Assembly : Methods

HDPE Pipe technical guidance (High quality Polyethylene Pipes)

What is electrofusion?

Electrofusion is a simple method of joining PE pipes in circumstances where butt fusion is not practicable, such as where valves, elbows, and tees must be added. Prefabricated fittings are used, incorporating an electrical heating coil which melts the plastic of both the fitting and the pipe, causing them to fuse together. The characteristics of the fitting to be welded, such as the fusion time, are registered via a barcode on the fitting. An electrofusion control unit (ECU) supplies the...

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What is butt fusion (hdpe welding) ?

Butt fusion is a thermofusion process Butt fusion involves the simultaneous heating of the ends of two pipe/fitting components which are to be joined, until a molten state is attained on each contact surface. The two surfaces are then brought together under controlled pressure for a specific cooling time and a homogeneous fusion joint is formed. The resultant joint is fully resistant to end loads and has comparable performance under pressure to the pipe itself. An electrical heater plate is...

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What is mechanical assembly?

Mechanical assembly requires the use of fittings, generally working on the compression principle, to join different materials together. It is most commonly used with PE for joining the PE to a pipe or fitting of a different material, or in circumstances where fusion is not feasible. Mechanical fittings generally include a stiffener which is placed inside the pipe or fitting to ensure stability when the fitting is compressed. These stiffeners are also designed to withstand end loading where...

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What methods can be used to assemble a PE pipe network?

PE pipe can be assembled into a pipeline network by means of fusion or mechanical assembly techniques. Fusion of PE pipe and fittings may be by either Butt Fusion or Electrofusion. Other techniques are available (socket fusion and induction fusion) but are not commonly available and will not be considered here. Fusion Fusion comprises applying heat and pressure for a specified time to the mating surfaces to be joined. The application of heat and pressure under the correct conditions allows the...

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Under what circumstances are the different methods used?

Butt fusion Butt fusion can be used for jointing pipes and fittings 63mm diameter and larger. However it is most commonly used for larger diameter pipes. Butt fusion jointing is equally suited to both coiled and straight pipe lengths. Only pipes and fittings of the same nominal diameter may be butt fused. Butt fusion can be used in new installations using traditional open cut trenching techniques. Additionally due to the low profile of the butt joint it is ideal for use in trenchless technology...

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What special equipment is needed for each assembly method?

Butt fusion To ensure that good quality butt fusion joints are made it is essential that the correct equipment is used. The equipment used must be robust enough to handle the size and weight of the pipe to be joined. It is essential that the correct pressures be maintained on the pipe ends during each phase of the procedure to achieve this only hydraulically operated equipment should be used. Many modern butt fusion machines include data logging facilities of the fusion process and parameters...

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Can different grades of PE be connected to each other?

Butt fusion It is possible to butt fuse pipes and fittings of different grades and SDR, but this should only be carried out under controlled conditions. In case of doubt please contact the pipe and or fitting suppliers. Electrofusion Similarly different grades and SDR's of pipe can be connected using electrofusion, again only under controlled conditions. Special care needs to be taken to avoid collapse of thinner pipes during the fusion period. Electrofusion fittings may also be of different...

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Are there any standards or codes of practice applicable to the assembly methods?

The major users of PE piping systems have developed codes of practice for fusion assembly. Many of these have become national standards. Butt fusion Butt fusion procedures require the application of temperature and pressure over time to the mated ends of the pipes or fittings. The procedures developed in different European countries are all similar in principle but different in detail. All have been tested and all produce satisfactory joints when the procedures are followed correctly. The...

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What training is necessary for operatives to assemble PE pipe networks?

A fusion operator badge is required for all personnel involved in fusion techniques during the construction of PE gas networks. This badge must conform with ISO 12176 Part 3, and is granted after completing a training course and passing a qualification exam. In most countries the badge has a validation period of 1 to 2 years after which it must be renewed by repeating the examination. A typical badge is shown on the right, click the image to enlarge. Every fusion operator must carry his badge...

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How can I verify that the correct assembly procedures have been followed?

Traceability is an integral part of modern, sophisticated, Quality Assurance systems used for PE pipe networks. The systems available, and mandatory at many end-users, enable tracing through the whole process, from the resin batch at the PE producer, through pipe extrusion, the utility company and the installation contractor's operations. All installations can be traced back to the resin batch from which they were produced, with full data on the history of the pipe or fitting at any...

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What procedures are used for testing the assembly?

Different methods of testing finished fusion joints in PE pipes have been developed in different European countries. They vary in their fundamental approach to the question of how a joint should be tested. At present work is proceeding among the relevant experts to establish a harmonised European method under a CEN standard. As soon as this is publicly available a summary of the approach will be added to this Paper.

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Members of the Association

BOREALISBOROUGEINEOS O&PIRPCKorea Petrochemical IND. Co., LTD (KPIC)LyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE
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