Cooling procedures optimized for HDPE butt fusion save time and money in the field


In the field, efficiency, performance, and productivity are critical to HDPE melting success, and McElroy Optimized Cooling is a real-time algorithm that can positively impact all three.

HDPE piping systems provide durable, leak-free infrastructure worldwide, with a growing presence in many small and large diameter construction applications. It is cost effective and can be installed in a number of environments, such as densely populated urban areas, which would prove challenging for traditional metal piping systems.

During the fusion process, most of the time for each fusion joint is allocated to cooling procedures. After all, cooling the seal under pressure is critical to seal integrity. ASTM F2620, the most widely used fusion standard in North America, dictates a minimum cooling time of 11 minutes per inch of wall thickness.

But what if these cooling times could be reduced, thereby increasing fusion productivity without compromising the integrity of the joint itself?

This question was answered nearly a decade ago, through a partnership with the University of Tulsa to re-examine and test standards for calculating cool times. Testing focused on fusing pipe with an outside diameter (OD) of 6 to 24 inches, with aspect ratios (DR) ranging from 7 to 32.5. During the tests, the pipes were fused under numerous conditions, with several cooling times, and then destructively tested.

Thousands of data points later, an algorithm has been developed that reliably predicts the optimum time needed to cool the HDPE pipe core before moving on to the next melt. This procedure is in accordance with ASTM F2620.

The first optimized cooling joint was registered in October 2017. Shortly after, a company installing 16.3 miles (26 km) of DR9 HDPE water pipe used the optimized cooling and recorded its results. Using standard cool times per ASTM F2620, the project would have required 1850 hours of cool time alone. This new algorithm has reduced that projected time to 1140, a reduction of over 700 hours that could mean hundreds of thousands of dollars saved.

Optimized cooling calculates cooling times based on environmental conditions, pipe material properties, and heat soak time while ensuring fusion joint integrity. In some cases, operators using optimized cooling procedures have reduced cooling times by up to 55%.

For example, a 10-mile (16 km) smelting project would require 1056 50-foot (15.24 m) tubes. Compared to the current ASTM F2620 standard of 11 minutes of cooling time per inch of pipe wall thickness, using optimized cooling at 90° Fahrenheit (32° Celsius) would save over 300 machine hours in reduced cooling time alone – and this is not the case when factoring in saved support hours, such as for pipe handlers and elevator operators.

So how were these results achieved?

The researchers determined that there are four main factors at play when it comes to cooling time: ambient temperature, bulk pipe temperature, heat soak time, wall thickness, and outside diameter.

Knowing that ambient temperature plays an important role in cooling time, testing was performed at 40˚F (4˚C), 70˚F (21˚C), and 120˚F (49˚C). These tests involved 18 inch DR 32.5 HDPE and 18 inch DR 7 HDPE. In these tests, fusions were performed in accordance with ASTM F2620.

During each test, the temperature dropped rapidly immediately after butt fusion, then slowly decreased to room temperature. For DR 7 and DR 32.5 pipes, the cooling time approximately doubled when the ambient temperature increased from 70°F to 120°F.

This was not a surprising finding – ASTM F2620 already notes that melting occurring at high ambient temperatures should consider increased cooling times. But after this initial rapid decrease, testing indicated that there was no linear reduction in joint strength as it was removed from the fusion machine.

The algorithm also takes into account the heat absorption properties of HDPE pipes. For example, a black pipe, in particular, can be much warmer than the surrounding ambient conditions because polyethylene is an excellent insulator. On a hot day, a solar-charged HDPE stick can reach temperatures of 150°F (65.6°C) and more.

Since operators routinely record the ambient temperature in their DataLogger, predictions can be made with high levels of accuracy as to the optimum length of cooling time.

Preparing a joint using optimized cooling is simple. Before the start of melting, the operator enters the ambient temperature, the surface temperature of the pipe to be joined, the pipe DR, the pipe material and the pipe diameter in the DataLogger. The DataLogger then provides graphical instructions to the operator regarding the heat soak time (in accordance with ASTM F2620) and the calculated melting/cooling time.

By dramatically reducing the cooling time for each joint, operators and contractors are able to complete more fusions in less time while maintaining the integrity of the fusion joint. This technology allows them to bid projects more competitively while reducing the number of man-hours at each site. Optimized cooling is a tested, proven and effective way to offer customers a way to save time and money.

For more information, visit McElory.

This article appeared in the July issue of The Australian Pipeliner.


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