Posted by lazypup ([email protected]
) on Wed, Feb 8, 06 at 13:05
I have been in the Plumbing trade for nearly 4 decades and throughout that time every time I noted a change to the codes I made it a personal point to find out the underlying reasoning for the changes. To date I have yet to find any change that does not make perfect sense once you find out what prompted the change.
In the case of PVC, when it was first introduced into the plumbing trade in the mid 60's it was approved for all potable water systems, both supply and distribution. At that time it was also a common practice to operate water heaters at or near 180degF.
It was soon discovered that PVC will exhibit wall softening and glue joint failures at temperatures approaching 150degF, which explains why the ASTM standard for PVC now limits it to applications not exceeding 140degF. )
The PVC formula was then improved upon to create CPVC which can withstand temps up to 190DegF for a short time.
Initially the codes were ammended permitting PVC in the cold water service, but requiring CPVC in all "Hot Water" applications, however this lead to a lot of confusion amongst the general public and it was soon discovered that homeowners and DIY'ers were erroneously using the PVC in applications that required CPVC. It must also be noted that initially CPVC was made in the same white color and to the same Sched.40 dimensional specifications as was the PVC which then lead to a lot of confusion by mixing both the pipe and fittings. CPVC is still made to sched.40 specs and the only method of distinguishing the two materials is to actually read the labelling printed on the pipe wall.
The CPVC that is commonly used for distribution piping today is not made to ASTM pipe Schedule standards, but rather it is CPVC-CTS,(Copper Tube Standard) which explains the difference in overall tube dimension.
In order to further enhance the differences between the materials the ASTM introduced a color coding system for plastic piping.
ABS pipe is made in Black.
PVC pipe is made in White, Gray, (rarely in blue) and Clear. The gray color is primarily only used for shed.20 and sched.40 dimension and is primarily intended to be used as electrical conduit. PVC clear pipe & fittings is used in commercial and industrial applications that were formerly constructed of Glass pipe, and limited to applications not exceeding 140degF working temps.
There is a variation of PVC pipe that is made to ASTM "SDR" (Size Dimension Ratio)standard and may only be used for sanitary and storm sewer applications outside of a structure. (SDR, Size dimension Ratio is a standard that was originally used to define the thickness of concrete sewer pipe walls. Under the SDR standard the average thickness of the pipe wall is determined by dividing the pipe diameter by the SDR reference number. By example, a 4" PVC SDR-35 pipe would have a wall thickness equal to 4"/35= 0.114".
The codes specifically state that all PVC piping used to make the DWV (Drain, waste & Vent) system within a structure MUST BE schedule 40. ( You may not use SDR pipe within a structure)
CPVC is made in white and the creme color that we most often see in the local hardwares, big box stores or plumbing supply houses. In addition to the CTS standard it is also made in sched.40, sched.80, sched.100, sched.120 and rarely in sched.180