Method for joining spiral wound pipes

A method of joining thermoplastics pipes (1) made by spiral winding of a hollow profile (2) with mainly rectangular cross section, characterized by the following stages:

• cutting an end of the pipe to be joined along an inside of a profile side wall that is fastened to a nearest preceding wound round of said profile, and with a section (3) that is cutting an outermost end of the profile in a right or an obtuse angle (α), of equal size for all ends of the pipes to be joined together,
• closing holes in such cut profile ends (3), and preparing the end surfaces of the pipes (1) to be joined along their entire peripheries, to present an even surface,
• positioning the two pipes (1) in alignment with each other so that the cut profile ends (3) are axially offset,
• inserting a disc-formed welding ring (5), having dimensions matching with the inner and outer diameters of the pipes;
• between the two pipes (1) to be joined, which welding ring comprises at least one loop of a resistance wire (6) covered by a thermoplastics sleeve (7),
• centering the two pipes (1), with an inner root support (8) and an outer root support (9) around the welding ring (5) and adjacent pipe ends,
• pressing said pipe ends together against each other,
• connecting the resistance wire (6) of the welding ring to a current source (12) for heating the thermoplastics material in the welding ring (5) and the thermoplastics material in the adjacent pipe ends so that the thermoplastics materials melt and form a welding seam,
• cooling the welding seam,
• removing the root supports (8, 9) and other accessories (10, 11) from the pipe welded together, and
• cutting off connecting wires (13) of the welding ring.