Put CPVC Piping In Its Place

By Donald Townley, Lubrizol

ChemicalProcessing.com

Understand where it fits in terms of cost and performance

Savvy specifiers know it’s not just the purchase price that matters when choosing a product that’s designed for long-term performance. When evaluating a piping system this certainly is the case. The key is to identify the best value for today, as well as tomorrow and beyond. And that typically requires a lifecycle cost analysis tailored to your specific plant, to reflect its fluid temperatures, line pressures, chemical environments, etc.

For such an analysis for piping materials, start by calculating the cost to install the system. Don’t focus only on the direct material costs — labor and related installation expenses can account for more than one-half of the total investment made in a piping system.

Then consider the cost to maintain the system and how maintenance requirements affect productivity, downtime and lost opportunity. Also evaluate expected service life — how long the system should last before a total repipe will become financially or operationally necessary — and its impact on profitability.

Here’s how chlorinated polyvinyl chloride (CPVC) piping typically stacks up.

Many choices

Depending on the demands and environment of the operation, you could consider dozens of materials for a plant’s piping system. On the low end of the cost spectrum are PVC, CPVC and carbon steel. At the other extreme are high-performance metals such as nickel, titanium and zirconium and alloys. Combination systems such as steel lined with rubber, polyvinylidene fluoride (PVDF) or glass fall in the middle.

Figure 1. CPVC piping has a proven itself at plants for about 50 years; new formulations extend the applicability of the material.

Metals. Historically metals have dominated the industrial piping market, largely because they’ve been used longer than any other material in such applications. In general, metal offers higher pressure-bearing capabilities than alternative materials. Additionally, metal systems’ pressure-bearing capabilities aren’t significantly reduced by increases in temperature. And metal’s rigidity allows hangers to be spaced farther apart to save on installation costs.

However, metal poses numerous disadvantages — the most serious of which is vulnerability to internal and external corrosion. Certain substances may cause metal to corrode from within, while elements such as salt in the air or low pH levels in the ground (for underground applications) can prompt external corrosion. Even high-end pricey metals such as titanium, which generally resist corrosion, are susceptible to degradation in certain environments.

Metal is also subject to flow-restricting scale buildup, which increases pressure drop and can contaminate the process. In addition, compared to plastic piping systems, metal is heavier and more expensive to install, both in material and labor cost. And, because metal has poor insulating properties, it sweats more when handling cold fluids, can create a burn hazard when transporting hot fluids and is less energy-efficient — all of which create the need to add costly insulation.

Plastics. Today many different plastics successfully serve in industrial environments. In general one of the greatest benefits of plastic pipe is its corrosion resistance. Various types of plastic piping can be buried in alkaline or acidic soils without requiring any paint or special coating. Plastics containing TiO2 for ultraviolet protection strongly resist weathering.

Most plastic pipe isn’t susceptible to scaling — so, such piping systems maintain their full fluid-handling capability throughout their entire service life. This means it’s often possible to downsize the diameter of the pipe when converting from metal, reducing material costs, and to opt for smaller pumps, saving energy.

Of course, the various plastics differ in cost and capabilities. PVC, for example, offers significant economic advantages but can’t handle high-temperature applications. CPVC, on the other hand, provides superior chemical resistance as well as a high heat distortion temperature, due to its molecular structure — large chlorine atoms surround the carbon backbone to protect it like armor plating. So, CPVC has grown in popularity in both corrosive and high-temperature applications.

Hybrids. In recent years manufacturers have been able to increase CPVC’s temperature and pressure-bearing capabilities by wrapping it with fiberglass. Other hybrid systems include various plastic-lined metallic pipe, which combines the advantages of metal and plastic while minimizing many of their disadvantages. This type of piping system eliminates scale buildup concerns while offering the same superior pressure-bearing capabilities as metal. Such pipe is immune to internal corrosion but still subject to external corrosion. A major disadvantage of plastic-lined pipe is cost. In addition, it requires a difficult labor-intensive joining process. And, any break that occurs in the lining can become a source for future pipe failures.

Of course, cost always is an overriding factor in pipe selection. An authoritative study documented that when allowing for direct and indirect costs — material cost, labor, maintenance, productivity, etc. — CPVC was the bottom-line best choice. Its nearest rival, strictly from a total-installed-cost standpoint, was carbon steel. At the extreme high end were PVDF and titanium.

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