Calculation of the bending radius of polyethylene pipes

Bending of pipes made of cross-linked polyethylene (PE) is directly related to deformation stresses, compressing the material on one side of the bending radius and tensile on the other. If the forming rules are observed, it is possible to avoid dangerous overvoltages leading to damage to the tubular product. To do this, it is necessary to correctly calculate the minimum bending radius of HDPE pipes, which is permissible when working with workpieces of this type.

Concepts and norms

Polyethylene belongs to sufficiently strong and at the same time plastic structures, which makes it possible to heat it to a softened state and give products the desired shape. With a well-organized molding process, critical violations of the material structure, as a rule, are not observed.

These properties allow the use of polyethylene blanks for the installation of pipelines, since in this case it is easy to bend around obstacles or change the direction of the intended laying. The minimum bending radius of a typical polyethylene pipe is understood as the limiting indicator at which it retains its resistance and does not break.

This parameter, expressed in metric units, depends on the following factors:

1. Tubular wall temperatures.
2. Technical parameters relating to its geometric proportions.

The latter refers to the SDR indicator, which is the ratio of the outer diameter of the pipe billet to the declared thickness of its walls.

Important! A regularity is valid, according to which, with an increase in SDR and the heating temperature of the walls, it is allowed to make a bending arc of a smaller radius.

It is these input data (SDR and material or ambient temperature) that must be adhered to when calculating the safe bending index for operation.

Methods for forming HDPE pipes

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To bend typical HDPE pipes in a domestic setting, you should use proven methods successfully used by craftsmen. Among the known approaches to this process, the following methods stand out:

• The use of a soldering or building hair dryer.
• Filling the cavity of the pipe with hot water (boiling water).
• Filling it with a loose composition heated to 80-90 degrees (salt or river sand).

Bending a plastic pipe at home is also allowed in other ways (with a gas burner, for example).

Note! The simplest approach is also possible, which consists in heating the pipe billet in the sun in the summer.

But this method of straightening the pipeline is realized only in very hot weather (at an air temperature of at least 30 degrees).

With a large volume of pipe blanks and the need to bend them with high precision, special forming equipment will be required. It is in demand in industrial production and is rarely used in everyday life.

Necessary tools and materials

In order to bend a plastic pipe based on low pressure polyethylene in various situations, the following tool may be required:

• special molding machine;
• building or powerful soldering dryer (with the possibility of changing the operating temperature);
• conventional gas burner;
• bending template, made taking into account the required forming angle.

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Each of these tools is suitable for a specific bending method and can be used at home. When laying a water pipe in a garden plot, it is recommended to use branded elements that provide reliable flange joints.

Their list is given below:

• Adapters for PE products.
• Tees and saddle angles.
• Fittings manufactured specifically for connecting HDPE pipes.

In addition, to join sections of different materials (stainless steel and PE, for example), you will need to stock up on DRC couplings.

And for the design of reliable branches within the area to be equipped, it is most convenient to use Fischer saddle branches, which are always available on the open market.

Calculation of the minimum diameter for a given length

For approximate calculations of the bend radius, two rigid rulers of 30 and 50 cm length will be required (their choice depends on the amount of bend). The procedure looks like this:

• First, the bend radius of the already formed pipe is measured, which must be copied to the original workpiece.
• When measuring a strong bend, a 30 cm ruler is taken and applied to the ends of the bent pipe, after which the distance between it and the middle of the workpiece is measured.
• With a small bend (greater pipe length), the same operations are done with a 50 cm ruler, as shown in the photo below.

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A — interval (clearance), mm.

D – arc diameter, mm.

R is the radius to which the pipe is supposed to be bent, mm.

To understand what the desired parameter R is, one should be guided by the photo below in the text, which shows a sample of an already bent workpiece.

Based on the data obtained during the measurements, then you need to select a suitable indicator of the radius (diameter) of the arc, the values ​​​​of which can be found in specially prepared tables. They are placed in sources on the Internet (where various options for preliminary measurements are taken into account).

Bending at an angle of 90 degrees

Often, when arranging a pipeline, a perfectly right angle is required, for which it is most convenient to use a bending template. It is a base in the form of a suitable size fibreboard with the right angles. The main condition for the admissibility of bending according to a template is the smooth heating of the bending zone, which excludes the possibility of breaking the structure of the material.

Additional Information! If it is necessary to arrange a pipe bend at 90 degrees, it is recommended to warm up a section whose length is equal to six of its diameters.

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Under this condition, the bend is smooth and even.

Expert advice
In the course of molding work performed by one of the described methods of bending blanks, it is recommended to adhere to the following rules:

• When heating a long fold, you should proceed slowly, performing this procedure in stages (smoothly moving from one molded area to another).
• It is forbidden to bring the building hair dryer very close to the HDPE product (otherwise it can simply be melted).
• Bending pipes of large diameter (up to 110 mm) is allowed only on special forming equipment.
• When self-manufacturing saddle branches, it is obligatory to control the heating temperature of the element.

Important! If the allowable value of 120 degrees is exceeded, the resulting angle may differ from the desired value in one direction or another.

It is allowed to start independent work with products based on polyethylene only after thorough preparation for these procedures. Before molding products, it is recommended to familiarize yourself with the materials presented in the article.