The Australian Pipeliner spoke with McElroy Manufacturing Vice President and Chief Technology Officer Jim Johnston to discuss the process of heavy wall pipe fusions and the power of McElroy’s productivity tools.
Jim Johnston has extensive experience across the pipeline industry and currently serves as vice-chair of the Board of Directors of the Plastics Pipe Institute (PPI). He is actively involved in many standards and industry organisations such as the International Standards Organisation, Alliance and the American Society for Testing and Materials (ASTM).
What is heavy wall pipe?
For decades, high-density polyethylene (HDPE) piping systems have proven to be a reliable and long-term option for a variety of markets, from municipal water systems and gas lines to the mining and natural gas industries.
For applications that call for a thicker pipe wall, HDPE continues to provide longevity, durability, and the reliability of a leak-free piping system.
Heavy wall* refers to the dimension ratio (DR) of the pipe itself. The DR of a pipe is the ratio of the wall thickness to the pipe’s outer diameter. Simply put, as a pipe’s DR decreases, the pipe’s wall thickness increases.
Butt-fused HDPE pipe is a growing choice for commercial and municipal piping systems due to its multiple methods for installation, reliability, and durability. Generally, heavy wall pipes are used in applications that will subject the pipe to higher pressure.
During the fusion process, HDPE pipe ends are faced, heated, and brought together under pressure to form a bond as strong as – or stronger – than the rest of the pipe itself. When working with heavy wall pipes, the process itself does not change, but operators and contractors should plan for longer heating and cooling times.
ISO 21307 single high pressure (SHP) fusion jointing procedure outlines the standard for polyethylene butt fusion using high interfacial pressure. The procedure defines the heating and cooling times required based on the wall thickness of the pipe being fused. Therefore, thicker walls result in longer heat time and cooling times.
How does heavy wall pipe affect the fusion process?
As heavy wall pipe has, by definition, a higher pipe wall thickness, the amount of time required to heat soak will also increase.
ISO 21307 SHP also defines the cooling time based on wall thickness. Accordingly, higher wall thickness will mean a longer total cooling time.
Other than heating and cooling times, the fusion process itself will not change, regardless of the wall thickness of the pipe being fused.
What are some of the best practices?
While the procedure remains unchanged, there are several best practices that will help ensure good fusions.
Due to the nature of large-bore, heavy wall pipes, it is not uncommon for there to be variation in wall thickness around the circumference of the pipe.
While this is minimised with low slump resins, there are still variations. To limit those variations, it is good practice to align the print line and the direction of extrusion so that the ID walls of the pipe are best aligned.
Due to the large mass of the heavy wall pipe, it is recommended that the user operate their heaters at the higher end of the allowable range. For ISO 21307 SHP, this allowable range is 215 +/- 15°C.
For the interfacial pressure, best practice is to operate at the lower end of the allowable range. For ISO 21307 SHP, this allowable range is 0.52 +/- 0.1 megapascal (MPa).
Another important consideration when fusing heavy wall pipe is the weight of the pipe itself. As a pipe’s DR decreases (because of an increase in wall thickness), so does the amount of material that makes up the pipe. A 250mm DR17 pipe can be picked up and moved by one person, but a 250mm DR7 is an entirely different story.
How can McElroy’s productivity tools help the process?
When working with heavy wall pipes, additional personnel may be needed to move the pipe from one location to another. Depending on the weight and size of the pipe, heavier equipment might be needed to manipulate or move the pipe or load it into the fusion machine.
In these situations, McElroy productivity tools like the PolyHorse® and Low Profile Pipe Rollers are invaluable assets on the job site.
The PolyHorse, which comes in two sizes, is a series of adjustable racks designed to hold enough pipe for a day’s worth of fusion work. It is designed to allow a single operator to load and align pipes without the use of extra machinery.
The standard PolyHorse is for 3-inch iron pipe size (IPS) to 20-inch outside diameter (OD) (90mm to 500mm) and is available in both manual and hydraulic modes, with the latter offering a hydraulic PowerAssist to help maneuver the pipe up, down, and into the fusion carriage.
The MegaMc® PolyHorse is used with pipe from 20-inch OD to 48-inch OD (500mm to 1200mm). The MegaMc PolyHorse features a powered, tracked pipe stand operated by remote control. It offers up to 24 inches of lateral and 34 inches of vertical movement.
McElroy’s Low-Profile Rollers are modular pipe rollers designed to make 4-inch to 18-inch IPS (100mm to 450mm) pipe easier. MegaMc Rollers are also available for 12-inch IPS through 54-inch OD (900mm to 2,000mm) pipe. Rollers can be paired with other productivity tools, to greatly reduce the amount of manpower and other equipment needed to move the heavy pipe from one location to another.
When using pipe rollers, the amount of force needed to move even heavy pipe and pipe joints is reduced. Pipe rollers have the added benefit of keeping the pipe off the ground, reducing the amount of wear and tear on the pipe itself during fusion and installation.
What can users expect from using McElroy’s products?
HDPE is growing in popularity, and projects continue to grow both in size and scope.
As the number of applications for large-diameter HDPE increases, it’s reasonable to assume that the use of heavy wall pipe will increase as well.
Despite the extra considerations and challenges presented by the use of heavy wall pipe, McElroy machinery and productivity tools are designed to keep the job going.
Whether fusing in a crowded metropolitan area or in the most remote and rural of locations, McElroy equipment is built for rugged reliability and is backed by a network of specialists and technicians but also by other professionals who are constantly searching for ways to further streamline the fusion process itself.
*For the purposes of this article, the definition of “heavy wall” will be a wall thickness greater than approximately 65mm.
This article featured in the July edition of The Australian Pipeliner.