Cold and windy weather conditions can greatly affect the polyethylene pipe fusion process. However, with a little preparation and precaution, pipe can be fused with the same great results as fusing pipe under ideal weather conditions—it will just take a little longer. The bigger the pipe and the colder it is, the longer it takes for an adequate bead to form during the heating process. So, patience is key while waiting for that pipe to melt.
Examine the Pipe
The first thing to consider is the pipe itself. While polyethylene pipe is incredibly strong, freezing weather does reduce its resistance to impact damage, especially if it is dropped or handled roughly. It should be inspected thoroughly to ensure it hasn’t been damaged. Any area of the pipe that has been compromised should be cut out. For the best results, the pipe manufacturer’s specific recommendations for fusing pipe in cold weather should always be followed, along with the cold weather procedures outlined in ASTM F2620.
Warm Up the Pipe
Can pipe be fused in sub-zero weather? The answer is yes, as long as the pipe is warmed before attempting a butt fusion. If the ambient temperature is less than 3° F (-16° C), this can be accomplished with heating blankets draped over the pipe or other warm air devices. Another option is to load the pipe into the fusion machine and place the heater plate within .25 to .5 inches (6.4-12.7mm) of the pipe ends. Thirty seconds to two minutes (for thicker-walled pipe) should be allowed for it to heat up. Torches or any other devices with an open flame should not be used to heat pipe due to the potential for pipe damage.
Plug the Pipe
Extreme winds blowing through the bore of the pipe can also interfere with the fusion process. These conditions create inadequate and inconsistent temperatures in the heater, which makes it difficult to heat the pipe effectively. This problem can be combated by using end caps or plugs on the open ends of the pipe to act as a wind barrier.
Shield the Fusion Area and Protect the Heater
Special measures should be taken if you are fusing pipe when the ambient temperature is less than -4° F (-20° C). On these freezing days, which may include high winds, snow, ice or rain, this can be accomplished by fusing inside a portable shelter or trailer or by erecting a canopy, tent or other similar device over the fusion area. This is needed to protect your equipment and pipe from the elements and to ensure that the environment will be conducive to fusing good pipe joints.
Wind, precipitation and freezing temperatures can also make it harder for heaters to reach an optimal, consistent temperature. To prevent heat from escaping, the heater should be kept in an insulated-type container. Keep the heater in a sling or other protective device so it stays hot up until the moment you are ready to use it.
Once the heater is removed, use a pyrometer to check the heater surface temperatures on up to four points on each side of the butt plates that will have contact with the pipe. This ensures that the heat is spread evenly throughout the plate, producing an even melt pattern and quality joint. Remember, the thermometer in the heater body reflects the internal temperature only, not the actual surface temperature of the heater butt plates, which is what needs to be measured to achieve a proper melt.
Keep Pipe End Surfaces Clean
The ends of the pipe must be kept clean and free of debris to achieve a complete fusion. Remove any ice, frost, snow, dirt or other contamination that may have collected on the ends of the pipe that will be fused. The pipe ends can also slip within the fusion machine when they are dirty. Since this can result in a failed fusion, cleanliness is critical.
Keep an Eye on the Temperature and Bead Size
Always monitor the ambient temperature when fusing polyethylene pipe and be prepared to make any adjustments as needed. Fusion parameters, especially your heating time, may need to be adjusted. As it gets colder out, it will take longer for the pipe to melt against the heater and reach the adequate bead width size. If any changes are made to fusion procedures, test fusions must be conducted as well as validation of the quality of the joints with side bend tests and visual inspections. Bend back tests have been performed in the field for years. This testing method places the entire wall thickness into tension and gives assurance of the ductility of joints. If no gaps or breaks are present in the fusion joint after the test, the result is a passing grade.
Please note that increasing the heater temperature and increasing the pressure during the heat soak to compensate for cold weather conditions is not recommended. Keep your heater surface temperature between the normally recommended 400°F to 450°F and maintain the pipe manufacturer’s recommended pressure settings and the minimum heat soak time according to the pipe’s wall thickness. Once these steps are followed, it is critical for the operator to allow the appropriate bead size to be achieved. If the joint does not pass a visual inspection, cut it out and make another butt fusion joint with the correct procedures.
Most U.S. pipe manufacturers have pictures and a good description of a proper butt fusion joint. Always consult the pipe manufacturer’s recommended parameters and procedures. For pipe outside the United States, use the temperatures prescribed by the applicable company, local, state, or federal standards.
Make it Quick
After the minimum heat soak time has passed and the adequate bead size has formed, remove the heater from the molten pipe ends and bring them together. Heat will escape rapidly when the melted pipe material is exposed, so this process should be done smoothly and rapidly — in three seconds or less. Take quick note of the melt patterns on both ends of the pipe. The melt patterns need to be even to form a good fusion.
Do watch for pipe slippage in the fusion machine. Polyethylene pipe becomes stiff in cold weather and the outer diameter can shrink, making it prone to slippage and causing a bad fusion.
Tips for Coiled Pipe
Coiled pipe is also uniquely effected in temperatures below 40°F (4.44°C). For easier handling, it is best to uncoil the pipe and allow it adequate time to straighten out before starting the fusion process. When removing packaging straps, watch out for the ends of the coiled pipe, which sometimes spring loose forcefully. Once the pipe is laid out, soil can be placed over it intermittently to weigh it down and keep it flat.
Extremely cold, coiled pipe can be stiff and difficult to uncoil. The ends can shift inward and have a toe-in appearance. In this situation, the distorted pipe ends can be removed by cutting off 3 to 5 feet to create a straight section. This will make it easier to handle and easier for operators to fuse and make tie in and fitting connections.
Using the proper hydraulic oil is mandatory to achieve maximum performance and machine life. Data logging information from the fusion process helps increase accountability on tough jobs and ensures that joints were properly fused before lines go into service.
Examples of statistics to record are ambient temperature, pipe temperature and weather conditions for each joint along with the pressures, heating times, open/close and fuse/cool times. Consider taking photos of the bead up and the final fusion to confirm visual inspection and provide better analysis of each fusion and job.
Jim Johnston is the Chief Innovation Officer at McElroy. He recieved the Plastics Pipe Institute 2019 Member of the Year award for his pursuit of standardizing practices and educating the industry and end users on heat fusion technology. He has also given his time and expertise to support the use of HDPE pipe in water and waste water applications as part of the Municipal Advisory Board, AWWA, at trade shows and in the development and writing of technical documents.