Document 4aOmVdY8pDvKD3mr840exGz3e

UTILITIES RELY ON PVC PTPE by Robert Walker, P.E. Throughout much of this century, revolutionary changes in pipeline engineering and material selection have resulted from the introduction of plastic pipes. The revolution was bom in polymer science and decades of technological refinement, while being nurtured by actual product performance and an ever-increasing understanding of plastic materials properties by specifying engineers. The polymer that has achieved front-runner status in this pipe revolution is polyvinyl chloride (PVC). Resistance to chemical attack, long-term strength and high stiffness account for PVC's popularity for both pressure and non-pressure pipe applications. Throughout North America and most of the industrialized world, the use and availability of PVC pipe has grown steadily since the middle of this century. PVC has become the dominant pipe material for such major markets as the gravity flow and pressure sanitary sewer applications and for pressure water distribution. In North America, the total length of PVC water main and sanitary sewer pipe installed each year exceeds that of all alternative pipe materials combined. North American PVC pipe and fittings sales exceed 3.7 billion pounds annually. Such statistics are the result of a successful product history and multiple product attributes. Water Distribution Usage PVC water pipes are conservatively estimated to comprise about 70 percent of all the buried water distribution pipes (< 12 inch) being installed in North America each year. PVC pipe's majority share in this very large pipe market can be attributed to a variety of performance characteristics. CTL026946 "Utilities Rely on PVC Pipe" Robert Walker, P.E. Page 2 The greatest single PVC water pipe attribute is its invulnerability to corrosion. Hundreds of millions of dollars are spent each year on maintenance, repair and replacement of corrosiondamaged pipelines. Unlike alternative steel and ductile iron pipes which depend upon protective liners, external coatings, encasement bags and/or cathodic protection, PVC is inherently wellsuited for direct burial and water conveyance. PVC is immune to both underground external corrosion and internal pipe corrosion. This eliminates the need to specify corrosion protection methods. With PVC pipe, long-term durability is not compromised when encasement bags are punctured or tom, or when thin coatings or liners are damaged. Installation and design are simplified with a single wall, homogeneous pipe material. A recently published international report entitled, "Problems of External Coirosion in Water Distribution Systems," found a dramatic shift towards the use of plastic pipe (primarily PVC) to minimize the high costs associated with corrosion. Specifically, the report found that plastics now account for 69.3 percent of the water pipes laid in recent years, with ductile iron a distant second at 20.5 percent, followed by asbestos cement (5.4%), steel (4.5%), and concrete (0.3%). Increasing public attention and awareness regarding water quality and health are also factors favoring PVC use for water distribution. A PVC water pipe delivers water as clean and pure as it receives. PVC imparts no taste or odor to the water it transports, nor is PVC pipe a source of lead or other chemical contaminants associated with metal pipes. PVC pipe does not react with even the most aggressive drinking waters. PVC pipes have been continuously certified safe against national drinking water standards since 1965. The absence of internal corrosion with PVC also eliminates tuberculation, i.e., the build-up of corrosion by-products, which cause a loss in hydraulic capacity and higher pumping costs. CTL026947 "Utilities Rely on PVC Pipe" Robert Walker, P.E. Page 3 Specifically engineered and carefully formulated, PVC pipe compounds are more expensive per pound than ductile iron, steel or concrete. However, PVC's high strength-to-weight ratio requires fewer pounds per foot of pipe. The weight advantage is quite significant, e.g., a 20-foot length of nominal 8-inch Class 52 ductile iron pipe weighs 570 pounds, versus 180 pounds for a Pressure Class 150 PVC pipe. This sizeable weight differential provides good economy on a per-foot-ofpipe basis and serves to lower shipping costs, facilitate installation and handling, and reduce injuries and accidents for installation crews. These and other beneficial attributes have combined to give PVC water pipes a favored status among most water pipeline specifiers. PVC water mains earned the highest mean satisfaction level in a 404 utility survey conducted by the University of California. In the same survey, utilities were asked to indicate whether repair rates were "Better," "Same," or "Worse" when compared to other mains. Again, PVC pipe received the highest better: worse ratio, i.e., 8.8:1, as compared to only 4.8:1 for iron and steel pipes, and 1.5:1 for asbestos cement pipes. With the 1988 approval and publication of American Water Works Association's (AWWA), "Standard for PVC Water Transmission Pipe, Nominal Diameters 14 Inch Through 36 Inch" (C905), there has also been a shift toward the use of larger diameter PVC water pipes for both water distribution and transmission. PVC pipe's superior performance and durability are expected to earn them a majority share of that market in the near future. Sanitary Sewer Usage Sanitary sewer applications pose a somewhat different set of pipe performance challenges. Cost efficient operation requires that all cracks and leaks be minimized or eliminated. Every crack or leak represents an opportunity for root intrusion and/or the entrance of surrounding embedment CTL026948 "Utilities Rely on PVC Pipe" Robert Walker, P.E. Page 4 soil. In both cases, the sewer may become blocked or obstructed and require costly maintenance or repair. The loss of embedment soil may further undermine the structural integrity of the sewer and adversely affect nearby structures, particularly paved surfaces. Concern for the environment has resulted in the construction of complex, multi-stage wastewater treatment facilities with significandy increased operating costs. Water leakage into sanitary sewer collection systems can significantly increase the volumes of wastewater that must be treated. The resulting wastewater volume excesses increase treatment costs and reduce the treatment facility's effectiveness. PVC pipes for sanitary sewers are engineered with deep insertion, gasketed joints that provide superior resistance to cosdy leakage. PVC sanitary sewers bend or flex when subjected to excessive loads rather than cracking or breaking. These PVC pipe design properties have enabled specifiers to upgrade their sanitary sewer requirements and performance expectations. Annual treatment cost savings alone are estimated to exceed $20 million, as a direct result of PVC sewer pipe usage. These measurable performance advantages have brought about an almost total conversion to PVC pipes for sanitary sewers. Over 90 percent of all the sanitary sewers currendy being installed throughout North America are made from PVC. With the development of the new profile wall constructions, the PVC industry has been able to properly engineer pipes up to 48 inches in diameter. In addition to lower leakage rates and the elimination of root penetration, PVC sewers provide exceptional durability. PVC pipes are resistant to virtually all of the chemical constituent CTL026949 "Utilities Rely on PVC Pipe" Robert Walker, PJE. Page 5 concentrations found in both domestic and industrial wastewaters. Sulfide corrosion does not occur with PVC pipe. Abrasion wear has been observed as insignificant. PVC sewer pipes come in longer lengths that reduce the number ofjoints needed and allow for faster, more efficient installation. PVC also provides a smoother internal wall surface that minimizes fluid friction and flow resistance. This hydraulic smoothness inhibits slime buildup and thereby lowers sewer maintenance costs. PVC sewer pipe's flexibility is perhaps its greatest asset. Not only does the ability to flex serve to eliminate fracturing and the leakage associated with cracking, but PVC pipe's flexibility, in combination with the surrounding soil, enables it to sustain loadings that would crush rigid pipes. Typical pipe embedment conditions will permit loadings approaching 12,000 lbs./ft2, without excessive deformation. Even higher loadings can be handled when special embedment conditions are employed. Other Applications Having proven performance in the demanding circumstances surrounding the broad range of water and wastewater pipe applications, PVC pipe's versatility is being carried over into other buried piping applications. For storm sewers and highway culverts, PVC products provide a higher quality alternative to traditional materials. Resistance to chemical attack, absence of corrosion, and abrasion resistance make PVC a more durable product High load bearing capacity, fracture resistance, water-tight joints, smooth inner walls and installation ease make PVC pipe a cost effective choice. CTL026950 "Utilities Rely on PVC Pipe" Robert Walker, P.E. Page 6 Throughout this decade and into the next century the pipe materials revolution that began 60 years ago will almost certainly continue. Out of that revolution, PVC piping products have risen to the top and are expected to improve upon their dominant position. PVC pipes and fittings owe much of their success to the inherent properties of PVC combined with an engineering approach intent on solving utility pipeline problems and reducing costs. The result has been an increasing reliance upon PVC pipes and fittings by utilities across North America and around the world. -End- ^^02 6951