Steel conduit wall thickness

[Marvo]

I'm hoping a few of the older members might remember this. I need to know what the standard wall thickness used to be for the very old type threaded steel conduit (20 and 25mm equivalents). I'm guessing the diameter and wall thickness was in imperial sizes so I also need to know what the newfandangled metric equivalent steel tube sizes would be. Also for good measure does anyone remember what the thread specifications were? Was it taper threads or parallel and any idea of thread pitch or TPI specs would be great.

Thanks in advance.

 

[Marvo]

Also much of the conduit installation is visible as will be our new installed areas. I'm not sure welding is going to be an option because the high standard of cleaning up is really a workshop job for us, we're not really geared up to do that on site.

 

[GLENNSPARK]

Lol, that might be tongue in cheek but it's probably the truth

I'm pretty sure the installation that's going to be giving me headaches will have been done to old British Standards rather than US standards. The entire installation is threaded. I have a threading machine but I'm concerned I might not have the tooling to cut the old threads, especially if they were tapered which thankfully it sounds like they won't be. I'll need to sourc some new pipework and I wasn't sure whether I'll need to make up some adaptor couplings and do the new stuff in metric threads or whether I can just continue with the original threads on the new pipe but wall thickness could be critical.

I'd rather use the original threads on the new installation because many of the very old light fitting and other fixtures screw directly on to the conduit tube.

if you are using metric then your dies will be as such......as i says BSP is a different threadform and what you`v got to remember as well is because british was on the bore.....what amounts to...say a 1" BSP die will have to take into account the wall thickness of the pipe....so the die is actually 1 1/4"...if you get an internal with a set of verniers.....

 

[Marvo]

Time to get your Thread Gauges out!

I can only disturb the installation when the works program starts, removing even a sample isn't as easy as it sounds. I was just hoping to get possible info to organise any necessary tooling in advance and cover as many bases as possible.

 

[Engineer54]

fair enough.....i just know that tapered threadforms are used on gas fittings.....
you can get BSP tapered n all...
the americans use NPT...national pipe thread...

And probably why they only use they're seamless heavy duty conduit in hazardous area installations!! lol!! It's similar to what we used to call our seamless HD conduit , ...''Barrel'' conduit.

There is a difference in physical size between Yank conduit and UK imperial/metric conduit. Pretty sure they size by internal bore where the UK sized on OD. To be honest it's been a very long time now, since using American conduit. What i can remember is, that the 3/4'' doesn't fit UK knockouts on metal back boxes, they had to be drilled out bigger, and the lock-nuts then hit the back box accessory screw lugs!! Cost the contractor a lot of time and money, as the best part of the initial system was pulled out and his conduit stocks replaced with metric conduit!! lol!!

 

[GLENNSPARK]

Also much of the conduit installation is visible as will be our new installed areas. I'm not sure welding is going to be an option because the high standard of cleaning up is really a workshop job for us, we're not really geared up to do that on site.

get all the crap and galv off the end....and just run a fillet in with a low hydrogen rod.....weld it lovely that will as low hydrogens tend to `freeze` dead quick....so you wont get any drop off......

 

[UNG]

BS 31 : 1940 is the spec for imperial conduit

You could always buy some from here they claim to still manufacture BS 31 conduit

 

[snowhead]

Imperial British conduit was 3/4 and 1" verses Metric 20mm and 25mm
The wall thickness was the same, give or take a thou' or 2 as the current metric is.

1" imperial is exactly(ish) the same outer diameter as 25mm, (1" is 25.4mm) we used to thread old 1" with metric dies to save using adapters which were scarce at the changeover.
The thread is not BSP, the wall thickness woulnd't take it, it's a specific Parallel conduit thread.

I did still have my Imperial dies somewhere

 

[Outspoken]

Marvo, your in SAFA so why not do it like all SAFA sparks...unwelded plastic conduit and flexible..you know, that stuff that looks like the exhaust from a washing machine..

Muhahahahahaha

 

[Marvo]

Imperial British conduit was 3/4 and 1" verses Metric 20mm and 25mm
The wall thickness was the same, give or take a thou' or 2 as the current metric is.

1" imperial is exactly(ish) the same outer diameter as 25mm, (1" is 25.4mm) we used to thread old 1" with metric dies to save using adapters which were scarce at the changeover.
The thread is not BSP, the wall thickness woulnd't take it, it's a specific Parallel conduit thread.

I did still have my Imperial dies somewhere

The unknown thread was what prompted my first question about wall thicknesses, I had a sneaky feeling that a standard BSP thread was too deep.

If you have original imperial dies somewhere and find yourself with enough time to rummage them out over the next few days I'd be very appreciative or any TPI/pitch and any thread depth info you can give. If as you say the old and new tube diameters and wall thicknesses are within a couple of thou it would make my life a lot simpler.

 

[Sintra]

Marvo the info you need might be on one of these pdf's. I don't have time to read them now but I do recall seeing it.

https://www.dropbox.com/s/dmwr5xs06syjqnh/SteelConduit.pdf

https://www.dropbox.com/s/0c94bueh9eavurp/Conduits.pdf

 

[ipf]

And probably why they only use they're seamless heavy duty conduit in hazardous area installations!! lol!! It's similar to what we used to call our seamless HD conduit , ...''Barrel'' conduit.

There is a difference in physical size between Yank conduit and UK imperial/metric conduit. Pretty sure they size by internal bore where the UK sized on OD. To be honest it's been a very long time now, since using American conduit. What i can remember is, that the 3/4'' doesn't fit UK knockouts on metal back boxes, they had to be drilled out bigger, and the lock-nuts then hit the back box accessory screw lugs!! Cost the contractor a lot of time and money, as the best part of the initial system was pulled out and his conduit stocks replaced with metric conduit!! lol!!

If I'm not mistaken, SDC, 'Solid drawn conduit'.

 

[somersetsparks]

I've got all the dies for imperial conduit, you can successfully thread 25mm with 1" BSP dies, most of our works pipe vices are old and have 1" formers, the difference is so minimal!

GLENN- You are right on taper threads usually only on gas, however I have seen them on water pipe where to lengths are joined in a coupler with no ptfe! Probably done in the 1930's