RU2410593C2 - Procedure for connecting pipes with internal coating - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: invention refers to pipelines connecting. The procedure consists in forming internal layers of weld seam and head-affected zone out of corrosion resistant steel and in successive application of insulation layer on internals surface of pipe. Preliminary, under plant conditions during pipe fabrication there is introduced an additional element out of corrosion resistant steel made in form of a ring and corresponding to a section of a pipe with external diameter equal to diameter of the said pipe, while internal diameter of the section of the pipe is equal to internal diameter of the insulation layer of the pipe. The section is connected with an end part of the pipe out of carbon steel by means of laser, electric-arc or high-qualitative welding producing qualitative weld connection. Also, the end part of the pipe is formed as reinforced rings. Under field conditions pipes are connected with reinforced rings out of corrosion resistant steel by means of electric-arc welding into the pipeline to achieve welding of high quality. Notably, insulation is applied partially on internal side of the seam of rings out of corrosion-resistant steel and basic material ensuring insulation of this joint.

EFFECT: increased reliability of welded pipe connection.

Description

The invention relates to the installation of pipelines and can be used in chemical, petrochemical, oil and gas and other industries when laying pipelines with an internal insulating coating.

The most common way to protect pipe metal from the aggressive effects of transported media is to apply a layer of an insulating anti-corrosion coating, such as polyethylene, to the inner surface of the pipes.

However, when connecting pipes with an internal polymer coating by welding, there is a significant problem - burnout of the coating in the heat-affected zone. Naked weld metal undergoes degradation during prolonged contact with aggressive media, which can cause an accident.

A known method of connecting pipes with an inner coating (AS USSR 1560873, application No. 4371764 from 01.02.88, BI No. 16, 1990, F16L 13/02). This method consists in fixing strips of glass-enamel fabric on the inner surface of the end sections of the pipes. The strips are fixed so that they extend beyond the edges of the joints. Then the pipes are joined. In this case, the enamel fabric sections protruding beyond the ends of the pipes overlap each other at the junction of the pipes. Joined pipes are welded around the perimeter from the outside. Due to the heat generated during welding, the glass-enamel fabric at the site of the weld is partially melted. To completely melt the enamel fabric and create a uniform, continuous, corrosion-resistant layer in the pipe connection zone, the docking area is subjected to additional heating to the enamel melting temperature, for example, by an inductor.

The disadvantages of this method include the increased technological complexity and complexity. Time-consuming installation of glass-enamel tape inside the pipes leads to a significant slowdown in the installation of the pipeline.

A known method of connecting pipes with an internal anti-corrosion coating (RF Patent No. 2080509 from 05/27/97, application No. 94015756 from 04/27/94, BI No. 15, 1997, 6 F16L 13/00), in which the pipe is connected by articulating them with after the intermediate element, hot air is supplied through the fittings into the cavity between the intermediate element, elastic seals at its ends and the inner surface of the pipes after welding. Fill with liquid hardening material. Purge the cavity with hot air until a solid protective film forms. Then the cavity is filled with non-hardening anticorrosive material.

The disadvantage of this method is the technological complexity, as well as the inconsistency of the cross-sectional shape along the length of the resulting pipe connection. This can lead to the formation of turbulent vortices during transportation of liquid media and, as a result, to dynamic loads and structural failure.

The closest in technical essence to the claimed method is a method for connecting enameled pipes (A.S. USSR 372403 from 01.03.73, application No. 1307401 / 29-14 from 03.03.69, BI No. 13, 1973, F16L 13/02) in which a layer of corrosion-resistant steel of variable cross section with a slope to the end of the pipe and subsequent enameling of the remaining pipe is applied to the end sections of the inner surface of the pipe.

The disadvantages of this method are the technological complexity, as well as the need for electric arc welding in the field of two-layer pipes with the formation of a mixing zone of dissimilar metals, in which a large number of defects - cracks, pores, etc.

The technical problem to be solved of the method of connecting pipes with an inner coating is to increase technological capabilities by simplifying installation, improving the quality and reliability of structures, and increasing the productivity of piping.

The task is achieved by the fact that in the factory, in the manufacture of pipes, an additional element of corrosion-resistant steel is introduced, made in the form of a ring, which is a pipe segment, the outer diameter of which is equal to the diameter of the pipe, and the inner one is the inner diameter of the pipe insulation layer, and connected it with the end part of the carbon steel pipe using laser, electric arc or high-frequency welding, with the possibility of obtaining high-quality welded joints, while receiving the end part of the pipe in the form of thickened rings, then, in the field, connections are made with thickened rings of corrosion-resistant steel of the pipe end parts using electric arc welding into the pipeline to obtain a high-quality welded joint, the insulation being partially applied to the inner side of the joint of the rings made of corrosion-resistant steel and main material, providing sealing of this place.

The manufacture of pipes with lugs in the form of stainless steel rings greatly simplifies the technology of installation of pipelines, avoids the use of additional transitional devices that violate the constancy of the internal section of the pipe along the length of the connection. In addition, the proposed method eliminates the need for welding of two-layer clad pipes in the field with the formation of a defective mixing zone of dissimilar materials.

Here is an example implementation of the method. For experimental substantiation of the possibility of obtaining high-quality welded joints of pipes with stainless steel lugs, two experimental pipes were produced by the claimed method. Each pipe was made as follows: rings (coils) 150 mm long were cut from the ends of the pipe billet from steel 20 (length 6 m, diameter 273 × 9 mm). Then, rings of steel 08Kh18N10T were welded by electron beam welding to the ends of the workpiece subjected to machining to ensure the required roughness of the abutted surfaces Ra = 12.5 μm, while welding was performed with the electron beam shifted to the edge of austenitic steel. Following this, an experimental electric arc welding of the butt joint of the pipes obtained was carried out using the technology of welding stainless steel pipes using austenitic electrodes TsL-11.

Samples cut from welded joints of stainless rings and the base metal of the pipe, as well as samples made from the connection of two rings from 08Kh18N10T steel, were subjected to comprehensive studies in order to assess the quality of joints. Metallographic studies of weld metal, mechanical tests of samples for static bending, static tensile strength and impact strength, as well as testing of welded joints for susceptibility to intergranular corrosion, showed that the properties of the obtained compounds satisfy the requirements of normative and technical documentation. The resulting fragment of the pipeline fully meets the requirements of strength and reliability.

The advantages of the proposed method in comparison with known analogues.

The proposed method for producing a welded joint of a pipeline with an internal insulating coating in comparison with analogues provides a significant acceleration of construction and installation works by eliminating labor-intensive technological operations. The assembly joints obtained by this method made in the field by electric arc welding are durable and reliable, since the welds of the joined elements do not contain a mixing zone of dissimilar metals, in which a large number of defects are localized.

Claims (1)

The method of connecting pipes with an inner coating, which consists in the formation of the inner layers of the weld and heat-affected zone from corrosion-resistant steel, followed by applying an insulating layer to the inner surface of the pipe, characterized in that an additional element of corrosion-resistant is introduced in the factory for the manufacture of pipes steel, made in the form of a ring, which is a piece of pipe, the outer diameter of which is equal to the diameter of the pipe, and the inner to the inner diameter of the insulating layer pipes, and connect it to the end part of the carbon steel pipe using laser, electric arc or high-frequency welding with the possibility of obtaining high-quality welded joints, while receiving the end part of the pipes in the form of thickened rings, then in the field make connections with thickened rings of corrosion-resistant steel of the end parts of pipes using electric arc welding into the pipeline to obtain a high-quality welded joint, and the insulation is partially applied to the inner side of the joint of the rings from corrosion-resistant steel and base material, providing sealing of this place.