RU2239120C2 - Method of protecting inner side of pipeline welds - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method comprises applying a protecting cover on the inner side of butted pipes. The protecting cover made of a roller is applied before welding and contains a mixture of metal protector with adhesive agent, a mixture of atactic polypropylene with heptane. The mixture contains (in mass %): 40-75 of metal protector, 5-10 of atactic polypropylene, and 10-50 of heptane.

EFFECT: enhanced reliability of protecting welds.

4 cl

Description

The invention relates to the protection against corrosion of metals and can be used in pipelines with an internal anti-corrosion coating intended for the transportation of oil, oil products, gas, various aggressive environments, water, etc.

In oil collectors, through which, for example, a water-oil mixture is transported by a laminar flow, products are separated into oil and water. As a result of the separation, mineralized water moves along the lower generatrices and the corrosion rate increases precisely in the zone of water location, mainly in the zone of welds.

A known method of protecting the inner surface of the welds of pipelines, including applying a coating of elastic hoses with an adhesive sublayer (ed. Certificate of the USSR No. 1564461, F 16 L 58/02, 1990).

The disadvantage of this method is the short service life of such coatings due to the separation of the edges of the coatings by the fluid flow, as well as the need to withstand the required temperature of the pipe in winter conditions during the construction of pipelines. In addition, when connecting the lashes there are additional problems associated with pulling the cable through the pipelines.

A known method of manufacturing a pipe with an internal coating, including coating the end sections of the pipes with a non-oxidizable metal alloy, applying a protective coating to the inner surface of the pipes, butt jointing and welding process (ed. Certificate of the USSR No. 1778427 A1, F 16 L 58/02, 1992) . As a non-oxidizable alloy, a self-fluxing alloy is used, which is applied to the surface of each of the connected pipes at a length equal to the zone of residual plastic deformation from temperature stresses during welding.

The disadvantage of this method is that the welds are not adequately protected from corrosion: with a small layer of self-fluxing alloy, it does not spread and the coating of the weld is of poor quality, as a result of which the corrosion rate decreases slightly.

The task: to create an effective method of corrosion protection of the zone of welded pipe joints.

The technical result consists in increasing the protective properties of the zone of pipe welds by coating the weld with a mixture of tread metal with adhesive.

The specified technical result during the implementation of the invention is achieved by the described manufacturing method (or repair) of the pipeline with an internal coating.

New is that the coating is applied before welding in the form of a roller, on the inner surface of the welds of the pipeline and sections adjacent to the welds, while a mixture of components is used as a coating: metal tread with adhesive of the following composition, wt.%: Metal tread 40 -75, atactic polypropylene (ALL) 5-40, heptane 10-50. In this case, a mixture of atactic polypropylene in heptane is used as an adhesive with an atactic polypropylene: heptane ratio of 1: 0.3-9.

An increase or decrease in the amounts (limits) of the components of the mixture and adhesive impairs the effectiveness of the protection of the weld. Thus, a decrease in the APP content of less than 5 wt.% Will lead to a decrease in the adhesion of the mixture to the pipe surface and the metal of the tread, and an increase in the heptane content of more than 50% leads to a decrease in the viscosity of the mixture and the inability to obtain a roll of the required height. A decrease in the tread metal content of less than 40 wt.% Leads to a decrease in its service life and to an increase in the dimensions of the roller.

An increase in the metal content of the tread more than 75 wt.% Leads to a decrease in the adhesion forces of the roller to the surface of the pipe and its scattering during application.

As the tread metal, one of the low-melting metals, for example zinc or aluminum, is used.

As a bonding adhesive, a component is selected that provides adhesion of the molten tread metal to the pipe surface and reliable electrical contact, for example, atactic polypropylene dissolved in heptane. As an APP, for example, an APP TU-2211-056-05796653-98 is used, which provides good adhesion with the tread metal and the pipe. As heptane, for example, heptane TU-38.101677-91 is used. The application of the protective coating is carried out in the form of a roller before welding with the claimed mixture, which melts and spreads during welding along the weld and the sections adjacent to it. Part of the seam in this case is a protected film of tread metal, and the remaining exposed part (not covered by the tread) of the seam forms an electrochemical pair with the tread metal, providing cathodic protection. The stated ratios of the components provide the necessary viscosity, which allows you to form the necessary shape. The roller is applied so that it cannot adversely affect the seam when the root seam is in a molten state.

Metal protector is used in powder form. A fine powder of fusible metal (0.5: 10 μm) with a minimum amount of impurities (up to 1.5: 2.5%) is selected to obtain a high-quality coating of the surface of the weld and pipe in the frontal zone.

As a metal tread for acidic environments take, for example, aluminum; and for alkaline environments - zinc.

When welding pipes, the tread metal melts (the melting temperature of aluminum is 660 ° С, of zinc - 420 ° С) and it spreads along the weld and sections adjacent to it. The seam forms an electrochemical pair with the tread metal, providing cathodic protection.

Example 1 specific implementation.

Use zinc powder (TU 12601-76) - 50; APP (TU-2211-056-05796653-98) -15; heptane (TU 38.101677-91) - 35.

The mixture is prepared in the following ratio of components, wt.%: Zinc - 50; atactic polypropylene - 15; heptane - 15.

The resulting mixture is applied to the pre-cleaned inner surface of the welds of the ends of the pipes and sections adjacent to the welds, for example, using a syringe.

The dimensions of the roller are determined taking into account the inner diameter of the pipe and the results of a pilot test. The selected dimensions ensure melting from the heat of the weld and prevent ingress of the components of the mixture into the molten material of the welding wire, i.e. eliminate contamination of the root seam at the time of welding. With an inner diameter of the pipe of 100 mm, the equivalent height of the roller is 4 mm, width is 18 mm, the distance between the end of the pipe and the roller is about 20 mm.

Electrode welding is carried out using electrodes of the UONI13 / 55 type, the wire of which has an identical composition with oilfield pipes. The seam temperature is about 1500 ° C.

During welding, the temperature of the ends of the pipes rises (at a distance of 20 mm from the end, the temperature of the pipe rises to 800-850 ° C), the deposited mixture melts and spreads along the weld and the sections adjacent to it.

Part of the seam in this case is a protected film of tread metal (zinc), and the remaining exposed part of the weld forms an electrochemical pair with zinc, providing its cathodic protection. Atactic polypropylene dissolved in heptane provides reliable electrical contact and adhesion between the pipe and the tread (zinc).

Example 2 specific implementation.

The mixture is prepared in the following ratio of components, wt.%: Highly dispersed aluminum powder TU-5494-95 - 55; APP (TU-2111-056-05796653-98) - 18; heptane (TU 38.101677 91) - 37. All operations of applying the mixture and the welding sequence are similar to example 1. During welding, the temperature of the ends of the pipes rises (at a distance of 15 mm from the end, the temperature of the pipe rises to 900 ° C), the applied mixture is melted and spreads along the weld seam and sections adjacent to it. Part of the seam in this case is a protected film of tread metal (aluminum), and the remaining exposed part of the weld forms an electrochemical pair with aluminum, providing its cathodic protection.

The number of gusts of welds after the claimed processing decreased by 2 times.

The method is expediently used in the repair of field oil pipelines and water pipelines, when it is impossible to reduce the corrosion damage of the weld by other methods.

Thus, the application of a coating in the form of a roller consisting of a mixture of metal, tread and adhesive on the inner surface of the pipes increases the efficiency of protecting welds from corrosion damage.

Claims (5)

1. The method of protecting the inner surface of the welds of pipelines, including applying a protective coating to the inner surface of the pipes, butt-welded, and welding, characterized in that the protective coating on the inner surface of the pipes is applied before welding in the form of a roller, and a metal mixture is used as a protective coating protector with adhesive. 2. The method according to claim 1, characterized in that the adhesive uses a mixture of atactic polypropylene in heptane. 3. The method according to claim 1, characterized in that a mixture of a metal tread with an adhesive of the following composition is prepared, wt.%: Metal Protector 40-75 Atactic polypropylene 5-10 Heptane 10-50 4. The method according to claim 1, characterized in that a low-melting metal is used as a metal tread. 5. The method according to claim 4, characterized in that aluminum or zinc is used as the low-melting metal.