Casing Spacers for HDPE Carrier Pipe in HDPE Casing

[coloeng]

We have a project where we will need to provide a casing for a 12-inch water line that crosses under an irrigation canal. Because the canal is on the sideslope of a hill, the casing will have to have a curvature in it. The casing only needs to have the same strength as the carrier pipe, which will be HDPE DR-11. We have not bid this project yet and a number of contractors are inquiring into whether or not casing spacers are required. They are concerned that the ribs in the inside of the pipe that are formed in the fusion process will make it difficult to use casing spacers. They are proposing to use a 16-inch HDPE casing for the 12-inch HDPE carrier pipe without the casing spacers. This is the first time we have used HDPE as the casing pipe and would like any thoughts on the proposed method.

Thanks in advance for any advice.

 

[BigInch]

Normally casing spacers are used on steel carriers when installed within steel casings to prevent electrical contact and shorting out the cathodic protection. Not sure why you would need spacers in an HDPE system as no CP is required.

Independent events are seldomly independent.

 

[cvg]

insulators are used to prevent electrical contact. spacers are used to center and support or set grade (for gravity sewers) for the carrier pipe inside the casing. rollers can be used to reduce force and allow the carrier pipe to more easily cross over any "ribs" in the casing pipe.

http://www.apsonline.com/pdf/CASING/CasingSpacers.pdf

 

[coloeng]

BigInch and cvg, thanks for your responses.

 

[BigInch]

cvg, Thanks for pointing out that there is sometimes a need for holding precise alignment in a casing. I didn't think about that one!

Independent events are seldomly independent.

 

[cvg]

your project sounds like it could be a candidate for directional drilling with no casing needed.

 

[frauk11]

Casing spacers wouldn't be an issue, as they usually detailed as leaving an inch or two between the top of the spacer and the "carrier" pipe. Having said that, if you're working on a low-bid award project that doesn't specify spacers, I don't know why you would be concerned about it prebid. Let them ask for them after award and get paid!

 

[coloeng]

cvg, we are looking at doing this with directional drilling because of the topography. Unfortunately, the ditch company requires a casing pipe that has the same strength as the carrier pipe.

frauk11, we are the owner, not the contractor.

 

[anasalk]

i have designed a 16" HDPE DR11 water main in a 36" HDPE DR11 casing, it was constructed by HDD, similar to your case they wanted to encase the water main. i specified PSI non-metallic spacers but the suppliers changed it to metallic. they were worried about the them wearing off when the carrier pipe is pulled into the casing.
what did you fill the annular space with?

 

[coloeng]

This bore has not yet been done and we have not seen the contractor's proposed method for review yet. Our concern with using spacers is them catching on the weld beads inside the casing pipe.

 

[77JQX]

All the spacers I've seen have substantial chamfered leading and trailing edges to allow them to move over imperfections. I don't think you'll have a problem with the weld beads.