HDPE flange adapter joined to steel flange and leaks.

[ramracer]

Has anyone had problems joining HDPE flanges to steel flanges? I think I am having expansion and contraction issues on the HDPE. We have to keep about 20 ft of HDPE un backfilled for inspection and a concrete pipe anchor. We are mating to a steel flange that sits a few feet from a 45 degree elbow and has 25 ft to 30 ft before concret encasement. We develop laeks through out theday with temperature change and pressure change. It also causes leaks by torqueing difernt flanges( HDPE to steel, steel to steel). The Hdpe is in a 300 ft radius and is still in the radius where connection is made. Does anyone have expeirence with joining HDPE to a fixed unit (steel)? we have followed torque patterns and exceeded torque to try to fix this. I am I shooting at a moving target and missing something?

 

[andrenov]

have you used the injection molded stub end flange for that?

 

[rconner]

Over the years I have heard of some problems at flanged joints in plastic pipe systems, and also specifically polyethylene pipe systems. In this regard the document at

http://www.klinger.co.at/pdf/ESA-e.pdf

now sort of summarizes generic non-metallic applications and issues on page 12 with the sort of politically correct language,

“Generally, these flanges are less robust and dictate a softer gasket material, able to be seated under lower gasket pressure. Operating temperatures and pressures are usually less severe.”

The flanged joint was of course originally designed with more rigid and stronger, metallic materials, that in conjunction with the greatly exaggerated thermal, Poisson, and/or Bourdon (associated e.g. with unblocked pressure thrust?) movement etc. effects also endemic to polyethylene is perhaps source of your problems. While you don't mention the size nor pressure conditions of your piping (I would think problems could get more pronounced with increasing size)I wonder however if a mechanical joint connection, along perhaps with a separate fused collar anchorage on the polyethylene close to the connection, might at least some more “robust” considering such behaviors?

 

[dicksewerrat]

Can you get a secondary metal flange as a backing plate on the HDPE side. Then you will have a gasket and a compressed HDPE flange. And the thermal issue should go away once the pipe is buried.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com