The underground piping market in North America has seen large development over the past 30 years in using thermoplastic supplies. Advantages akin to corrosion resistance, improved hydraulics, and diminished set up prices have been paying giant dividends for homeowners of watermain, sanitary and storm sewer programs.
Essentially the most extensively used and accepted of this group of nonmetallic polymers is Polyvinyl Chloride, often known as PVC tarpaulin manufacturers ‘PVC’ or ‘vinyl’. Vinyl has a profitable track-record within the utility of underground pipe courting again to the rebuilding of post-WWI Germany. It has lengthy been thought-about to be one of the crucial sturdy polymers for each underground and above-ground piping programs.
One other thermoplastic used within the underground pipe market is Excessive-Density Polyethylene (HDPE). This materials has been used for effectively pipe, gasoline piping and drainage tubing earlier than latest entry into the watermain and sewage forcemain markets.
HDPE and PVC are remarkably comparable of their nature of responses to such stress loadings as inside stress and soil hundreds. Though responses are comparable, they don’t seem to be an identical. Actually the magnitudes of their respective strengths are dramatically completely different.
This report is meant to analyze among the similarities and variations between the design of PVC and HDPE by way of the appliance of underground stress piping.
PRESSURE RATING
The long-term stress ranking of a thermoplastic pipe is outlined as the utmost inside stress at which the pipe can function constantly. The scores of each PVC and HDPE are discovered utilizing the ISO Equation for thermoplastics:
Equation (1) P = 2S / (DR-1)
the place P = stress ranking of the pipe
S = design stress of pipe materials
DR = dimension ratio of the pipe, (OD/t)
The principle distinction between PVC and HDPE stress capability lies within the worth of the design stress. For PVC 1120 compounds, the design stress is 2000 psi whereas that of HDPE 3408 is just 800 psi. These design stresses have been each derived in precisely the identical trend. An element of security of two.0 was utilized to the long-term hydrostatic power (i.e. the Hydrostatic Design Foundation – HDB) of every materials. The HDB for PVC 1120 is 4000 psi whereas that of HDPE 3408 is 1600 psi.
The next examples illustrate using the ISO Equation to find out stress scores.
Instance 1 – Discover stress scores of DR21 pipe for each (a) PVC, and (b) HDPE.
Resolution – use equation (1)
P = 2S / (DR-1)
(a) for PVC, S = 2000 psi
Substituting, P = (2) x (2000 psi) / (21 – 1)
= 200 psi
(b) for HDPE, S = 800 psi
Substituting, P = (2) x (800 psi) / (21 – 1)
= 80 psi
Instance 2 – (a) Discover the stress ranking of PVC DR41 after which (b) discover the equal DR of HDPE to yield the identical ranking.
Resolution – use equation (1)
(a) P = 2S / (DR-1)
= (2 x 2000 psi) / (41-1)
= 100 psi
(b) rearranging equation (1),
DR = (2S / P) + 1
= [(2 x 800 psi) / 100 psi] + 1
= 17
Due to this fact, to acquire a 100 psi stress pipe, the two choices could be PVC – DR41 or HDPE – DR17.
The next factors may be concluded from the above info:
(a) The ratio of PVC to HDPE by way of tensile power is the same as the ratio of the design stresses, i.e. 2000:800 which is 2.5:1, and
(b) The wall thickness of HDPE should be 2.5 instances thicker than that of PVC to acquire pipe with equal stress scores.