RU2554172C2 - Repair of potentially dangerous pipeline section - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to repair of buried main gas lines. In compliance with this process, operating conditions of potentially dangerous pipeline gas line is estimated with due allowance for higher level of strained state. Then, local soil density under said pipeline is increased to redistribute the load and to correct is elevation position, hence, to increase the radius of curvature, therefore decreasing the bending stress.

EFFECT: lower strains, material and labour input.

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Description

The invention relates to the operation of main gas pipelines, in particular to the operation of potentially hazardous sections of gas pipelines with an increased level of stress-strain state (VAT).

As a potentially hazardous area, a gas pipeline crosses an obstacle, such as a ravine, while approximately in the center a concave section with a radius of elastic bending is formed, the stresses in which can exceed the permissible ones according to SNiP 2.05.06-85 *. Trunk pipelines. - Instead of SNIP P-45-75; enter 10/10/1996. - M.: TsITP Gosstroy of the Russian Federation, 1997 .-- 97 p. [one].

A known method of repairing a section of a gas pipeline with a defective ring weld (Guiding document on pipe welding technology in the repair and restoration of gas pipelines: RD 558-97: approved by Member of the Management Board of RAO Gazprom BV Budzulyak 02/25/1997: introduction. effective 25.02.1997. - M .: Gazprom, VNIIGAZ, 1997. - 231 p.) [2] in potentially hazardous areas with a VAT level higher than permissible according to [1], which consists in exempting the gas pipeline from the gas, opening the gas pipeline and replacing it area with a defective annular weld.

The disadvantages of the known method of repairing a gas pipeline are its high material consumption and laboriousness, as well as the need to vent gas from a section of the gas pipeline due to a stop of gas transportation.

The prototype is the repair method (Instructions for repairing defective pipes of main gas pipelines with polymer composite materials: VSN 39-1.10-001-99: approved by the Design and Expertise Department of Gazprom OJSC on 10/19/1999: put into effect on 05.03.2000. - M .: Gazprom, 2000. - 17 p.) [3] of potentially hazardous sections of gas pipelines with a VAT level higher than permissible according to [1], which consists in opening the gas pipeline, reducing the pressure to 70% of the allowed operational for a period of time due to the work schedule, compositional couplings and backfill of the repaired area.

The disadvantages of the prototype are the large consumption of materials, the complexity and lower productivity of the pipeline. In this case, a reduction in the level of VAT is achieved at a local site equal to the length of the composite sleeve.

The objective of the invention is to reduce material and labor costs when repairing a potentially dangerous section of a gas pipeline with a VAT level higher than permissible according to [1] and eliminating gas bleeding into the atmosphere (operation to reduce gas pressure).

The technical result from the use of the invention is to reduce the VAT level of the repaired section of the gas pipeline to standard values with low material and labor costs without bleeding the gas.

The technical result is achieved by the fact that after assessing the technical condition of a potentially dangerous section of the gas pipeline with an increased level of VAT according to [1], increasing the local soil density under this section of the pipeline and redistributing the load, adjust its height position, which leads to an increase in the radius of bending and, therefore, lower bending stresses.

The bending stress σ _u are determined according to the requirements [1]:

Where

E - deformation modulus of pipe steel, MPa;

D is the outer diameter of the pipeline, cm;

ρ is the radius of elastic bending of the plot, see

Since the radius of elastic bending is in the denominator, when it increases, loads are redistributed and bending stresses decrease.

Repair of a gas pipeline section with an increased level of VAT according to [1] by the proposed method is carried out in the following sequence.

A comprehensive assessment of the potentially dangerous section of the gas pipeline is carried out, including analytical and diagnostic types of work performed in stages in the sequence indicated below.

At the first stage, analytical work is carried out, including:

- analysis of project documentation;

- analysis of executive documentation;

- analysis of the results of in-line diagnostics;

- analysis of information on repair work on the gas pipeline section, including information on the types of defects eliminated;

- assessment of VAT according to a comprehensive analysis according to the Instructions for determining the actual VAT of sections of gas pipelines located in territories with dangerous geodynamic processes according to geodetic survey data and assessing their performance: approved. Gazprom OJSC 11/18/2008: introduction. effective 01.02.2009. - M.: OAO Gazprom, 2003. - 146 p. [four].

When performing analytical work, the position of the pipeline section in the vertical plane is considered. According to the design documentation, potentially hazardous areas of the possible occurrence of longitudinal tensile stresses exceeding the permissible ones are determined [1]. In addition, a potentially hazardous area can be determined by in-line diagnostics and other diagnostic examinations.

When analyzing the executive documentation, the actual laying of the gas pipeline section in the vertical and horizontal planes is compared with the design documentation data. In case of mismatch of the rotation angles and bending radii in the vertical plane, according to the design and executive documentation, sections of the gas pipeline can be conditionally considered potentially dangerous from the point of view of VAT according to [1].

The analysis of the results of in-line diagnostics is carried out in two directions:

- comparison of the results of measuring the rotation angles and the bending radius of the gas pipeline in the vertical plane revealed by the in-tube shell with the data of the design and executive documentation;

- identification of defects in the pipe body of a circular (transverse) direction, such as corrosion cracks, grooves, risks, groups of caverns, whose geometric dimensions in the transverse plane (width) significantly exceed the dimensions in the longitudinal plane (length) in potentially dangerous sections of the gas pipeline.

Analysis of information on repair work includes determining the places for eliminating defects on a gas pipeline section, their types and geometrical dimensions, as well as their location relative to potentially dangerous areas of occurrence of stress corrosion cracking (SCC) defects of a circular direction.

At the second stage, according to a comprehensive analysis, measurements of its actual position by geodetic methods and a control calculation of the VAT of a potentially dangerous section of the gas pipeline are carried out according to [4]. Based on the results of the control calculation, a decision is made to conduct the third stage - the technical diagnosis of the gas pipeline in pits, including:

- opening a section of the gas pipeline of the estimated length L in such a way that the pipe lash on both sides and from above is free from soil, but remains on the bed;

- identification of defects in oil and gas, as well as other defects by visual and instrumental methods (in case of detection of defects - an assessment of the degree of their danger and repair work in accordance with the Instructions for the assessment of defects in pipes and fittings during repair and diagnostics of gas pipelines: R Gazprom: approved by Gazprom "November 18, 2008: entered into force on February 1, 2009. - M.: OAO Gazprom, 2009. - 56 p. [5];

- geodetic positioning of the gas pipeline section (planned elevations of the pipe) in accordance with [4] with the assessment of VAT in accordance with [1];

- decision making on the repair method.

The calculated length L begins and ends in places where the bending stresses are close to zero, the transition from the convex (straight) to the concave part (according to the design drawings of the profile of a potentially hazardous area).

In the case of VAT compliance of the gas pipeline section with the requirements of regulatory documents, work is underway to consolidate the existing position of the pipe lash and backfill with soil from the dump.

With an increased level of VAT (non-compliance of the VAT of the gas pipeline section with the requirements of regulatory documents), work is underway to adjust its spatial position in the vertical plane (increasing the bend radius, formula (1).

The essence of the invention is illustrated by a longitudinal section of the opened repaired section of the gas pipeline shown in FIG. 1, where 1 is the gas pipeline, 2 is the bed of the gas pipeline, ρ is the bending radius.

In order to increase the bending radius, from the bed side of the gas pipeline section, in places of the minimum bending radius ρ (Fig. 2), distributed forces q are applied vertically upward, with a length of at least 0.8 the total length of the opened section, which increase the bending radius to ρ ₁ , which means they change the altitude position of the site, redistributing the loads and reducing bending stresses.

The effect of the distributed forces q is achieved by adding soil 3 on both sides of the pipe (Fig. 3, section aa), regardless of the presence of a gap between the lower generatrix of the gas pipeline and the bed or its absence, which is then sealed with a hydraulic hammer 4. The distance between the edge of the hydraulic hammer and the gas pipeline should be 0.2 ± 0.05 m. An inert material, such as a sand-gravel mixture, can be used as soil.

The poured soil is mechanically pressed into the lower generatrix, providing a manifestation of distributed distributed force under the gas pipeline section and its upward movement, which changes the position of the gas pipe bed from 2 to 2 ′, increases the bending radius, which means it redistributes the loads and reduces the bending stresses on the gas pipeline under repair ( Formula 1)).

The indicated impacts, if necessary, are carried out on both sides of the gas pipeline.

Geodetic positioning of the new position of the gas pipeline section (planned elevations of the pipe) is carried out with the VAT assessment according to [4].

An advantage of the invention is that the VAT level of the repaired section of the pipeline is reduced without reducing the productivity of the pipeline, involving relatively small material and labor costs.

Testing the claimed technical solution at Gazprom Transgaz Ufa LLC allowed VAT to be brought in five sections of gas pipelines with a diameter of 1420 mm to regulatory requirements. Moreover, the actual economic effect of eliminating the need to vent gas in these areas amounted to about 85 million rubles.

Claims (1)

A method of repairing a potentially dangerous section of a gas pipeline with an increased level of stress-strain state, which consists in opening a section of a gas pipeline and assessing its stress-strain state, characterized in that, by increasing the local density of soil under this section of the gas pipeline and redistributing the load, its altitude position is adjusted, which leads to an increase in bending radius and, consequently, a decrease in bending stresses.

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