Why not use seamless copper tube ? The type used for air conditioning has a higher pressure rating. Available in lots od sizes up to 4" dia.

Paul.

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I don't think it matters in a small low-pressure wobbler boiler but seams are best avoided in pressure vessels. Longitudinal seams are by far the most vulnerable with many fatalities due to full size boilers failing along them.

More than one reason for seam failures. Seams are always weaker than solid metal, even when well-made. Even with good workmanship there's a risk the seam won't be perfect throughout. Then, in use, the seam acts as a stress concentrator that fatigues the adjacent boiler wall every time the boiler expands and contracts. This it does when heated up and cooled down and as steam is consumed by the engine. The seam also provides a focus for corrosion, which weakens the joint. Add to this the difficulty of inspecting seams inside a boiler and it's not a good combination! Unlike most other problems developed by ageing boilers, fatigue and corrosion are difficult to spot, making the eventual failure a surprise.

When longitudinal seams were unavoidable during construction of a big boiler, best practice reduced stress concentration by not overlapping the edges, and by placing the joint so it was easier to inspect. Later, continually extruded parts or carefully welded joints were preferred.

Seams running around a boiler drum are less subject to these problems and hoops are easier to make strong.

As off-the-shelf extruded pipe also makes it easier to build small boilers, it makes sense to use it.

Dave

Edited By SillyOldDuffer on 15/02/2019 15:13:44

I would recommend using tube for your boilers and not pipe. Pipe has a much heavier wall thickness and is measured by its nominal bore and not its outside diameter. Tube and Pipe are not the same. Tube is measured by its outside diameter.

I recently had to return some boiler valves which were advertised as suitable for 1/4" pipe. (1/4" British Standard Pipe has an OD of 0.54" ). When they arrived they had ports of 1/4" diameter.

Paul.

Paul's description is spot on for the USA, but is it true this side of the Atlantic? Those Americans might be more logical than us! In the UK I think:

• A pipe is just a type of tube.
• Pipes and tubes can be both used to transfer fluids and that makes no difference to what you call them.
• Although pipes are rarely structural and tubes are often structural, both can do either. Again, it doesn't decide what they're called.
• In the UK the technical difference between a pipe and a tube is that pipes are always round. Tubes can be of any cross-section, though they are mainly round.

British English provides many exceptions. The downpipes from my gutters are all box section, but they aren't called tubes. My junior school's climbing frame was made of steel water pipe and pipe connectors. In a Chemical Lab the thick-walled pipe used to connect burners and glasswear is called rubber tube. Pipes sort of imply bulk transfer, but then we have tube trains. Guns have barrels, but an artillery barrel will contain at least one tube. Electrical conduit is often just called 'conduit', but it's sometimes sold as 'conduit pipe' or 'conduit tube'.

I believe in the UK the terms 'pipe' and 'tube' are either interchangeable, or when one is preferred, it's been named informally rather than logically. For a non-standard use, you have to specify O/D, I/D and/or wall thickness to get the right size. Am I wrong?

Dave

M'lord, may I present some counter-examples to the jury.

Exhibit A – steel tubes specified by bore, and not called pipes:

"""

"""

Also, Exhibit B, BS EN 1220 'Plastics rainwater piping systems…' which measures pipe by O/D in mm, and doesn't refer to tubes.

That's two British Standards up the spout.

And to show the USA aren't completely innocent, their 4" Schedule 80 pipe is actually 4.5" O/D and 3.826" I/D

No wonder I'm dazed and confused!

Dave

Edited By SillyOldDuffer on 17/02/2019 17:21:07

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Back to the original question in this post.

Model Engineer magazine published designs for making boilers from sheet metal including a flush dovetail type of joint in its January, 1969 edition. (see link below)

Paul.

**LINK**

True pkp,

But this is a Model Engineers site and we should be using engineering terminology and standards.

Paul.

Sorry I can't agree – This is a Model Engineering site and so we should be using Model Engineering terminology and standards. A quick look at single articles by LBSC, Martin Evans and Keith Wilson gave examples where they used both terms interchangeably. The current edition of ME has drawings in fractional inches, number drill sizes and ba threads – none of these are engineering standards used in new work today.

We also have our own standard ME threads – OK whitform, but unlikely to be found outside model engineering. The fact that your supplier did not use the terms tube and pipe in the same way as you wanted to only confirms that there are different opinions here and the advice to check before ordering, given above, is the key.

Well here's my penny worth and the way I tend to think of the terms. A bar with a hole up the middle is a tube and it describes it's shape. Use the tube to pass a fluid and it becomes a pipe which describes it's function. So all pipes are tubes but not all tubes are pipes. If it's used to store rather than pass a fluid it might be more sensible to call it a tank. As usuall with term like this there tends to be some spreading out of usage. For example it is very usual to talk of boiler tubes when describing the flues and boiler barrel when talking about the bit that contains the water. You pays yer money and takes yer chance.

A pipe can also refer to a fluid measure for wine and is I believe 1008 pints. Funny old stuff language innit.

regards Martin