Fusion joints

The electrochemical examination of fusion joints between nine pairs of dissimilar metal couples in seawater showed that in most cases the HAZ was anodic to the weld metals" . Prasad Rao and Prasanna Kumarundertook electrochemical studies of austenitic stainless steel claddings to find that heat input and 5Fe content significantly affected the anodic polarisation behaviour under active corrosion conditions whilst Herbsleb and Stoffelo found that two-phased weld claddings of the 24Cr-13Ni type were susceptible to inter-granular attack (IGA) as a result of sensitisation after heat treatment at 600°C /pa was unaffected by heat input. 

ISO/TR 11647 1996 Fusion compatibility of polyethylene (PE) pipes and fittings ISO 12176-1 1998 Plastics pipes and fittings - Equipment for fusion jointing polyethylene systems - Part 1 Butt fusion... 

Joints of all sizes may be made with heat fusion techniques. Fused joints may be made with either electrofusion or conventional heat fusion. Electrofusion joints are made with fittings which have embedded heating wires. Conventional fusion joints are made with special machines which trim the pipe ends, apply heat, and then force them together to form a bond. Consult the manufacturer regarding the sizes for which electrofusion fittings are available. 

A gas distribution system can be assembled using compression fittings, similar to those used on domestic water pipes, for pipes of diameter <63 mm. However, fusion joints which caimot leak, are more common. Socket fusion, used to join pipes of sizes up to 125 mm, involves the use of an injection-moulded socket that fits on the pipe ends. A simple socket allows straight continuation of the pipe, whereas 45 and 90° elbows allow sharp corners, and equal tees allow branches to be added. Butt fusion, used to make axial joints on pipes of diameter 63 mm and above, is preferred for diameters >180 mm. 

EN 1042 Fusion joints between polyolefin pipes and/or fittings - determination of resistance to internal pressure at constant temperature. 

When butt fusion joints are to be used inside the shell, the preparation for these inside welds should be inspected. 

For the characterization of polyolefin fusion joint pipes fittings and valves, one or more of the following tests should also be considered. 

Heat fusion offers 3 types of joints. They are butt joints, saddle joints, and socket fusion. There are two spinoff joints for producing socket- and saddle-heat-fusion joints. The concept of a heat-fusion joint is simple. You heat two surfaces to a specific temperature and them fuse them together with an application of sufficient force. Done correctly, the two materials mix together and form a joint. This type of joint can be as strong as the pipe being joined. When a fused joint cools to near ambient temperature the joint can be handled and worked with. 

After the heating application reaches the proper temperature, the heating device is removed and the pipe ends are put together to form the fusion joint. Consult manufacturer recommendations for interface pressure and the bead size of molten material required to make a solid joint. 

Standard inspection techniques should be followed for assessing quality of butt and electro fusion joints... 

In the case of PE, PP, and PVDFISYGEF ) heat fusion joints have practically the same chemical resistance as the respective material. In conjunction with media which cauld cause stress cracking, the fused joints can be subjected to an increased risk due to residual stress from the joining process. 

During are and gas welding, the workpieces to be joined and the filler material (i.e., welding rod) are heated to a sufficiently high temperature to eause both to melt upon solidification, the fOler material forms a fusion joint between the workpieces. Thus, there is a region adjaeent to the weld that may have experieneed microstructural and property alterations this region is termed the heat-affected zone (sometimes abbreviated HAZ). Possible alterations inelude the following ... 

ASTM DOT compliance testing was conducted at Continental Industries test facility in Broken Arrow, OK. Seven hundred forty seven (747) performance tests are complete or in progress to evaluate the use of PA 12 material for natural gas mechanical fittings. Most of the tests are eonducted with Performance 8100 PE gas pipe. PA 11 butt fusion joints have also been tested in our evaluation of PA 12 because that is the method Continental uses to join Con-Stab ID Seal stab fittings to the outlet of PA 11 mechanical tapping tees. Fusions were made with the same temperatures and melt times as used on PA 11 fittings. We did not experience any PA 12 fusion joints failures in the eourse of this evaluation. 

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