what is the definition of a dead leg when related to pipe work?

Question

Particular reference to industrial pipe work installations

Answer 1

Dead leg piping (noncirculating lengths of pipe greater than three to six pipe diameters).
* Do you mean a branch having its nozzle blanked?That is of no use or can be utilised during an opportunity , which may be provided with an isolation valve.

Answer 2

As has been described by the other answers, it is a length of pipe which was a feed to some outlet but is no longer required.

Because the water is no longer flowing it can be a hazard, collecting silt, normally flushed through, and collecting chemical particles which can combine and cause chemical decomposition of the metal pipe from the inside.

Another problem, which can be considered possibly dangerous, is water hammer, if the dead leg rises from the main feed it will never fill completely from the initial emptying, it will also gather any air or gasses generally leached from the water causing an air bottle to be formed.

If this is a high pressure (or mains) supply, and a valve that is past the dead leg is closed suddenly, the momentum of the water column still moving and approaching the dead leg causes the water to compress the air/gasses completely and it hits the end of the leg with a bang.

In domestic premises this effect is often noticed when a washing machine valve closes the cold mains feed during its cycle, the sound is heard 1/2 second later or so.

The Dangerous part comes where the conditions are right for there to be enough violent hammer effect for a cap, valve or whatever is used to stop the flow, being blown off by the constant strikes the fittings are being subjected to.

This power battle should not be taken lightly and steps should be taken to prevent it occurring.

Answer 3

there are many situations that can cause a dead leg. if you go onto a job and remove a drinks machine, probably you would turn the isolation valve off, cap off and remove the machine. what you have done is cause a dead leg there is no movement of water, this will allow bacteria and chloriforms to grow, what you should have done was trace the pipe to the main and cap off as close to the main as you can. hospitals nowadays take dead legs to the extreme i have had to tee into mains cold water pipe work 200mm away from the tank feed incase nowbody uses the tank water supply, the tee i have cut in that is then taken to feed a frequently used item like a toilet, to guarantee fresh water going into the tank. basically to avoid a deadleg whatever you dissconect cap it at the main this applies to mcws, heating and gas. if you are installing two water heaters side by side make sure the isolating valves to each unit are close together not just close to the unit because if one is offline you could also be causing a dead leg in the pipe work.

Answer 4

It is a place where stagnant fluid can be trapped. This is not good when you are dealing with steam because it can get trapped in the dead leg. Since the trapped steam is not moving and away from the heat source it will condense. When the block valve is initially opened on the dead leg it will blow out a slug of hot water. Not good because some equipment is not designed to be doused with a cool slug of water when it is at high temperatures.

Answer 5

A 'Dead Leg' is a no longer used stretch of piping that has been disconnected from the downstream side.
It will or may be isolated by a valve and the end flange will be capped if small size, or 'blinded' (blank flange) if larger size.
In some cases, a small test line may be incorporated into the blind flange to check for valve leakage between it and the blank flange.

Answer 6

It's usually a stub or side connection off a main run that has been capped off. The main run is 'live' but the stub is now a 'dead leg'

Answer 7

It is when a pipe is closed off and goes no where - problems like legionellas can occur

Answer 8

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