buried copper pipes

STEAM DOCTOR

Does copper react with concrete the same way that steel does? I have a customer who has part of his hot water heating pipes buried( ths was done to avoid being hit by the boiler room door).

TWar

buried copper

Up here in Canada, code tells us copper or steel needs to be sleeved where it penetrates concrete.  The only type allowed for underground is Type K.  That being said, I have seen more than a few instances (mostly older buildings) where it comes through concrete unsleeved and there are no problems, YET.

hot_rod

it depends

on what was blended in the concrete. The concrete that seemed to attacked copper had high sulpher fly ash blended in. It also need moisture to become corrosive.



The steel pipe systems i have removed failed where the pipe was in contact with the fill material below and had a source of moisture to corrode away. Cinders and blast furnace slag were common backfill products that played a part in those early steel pipe failures.



If the tube is encased in the concrete and stays dry it should last just fine. There should not be water or moisture in or below the slab anyways.



Certainly sleeving the pipe be it steel, copper, or pex is a good idea for extra protection, from the arbitrary.



hr

Big Ed_4

Expansion

The chemistry of the concrete is not the cause of leaky pipes it's the expansion and wearing though the wall of the pipe. Electrolysis can happen is in contact with other metals as well. Wet concrete if high in alkalinity but once set the lime and the sand is more on the base side of the scale. But hard and gritty. The sleeve let's the pipe move with out the grit contact.with concern of the soil ph ... Bury the pipe in lime , marble chips or lime stone all the same which would neutralize the areas around the buried pipe.

hot_rod

From a CDA

Copper Development Association panel discussion back around 2000.





"There had been some resistance to the use of copper in radiant heating systems because of the perception that it has a tendency to corrode when in contact with concrete. The objection may have been based on failures of copper tube at the Levittown development in New York State some 50 years ago. Those failures have been attributed to the high levels of sulfur in fly-ash, which was an ingredient in the Levittown concrete slabs. Copper tube should not be used in installations where fly-ash or any other ingredient of the concrete mix results in elevated sulfur content."

croydoncorgi

The Problem is NOT only corrosion!!

Here's a cautionary tale: the fix (in 2008) involved cutting new tracks in the concrete slab and laying new pipe across the WHOLE ground floor of a 1970s built house.  Very messy and expensive.



The problem was that copper pipes carrying hot, cold water supplies and radiant heating had been laid on the slab and then covered with weak-mix concrete / flooring screed.  No protection or insulation of any kind.



In 40 years there had been little obvious surface corrosion BUT there were several longitudinal cracks in various places - too many to dig out and repair. 



The cause was 'Stress Corrosion Cracking'.  The pipes expanded and contracted due to heat.  The expansion forces were enough to move sections of pipe in the concrete but when the pipe cooled, it only contracted and moved back part-way and was left under tension.  It was this stress that was primarily responsible for the cracks.  Copper Development Association (in UK) has some data on stress-corrosion.

Jean-David Beyer

I wonder how much heat was required.

I wonder because I have 1/2 inch copper tubing embedded in an on-grade concrete slab to heat my downstairs heating zone. I have no idea if there is any insulaton under or around the slab, or any protection around the tubing itself, but I very much doubt it. The house was built around 1950, so it is about 60 years old now. I normally run my heating system with the make-up water supply valve turned off. I have a low-water cutoff detector in place, and I check the pressure almost every day and it does not go down. So I guess I have no leaks.



I have a mod|con boiler now with outdoor reset. The water going into that would be in the range of 75F to 120F, but I doubt it would ever exceed 110F. On the other hand, I have no idea what temperature my former oil burner with no reset put into the floor. It was hotter than the present system.

Gordy

Real evidence

 The only real evidence to the cause of copper tube in concrete failures is as Hot Rod pointed out. High sulphar flyash. As far as expansion scour on tubing thats a reach when the coefficient of linear expansion of the two materials (concrete, and copper) are very similar if not the same.



JD I also have copper tube slab radiant from the 50's in my basement with copper tube ceiling radiant on the main floor. second dwelling has copper tube radiant slab on grade from the 50's No leaks ever. I think this in itself caps the expansion scour theory.



As far as insulation under these slabs the technique seems to be in my build is they stayed 30" away from the outside walls in the slabs. Makes sense usually furniture there anyway.



Gordy

Jean-David Beyer

I also have copper tube slab radiant from the 50's

Thank you.

GREENMAN

BURIED COPPER PIPES

THE PROBLEM IS NOT THE COPPER IS THE JOINT IT INTERACTS WITH THE CEMENT TO THE POINT OF BREAK DOWN . IF YOU BRAZE IT N THEN INSULATE IT IT WILL BE FINE OR USE PEX.

Jean-David Beyer

Joints?

I still wonder about all this. I cannot believe they braised all the joints when they installed the system. I hope they used no fly-ash in the concrete mix. I do not even know if they used long sections of flexible copper tubing, or a bunch of elbows to make the tubing go back and forth. All I know is there are 5 1/2" tubes going into the slab, and one 1" tube coming out, and that there are 5 rooms on that floor. Since I doubt anyone cared about lead in the solder in those days, they are probably all 40% tin, 60% solder. In those days, the fittings and tubing all fit tighter than they do now, so less solder was required, according to one old-time plumber I hired at one time.



If the concrete of the slab was going to react with the lead in the solder, would this reaction be so slow as not to occur for 60 years?



P.S.: The water table is six to eight feet below the slab, whatever that proves.

Gordy

Type L

 Soft copper is what all mine is JDB. There may not be any, or very few joints in the concrete. Big rolls in those days i'm sure they wanted to avoid buried joints like today if at all possible.



Gordy

ScottMP

Buried pipes

The town next to me has a section of slab on grade homes .. ala Levittown, with copper buried in cement. Heat and domestic water.

A large majority have replaced the the tubing in the slab as they have failed.

Fly ash or expansion the question is will it last and the answer is "not for ever". 60 years is a good life for these systems. My suggestion would be to starting planning a renovation and do it on your time not the systems. It will pick Christmas Eve or New Years Eve.

Scott

Jean-David Beyer

Joints in concrete...

I tried to figure out what the piping layout must be in the slab under my house. I assume each of the five 1/2-inch input pipes is under each of the five rooms, because there was a mainfold gizmo with 5 screw-slots on the top. When I bought the house, I assumed that each slot was a valve to control the flow under each room, but some of those would not turn without risk of stripping the slot off the top, and one would turn forever without changing anything. So when I had the boiler replaced, I had that manifold replaced, and there are five ball valves there. Three I run wide open, the one under my bedroom is slightly closed, and the one under my computer room is almost off.



Since there is only one 1-inch tube coming out,  there must be at least 4 Ts soldered in the concrete slab. In trying to guess the in-concrete layout I assumed they never did any crossovers because that would be just too sloppy. But I do not know. My first guess was the simplest, but it did not correspond to reality. To get the valves to agree with the rooms required the one-inch pipe to go the entire length (32 feet) of the house on one edge, half the width of the house (half is about 12 feet) on the next edge, and then most of the length of the house again down the middle. Each room is Tee'ed off that except the last room that needs no T. Three of the Ts are pretty close together, and the first one could be close to the other three, but need not be. Quaint.



Since my new boiler has outdoor reset, I keep the water temperature in the slab as low as possible (does not go over 110F until it gets below design day) and that gets enough heat for the house. But the first 50 years of this house I am confident they ran higher temperatures in the slab because the floor was too hot to walk on barefoot on very cold days. Not enough to make me jump off or anything, but I did not like it that warm. Remember the warm floors you were supposed to have? Now sometimes I can tell that the floor has heat in it, but not often. And they are never what I would call warm. It is now 48F outside and the water in the slab, if the thermostat is calling for heat, would be 81F and the surface somewhat less.



If the slab tubes start to leak and it is at a joint, I might get the floor chopper upper people to expose the joint and repair it (or all of them if they are close together). If it can be found accurately enough; my infra-red thermometer is not accurate enough for that, but an IR camera might be. But if the tube has turned to sponge, the contractor said to put in baseboard. That does not appeal to me at all. I would consider radiant panels on the ceiling, but the ceiling is so low (8 feet less floor covering) that I am not sure. I wonder what the installed thickness of the panels would be, and I guess they would have to rip open all the ceilings to run the tubing and secure the panels to something other than lath and plaster.



At present, I turn off the water feed, watch the pressure almost every day, and hope the McDonnell & Miller GuardDog Model RB-122-E Conductance Type Low Water Cut-Off does its duty. So far, I can go over a month with no pressure loss, so I assume if it leaks, it is very slow.

Gordy

Pipes in Plaster

 Scott you may be right about the copper in concrete. But my ceiling radiant inbedded in the plaster looks like brand new after some kitchen renovation I had to remove an old soffit, and expose some pipes.

 I also have been throwing down sleeper floor radiant in some rooms when redoing flooring....a radiant ceiling + radiant floor = sandwich so to speak.



Gordy