Propane shelved

[kevingranade]

Summary

None

Purpose of change

Noticed in #73690 that the propane torch is currently usable for welding.
Not sure why I never connected the dots before, but no, it's not remotely hot enough to weld any materials we're interested in, much less cut through steel doors.

Describe the solution

Removed propane torch from welding requirement groups and removed it's OXYTORCH use action.
Adjusted the description to match.

Additional context

Do let me know if there are sources indicating otherwise, but a quick search is very clear that no, this kind of propane torch is not usable for general metal welding or cutting.
To clarify something, you evidently CAN cut with propane with copious amounts of oxygen, but AFAIK that's not the kind of propane torch this is depicting, and that would require carting around propane plus oxygen (or fusing it together into some composite fuel?)
You definitely can't weld though for chemistry reasons.

[Kamayana]

Propane isn't hot enough for welding, but it is hot enough for brazing and soldering. Welding is melting metal parts enough to melt them both together, and propane isn't hot enough to do that. Brazing and soldering, on the other hand, are joining metal parts together using a lower-melting-point filler metal/solder. While weaker than a full-on weld, it's easier, and unlike welds it can connect dissimilar metals together. Propane actually seems to be a popular gas for non-weld-metalworking because it's cheap and easy to get ahold of, unlike acetylene.

Propane brazing two small steel rods together, has a stress test, he also talks about the limitations of propane torches: https://www.youtube.com/watch?v=EsAzx3Od__U
Propane brazing a broken hardened steel wrench back together, sadly no stress test: https://www.youtube.com/watch?v=WQ2Yr-QLkjE

https://www.thewelderswarehouse.com/blog/can-i-use-propane-instead-of-acetylene/

Propane is the easiest fuel gas alternative to Acetylene to obtain and is normally supplied in cylinders on a Deposit basis, rather than rented (as is usually the case with Acetylene).
For most users, Propane works out cheaper, especially for infrequent users of Oxygen + Fuel kits. The only real downside to using Oxy/Propane is that it can’t be used for actual Welding. Oxygen and Propane fuelled kits are however, ideal for Silver Solder, Brazing, Cutting and Heating. So as long as you don’t want to Weld, Oxygen and Propane is a great way to go! Oxygen + Propane produces a flame temperature of around 1800⁰C.

Note that that's specifically talking about propane with oxygen, which is a concern you had, but the thing is that many acetylene torches also require an oxygen tank. There are basically two kinds of gas torches - Oxy-Fuel and Air-Fuel (also called atmospheric torches, since they use oxygen from the air). Air torches are very portable because they only use a single tank, while oxy torches need a separate tank of air attached. Air torches are significantly less hot than oxy, so they can't work with steel, but even an air-propane torch is hot enough to work aluminum, silver, and brass, for brazing, repairing, or potentially even welding as long as it's only those metals.

https://www.achrnews.com/articles/126863-comparing-air-fuel-and-oxy-fuel-torches

https://contenti.com/resources/gas-melt-temperature

Portable air-Fuel torch (there are also acetylene torches in this form):

Portable oxy-fuel torch (the non portable form is basically just this but without the tank container):

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As for metal cutting, it seems that you absolutely need an oxy-fuel torch - I couldn't find anyone who cut metal with an air-fuel, not even with air-acetylene. Metal cutting is about using the fuel fire to heat the metal up enough to where the oxygen fire can slice through it - without oxygen there's no cut. An oxy-propane torch is perfectly capable of cutting metal, though. This video is a good demonstration:

https://www.youtube.com/watch?v=Nt__etyFhLY

Edit: Heck, I might even be selling the propane cutter short; this guy is able to cut through 40mm/1.5'' steel plate with one.

https://www.youtube.com/watch?v=fCPJNJ8WFxA

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So, my thoughts are that while you're correct that propane shouldn't be able to weld heavy-duty thick steel for projects like a car frame, it seems more than capable of doing lighter metalwork like minor repairs or working with aluminum, if maybe taking a little longer than an acetylene torch. We could maybe stand to audit the torches to clear up the difference between welding and brazing and make propane only capable of the latter, but I feel like removing its ability to repair and cut altogether is a step too far.

[kevingranade]

but I feel like removing its ability to repair and cut altogether is a step too far.

Due to the lack of nuance as currently implemented, it's absolutely warranted. If someone wants to start adding braising as a repair option where appropriate sure they can use propane torches as an option for that, but that braising distinction needs to exist because it's not universal. You're suggesting a huge overhaul to metalworking here.

Likewise with cutting, we currently assume that our acetelene fuel is actually an acetelene and oxygen tank strapped to each other or something, but we are definitely not making a similar assumption about propane.