Steel pipe in CH system

[Richard]

Friend is removing one rad and replacing it with two others. In lifting the floor he has found that the main supply around the first floor is in thin wall steel pipe with what appears to be 15 mm copper tee-ed off to the actual rads. I've measured an offcut of the steel as being 21.5 mm OD with walls of about 2.5 mm.

WTF????

The offcut is showing only very faint signs of rusting the (hacksaw) cut end. The pipe can be cut without difficulty with an ordinary pipe cutter. It is not, according to my magnet, stainless steel - is that a reliable test?

He's a little perplexed as to how he inserts new tees to supply the new rads. Slipping a 22 mm end feed joint onto the offcut reveals a large gap that I think is too big for soldering.

Q: What is the steel pipe? What fittings should/can he use? Is all lost!

TIA

Richard

[Aidan]

How was the 15mm copper attached to the steel?

The steel was probably an ersatz substitute for 3/4" copper pipe, which was used until 1971. The 1/2" pipe was the same OD as 15mm tube, hence the apparent 15mm tube to the rads. There were material shortages from the end of WW2 until the early 70s and all manner of stuff was used.

You could probably get a joint if you get some 3/4" x 22mm compression adaptors from a plumbers' merchants, or 3/4" compression olives to fit in a 22mm compression joint. 3/4" pipe is about 21mm OD (can't find the micrometer).

You could rip it out and repipe with PEX.

[Dave Plowman (News)]

No reason why it should rust anymore than the rads themselves. Water in a near sealed system doesn't contain oxygen, therefore no rust.

[Richard]

Thanks

Further information from steel pipe-owner:

The 15 mm pipe is not, as he first thought, copper: it is in fact steel!

A 15 mm compression fitting seems to provide a good fitting. We think that we (shared blame when it all goes horribly wrong!) are going to connect 15 mm copper to the steel using a compression fitting.

How does that sound?

BTW rip out and replace with polypipe is not even worth suggesting to him. It's taken his wife over a year to persuade him to fit the two rads and get as far as lifting boards and actually hang the rads.

Richard

[Lobster]

Wasn't there also, specifically, a Great Copper Shortage for a relatively brief period around 1980(?) when other materials were used?

David

[Aidan]

Quite likely, but I'm too young to recall it. :-0

[Set Square]

As others have said, so-called stainless steel pipe was used in the 60's and

70's when there was a copper shortage. The sizes will be 1/2" Imperial** (virtually identical to 15mm) and 3/4" Imperial - whose OD is just slightly less than 22mm. You can use 15mm compression fittings on the 1/2" stuff, and 22mm compression fittings with special imperial olives on the 3/4" stuff. I wouldn't advise trying to use solder fittings on this pipe. ** Imperial pipe sizes refer to the nominal ID rather than the OD - which is why 1/2" pipe is actually more than 1/2" in diameter - and the same for 3/4"

[Huge]

Yes. Our first house, which we bought in 1977, had stainless steel heating pipework.

British Gas refused to issue a maintenance contract for it, although they had installed it (not for me).

My relationship with BG was all downhill from there.

[Dave Plowman (News)]

Bit earlier than that IIRC - more like '70? UDI at Rhodesia? Or the three day week?

[Richard]

So, my 'magnets won't stick to stainless steel' test is flawed?

Where the 'large' steel meets the 'small' steel the fittings are sealed by what appear to be soldered joints. Could these be silver soldered rather than lead soldered? We tried soldering a pre-soldered copper joint onto the steel offcut without success.

Anyway, thanks for the sizing and olive information.

Rgds Richard

[Ian Stirling]

Yes. Some stainless steel is magnetic, and some stainless becomes magnetic after it is stressed.

[bigcat]

realise that olives wont bite into the steel the way they do with cu, so it will always be a weaker joint than with cu pipe.

NT

[Richard]

Ah! Thanks for that. The offcuts that we tested are not particularly shiny - which is what I'd expect for SS - and have the sort of rainbow sheen that you see on steel tent poles. Would SS have been used on pipes that never saw the light of day, even in days of copper scarcity?

How are the existing joints made? As I said above they are some sort of heated joint into copper fittings. I jokingly suggested that my neighbour silver solder or braze the new fittings.

Rgds Richard

[Richard]

(*) or perhaps brass.

Richard

[Aidan]

It might be Bundy tube, rolled steel tube galvanized or copper coated. I think it's used for brake-pipes, compressed air & hydraulics.

[Ian Stirling]

I honestly have no idea.

SS occasionally has that sort of sheen.

If you own a blowtorch...

A small bit of it. Galvanised will burn off with an whitish fume (don't breath it) when it gets near red hot.

It's certainly not plain steel, as that would at least be showing some evidence of rust.

[Dave Plowman (News)]

If so, you don't use ordinary compression fittings with an olive which won't bite into the pipe properly. You use a rolled flange on the end.

[Ed Sirett]

IME the OD of 1/2" pipe is just slightly bigger than 15mm so that everything is very tight and generally rather awkward.

[Baz]

Hi Richard. At 21.5 you will find it is 1/2" Nominal Bore PIPE (NOT TUBE). (actual size

0.840" OD or 21.336mm). You could cut a thread on it or look for a 1/2" Nominal Bore compression fitting. Baz

[Richard]

Hi Baz,

Are you saying that a 1/2" compression fitting for copper is not suitable?

Richard