I would be interested in your list of reasons why plastic is better. Do you use the type of pipe with the plastic bands at the joints or the type that interlocks and why one or the other is better. THANKS FOR ALL THE REPLYS
I build logging roads in the Pacific Northwest. All of the timber companies that I work for use CPP/ABS on all ditch relief crossings as well as stream crossings that require a 48" or smaller pipe. CMP, a CMP Multiplate or occasionally a bridge is installed when larger/wider crossing are required.
Storm runnoff in this part of the country consist of a lot of organic acids that build up in the topsoil from natural regeneration of vegetation. These acids quickly remove the galvanized coating thereby allowing the pipe to rust and subsequently fail. Thirty five to forty five inches of rain a year of course greatly accelerates this failure.
I am also told that gov't biologists have determined that a single spec of rust in a fish bearing stream will instantly kill any Salmon or Stealhead that comes in contact with said spec?????????????????
In my experience the biggest problem with CMP these days is poor quality as I have dug up countless sections of 20+ year old CMP that has some rust inside but nowhere close to failure.
To answer your questions:
CPP/ABS withstands continuous heavy loads just fine even at depths as shallow as 12" of cover. Loaded log trucks here gross anywhere from 80 to 100 thousand pounds. A single pipe often will have 20 or more 80 thousand pound loads a day cross over it for weeks in mountainous terrain. Thats roughly 1.5 million pounds per day!
CPP is somewhat flexible so it withstands a huge amount of deflection at shallow depths and still maintain its shape. Metal often gets ovaled and easily develops dents in the top from vehicle traffic with less than 24" of cover.
Most of my crossings have shallow inlets with outlets often much deeper. In my case the flexibility of CPP greatly reduces installation costs as it doesn't require an absolutely perfect bed to lay in, slight bends and imperfections do not affect the performance or lifespan of the pipe as long as it drains.
For flatter shallow installations such as driveway crossings I would recommend much more emphasis on grade of course.
Ease of installation, one man, one machine can handle installation of 3 or 4 sections of 24" CPP without to much trouble. A two man crew can fly.
Plastic bands are similer to metal bands except they come with manufacturer supplied zip ties instead of nuts and bolts. First time I saw the zip ties I wasn't impressed but I can honestly say I have yet to see a joint failure.
Plastic bands reduce costs as they are really easy to install and do not require repeated hammering and tightening or air tools like the steel bands.
Have extra zip ties on hand, occasionally they do break.
Twistlocks, interlocks or any kind of rubber gasket jounts are a PIA. Sometimes required when continuous high flow is a concern. I believe these styles are primarily intended for municiple storm sewer applications.
Interlock types of joints must be absolutely clean and require a lot more effort to properly install.
CPP is easily cut with a chainsaw, no sparks!
Biggest drawback with CPP in my experience is although flexible it is brittle so care must be taken when backfilling. Rocks up to about a foot or more are fine but don't dump anything larger from 10' high as it will go right through. Once you have the pipe covered your ok but as with any pipe installation care should be taken when backfilling.
As mitch504 says CPP does burn like a barrel of diesel. Controlled burns and slashpile burning is common practice on public and private timberlands in the spring and fall here as well. Slashpiles are placed as far from CPP as possible and the folks that do the burning go to great lengths to avoid burning pipes out.
