- Features of the design of polypropylene pipelines
- Preparation of materials
- Socket welding of polypropylene products
- Required tools
- Preparation for welding
- Welding procedure
- Connection defects and their causes
We will understand the technological features of the design and installation of pressure polypropylene pipes, we will master the rules and subtleties of socket polyfusion welding of products based on propylene. Consider the causes of possible connection defects and learn how to avoid them.
The physical properties of polypropylene dictate specific requirements for the planning and installation of the piping system.
Features of the design of polypropylene pipelines
Polymer articles tend to shrink when cooled and lengthen when heated. The characteristic does not affect systems with cold water, but is relevant when planning heating systems and hot water supply.
There are several options for compensating linear expansion of pipes with a length of more than 5 meters. The natural flexibility of the polymer is used in corner sections that are anchored in sliding bearings and flex with temperature fluctuations.
U-shaped expanders made from couplings and pieces of pipes work in a similar way..
Factory-made loop-shaped expansion joints are suitable for damping expansion in the range of 45–80 mm, depending on the pipe diameter.
Another simple and quick solution is the installation of an axial expansion joint, equipped with fasteners and taking up a minimum of space.
When replacing pipes within the bathroom, a movable fastening of the mains is designed, which ensures the free movement of pipelines in the supports and does not require additional expansion joints. When laying pipes in channels and shafts, the risers are placed away from the walls, thereby increasing the bend shoulder.
Preparation of materials
Taking into account the peculiarities of the operation of the future pipeline, choose a suitable type of polypropylene pipes, divided into classes and having different markings:
- For cold water – PN10, PN16.
- For hot – PN20.
- For heating systems – PN25.
There is little price difference between the brands PN20 and PN16, therefore, with a complete replacement of communications, PN20 pipe is usually used for all water supply systems. The equipment is supplied with thin pipes (21.2 – outer diameter), thicker products are used for risers and connecting several consumers.
A water supply scheme is preliminarily made, internal highways are designed on welded couplings, detachable connections are planned in places accessible for inspection. Based on the created drawings, the length of the pipes and the number of components are calculated.
An example of wiring polypropylene pipes in a bathroom: 1 – ball valves; 2 – a square with a mount for connecting a toilet bowl; 3 – polypropylene tee; 4 – polypropylene pipes; 5 – double elbows with fasteners for connecting sink and bath mixers; 6 – polypropylene corner 90 °
Socket welding of polypropylene products
Polypropylene pipes with a caliber of up to 63 mm are connected by means of socket welding. Two pipes are joined using a third element – couplings, and threaded assemblies are organized using flared fittings.
For self-welding of a polypropylene pipeline you will need:
- Polyfusion welding machine, nozzles of the right size.
- Contact thermometer.
- Tape key.
- Electric carrying extension cord.
- Pipe cutter for plastic pipes.
- Roulette, marker, sharp knife.
- Degreasing alcohol.
- Rag made of natural fabric.
- Mounting clamps.
It makes no sense to purchase a welding unit for one-time use – it is more advisable to rent a full set of tools, including everything you need for installation work.
Preparation for welding
Before welding, carefully examine all material for deformations. Check the fittings by putting them on the nozzle – parts that are “sitting” too loosely are rejected. The serviceability of valves and taps is monitored, the threads are driven with a counterpart.
A test cut of the pipe is carried out with scissors, in the case of squeezing the walls of the product, the working parts of the tool are sharpened.
The welding unit is placed on a flat surface, attachments are attached. By setting the temperature regulator to 250–270 ° C, turn on the power to the device. After warming up the device (10-15 minutes), clean the nozzles with a tarpaulin cloth from the dirt left over from the previous welding. They begin to work after warming up the instrument to 260 ° C, as evidenced by the indicator and check the temperature of the nozzle with a contact thermometer. Then proceed directly to welding:
- Cut the pipe to the desired size at right angles, taking into account the entry into the fittings.
- When sawing with a hacksaw for metal, the edges of the cut are cleaned from burrs with a knife.
- When processing aluminum-reinforced pipes, the plastic and foil are removed by stripping for the length of the weld.
- At the edge of the pipe, a chamfer is cut at an angle of 30-45 °.
- Place a marker at a risk at a distance corresponding to the depth of the fitting plus 1–2 mm.
- The surfaces to be welded are cleaned and degreased.
- Put a sleeve on the heated nozzle, then insert the pipe into the sleeve, pushing it to the mark.
- Withstand both parts for the same time according to the technical parameters of welding.
- At the end of heating, the polypropylene products are removed and the fitting is pushed onto the pipe with a measured movement to the mark, excluding the slightest axial rotation.
- A fresh seam is fixed for 20-30 seconds to partially cool the joint, sufficient to hold the pipe in the sleeve.
- Leave the connection still for 3-4 minutes, avoiding any bends.
- They check the visual quality of the joint made.
In the process of work, they monitor the cleanliness of the Teflon coatings of the nozzles, remove plastic residues.
Technical parameters of welded joints
Pipe diameter, mm Welding joint length, mm Time Heating, sec Expectations, sec Cooling, min 20 fourteen 6-8 2-5 2 25 15 8-11 4-8 2 32 17 9-12 6-10 4 40 18 12-16 6-15 4 50 20 14-18 6-15 4 63 26 22–32 8–20 6 75 29 30-40 10-30 6
A correct welded joint has a solid bead of molten plastic at the edge of the socket. Unsuccessful docking is corrected only by removing the fitting and installing a new one, so it is better to practice a little on the scraps and understand the intricacies of welding.
Connection defects and their causes
Absence or separation of the shoulder from the weld:
- Heating temperature exceeded.
- Excessive attachment length.
- Deviation from heating time.
Low shoulder height:
- Low heating temperature.
- Insufficient warm-up time.
- Inconsistency of diameters of parts.
Oblique joint: misalignment of fitting and pipe.
Out-of-roundness of the edges: incorrect fixation of workpieces.
- Damaged pipe surface.
- Axis offset when connecting.
- Significant deviations in the dimensions of parts.
- Dirty surfaces.
- Burn plastic on the attachments.
Partial weld length:
- Insufficient temperature.
- Short heating time.
- Docking time exceeded.
- Uneven pipe end.
Narrowed passage at the welding point:
- Excessive docking pressure.
- Overheating of materials.
A trial filling with water is carried out one hour after the completion of the last joint. Having released the air at the upper points of the system, fill it with water and hold the pressure for 30–40 minutes. Having examined the water conduits, they are convinced of the absence of leaks.
Mastering the soldering of polypropylene units is the main task solved when replacing old pipes. Otherwise, the installation of this type of pipeline is carried out in accordance with generally accepted standards..