RU2448297C2 - Protection method of weld joint of pipes with inner coating against corrosion - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: method involves arrangement at connection point with overlap of end sections of pipe coating of inner protective sleeve and weld joint of pipes. Sleeve has corrosion resistant design and ends of its external surface are provided with O-rings located in annular grooves and made from elastic material, for example hydrophilic rubber, expanding during contact with water. Rings made from porous elastic material, which are saturated with water, are arranged tightly to O-rings on one side or both sides. Rings from porous elastic material can be located between two O-rings.

EFFECT: reducing material costs and labour intensity for implementation of the method.

3 cl, 3 dwg

Description

The invention relates to methods for protecting pipelines against corrosion and pipeline transport and can be used in the construction of pipelines with an internal anti-corrosion coating.

A known method of permanent connection of pipes with a protected inner surface, including forming the ends of the pipes in the form of sockets, applying an internal protective coating, installing a counter cylindrical sleeve with an internal protective coating inside the sockets and connecting the pipes together by butt welding. The sleeve is provided with sealing elements located on the cylindrical portion of the sleeve, and is made with an annular groove opposite the weld, which is filled with insulating material (US Pat. RF No. 2116549, class F16L 13/02, publ. July 27, 1998).

The disadvantages of this method are the high complexity of its implementation, associated with the need to form the ends of the pipes in the form of sockets, and the low efficiency of protecting pipe joints against corrosion due to insufficiently reliable sealing of the zones of the welded joints from the penetration of aggressive transported medium. The latter is due to the fact that the sealing elements (rings) are located on the cylindrical section of the sleeve and are pressed against the sockets and the sleeve only due to the elastic deformation of the rings created when the sleeve is inserted into the ends of the pipes. An aggressive medium under high pressure overcomes the elastic deformation of these rings and penetrates to the joint.

There is also known a method of connecting pipes with an inner coating, including expanding the inner diameter of the ends of the pipes before coating, placing at the junction with the overlap of the end sections of the coating an internal protective sleeve provided with a corrosion-resistant coating and having sealing elements on the outer surface at the ends and a ring of heat-insulating ring in the center material, and pipe butt welding. In this case, the sealing elements are placed in zones of variation of the inner diameter of the pipe ends, the outer surface of the sealing elements corresponds to the configuration of the inner surface of the pipes in these zones, and the longitudinal fit of the sleeve is larger than the corresponding size of the expanded pipe ends (US Pat. RF No. 2226637, class F16L 13 / 02, publ. 10.04.04, Bull. No. 10).

The disadvantages of this method are the complexity of forming the expanded sections at the ends of the pipes and the difficulty of joining the pipes when they are connected, since the joining requires force closing of the welded pipe edges to each other.

The closest in technical essence to the proposed one is a method of protecting pipelines from corrosion, including applying an anticorrosive coating to the inner surface of the pipes, placing in the pipes at the junctions of them protective sleeves equipped with an anticorrosive coating and having annular grooves on the outer surface along the edges with sealing rings of elasto-elastic material and in the center an annular groove filled with heat-insulating material, pipe connection by welding, while the weld zone between the sealing rings under pressure fill with a low corrosive plastic fluid by crimping the pipeline using this fluid (US Pat. RF No. 2229653, CL F16L 58/04, publ. 27.05.04, bull. No. 15).

The disadvantages of this method are the complexity and high cost of the process of filling the weld zone between the sealing rings with plastic fluid, because according to building standards, the pipeline is pressure tested usually with water, and additional pressure testing with special plastic fluid requires complete removal of this fluid from the pipeline cavity after pressure testing and its disposal . In addition, with a large diameter and length of the pipeline, very large volumes of this liquid are required, the cost of which is many times higher than the cost of water.

The objective of the invention is to reduce material costs and the complexity of the method.

The problem is solved in that in a method for protecting a welded joint of pipes with an internal coating from corrosion, including placement of protective sleeves in the pipes at the places of their connection, made in a corrosion-resistant design and having annular grooves on the outer surface along the edges with sealing rings of elastic material , and the connection of the pipes by welding, according to the invention, into the annular grooves of the protective sleeve before installing it, the tubes are placed in the rings of elastic material, expand contact with water, for example hydrophilic rubber, and process rings made of porous material, impregnated with water and interacting with the sealing rings, on one or both sides of the sealing rings.

The protective sleeve may be provided with additional o-rings of elastic material, expanding upon contact with water, placed in separate grooves on the side of the weld, while the technological rings of porous material, impregnated with water, are placed between the two o-rings.

The method is illustrated by the drawing, which shows longitudinal sections of the zone of the welded pipe joint, which is subject to corrosion and requires separate protection.

Figure 1 shows a connection with a protective sleeve provided with an anticorrosive coating; figure 2 is the same with a protective sleeve made of corrosion-resistant metal; figure 3 is a variant with a water-saturated porous ring placed between two o-rings.

The method is as follows.

Before connecting the ends of the pipes 1 (Fig. 1) with an internal anti-corrosion coating 2, a protective sleeve 3 of carbon steel is inserted, all surfaces of which are provided with an anti-corrosion coating. At the ends of the sleeve, outside the destructive thermal effect of welding on the coating of the pipe, O-rings 4 are placed in the annular grooves, the outer diameter of which in the assembly is equal to or slightly smaller than the inner diameter of the pipes. Next to the sealing rings 4, rings 5 of a porous material saturated with water are mounted on one or both sides.

In order to prevent thermal destruction of the anticorrosion coating on the inner surface of the sleeve opposite the welding site, it is provided in the central part with an annular groove filled with heat-insulating material 6, which is protected from mechanical stresses by a metal casing 7, which has a persistent annular protrusion in the center that enters the gap between the ends of the pipes. After this, the pipes are joined by butt welding with the formation of a seam 8. O-rings 4 are made of an elastic material that expands upon contact with water, for example hydrophilic rubber.

The protective sleeve can also be made of corrosion-resistant and heat-resistant material (figure 2), in this case, the need for a heat-insulating layer 6 and a protective casing 7 disappears.

The protective sleeve is provided with additional sealing rings 9 (Fig. 3) of an elastic material expanding upon contact with water placed in separate grooves from the side of the weld, while the technological rings 5 of porous material, impregnated with water, are placed between the two sealing rings 4 and 9.

When a pipeline is pressurized with water, before it is put into operation, or when the pipeline is filled with pumped water or a liquid containing an aqueous phase (for example, flooded with oil), the sealing rings absorb water and expand in all directions, blocking the gaps between the protective sleeve and the pipes. For example, Hydrotight tapes are able to increase in volume by 2 times, creating great efforts to compress the sealing rings to the surfaces of the sleeve and pipes. In this case, at the initial moment of contact with water, pressurized water or pumped liquid (if pressure testing is not performed with water) can fill the cavity between the sleeve and the pipes, since the expansion of the sealing rings after contact with water does not occur quickly. Therefore, to eliminate the initial ingress of fluid into the cavity between the sleeve and the pipes, technological rings 5 of a porous material saturated with water are installed next to the sealing rings 4. In this case, the expansion of the sealing rings 4 occurs in advance, even before crimping the pipeline.

To increase the pressure of the sealing rings in the radial direction, they are made of two components placed in separate grooves (see figure 3). In this case, the outer o-rings 4, expanding, squeeze out water from the process rings 5 towards the inner o-rings, which, being in separate grooves with rigid walls, can expand only in the radial direction and therefore are able to create a stronger radial pressure.

Concrete example

The ends of steel pipes with a diameter of 273 mm, a wall thickness of 8 mm, corresponding to GOST 8732-78, were calibrated by the inner diameter to the maximum value, taking into account the tolerances of this standard - up to 262.8 mm - to a depth of 300 mm. After that, an epoxy-based coating was applied to the inner surface of the pipes using a known technology by electrostatic spraying with a thickness of 0.25-0.35 mm. The same coating was applied to all surfaces of the carbon steel protective sleeve with an outer diameter of 262 mm, an inner diameter of 250 mm, a length of 500 mm, and ring grooves 4 mm deep and 36 mm wide at the ends and an annular groove 5 mm deep and 100 mm wide in the center . O-rings made of a water-swelling cord of the GX-7615/2004 brand 20 mm wide, 4 mm thick, which is capable of expanding in the free state by 6-8 times, were installed in the grooves. On both sides of the o-rings in the same grooves were placed foam rings 8 mm wide, 5 mm thick, saturated with water. Asbestos fabric with a total thickness of 3 mm was wound around the central bore of the sleeve and a steel ring split casing with a width of 99 mm, a thickness of 1.5 mm and a persistent ring protrusion in the center with a height of 1.5 mm and a width of 1 mm was put on. The protective sleeve was inserted into the ends of the pipes to be joined to the stop and the joints were welded. 3 days after welding, hydraulic tests were performed of the tightness of the pipe connection zone between the sealing rings. Such a seal provides tightness up to 4 MPa. At higher pressures, it is necessary to use o-rings made of hydrophilic rubber with a hardness on a scale of Shore more than 60 units.

Claims (2)

1. A method of protecting a welded joint of pipes with an internal coating from corrosion, comprising placing in the pipes at their junctions protective sleeves made in a corrosion-resistant design and having annular grooves on the outer surface along the edges with sealing rings of elastic material, and connecting the pipes by welding , characterized in that in the annular grooves of the protective sleeve before installing it in the pipes are placed o-rings of elastic material, expanding upon contact with water, for example, hydrophilic rubber, and process rings made of porous material, impregnated with water and interacting with the o-rings, on one or both sides of the o-rings. 2. The method according to claim 1, characterized in that the protective sleeve is provided with additional sealing rings of elastic material expanding upon contact with water, placed in separate grooves from the side of the weld, while the technological rings of porous material impregnated with water are placed between two o-rings.

Images