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Pipe names and measurements

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Pipe names and measurements

Unread postAuthor: Marco321 » Sun Aug 19, 2007 7:01 am

Hey
I went to buy some pvc pipe, i needed it 20mm in diameter, so i asked for 20mm pressure pipe. I got home to find it was 25mm in diameter, so i went back claiming i was given the wrong pipe, the guy showed my the pipe he cut it from and it had 20 on it, and he said this was 20mm pipe. He claimed the pipe was not called 20mm because of its diameter, so i had to buy another length of pipe...

My question is why is it called 20mm pipe if its not 20mm in diameter, its ID is not even 20mm.
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Unread postAuthor: Gepard » Sun Aug 19, 2007 7:28 am

Well if the Aussie system is the same as over here in the UK which I assume it is since we use PN10, PN16, Sch80 coloured parts etc etc. Then you're right the size of the pipe is the pipe's OD.

Small bore pipe can often have ratings higher than others of the same class so I'm thinking the 20 could have been 20bar.....

I take it you didn't ask him for a 20mm fitting and try to fit it in there?

Michael
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Unread postAuthor: Marco321 » Sun Aug 19, 2007 7:29 am

It said pn14 on the pipe, but it said 20 on it, the guy said it was indicating 20mm pipe, but nothing on the pipe measured 20mm.

EDIT: I had to buy pipe with 15 on it to get 20mm pipe... That was according to the guy, he also claimed just because it was called 20mm pipe doesn't mean it was 20mm in diamter, which sounds very odd...
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Unread postAuthor: chaos » Sun Aug 19, 2007 8:52 am

I-D's and O-D's thats where i think the confusion is...

I do know that some materials (stainless steel for example) are measure I-D most of the time for pipe but is measure O-D for tube (both are commonly used at my workplace so i get confused somtimes also, so probably best off asking for the dimensions where you buy it/ or take a rule and measure yourself (not that hard :o )

Wikipedia wrote:'Pipe' is generally specified by the internal diameter (ID) whereas 'tube' is usually defined by the outside diameter (OD)

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Unread postAuthor: boilingleadbath » Sun Aug 19, 2007 5:39 pm

Well, that's a fairly bad case of name-size disparity, but it's not uncommon for pipe to be quite a bit different than it's nominal size.
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Unread postAuthor: Marco321 » Mon Aug 20, 2007 1:42 am

Hey
I know what you are all saying, the pipes ID and OD are not what the guy claimed the pipe was called, it was pressure pvc.
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Unread postAuthor: rna_duelers » Mon Aug 20, 2007 1:53 am

A piece of 40mm pn12 PVC has an ID of 43mm(from memory) every single piece of pipe I have ever layed my hands on never match there set size,go measure the ID of a 100mm piece of pipe you will see its more closer to 120mm.Aslong as you match the fittings with the said pipe diameter you will never have trouble.
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Unread postAuthor: Hubb » Mon Aug 20, 2007 5:22 am

I read an article a while back about this issue becuase it confused me as well. Back in the day when pipe was first made, it was made out of copper and had a set wall thickness of 1/16". Over time, companies began coming up with different materials to use instead of copper and found that 1/16" was not the best wall thickness for all types of pipe. As improvements were made, companies began increasing the inner diameter of the pipe instead of the outside diameter so that the existing fittings would still work or something like that. I may be wrong about some of this but it sounds good at least. I can't remember where I read about this at but I will try to find it so others can read about it too.

Edit: I found the site I spoke of.
http://www.gizmology.net/pipe.htm
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Unread postAuthor: Marco321 » Tue Aug 21, 2007 1:31 am

Ok thanks everyone for the help
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