So far, the industry hasn’t been able to establish a non-destructive test method which indicates us which it will be the behaviour of the long-term butt welding for polyethylene (PE) pipes.
As it can be done non-destructive testing in pipes, we should always do an exhaustive control of the welding parameters, the cleanness of both parts to be joined, the temperature of the sheet and the times to have a higher safety of the job that we are doing.
Besides, this limitation makes more appropriate to remember which destructive testing can be done in electrofusion and butt welding.
Which testing is done in the butt welding?
Firstly, it must be pointed out that it is the normative UNE-EN 12814 the one which regulates the destructive butt welding testing in semi-finished thermoplastic products. According to it, we distinguish the following types:
- Bending testing
- Tensile testing
- Tension creep testing.
In the bending testing, a section of the polyethylene pipe, cut transversally and with a thickness higher than 3 millimetres, joined by a butt welding, is subjected to bending. From this, it derives a bending angle to the break which results to be between 151.26 and 153,88 grades, with forces that go from 12552 N up to 14999 N and without producing a break. Both the bending angle like the highest strength are recorded and the surfaces in which it is achieved similar results which after that are examined with the aim of detecting fragile areas.
In the tensile testing, according the normative ISO 13953, it is applied a speed of five millimetres/minute in pipes of PE 100 DN 500 x 45.4 SDR 11 PN 16 bar. The samples extracted longitudinally from the join of the pipe show us if the break is ductile (it suffers material removal in the break) o fragile (there is no break). In the ductile break, the welding conserves certain lengthening and resistance to the break.
TENSION CREEP TESTING
The tension creep testing of welded joins subjected a sample to a load which is applied constantly up to producing the break. When this arrives, it is recorded the time which has delayed to arrive and it is measured its size. This method helps to compare the difference between different welding, under the same parameters, if the break starts after or before. In order not to take too much time, in some occasions it is used in the welded samples some substances like tensoactives as a means of contact.
>>> Testing the resistance of the samples welded under hydraulic pressure is also a more and more common check. It is usually used chemical agents or high temperatures to test the breaking resistance of the welding, a very useful method and which detects quickly if a butt welding hasn’t be dome with every guarantee.