for steam, air, nitrogen, acidic fluids etc).
The results of an engineers calcs decide a given pressure test (max allowable, and service pressure and temp). The usual spec for testing is 1 1/2 times the working pressure held for a specific period of time. A failure is deemed if any part of the vessel/pipe including the weld leaks.


Safety Valve, this may surprise you, then.

I do DOT required vessel retests for liquid hydrogen vessels. These tests are pneumatic (compressed nitrogen), not hydraulic. Every five years, I take the vessel to 125% of MAWP in controlled conditions.

The reason this is permissible is this is a vacuum jacketed vessel, and a catastrophic failure "should" be contained and vented through a relief port intended for that purpose.

We also retest CO2 trailers that are not jacketed, and these are hydro-tested for the reasons you explained.

The test for jacketed vessels at 125% MAWP is done with the jacket under full vacuum, so you can add another 14.7 PSI to the gauge pressure.

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Re: 1st yr welding apprentice project

Postby Sftyvlv » Mon May 08, 2017 11:37 pm

Yea Otto, I've been on a crew at a refinery that used nitrogen as the test medium. Because of the potential energy inside of the pipe we had to rope off a specific distance away from it.
The engineer equated the energy in the pipe to a certain amount of TNT.
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Re: 1st yr welding apprentice project

Postby Otto Nobedder » Tue May 09, 2017 6:12 pm

Sftyvlv wrote:Yea Otto, I've been on a crew at a refinery that used nitrogen as the test medium. Because of the potential energy inside of the pipe we had to rope off a specific distance away from it.
The engineer equated the energy in the pipe to a certain amount of TNT.


I can see TNT as a good measure of the stored potential energy. I've taken 8' dia. vessels to 219 PSI in nitrogen, always done outdoors, and I get a bit more attentive once I'm above 185 PSI. Since it's a vacuum-jacket, I'm monitoring vacuum for any sign of a rise to warn me of an impending failure. I have yet to have one, though working outside for several hours, the sun on the vessel will cause the vacuum to creep a few microns. I know this is going to happen, but once I'm above MAWP, it gets my attention.

The highest pneumatic test pressure I've done was 9670 PSI, on 1/2" sch. 160 304SS pipe that I welded myself. 25% had been x-rayed, and those were all bench welds. None of my field welds were x-rayed. Let's say I was "alert" that day...

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