Overfilled propane tank warning.

[Steve and MA]

Last week during some unusually cold south Texas weather we ran both of our 30 lb tanks to completely empty. We took them to a nearby U-Haul for refill while the temperatures were still in the low 20's.  We were charged for volume (16.9 gallons), not weight of propane. After getting them home, as the weather warmed, we noticed a faint smell of the gas odorant.  We found that the pressure relief valves were bleeding off propane. We had a serious fire hazard. 

A little online research suggested that based on volume, tanks are sometimes overfilled in cold weather.  Liquid propane is denser at low temperatures, so more (by weight) can be filled in colder temperatures before the Overfill Protection Device (OPD) shuts off the flow. There are also recommendations for the entire valve to be replaced whenever the pressure relief has popped.

We took the tanks to Propane Depot, a specialty supplier.  They weighed the tanks.  One weighed 65 lb and the other 66 lb.  The tare weight for our tanks is 25.5 lb each. Neither should have weighed more than about 55.5 lb when full.  They had been overfilled by about 20% of their rated capacity.  Texas regulations state "containers of less than 101 pounds LP-gas capacity shall be filled by weight only", so this rule was not observed when the tanks were refilled.  

After bleeding off the excess, the guys at Propane Depot checked the pressure relief and the tanks were no longer leaking.  They didn't think the temperature had been cold enough to explain the extreme overfill so the OPD is suspect, though it seems odd to have failed on both our tanks. The propane guys said they only refill by weight and never depend on the OPD. We plan on replacing the valves before the next refill anyway.  

The takeaway is to make sure the tanks are weighed before and after being refilled. The filled tank shouldn't weigh more than its rated capacity plus its tare weight. 

Stay safe, Steve

[Steph and Dud B]

One of my tanks was overfilled by someone relying on the OPD to shut off the flow. I was watching the gallons readout and made her stop and call a supervisor. At my insistence he weighed it and vented a fair amount to bring it down to 55#. You can't trust the OPDs.

[jd1923]

17 hours ago, Steve and MA said:

We were charged for volume (16.9 gallons), not weight of propane.

We’ve never yet run out of LP while on a trip. So we always fill up at the same company in Prescott, where an empty 30# tank consistently takes 6.8 gallons.

My understanding is they should be filled 80%. 16.9 / 2 = 8.45 and 6.8 / 8.45 = 80%. Your tanks were filled 100% with no expansion room for the liquid to turn to gas. In the future know that 6.8 gallons is the correct volume. Tell any unaware attendant to stop filling when it hits this number!

[Steph and Dud B]

3 hours ago, jd1923 said:

6.8 gallons is the correct volume

That's a good ballpark for roughly room temperature. The volume of liquid propane changes based on ambient temperature. Since the bulk storage tanks are outside, it can vary by a fair amount. The most accurate way to measure it is by weight. 6.8 gallons at 17 degrees F would be a lot more propane than 6.8 gallons at 85 degrees.

https://www.propane101.com/propanevolumecorrection.htm

[jd1923]

58 minutes ago, Steph and Dud B said:

That's a good ballpark for roughly room temperature.

True although as the article states, “Propane is stored and delivered as a liquid.” And later it states, “These meters include a volume correction device known as an automatic temperature compensator.”

Given delivery is adjusted for temperature, when you buy a gallon of LP it should be the standard weight of a gallon at the standard temp 60F. If it’s a cold day your getting less actual volume, but the gauge in the dispensing tank is temp-compensated standard. The person filling should be trained, but if not, do not allow much more than 6.8 Gal on the gauge to be added to an empty 30# tank! (4.5 Gal for 20#)

Temp swings up and down is why the tank should be only 80% full. The 20% gas portion allows for expansion and contraction. The cold tank filled with over 8 gallons had no room for expansion, so it had to be released out of the tank when the temp increased.

Edited Wednesday at 10:33 PM by jd1923

[rich.dev]

5 hours ago, jd1923 said:

So we always fill up at the same company in Prescott, where an empty 30# tank consistently takes 6.8 gallons.

 

Yup, our empty 20# tanks consistently takes 4.5 gallons = 6.75 gallons for a 30# tanks, so you have overfilled your tanks by 0.05 gallons John!😜 

Edited Wednesday at 11:12 PM by rich.dev

[jd1923]

1 minute ago, rich.dev said:

Yup, our empty 20# tanks consistently takes 4.5 gallons = 6.75 gallons for a 30# tanks, so you have overfilled your tanks by 0.05 gallons!😜 

Rounding error! 🤣

[John Dorrer]

6 minutes ago, jd1923 said:

Rounding error! 🤣

Young kid at the hardware store over filled my 30lb tank. When I got home I noticed a problem and ended up releasing pressure some. Now I go to Tractor Supply.