RU2465560C1 - Strength testing method of butt welded joint of polymer pipes - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: testing method of butt welded joint of polymer pipes for determination of strength of the weld consists in test of specimens of blades of the above weld joint at expansion speed of clamps of the test machine of (20÷50) mm/min. Specimens of blades with defects applied prior to welding are tested, owing to which the welding surface area is not more than or equal to section of working part of parent material of blade specimen.

EFFECT: determination of strength of butt welded joint of polymer pipes along the butt weld considering the influence or exclusion of the contribution of burrs both of external, and internal or middle part of welded pipe.

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Description

FIELD OF THE INVENTION

The invention relates to the field of testing a welded butt joint of polymer pipes and can be used to determine the strength of a welded joint at the joint of welding of polymer pipes.

State of the art

A technical solution is known (1. Design and construction of gas pipelines from polyethylene pipes and reconstruction of worn-out gas pipelines SP 42-103-2003. Official publication. Polymergaz CJSC: Moscow 2004. - P.75), in which, in order to determine the quality of the welded joint, machining of sample-blades of type 2 according to GOST 11262, where the investigated weld should be located in the middle of the sample with an accuracy of ± 1 mm. Before the test, the samples are conditioned in accordance with GOST 12423 at a temperature of (23 ± 2) ° С for at least 2 hours. The tests are carried out at a speed of separation of the clamps of the testing machine equal to (100 ± 10) mm / min for pipe samples with a nominal wall thickness of less than 6 mm and (25 ± 2.0) mm / min for pipe samples with a nominal wall thickness of 6 mm or more. During the test, the nature (type) of fracture of the samples, as well as the elongation at break and the yield strength under tension, are determined. The disadvantage of this technical solution is the inability to determine the strength of the welded butt joints of polymer pipes at the weld joint.

The closest is the technical solution (2. G.K.Kaygorodov, V.Yu. Kargin. The influence of the cooling rate of a polyethylene weld on its strength // Pipelines and ecology. - 2001. - No. 2. - P.13-14), where the dependence of the properties of the weld such as elongation and yield strength on the cooling temperature is given. Samples for studying the effect of the cooling rate on the strength characteristics of a welded joint are obtained from polyethylene pipes heated to 180 ° C, followed by cooling at various temperatures. The disadvantages of the method are the absence of the operation of deposition under a certain pressure for a particular pipe size, due to which the burr is formed, and the inability to study the effect of the burr on the strength, both external and internal, which are formed during real butt welding of polymer (polyethylene) pipes, as well as the inability to determine the strength of the welded butt joint of polymer pipes at the weld joint.

Disclosure of invention

The task of the invention is the development of a method for determining the strength of a welded butt joint of polymer pipes at a weld joint.

The technical result obtained by the implementation of the invention is to determine the strength of the welded butt joint of the polymer pipes at the weld joint, taking into account the influence or exclusion of the contribution of the burr of both the outer and inner or middle parts of the welded pipe.

The essential features characterizing the invention.

Restrictive: tests are carried out at a speed of separation of the clamps of the testing machine equal to (20 ÷ 50) mm / min. The tensile strength is determined.

Distinctive: blade samples are made from a welded joint zone containing an artificial defect, where the welding area is equal to or less than the cross section of the working part of the tested sample blade.

It is known that the strength of a welded butt joint of a polymer pipe is less than the strength of the material of the polymer pipe itself, however, during testing, the formation of a “neck” occurs along the main material of the polymer pipe due to the larger cross-sectional area at the weld joint due to the formation of external and internal burrs (1. Design and construction of gas pipelines from polyethylene pipes and reconstruction of worn-out gas pipelines SP 42-103-2003. Official publication. Polymergaz CJSC: Moscow 2004. - P.52, 75).

Brief Description of the Drawings

Figure 1 shows a template with artificially applied defects for examining the strength of a welded butt joint so that the actual welded area is equal to or less than the cross section of the working part of the sample blade. The section of the welded pipe along the plane of the template is shown below. 1 - the location of the pipe during welding, 2 - the cutout for welding the ends of the pipe, 3 - the material that prevents the welding of the ends of the pipe, 4 - the area of the welded end of the pipe, 5 - grata external, 6 - grata internal, 7 - the width of the cut sample of the blade. Figure 2 shows a template with artificially applied defects for studying the strength of a welded butt joint without taking into account the influence of external or internal burr. The section of the welded pipe along the plane of the template is shown below. Figure 3 shows a template with artificially applied defects for testing the strength of a welded butt joint. The section of the welded pipe along the plane of the template is shown below. Figure 4 shows the scheme of deposition under pressure of a welded butt joint with an artificially applied defect (template). 8 - template, 9 - polymer pipe, 10 - clamps of welding equipment.

The implementation of the invention

The method is as follows. For the studied welded butt joint of the polymer pipe of a given size, templates of thin material 3 are prepared in advance, which prevents welding of the ends of the pipe 1, for example, of paper for office equipment “Snegurochka”, according to FIGS. 1, 2, 3 or other combinations of artificial defects. Cutout 2 for welding the ends of the pipe is located so that in the samples of the blades for tensile testing, the areas of the welded sections 4 are equal to each other, and equal or not larger than the cross section of the working part of the main material of the sample of the blade 7. Then the ends of the welded polymer pipes 9 are installed in the clamps of the welding equipment 10, centered on the outer surface, the pipe end roughness is cut, the pipe ends are brought into direct contact with the material melted at or above the melting temperature pipes with a tool having a flat reflow surface, then the tool is removed, and one of the prepared templates is introduced instead, and the fused ends, between which the template 8 is located, are deposited under pressure and kept under this pressure for a certain time, dictated by the cooling rate and relaxation processes in the welded connection (figure 4). Material displaced from the joint under upsetting pressure forms an external 5 and internal 6 welding beads, as in conventional welding without using a template. Then, 24 hours after welding, type 2 blades are made according to GOST 11262 uniformly along the perimeter of the weld of at least five samples so that the welding area is in the middle of the sample blades. Tensile tests of blade samples are carried out in accordance with GOST 11262. Processing of the test results is carried out by accepted methods. Since the region of the welded joint has the least strength, then, provided the cross section of the sample-blade and the weld joint are equal, the destruction occurs at the joint of the welded joint.

Thus, by the proposed method, it is possible to determine the strength of the welded butt joint of polymer pipes at the weld joint, taking into account the influence or exclusion of the contribution of the burr of both the outer and inner or middle sections of the joint of the welded pipe.

Claims (1)

A method of testing a welded butt joint of polymer pipes to determine the strength of a weld, which consists in testing samples of the blades of the specified welded joint at a speed of separation of the clamps of the testing machine (20 ÷ 50) mm / min, characterized in that the tested samples of the blades with pre-applied before welding defects due to which the welding area is not greater than or equal to the cross section of the working part of the main material of the sample of the blade.

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