Chit,

This may help a bit! You are not alone

thats a winding thread! thnx.

It's a biggun eh! Hope it helped on the pipe/tube dilemma! As for duct and conduit, I call anything fabricated to be duct, and anything that is round and used for electrical circuitry as conduit, but, here in Spain it's called tubo so the discourse continues as to the location! I have my own personal idea as to which is which, which (that's an awful lot of which's) may differ to the next man but with a little imagination, we can understand the context it is written in!

Good luck in your quest

I believe Ducts are for gas flows, while pipes are for liquid flows.

you can find an Air Duct and a Water pipe!!

But you commonly also find reference to a GAS pipe. Water will flow under a road in a conduit. But then the conduit could also be called a drain!

Oh and very short pipes and tubes are called washers! Which means that you should never use conduit for making washers as the wall thickness is invariably too thin!

Just watch out for Scotsmen that can do fairly perverse acts with pipes!

i seem to recall 'duct' also as a 'way' for wiring.

"Tube" infers a mechanical function.

'Pipe' i take to be a minimum spec; usu for lowpress flow.

When does one use the terms duct, pipe, tube or conduit. I find them often used interchangeably

First, understand that they are not being used interchangeably, only contextually...in order to convey with best clarity and precision what is in the speakers mind. Now...

The question you ask evaporates when considered in the context of (English) language and speech (and nomenclature) development, rather than in the context of any particular hardware item or item class. Take the related words duct and conduit (can you see the similarities suggesting they have a common origination). By definition and by common usage, these words (we'll concentrate on Duct for sake of simplicity) carry the connotation of some kind of action...of the conducting of a homogeneous collection of something, it could be liquid fluid, gas fluid, cars, people, electrons, wires...anything, along a certain pathway from any one one point to any other point. (Bear in mind, it is the movement being done, not the thing that constrains the movement, that's at the heart of the matter.) So you might refer to viaducts, aqueducts, AC ducts, air ducts...cable conduits, wire conduits, traffic conduits...and so on whenever you wanted to speak of moving something from one point to another. Pipe on the other hand, does not need any underlying assumption of action, or motion, or carrying a particular something, to have meaning. It would be a word that exists in its own right as describing (not a concept like movement ordisplacment, but) a discrete thing, a tangible (and only tangible) object...but also an object that can be put to use to achieve (yes, you guessed it) a ductwork (which is what people usually mean when they say duct) or conduit. By way of example, we can assemble pipes in order to obtain a water duct or conduit; duct work pieces in order to obtain an air duct; concrete slab pieces in order to obtain a viaduct; and so forth. We can fabricate a tube/hose/sleeve/whatever you want to call it in order to gather wires to make up an electron conduit to conduct electrons along paths.

Summarizing, the key to being comfortable with this particular, seeming English language discrepancy, is to distinguish between when you need to specify an object such as a pipe, and when you're really wanting to describe conducted movement...such as through/over/via... a pipe line, conduit, or ductwork, etc, etc.

English Language: Duct = Stuff goes through this thing.

Pipe = A structure that includes a void space for the conveyance of a (usu) liquid medium.

Tube: a conductor for fluids; nearly = 'pipe'; more precision implied.

Tubing: a Mechanical term for a load bearing entity (load may be fluid: ie, 'tube' also may apply) Most usu applied to a STRUCTURAL MEMBER.

Conduit: again, a way of directing something down this path; usu used as an electrical term; occasionally as 'a path for gasses'

This bit of apparent sloppiness (think rather: Overlapping definitions) also allows a bit of free thinking

Other thing here in the US is pipe is called out by outside diameter and pressure rating, e.g., Schedual 40, Sch. 80, and such, or in the case of copper pipe, it's hardness.

Tubing however, is usually called out by outside diameter AND wall thickness, along with alloy and hardness, plus the manufacturing process, such as 'DOM' (drawn over mandrel).

Go figure.

Just as an add on to Al's comments, I recently had to design a bracket to go between 1/2" sched 40 pvc pipe and 1" sched 40 pvc pipe. I got out the calipers and measured:

1/2" sched 40 pvc o.d =.847" i.d. = .594"

1" sched 40 pvc o.d = 1.325" i.d. = 1.035"

Of course plastic pipe was designed to handle the flow of metallic pipes but with thicker walls to handle the pressures of sched 40, sched 80 etc.

Bill

If you use duct tape on the joints, it's a duct. If you use pipe tape on the threads, it's a pipe.

Of course there is the old duck tape and duck seal!

Quack - Quack

I use duct work for air - hot or cold - pipe for product, steam, petroleum, chemicals, and conduct for wiring.

I am not into conducting irrigation water

1) Passage used to pass air and gases is duct

2) Conductor used to pass pressurised gas, oil and water - pipe

3) Smaller dia piping for instrumentation is tube

4) Embeded Cable carrier is conduit.

Bet you wish you had never asked. There is an explicitly correct answer to your explicit question in there somewhere. Hope you found it. Ha ha. LOL

You use them when you feel like it!! I would say that common practice would dictate the usage, but there is no hard and fast rule. Maybe use them when you wnat to impress someone by showing them that you have these various terms at your verbal command!!

That makes two.

Duct is for moving "Air."

Pipe is for moving "Liquid." What ever is a gas can also be a liquid so it too is passed through a pipe. Pipe can be "HIGH PRESSURE and LOW PRESSURE." Pipe is for things that you don't want to leak.

Tube is just the shape of material for construction of something.

Conduit is for routing "Wires."

Do you mean like the "air" that runs through "tear ducts"? Or the liquid that runs through the wind-"pipe" that carries air to the lungs? And what do we "construct" with the fallopian tubes that deliver unfertilized eggs to the uterus? Or the "wires" running through the "conduit" that delivers water to your house every day?

Your generalization is more what I called common usage. But, again, the terms are nearly interchangable. And if, as you say, "Whatever is a gas can also be a liquid..." is true, is not the converse true, "Whatever is a liquid can also be a gas?" as in the case of your air (a gas) ducts?

You're right they are general but this is an engineering site and what you are mentioning are anatomy.

The tear duct is open to the open air.

We might also relate a tube as something flexible that serves the same purpose as a pipe for liquids.

Well, you are getting closer. You say that "...a tube as something flexible that serves the same purpose as a pipe..." So, to carry that further, it would seem that if it serves the same purpose as a pipe, it can be correctly referred to as a pipe. Hence, the terms are interchangable.

As for the anatomical references, there are also oil "ducts" that are used to lubricate machinery. And there are torpedo tubes that are neither a structural member nor are they flexible.

Not trying to be argumentative, just trying to expound on my original premise that the terms are nearly interchangable. I believe they are.

So that would be called a hose then! When you see the various uses for all the words relating to this topic, it's not surprising everybody is so confused! Anyway, I'm going to have a tubo of beer (remember, I live in Spain!) and maybe smoke my pipe a bit!

Should a tube train be called a duct train?

Or could I smoke a conduit while listening to some Ducted organ music?

Now I'm just being silly, but you get the idea!