I have some general questions about HDT.
I'm not currently trying to perform an inspection, just trying to learn about a test method I've never been involved with.
Thanks in advance for any info.
At first glance, HDT seems to be a complex process, utilizing expensive equipment and tracer gases that are affected by regulations concerning release to the environment.
1. Is it safe to assume that HDT is primarily used as a means to leak test systems whose main function is to store or convey refrigerants?
2. After performing HDT, does the residual tracer gas have to be collected to prevent environmental release?
3. Is HDT capable of detecting minute leaks that other testing methods may miss?
4. Is leak testing performed by pressurizing a system with halide gas and checking for leaks with an oxy/acetylene flame (flame color change) at all practical or often done?
What color does the flame change to when a leak is found?
Thanks,
Tim
You might consider purchasing a book on leak testing from ASNT.
The bottom line is that everything leaks, it is a matter of how fast it leaks which is dependent on what is being contained.
Consider a weld made with E6010 electrode. The decomposition of the flux covering produces hydrogen which is highly soluble in liquid iron, i.e., the weld pool. Upon cooling and solidification, the solubility of hydrogen is reduced substantially. The excess atomic hydrogen (monatomic) is small enough to diffuse through the atomic lattice and effuse into the atmosphere. In other words, the monatomic hydrogen "leaks" into the surrounding air over time. While it is escaping the solidified weld and surrounding HAZ, it has a nasty tendency to initiate cracking problems in the form of delayed cold cracking, hydrogen assisted cracking, under bead cracking, etc.
In a hydrogen rich environment where the temperature is elevated and under high pressure, the hydrogen can permeate the vessel wall and cause blistering.
The bottom line is that a vessel that can easily contain one type of fluid may leak a different fluid. The leak rate is dependent on the path followed and the "size" of the fluid's molecule, and of course, one must not forget "time".
Fun stuff.
Best regards - Al
Thanks everyone for the replies.
I'm still trying to wrap my mind around the reason why HDT would be used rather than hydro or bubble testing.
I understand that when leak testing, pressurized diesel fuel will leak through an opening too small for water to seep through as diesel is thinner, and pressurized air will leak through an opening too small for diesel to seep through.
Will halides leak through an opening too small for air molecules to pass through, say from hydrogen cracking?
Tim
I would be interested to learn more.
Isn't He leak test the gold standard though?
I have to help solve a He leak problem for the project I am working on.
But, so far, we don't have a way to isolate the leak to see where it is occurring - ie which weld and which location on which weld...
I just got off the phone with a vendor and he has nitrogen-hydrogen leak testers for sale or rent.
I was not aware of hydrogen leak testing until today.
I want to find out how the accuracy compares to He leak testers.
To get to 10 -7 we might need He only.
By DaveBoyer 
Date 07-03-2012 05:02
Edited 07-03-2012 05:09
The torches are seldom used anymore, and not particularly sensitive at that.
The electronic leak detectors have replaced the old torches. I have not priced them lately, but a simple one used for HVAC work that I got in the mid '90s was a little over $100. It just beeps, more frequently as You get into higher concentrations of refrigerant.
Halides are ozone depleeting gasses, and heavily regulated in countries that follow Montreal Protocall. This means You can not release them into the atmosphere, and need a liscence to handle them.
There are allowances for release of "deminimus" ammounts, I don't remember if there is a specified ammount or not.
I don't know if My section 608 universal would cover Me for NDT of non refrigeration equipment or not, it was not mentioned when I got it. My understanding was it covers everything except motor vehicle air conditioning, which takes a 609 liscence that isn't good for anything else.
