r/ChemicalEngineering • u/ChemicalMurdoc Cell Manufacturing/10yrs • Apr 30 '25

Design Propane tanks don't require secondary containment. Right?

I'm having an argument at work that propane nor refrigerant tanks secondary containment. I don't believe they require it, as that's how I've always seen them built and I can rationalize why. But I can't seem to find anything to support that.

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62

u/gggggrayson Apr 30 '25

Looks like NFPA 58 covers liquified petroleum gas, which is likely to encompass propane. I would get your boss to pay for a copy, or find a free pdf online and consult that

15

u/rprstriker Apr 30 '25

NFPA 58 will tell you what you need. The name of the game is keep it in the tank. All large fittings on the tank have to be equipped with special valving, often internal with excess flow mechanisms or some type of check valve. If you break a pipe or something those keep the material in the tank. Often times accompanied by point LEL detection at unloading areas and pumps, which will trigger isolation of the tank if it detects over 25% LEL.

1

u/Totallynotthebanana May 02 '25

Until its a 75 yo facility that nobody did any level of maintence on and there's leaks in every single flange T.T Propane poisoning sucks when you are the one asked to wander around :/

9

u/bombadil_bud May 01 '25

Nfpa allows free viewing of all of their codes. Super helpful but the viewer is not as easy to read as the purchased PDF.

2

u/rkennedy12 May 01 '25

Nfpa has a website that allows for free viewings. I have a paid nfpa link account but can easily share free view only copies as needed.

1

u/Tanksfornothing79 May 04 '25

As others have said, NFPA allows you to download free copies of their codes. I believe you need to create an account. I've done it before so can confirm.

9

u/goodedm May 01 '25

You don’t want containment for LPG, especially propane which will vaporize immediately if released to atmosphere. Propane is heavier than air and vapors will end up being trapped within the containment area making for an explosive atmosphere. You want airflow underneath the tank to disperse the vapors if a leak were to ever occur. Experience: My group has built LPG tanks at over 100 terminal and pipeline facilities, mostly for butane service.

1

u/uniballing May 02 '25

Did you ever build any butane bullets north of Amarillo? I used to work at a place that’d cut gasoline with butane because gasoline was worth more. Like a coke dealer adding baking soda Columbia’s finest booger sugar.

2

u/goodedm May 02 '25

Guilty as charged!

8

u/sakurakoibito May 01 '25

i tell you hwat

8

u/[deleted] Apr 30 '25

[removed] — view removed comment

17

u/Ritterbruder2 Apr 30 '25

Propane’s vapor pressure is low enough where they store it as a liquid under pressure. Never heard of cryo propane.

2

u/Anon-Knee-Moose May 01 '25

Like a deeth reboiler maybe?

1

u/SpeedyHAM79 May 03 '25

It's done when storing VERY large volumes of propane. I worked on a facility recently that has a cryo-propane storage tank to avoid having to pressurize it. They have two 5 million gallon capacity tanks at -60 degrees. Each tank has 10 feet of insulation. Supply is via a pipeline from a few nearby oil refineries.

6

u/ChemicalMurdoc Cell Manufacturing/10yrs Apr 30 '25

Liquid at ambient temperature, just a normal propane tank. 1000 gallons.

3

u/ferrouswolf2 Come to the food industry, we have cake 🍰 May 01 '25

I’ve never seen that and I live and work in propane country. Heck, the propane dealerships here don’t have secondary containment and they have 10,000+ gallons of the stuff. If a train derailed at my job, it’s possible I would never know because half the town would blow up

-9

u/TrustM3ImAnEngineer Apr 30 '25 edited May 01 '25

It is in fact not a liquid at ambient temperature and pressure.

For the downvoters: https://www.youtube.com/watch?v=Tol2vN437p0

12

u/DisastrousSir Apr 30 '25

He didnt say pressure, just temperature

7

u/TrustM3ImAnEngineer May 01 '25 edited May 01 '25

At what temperature and pressure do you suppose the secondary containment would be? I was hoping that people would get to the conclusion of secondary containment quicker.

If the secondary containment is vented to atmosphere and equipped with some type of sensing then it is considered leak detection.

-2

u/DisastrousSir May 01 '25

That would depend on a number of factors in the design of such secondary containment. If a double skinned tank, in a leaking scenario, I'd imagine cooled down a bit depending on any flashing and relatively high pressure.

3

u/TrustM3ImAnEngineer May 01 '25

Any leaking propane would be vaporized at atmospheric pressure. The vapor would be vented and therefore is not contained. That’s the whole crux of this. The very definition of containment is that there is no mass lost outside of the secondary vessel. I can think of no example where such a vessel has been built or legally required in the US for propane.

0

u/Critical-Tomato-7668 May 01 '25

Can you read? They said ambient temperature, not ambient pressure.

5

u/TrustM3ImAnEngineer May 01 '25

I was hoping people could reach a conclusion about the nature of the secondary containment. There are no pressurized secondary containment vessels for propane. Secondary containment would be at atmospheric pressure. For propane, secondary containment would be useless as all the liquid would evaporate.

5

u/uniballing May 01 '25

Containment under propane tanks is a terrible idea. You’d literally be creating the potential for a pooling fire where it didn’t exist before. Most of the newer installations I’ve seen have crushed limestone under the tanks. Lots of surface area to help evaporation

2

u/ChemicalMurdoc Cell Manufacturing/10yrs May 01 '25

This is a great answer, I'm going to use this. Thank you!

7

u/uniballing May 01 '25

I’ve worked at a lot of propane terminals and our tanks never had containment around them. One of my terminals was in the desert and on a particularly cold day an atmospheric relief valve on one of the bullet tanks lifted and stuck open. It started raining liquid propane which started puddling on the ground creating a small river of propane that ran downhill.

3

u/strugglin_man May 01 '25

For it to rain propane the temp would have to be LT -42C. Where TF were you, Siberia in January?

1

u/uniballing May 01 '25

Not necessarily. Most of it vaporizes even at -10F, but a lot stays liquid long enough until enough heat can reach it to boil it. You can actually fill a bucket with propane if you’re okay with a lot of it boiling off. Look into how they did pooling fire experiments: they literally filled a “pool” with liquid propane at atmospheric pressure and lit it on fire

0

u/strugglin_man May 01 '25

For it to rain propane it would have to condense.

3

u/uniballing May 01 '25

Not necessarily. It just had to never be vaporized in the first place

3

u/Nowhere_Man_Forever May 01 '25

Have you ever used an Instant Pot style pressure cooker? When you open the pressure release valve, you'll notice that what's coming out isn't just steam, it's a mixture of steam and water even though theoretically it should just be steam since it's all water heated above it's normal boiling point being depressurized by a valve on the top of the vessel. The liquid sputters through the valve and is shot out, and like others have said, it takes a bit to boil off the rest. That's why you usually have to assume bi-phase flow when designing relief devices on stuff like this.

3

u/Cook_New PE, Environmental/25+ ye May 01 '25

What would be the point of containment. It’ll never stay a liquid at ambient conditions, right?

1

u/ChemicalMurdoc Cell Manufacturing/10yrs May 01 '25

That's what I'm arguing! But some people think it's necessary.

4

u/uniballing May 01 '25 edited May 01 '25

Another question to ask: what’s the purpose of secondary containment? It’s to mitigate the environmental consequences of a loss of primary containment. A propane LOPC is a vapor release. Build a bubble around the bullet tank if you really want secondary containment.

Get an environmental person on the call to quote your state regs. Make sure he talks about their SPCC plan

Defining “Oil” Under the SPCC Rule

2

u/Cook_New PE, Environmental/25+ ye May 01 '25

Exactly. Environmental person here. Neither SPCC nor SWPPPs (some state IGPs dictate containment) require it.

3

u/duckerengineer May 01 '25

Depends on if it is cryogenic. And then it is usually for perlite.

2

u/Notoriousley May 01 '25

Not quite propane, but:

Plant I used to work at had a pressurized CS2 tank. This tank was inside a water-filled bund. This was just to blanket any released CS2 as it will sink in water.

0

u/jcm8002204 Apr 30 '25

You need secondary containment but nothing too crazy. I think API 210 says you can reduce the required secondary containment by 25%-75% of the volume of the vessel. For an LPG like propane I would think you can reduce it by 75%. I just went through this.