Companies spend a significant amount of time and energy selecting the best type of pipe material for the application, calculating size and lengths needed, and following and implementing standard instructions for proper pipe installation. Even when all this is carefully completed, there still can be problems with premature pipe failure or pipe damage that leads to leaks. In either case, the result is the same — costly downtime for repairs or replacement.
The main reason plastic piping failure occurs is that many in the industry design and install thermoplastic piping systems in the same way as metal. Using metal pipe methods in plastic systems causes mechanical stresses to become permanently locked into the piping system, reducing its life expectancy.
Metal design and installation methodologies also do not take into consideration the fact that plastic piping systems are dynamic: Plastic expands and contracts at a greater rate (10 times faster) than metal. Temperature changes in the ambient environment as well as the media being conveyed can cause the plastic pipe to expand and contract. Significant expansion or contraction also can occur due to temperature differences between the conditions at the time of installation — when the pipe gets clamped in place — and the conditions when the system starts operating. In process heating applications, for example, a 100’ straight run of plastic PVDF pipe installed on a cool (50°F [10°C]) morning will expand 2.88’ in length when the media temperature in the pipe runs at 80°F (26°C). All of these factors must be taken into account for proper installation.
Traditional Pipe and Valve Supports Stress Piping
Traditional pipe and valve-support products — even some of those designed for plastic piping systems — can create problems in process heating systems.
- Many clamps designed to hold pipe firmly allow the installer to overtighten against the pipe. This can stress the pipe — at time of installation as well as later when it needs to move naturally.
- Clamps with sharp metal edges can damage the pipe.
- Pipe guides that allow movement do not provide enough support during an earthquake. Pipes that can move freely from side to side — perpendicular to the axis — can become damaged. Engineers need to consider the supporting structure beneath the pipe guide if large forces are transferred during an earthquake.
- Valve manufacturers usually recommend that valves be independently supported in a piping system. In practice, installers often clamp valves down as fixed points. This creates concentrated stresses when the pipe cannot move naturally.
FIGURE 2. The pipe guides are designed with a 0.118” (3 mm) oversized gap between the plastic insert and the outer diameter of the pipe it supports. By design, the metal bracket cannot touch the plastic pipe.
All of these issues contribute to stress concentrations that increase the risk of premature failures and leaks.
Overcoming Installation Challenges
To address these problems, a pipe- and valve-support system was designed to eliminate stress transfer to plastic pipe due to thermal expansion, installation or seismic events (figure 1). The system includes pipe guides and valve supports, and it can be used with any thermoplastic piping system material as long as it is IPS (inch) or metric size.
Pipe guides in the system are designed with an oversized gap (approximately 0.118” [3 mm]) between the plastic insert and the outer diameter of the pipe it supports. Because the pipe and valve supports are molded from low friction, UV-resistant high density polyethylene (HDPE), they allow the piping to slide freely in the axial direction with minimal stress and wear during each thermal expansion cycle. Additional strength is provided via an outer metal bracket that withstands myriad operating conditions, including strong seismic events.
By design, the metal bracket cannot touch the plastic pipe (figure 2). No matter how hard the installer bolts down the metal bracket, the guide will not squeeze the pipe.
The valve supports allow the valves to move in two directions (±3” [76.2 mm]) as the pipe expands and contracts. The piping moves in a controlled manner while being supported. Because the support base and slide components are made of low friction polypropylene (PP), valves can slide with little to no resistance. Piping centerlines are aligned when the pipe guide is properly mounted.
The pipe- and valve-support system can extend the life of thermoplastic piping systems in high purity facilities and corrosive environments. Applications with aggressive media, indoor-to-outdoor transitions or those subject to wide temperature variations can benefit.
The pipe guides can mount on flat surfaces, standard strut, horizontally or vertically. In the vertical orientation, an elastomer material is inserted to create sufficient friction and snugly secure the pipe. In a horizontal mount, the pipe is free to move. A hanger kit allows mounting to the ceiling. In all cases, the pipe never touches the metal bracket or hardware.
In conclusion, the support system can extend the life of thermoplastic piping systems in both high purity facilities and corrosive environments. Applications with aggressive media, indoor-to-outdoor transitions or those subject to wide temperature variations will especially benefit.