Propane tank replacement

[GeorgeRa]

Originally Posted by InterBlog

................................. But the threads IN the tank are sub-millimeter sized structures that are far more fragile.

A chain is only as strong as its weakest link. The weakest link here appears to be the threads.

Thread pitch could be sub-millimeter but I am not sure if it makes any difference. These threads are sealed with sealant or sealing tape to not allow propane to go out, if propane can’t get out oxygen can’t get in, so without oxygen these threads will not corrode.

I agree that the weakest link will dictate tank's life limits, but I doubt that tank's threads are these links.

[dicktill]

Originally Posted by InterBlog

However, the threaded line ports are fragile (anyone who has studied materials science could tell you why, but I'll skip the explanation for brevity). If the THREADS rust out, then there's no way to stop leaks aside from either re-threading (= a repair) or replacing the tank.

Hi IB,

I did study materials science, but I can't tell you why ...

An explanation would be appreciated.

Thanks, Dick

[JohnnyFry]

The pressure on the tank side of the regulator is much too high (70 to 250 psi depending on temperature) plus the fact that as long as there liquid remaining in the tank the pressure remains constant. To test in that manner you would have to remove all propane and pressurize the tank with compressed air.

[InterBlog]

My tank threads were in the process of failing due to corrosion, and I got propane blow-by as a result of that.

Before Shuttle Challenger blew up via an analogous failure, engineers didn't think THAT was possible, either (NASA's original risk analysis erroneously concluded that there was a 1 in 100,000 chance of a catastrophic shuttle loss). If not for Feynman and his C-clamp, I sometimes wonder if they ever would have figured out what went wrong.

I actually heard propane hissing out before I smelled it - it was a high-pitched whiny sound. Fortunately I caught it when the leak was still small.

I don't know anything about SCUBA tanks, but common sense tells me that anything with threads is subject to differential thread wear, and thread failure. O-rings, too.

[GeorgeRa]

Originally Posted by InterBlog

....................... Before Shuttle Challenger blew up via an analogous failure, ...................

I don't think it was analogous to the leak due to thread pitch in your tank, it was due to O-rings misapplication. There were folks questioning the O-ring design just as during the deployment of the Hubble telescope when wrong decision was made. For the Hubble a simple, centuries old, test with a candle and a knife could determined the bad mirror with the shuttle’s O-rings test was more difficult.

Your provided example of the shuttle disaster but didn’t shed light on the mechanism of corrosion of LPG tank fittings and it is relationship to thread pitch. Perhaps someone crossthreaded these threads?

Originally Posted by InterBlog

……………………..I don't know anything about SCUBA tanks, but common sense tells me that anything with threads is subject to differential thread wear, and thread failure. O-rings, too.

Thread wear happens if fittings are remove many, many times which I don’t think is common with LPG tanks. I think you had a case of crossthreading.

[InterBlog]

I used the word analogy. I did not make a literal comparison in terms of pitch, orientation, rheology, or other physical factors.

In my functional analogy, both examples involved a small part that was perceived to be robust to the point of inviolability. In fact, lives were bet on exactly that assumption.

But both of the parts in question actually have insanely high surface area to volume ratios. Anyone who has ever studied materials science knows that the rules change in such a realm, and both intuition and assumptions need to be questioned as a result.

Do I know how my threads managed to get corroded? Nope, but I strongly suspect that 50,000 miles of road vibration and successive impacts due to pot holes and other road surface irregularities were factors (MB Sprinters are cargo vans, and are legendary for their rough rides). The constant jostling of the fittings may have allowed enough flexure over time for water to get a toe-hold and for corrosion to begin.

Propane blow-by due to corroded tank threads. I hope that nobody gets killed by it someday.

[booster]

Interblog, are you certain the leak was from around/through the threads?


The reason I ask is that I have seen plenty of leaking tanks of various types, but not necessarily propane tanks, and lots of rusted threads that don't leak, but tear up the the threads when removed as the rust is either on the inside and rip out the threads on the way out or the first thread or two on the outside which leave damage that show on the whole fitting when removed.


What is far, far, more common in what I have seen is that you can get fooled into thinking you have a fitting leak, but it doesn't go away with resealing (or you destroy the thread taking it apart so can't reseal and can't test it), and it turns out to be a pinhole or rust crack in the weld of the threaded bung into the tank. The welds seem to be particularly prone to rusting before everything else and the welds are commonly just laying on the surface of the tank and side of the bung, without penetration at the actual interface of the two parts on diameter. This leave a gap under the weld open to the inside of the tank and is a prime spot for moisture to accumulate even in products that don't hold much moisture.



Threads do have high surface to volume ratio compared to other shapes, but if the fittings are made correctly almost all of that area is in compressed contact with the mating piece and normally sealed with a sealer, so rusting corrosion will be much reduced, except in the areas that are outside the contact area, and rust there will cause breakage, not leaks.

[GeorgeRa]

Originally Posted by InterBlog

I used the word analogy. I did not make a literal comparison in terms of pitch, orientation, rheology, or other physical factors.
In my functional analogy, both examples involved a small part that was perceived to be robust to the point of inviolability. In fact, lives were bet on exactly that assumption.
But both of the parts in question actually have insanely high surface area to volume ratios. Anyone who has ever studied materials science knows that the rules change in such a realm, and both intuition and assumptions need to be questioned as a result.
Do I know how my threads managed to get corroded? Nope, but I strongly suspect that 50,000 miles of road vibration and successive impacts due to pot holes and other road surface irregularities were factors (MB Sprinters are cargo vans, and are legendary for their rough rides). The constant jostling of the fittings may have allowed enough flexure over time for water to get a toe-hold and for corrosion to begin.
Propane blow-by due to corroded tank threads. I hope that nobody gets killed by it someday.

I think the reason for this discussion to highlight potential problem with an LPG tank and I have hard time following your explanation. You mentioned “insanely” high surface area, in direct comparison of a thread to the same diameter cylinder’s surface the thread surface area is 30-50% larger, so not necessarily insanely larger. But in this case, it is a moot point. High surface area to volume ratio can accelerated a chemical reaction like corrosion only of this surface is exposed, this is not the case with a fitting’s thread, only outer threads are exposed.

As Booster wrote, fitting welding or crack could have been the issue.

[dicktill]

Originally Posted by cdahle

After smelling propane on w/e trip then finding a leak AND a rusted tank on our 2014 RT 190 Popular we are having the tank replaced. Manchester brand for our model $1100 and 7-9 weeks for delivery! (then labor..). Hoping to get it done by time we leave Maryland for Florida end of Jan.
I've seen some discussions re new tank certification and must be less then 10 years old?? But I've not seen any discussions/complaints about cost of tank replacement.
Does everyone get new tank every 10y?
Thanks,
Cindy & Mike

Have you made any progress on this? Have you (or your mechanics) been able to tell exactly where the leak is?

[GallenH]

Originally Posted by InterBlog

The fitting threads. It boggles my mind that some people cannot parse this logically (comment not limited to this thread and I’m not intending to target Gallen - this issue has come up repeatedly in the 5 years that I’ve owned a Class B). The tank is heavy gauge steel and almost indestructible. But the threads IN the tank are sub-millimeter sized structures that are far more fragile.

Sorry but I do feel targeted. ASME tanks are certified for life. Period. No argument. My comment was two-fold. First, certified propane dealers who specialize in the product realize this and will fill your tank. They ARE reputable, despite what you implied. Second, continually test your tank for leaks and have it inspected for rust deterioration. Seems simple and not an issue of people "unable to parse logically."

I do agree with your comment about flex lines. Some owners should be aware, however, that it might have limited application. The only flex line I have, for example, is from the regulator to the hard line in the propane compartment. Everything else is a hard line.

[TatraDog]

As stated by others, ASME tanks are NOT required by law or regulation to be re-certified or replaced after a certain age. They are considered permanent mount and are good for life. Unless, of course, they get damaged.

As to propane leaks, I have had two issues/leaks with older RV propane systems.

1 - 1989 Mallard Sprint 19' Class C/B+
Smelled propane leak and took it to the RV shop. They found that a "brass fitting" had cracked. Fitting was replaced and leak fixed. The tank was just fine.

2 - 1995 Coachmen M19-RD Class B
Heard a hissing sound when opening/closing the shut-off valve of the tank. The valve had gone bad (not the tank or the threads). Only heard the hiss/leak when the valve was partially opened. When fully closed or fully open, the valve did not leak. In any case, I found a brand new replacement tank and took it to the RV shop.
Turns out that I did not need to buy a new tank. The RV shop told me that they could had just replaced the shut-off valve in the old tank and then tested the tank.
They did advise that occasionally the old shut-off valve can break off while removing it - about 10% of the time. Otherwise, they said I really didn't need a new tank.

So, basically in my experiences the tank itself rarely, if ever fails. Worn or faulty valves, fittings, connectors and regulators are likely the cause of 99% of propane leaks.

David

[Floorman]

Have my old rusty Manchester 68001 dropped out of the 02C190P Roadtrek. Have severely wire brushed 99.9% of the rust away. Used Rustoleum rust reformer and multiple coats of "Performer" white Rustoleum paint. I want to have the existing service valve (RegO 901c3) replaced and the Marshall 290 2 stage regulator. I'm removing the BBQ regulator, the Tee fitting and hose and replacing the POLx1/4 pigtail with a new one about 10" long made up at the local propane dealer who also does RV work. Having a difficult time finding the RegO 901c3 valve. Manchester Tanks emailed and says their V20373.3 is the correct valve for the 68001 Tank. Most important info to share is that the RegO 901c3 and c5 have a National Highway Safety recall for valves manufactured between Feb 2021 and Feb 2022 due the 3/4" threads being out of spec. The only RegO 901c3 valve I've found is on Ebay and of course the time stamp is April 2021 and is in the timeframe of the recall. You'll have to Google RegO 901c3 to scroll to the recall post. I did an Ebay contact seller asking if they had a valve available that was time stamped out of the recall and got the simple answer "NO". The V20373.3 valve if I can find one will be the choice and a MEGR 298 looks like the 2-stage regulator choice. While I think it's possible to R&R the valve without dropping the tank the regulator might be a different story. There are some great photos of this type of Project from Jon Kerman Blackburn on Jan 13 ,2023 on FB Chevy Roadtrek Group. Good Roads to you all.

[jjrbus]

Interesting. I have had an RV for over 20 years, both DOT and SAE tanks. I have had tanks filled from FL to NY, on the west end of the country and in the middle, never seen a 10 year sign!

I did have a LP dealer refuse to fill a SAE tank that was out of date and simply drove down the street to an RV dealer and they filled it without looking. I also had a Tractor Supply refuse to fill a horizontal tank. I had the tank filled there before and inquired why. The young man responded that he was working under his managers license and had never seen a tank like it and did not want to get his manager in trouble. So much for the highly trained, professional LP technician! Again drove down the street and had the tank filled, no big deal.

[GallenH]

Yeah. UHaul, where we always filled, stopped filling tanks more than 10yrs old 2-3 years ago. My suspicion always has been that they didn't want to take the chance that their employees couldn't tell the difference between a DOT and an ASME tank. I've never had any problem filling mine at any other place since.

[jjrbus]

Originally Posted by GallenH

Yeah. UHaul, where we always filled, stopped filling tanks more than 10yrs old 2-3 years ago. My suspicion always has been that they didn't want to take the chance that their employees couldn't tell the difference between a DOT and an ASME tank. I've never had any problem filling mine at any other place since.

Don't recall ever having a tank filled at Uhall?