Procedure for denso tape around copper pipe

Yes, it is, when the pipe ends are not able to move a few millimetres to allow the pipe to expand an contract the strain on joints can over time create leaks. For example elbows at the end of long straight runs with the vertical pipes held rigidly by the screed will not allow for expansion and contraction.

Where did you google that nonsense from, Bernie?
 
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Where did you google that nonsense from, Bernie?

18 years BG ( Before Google ) damp patches in carpets in a new bungalow ( one of three in a new development ) were traced to failed joints in the central heating pipework buried in the floor screed. Quick fix was to re-plumb with drops from the ceiling. Excavating one joint found the joint appeared to be well soldered but the elbow was loose on the pipe. Owners of the other two bungalows ( built the same way ) sought advice and were advised to consider re-plumbing )

34 years BG the forces involved in expansion and contraction were demonstrated in the school laboratory using the bar breaking rig.

bar break rig.jpg


Small cast iron bars are used in this experiment, replacements can be found through many lab suppliers. Cast iron is used primarily because it is easier to snap than say steel.

The centre of the main bar may be heated directly with a bunsen burner. During heating, the main bar should expand slightly allowing the small bar to be inserted into the gap at the end of the large bar or on other versions, allowing a srew to be tightened, holding the small bar in place. When the bar cools down, it will contract to its original size putting immense pressure on the small bar until it snaps.

Copper pipe and lower temperatures mean the forces on the soldered jopints are considerably less than those that snap the cast iron bar but repeated cycles of forces from cycles of hot and cold do weaken the solder joints.


Google started in 1998 ( according to Google )
 
My previous home was a detached bungalow built in 1970 and which we bought in 1978. The seller wanted us to pay extra for the carpets. We declined as we very stretched financially - it was our first mortgage. When we moved in we were surprised to see that they had left the carpets and thought that they had taken pity on a young couple just starting out. The central heating had been off for quite a while before we finally moved in; being March it was still pretty cold and wet so we put it on and it wasn't long before we noticed damp patches appearing around the skirting boards. In our naivety we first assumed it might be rising damp but we had a survey done and the guy said that the moisture content was far too much for that. When we pulled up the carpet in the lounge all was revealed. The vinyl tiles under the carpet were encrusted around the edges with mineral deposits and the underlay was, well, not nice! Being generous I wonder if the previous owners were unaware of the problem or did they really leave the carpets for altruistic reasons - I guess we'll never know.

I "excavated" the screed in one corner of the room and sure enough water was seeping from an elbow joint. Most of the pipe was covered in a PVC sheath but obviously not where the elbow was soldered. The pipe showed severe corrosion at that point. Hence we took the plunge and went for the "drop" system. This is where I learned my plumbing skills as we could not afford to have the work done professionally!

Bit of a ramble there sorry but I am coming to the point - was the problem due to expansion/contraction as suggested by Bernard or simply corrosion by chemical reaction with the cement? Maybe both? Anyway the moral of the story is that it is probably not a good idea to bury C/H pipework in concrete!
 
I have written before about a job I went to, years ago. The problem was 2 corners showing damp. I dug up the floor and found joints in both corners that had NEVER been soldered. The chances are your joints were poorly soldered in the first place.

Millions of feet are buried in screed. They are not all squirting water out of the joints.

Bernie is somewhat guilty of extrapolation (spell?), I haven't looked at the link as yet, but the provided text actually says the bar used was Cast Iron - as it is easier to break!!!

EDIT: The address is NOT FOUND.

But, the device presumably demonstrated "metal fatigue", but that has sod all to do with your original assertion. Your story states that the firm who found the leaks recommended that the neighbours also paid for a repipe (presumably just in case". I assume and hope they were not so stupid as to go for it. Did they write to all the other homes in the UK piped in a similar fashion?

If Bernie knew anything without Google, he would know that a joint that has been successfully "blown" can be ruined by movement before the solder has cooled. Resulting in a perfect looking joint that will leak.

This demonstrates the danger of the internet. Bernie writes garbage, and unsuspecting people like Gofer, above, take it as gospel. NOI, Gofer
 
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EDIT: The address is NOT FOUND.

http://www.preproom.org/equipment/eq.aspx?eqID=5008

Millions of feet are buried in screed. They are not all squirting water out of the joints.
Agree with that, not ALL of them.

But, the device presumably demonstrated "metal fatigue"
Metal fatigue occurs after repetative strain cycles, the bar snaps first time.

he would know that a joint that has been successfully "blown" can be ruined by movement before the solder has cooled.
Yes I do know that, those joints will fail ( leak ) within days, the joints that I am talking about failed ( the leaks became obvious ) more than 18 months after the people moved in.

The chances are your joints were poorly soldered in the first place.
Examination of the joints excavated from the screed showed no signs of poor soldering at time of installation.

To save scanning pages from a hard cover book I used google to find a easy to copy document
https://www.copper.org/applications/plumbing/cth/design-installation/cth_3design_gencon.html ( New York based but the laws of physics are international )

Expansion Loops

Copper tube, like all piping materials, expands and contracts with temperature changes. Therefore, in a copper tube system subjected to excessive temperature changes, a long line tends to buckle or bend when it expands unless compensation is built into the system. Severe stresses on the joints may also occur. Such stresses, buckles or bends are prevented by the use of expansion joints or by installing offsets, "U" bends, coil loops or similar arrangements in the tube assembly. These specially shaped tube segments take up expansion and contraction without excessive stress. The expansion of a length of copper tube may be calculated from the formula:


Temperature Rise (degrees F)
x Length (feet)
x 12 (inches per foot)
x Expansion Coefficient (inches per inch per degree F)
= Expansion (inches)


Calculation for expansion and contraction should be based on the average coefficient of expansion of copper which is 0.0000094 inch per inch per degree F, between 70°F and 212°F. For example, the expansion of each 100 feet of length of any size tube heated from room temperature (70°F) to 170°F (a 100°F rise) is 1.128 inches.


100°F x 100 ft x 12 in./ft.
x 0.0000094 in./in./°F
= 1.128 in.


This demonstrates the danger of the internet. Bernie writes garbage, and unsuspecting people like Gofer, above, take it as gospel. NOI, Gofer

Training how to do a job without adequate background science about the processes involved being included in the curriculum can create problems.
 
Fantastic Bern. You've just shown us that metals experience expansion when heated. I never knew that:eek::rolleyes:.
Show us where the evidence shows that properly made joints will come apart.

Every proper plumber or RGI here will have seen joints that have been badly blown or not blown at all that have NEVER leaked after years. They come to light only when ripping out to, eg, replace a boiler.

Examination of the joints excavated from the screed showed no signs of poor soldering at time of installation.

Who "examined" the pipe fitting. What methods were employed? If, as I suspect, it was the guy who found the leak, then what were his specific qualifications. Apart from wanting to sell a job to the punter and his neighbours.

I had already found the link above, but not he specific page showing the kit, which would only show that Cast Iron is easy to break under pressure. Another amazing revelation. At least no real ink or paper was wasted.
 
Who "examined" the pipe fitting.

As I recall it was the loss adjusters employed by the insurance company who arranged for the plumbing to be inspected by an accredited organisation.

The owners still live in the bungalow, I could ask them for details.

Show us where the evidence shows that properly made joints will come apart.

Hard to find that, other than joints that have failed due to the mechanical stress causing laminar fractures in the solder.

Google for "stress in pipework" that might be educational.
 
FiremanT - sorry to disturb your slanging match with Bernie. Just to say that of course I'm sure there must be lots of faulty solder joints out there and Bernie's theory may/may not be correct but when these faults are "above ground" they are readily corrected. When buried in concrete screed, well that's a little different. In my case I couldn't have cared less about the scientific explanation - I was rather more concerned about having to fork out several hundreds of £'s sorting out my C/H system (which was a lot of money in 1978!). On the plus side I learnt a lot about plumbing and have been able to do most of the simpler plumbing jobs stuff myself ever since.
 
Just thinking anybody ever had to seal bolted flanges using denso putty and tape now that's messy
a typical appo job.Bob
 

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