RU2004626C1 - Method of cathodic protection of welded joint of pipe line against corrosion - Google Patents

Abstract

SUMMARY OF THE INVENTION: the ends of the pipes to be welded are stripped, a soluble protector is placed along the edges. Tread placement is carried out by surfacing on the protected surface of the aluminum-based alloy roller at a distance from each of the welded edges, determined depending on the pipe wall thickness, the amount of blunting when cutting the edges, the angle of the edges and the correction factor The welding of the roller is carried out in sections of length are determined depending on the radius of the pipe and the central angle that determines the length of the section. Before surfacing the aluminum-based alloy roller, a layer of metal is deposited onto the surface to be protected. carbon-carbon steel or titanium with a thickness of less than 3 mm, a width of 1.0 - 1.5 width of the roller 3 s f-crystals, 3 tab. 3 silt

Description

The invention relates to electrochemical corrosion protection of a weld zone of steel pipelines.

A method of protecting against corrosion of the inner surface of pipelines is known, according to which soluble anodes are placed inside a pipeline on a copper electrically conductive rod. The known method, with its considerable complexity, significantly reduces the working section of the pipeline.

The closest technical solution is a method of protecting the inner surface of pipes into a weld zone. The known method includes stripping the ends of the pipes being welded and arranging along the edges of the annular tread metal inserts on both sides of the seam in an area protected from internal insulation. Radially placed grooves are made in the tread body, into which fixing metal tapes are inserted. The tread contacts the pipe metal over the entire surface of the mechanical contact.

This method of protecting the inner surface of the pipes in the weld zone requires a large amount of turning work with increased accuracy. Moreover, due to the large tolerances on the inner diameter of the pipes, it is practically impossible to achieve a tight fit of the tread body to the inner surface of the pipe around the perimeter, which, increasing the electrical resistance, reduces the protective current, increases the local hydraulic resistance created by the tread and makes it difficult to fix the tread. When a tread is installed, a so-called crevice effect occurs, as a result of which the metal of the pipe with the accessory fixing tape is exposed.

The aim of the invention is to increase the efficiency of protection by creating a strong metal bond of the tread with the protected surface and reduce the complexity of the work.

The essence of the invention lies in the fact that when implementing the method of corrosion protection of the welded joint area of the piping, including stripping the ends of the pipes to be welded and placing a soluble tread along the edges, the tread is deposited on the protected surface of at least one aluminum-based alloy roller on distance I from each of the welded edges, determined from the relation

i- (S-a) tg «+ Ki,

(1)

where S is the wall thickness of the pipe, mm;

a - bluntness value when cutting edges, mm;

a-angle of cutting edges, degrees; K is a correction factor depending on the wall thickness, K 2-5 mm, while the ratio of the parameters of the deposited bead is N / B 0.3-0.6 and h / H 0.2-0.3,

where B is the width of the surfacing, mm; H - the height of the surfacing, mm; h is the penetration depth, mm. The essence of the invention also lies in the fact that the surfacing of the roller is carried out in sections of length

l

./J,

(2)

20 where g is the radius of the pipe, mm;

P is the central angle defining the length of the plot,

25

„Si3, oi rpafll.

0

left between them unmelted sections of the same length, the filling of which is carried out after the shrinkage of previously deposited

plots.

Before surfacing the aluminum-based alloy roller, a layer of mild steel 3 mm thick, 1.0-1.5 wide of the width of the aluminum roller is melted onto the surface to be protected.

Before surfacing the aluminum-based alloy roller, a titanium layer 3 mm thick and a width of 1.0-1.5 of the width of the aluminum roller is melted onto the surface being cleaned.

On Fig, 1 shows the annular joint of the pipeline with a protector placed in it, a longitudinal section; in FIG. 2 is a cross section AA in FIG. 1; in FIG. 3 is a diagram of cutting edges for welding.

The method is carried out as follows.

First, the ends of the pipes 1,2 are cleaned in the n sections of the tread 3.4. In this case, the internal insulation is removed, if any. Then, on each of the stripped sections of pipes 1, 2 at a distance from the welded edge, tread material 3, 4 of aluminum-based alloy material is deposited in the form of rollers. The distance I (Fig. 3) from each of the edges to be welded is determined from relation (1). The ratio of the height H of the surfacing to the width B of the surfacing is chosen in the range of 0.3-0.6. and the ratio of depth h

penetration to the height H of the deposition is within 0.2-0.3 (Fig. 1).

Surfacing of the tread roller is carried out either in a closed circuit around the entire perimeter of the pipe, which is suitable for pipes of small diameter, or in sections of length L selected from relation (2), leaving between them unplated sections of the same length, filling of which is carried out after shrinkage of previously deposited plots. Such an order of surfacing is suitable for pipes with a diameter of more than 400-420 mm.

When the tread is welded onto steel pipes, a zone of brittle intermetallic compounds with a hardness of up to 300-400 Hv is formed on the alloy line between the aluminum roller and the pipe metal, the presence of which increases the likelihood of cracking of the base metal, especially in pipes of category I and II of the 1st strength category with a limit yield strengths of 300 and 400 MPa, respectively. In order to eliminate the negative influence of the zone of brittle intermetallic compounds with increased hardness, a layer of mild steel up to 3 mm thick, 1.0-1.5 wide of the width of the aluminum bead is melted onto the surface to be protected before welding the aluminum-based alloy roller.

In order to increase the service life of the tread on pipelines transporting corrosive media, a layer of titanium, as a well passivating material, with a thickness of up to 3 mm and a width of 1.0-1.5 of the width of the aluminum roller can be deposited before welding the aluminum-based alloy roller. .

The method was carried out as follows.

For welding of a soluble tread, filler wires AK4 and 1201 and electrodes OZANA-1 / Sv-A5 were selected. Surfacing modes are presented in table. 1 and 2.

Soluble tread was surfaced on pipe samples with a diameter of 114-530 mm with a V-shaped groove with a cutting angle of 30 ° and a blunting value of 2 mm from domestic steels of the following grades: steel 20 (table 3, examples 1-11, steel 12GF I -th strength category (example 12) and steel 16GFB lll-strength category (examples 13-15). Surfacing was carried out manually by argon-arc method with a tungsten electrode with filler wire of grades AK4 with a diameter of 4 mm (examples 1-7,10, 11, 15 ) and 1201 with a diameter of 2 mm (example 9), as well as with a manual electric arc method OZANA-1 / Sv-A5 (examples 8,12-14), deposition modes were selected according to Tables 1 and 2. In examples 1-6, the tread was deposited at a different distance I from the welded edges, and the deposition was carried out in a closed loop 5 along the entire perimeter of the pipe. The distance was calculated by the formula (1). The values of the correction coefficient K-1, K- - 2, ..., K - 6 mm were accepted for each value of K; the distance I from the welded was calculated

0 edges to the deposited tread and at this distance the tread is welded to the protected inner surface of the pipe. Then, ring joints were welded from tube samples with a protector deposited inside them (one pair of 5 samples for each K value), from which samples were cut for electrochemical, metallographic and mechanical tests.

0 At a value of K 2 mm, the tread is located in the zone heated by welding the annular joint to temperatures close to the melting temperature of aluminum (TPL - 657 ° C), as a result of which the tread roller melts and aluminum enters the weld metal, which sharply worsens weld quality. At a K value of 5 mm, the deposited tread is removed from the welded joint area and thereby the protection efficiency of the seam and the heat-affected zone is reduced. As the wall thickness increases, lower K values should be chosen, as can be seen from Examples 5 and 7.

5 Tread surfacing was conducted both in a closed loop around the entire perimeter of the pipe (examples 1-6, 8, 10, 12-15), and sections of length L (examples 7, 9, 11, 16). The length of the sections was chosen from the ratio

0 (2).

The results of the experiments showed that when the pipe diameter is up to 426 mm, the weld-off weld is cooled down along the entire perimeter of the pipe

5 does not occur (examples 1-6, 8, 12-15).

When welding the tread roller in a closed loop around the entire perimeter of the pipe with a diameter of more than 426 mm, a local separation of the deposited roller from the

0 metal pipe (example 10), which reduces the effectiveness of protection. In these cases, it is preferable for the tread to be deposited in sections of length determined from relation (2).

5 In examples 12-14, for pipes of the second strength category 12ShF (yield strength 300 MPa) and the third strength category 16HFB (yield strength 400 MPa), a soluble tread was placed on a previously deposited layer (substrate) of

mild steel, which was deposited on each of the protected sections of pipes 1, 2 (see Fig. 1) at a distance of 8 mm from the welded edge by manual arc welding with E50A electrodes with a relative elongation of 6 to 20%. The width of the layer was 10 mm, and the thickness was 2, 3 and 4 mm, respectively, for examples 12,13, 14. After that, a soluble tread was melted onto this layer by the method of manual arc welding. The use of such a layer allows the zone of brittle intermetallic compounds with hardness up to 300-400 Hv formed outside the pipe wall to be formed during tread surfacing, preventing cracking of the base metal in this zone. For normal strength pipes made of mild steels, the use of substrates is not required.

An increase in the thickness of the substrate over 3 mm is impractical, since the local hydraulic resistance created by the tread is noticeably increased (Example 14).

In examples 5-7 and 15, the protected surface of the tube samples was melted

a titanium layer onto which a roll of a soluble tread was then fused; moreover, in Example 15, the titanium layer was not fused directly to the surface of the pipe

sample, and on the previously applied layer of mild steel.

A titanium layer was deposited onto the protected pipe sections at a distance of 8.5 mm from the welded edge of a manual argon-arc

by surfacing with filler wire SPT-2. The layer width was 10 mm, and the thickness was 1, 4, 3, and 2 mm, respectively, in examples 5, 6.7, and 15. After that, a bead was deposited onto the titanium layer in the same way

soluble tread.

Surfacing of the titanium layer can significantly increase the efficiency of protection, increases the service life of the tread due to the fact that titanium, as a well-passivating material, promotes uniform dissolution of the tread, preventing undercutting along the fusion line with the pipe metal.

(56) Patent GDR, No. 244572, cl. C 23 F 13/02. GDR patent, No. 130071, cl. F 16 L 58/00.

Table1 Manual electric arc surfacing with a tungsten electrode in argon

Manual electric arc surfacing with coated electrodes

Table 2

Table3

 - manual argon-arc surfacing with non-consumable electrode - manual electrode of surfacing

) - OZANA-1

Continuation of the table. 3

Claims (4)

1. METHOD OF PROTECTION AGAINST CORROSION OF A PIPELINE WELDED CONNECTION AREA, which consists in cleaning the ends of the pipes to be welded and placing along the edges of the soluble tread, characterized in that the tread is deposited on the protected surface of at least one aluminum-based alloy roller onto the distance I from each of the welded edges, determined from the relation I (S-a) tga + K, where S is the pipe wall thickness, mm; a - bluntness value when cutting edges, mm; a - angle of cutting edges, degrees; To 2 - 5 mm - correction factor, depending on the wall thickness, while the parameters of the deposited bead is selected from the relations N / A - 0.3 - 0.6 and h / N 0.2 - 0.3, where B is the width of the surfacing; H is the height of the surfacing; h is the penetration depth. 2 I L FIG. 7 2. The method according to claim 1, characterized in that the bead surfacing is carried out in sections of length L. leaving between them unplated sections of the same length that are filled with the deposited material after shrinkage of the previously deposited sections, while the length L of the sections was measured 10 are made from the ratio Z 180 g / where g is the radius of the pipe, mm; 2 s-s / -: - the central angle defining the length of the plot, degrees; 5 3. The method according to claims 1 and 2, characterized in that prior to surfacing the aluminum-based alloy roller, a layer of mild steel with a thickness of not more than 3 mm, 0 with a width of 1.0 - 1.5 of the width of the aluminum roller, is melted onto the surface to be protected . 4. The method according to claims 1 and 2, characterized in that prior to surfacing the aluminum alloy-based roller 5, a titanium layer is deposited with a thickness of not more than 3 mm and a width of 1.0-1.5 of the width of the aluminum roller. b: kA FIG. I Fig.Z