Preinsulated Piping Experience

[jonasinc]

Does anyone have experience with preinsulated piping installed underground in a wet environment (high water table)? What materials are recommended for the insulation, conduit and outer shell?

Have you experienced ID corrosion of the steel conduit due to water ingress into the insulated annulus around the carrier pipe?

If so, what were the sources of the water ingress?

 

[bimr]

It is difficult to predict the corrosion because the installation depends on the workmanship of the installer as well as the design of the piping system.

For cold and hot water applications, insulation generally consists of either piping covered with a foamed-in place polyurethane covered with a high impact resistant formed plastic covering.

For steam lines, preinsulated conduit is used with an annulus air space around the insulation.

You may be interested in pursuing a field-installed system that uses cellular glass covered with an asphaltic membrane and sealed with sealants.

Another possibility is loose fill consisting of calcium carbonate poured into the pipeline trench and surrounding the pipeline.

The best solution to prevent water infiltration would involve installing a perforated drain 6" below the bottom level of the pipeline. It is also important to very carefully consider the potential for damage to the insulation from uncontrolled pipe movement.

 

[stanier]

IF you want to avoid the corrosion use the Tyco product KFLo manufactured in ABS. I know this may not be suitable for hot water >60C but it is a good solution for cold or chilled water.

Systems up to DN800 are bing used for chilled water around the globe. No concerns about loss of integrity of the vapour barrier causing corrosion beneath the insulation.

http://www.tycoflowcontrol.com.au/t...ine_systems/Overview/plastic_products#ABSKFLO

 

[cub3bead]

Look at the stuff on Perma-Pipe's web page:

http://www.permapipe.com/

 

[Ashereng]

Hi jonasinc,

Just for my benefit, why are you insulating a buried pipe? Here, we typically bury pipe uninsultated, and only insulate at the risers as they come up/down.

Although you did not state what is in the pipe, and the process conditions, have you considered a polymeric pipeline (HDPE or PEX)? Because these pipelines are "plastic", water corrosion is not an issue in buried service. Also, they have a temperature range of around -29°C to 140°C for HDPE (180°C for PEX).

One name brand is Fiberspar, out of Huston Tx. Their web is

http://www.fiberspar.com.

 

[jonasinc]

The pipe is carrying steam at 400F so it must be insulated.

 

[Ashereng]

Hi jonasinc,

Oh. Sorry, the poly pipes would not work.

I don't have much experience with steam pipeing (above or below ground).

I am curious though. Why are the pipes underground? Are you crossing under water or other obstacles. This is strictly my curiosity.

 

[TBP]

Probably district heating lines. My experience with pre-insulated steam lines is that they routinely fail at the field joints. Not the carrier pipe, but the insulation jacket. The preinsulated systems cost a small fortune, and then there are the delivery issues. If you hit a "surprise" like an un-located sewer during a excavation (unlocated utilities are very common in old downtown sections), you can't just fabricate around it - you'll wait weeks for the offset bits from the manufacturer to show up. This can make you extremely unpopular with city engineering people - especially if the hole is in the middle of a busy street - or even better - a busy intersection.

We didn't have to deal with lines below the water table, but we typically used Foamglas and just heavy tar paper tied on with wire. You might consider something like snow & ice shield - very sticky and hard/messy to work with, but likely as good as anything when combined with Foamglas. Plus it's much cheaper, and you can field fabricate around surprises.

 

[bimr]

Preinsulated piping systems are not generally recommended for steam piping because of the temperature limitations of the insulation. The ground water infiltrates the insulation materials and vaporizes on contact with the piping deteriorating the insulation.

You best option is to use a field installed instulation using cellular glass. The cellular glass can withstand the temperature, the glass structure also resists penetration from ground water.

It is recommended to use a perforated drain 6" below the bottom level of the pipeline to prevent the ground water from infiltrating the piping system. It is also important to very carefully consider the potential for damage to the insulation from uncontrolled pipe movement.

 

[jonasinc]

The pipe is a part of a district heating system. Unfortunately, the water table is very high and it often above the level of the pipes.

 

[rconner]

This is probably a stupid question (as I have little/no experience in this field) but could the pre-insulated piping e.g. in a very high water table area be run through a larger pipe, casing, or tunnel etc., that with or without sumps de-watering means etc. perhaps could thus be designed to minimize water or moisture-related issues it appears at least such as loss of insulating value (I realize this would be at increased cost/space consumption etc.)

 

[TBP]

District heating is a weird adventure, and local factors dominate. What makes perfect sense in one city, is totally unsuitable in another - sometimes even just a few miles down the road. Soil and groundwater conditions, local politics, etc. Plus, no other utility has to deal with HOT pipes. Maintaining slope on lines, manholes for drip legs and expansion joints, and threading the needle through existing utilities.