RU2170875C2 - Pipeline restoration method - Google Patents

Abstract

FIELD: repairing gas conduits, oil condensate conduits and other cylindrical metallic constructions such as vessels, reservoirs and so on. SUBSTANCE: method comprises steps of repairing pipeline with use of coupling mounted onto repaired portion of pipeline in order to apply controllable load reducing said coupling due to use elastic chamber filled with pressurized liquid or gas; preliminarily measuring residual pressure in pipeline and remained thickness of repaired portion; determining value of reducing pressure in elastic chamber according to relation

, where Pop - operational pressure in pipeline, MPa; Pres - residual pressure in repaired pipeline, MPa; t₁ -equivalent remained thickness of repaired pipeline, mm; t₂ - coupling thickness, mm; Rout - outer radius of pipeline, mm; Rin - inner radius of pipeline, mm; E - elasticity modulus of pipeline material, MPa; L' - distribution length of zone of "eddy effect", mm; a -length of portion for applying reducing load to coupling along axis of pipeline, mm; f -friction factor at sliding of coupling along pipeline; ε_r.d.- mean relative deformation values of pipeline caused by thermal shrinkage of welded seam of coupling; σ_result -resulting annular stresses of pipeline wall after mounting coupling, MPa. EFFECT: enhanced strength and stability of repaired portion. 4 dwg

Description

 The invention relates to methods for repairing pipelines and can be used in the repair of gas pipelines, oil condensate pipelines and cylindrical metal structures, such as vessels, tanks and apparatuses.

 When repairing pipelines, banding of defective areas with clutches, clamps, tapes, etc. is used. Partial or complete unloading of the damaged pipe wall from ring stresses due to preload (compression) by the coupling is important. Reducing stresses under the coupling reduces the likelihood of a defect developing at the repair site, and increasing the pipe wall thickness when installing the coupling prevents the development of deformations in the defect zone and the formation of cracks. There are various methods for achieving compressive stresses in a pipe.

 A known method of repairing a pipeline using couplings, in which two longitudinal halves of the coupling are pulled together with bolts after installation at the repair site. A sealing adhesive mass is pumped into the space between the pipe and the coupling [1].

 The disadvantage of this method is the lack of accuracy in determining the applied load and the complexity of the design of the coupling.

 Closest to the claimed purpose and a combination of essential features is a method of repairing a pipeline by installing a sleeve on a repaired section of the pipeline, including creating an adjustable compressive sleeve load through an elastic chamber filled with liquid or gas under pressure. The accuracy of achieving the compression load on the parts of the coupling is determined by the pressure gauges of the compressor station. Upon reaching the required pressure in the elastic chamber, half of the coupling is welded with longitudinal seams [2].

 However, in this method, the necessary pressure in the elastic chamber is arbitrarily selected without taking into account the parameters of the pipeline being repaired and the applied coupling, friction forces, etc. If the selected compression pressure is below the required level, then the small unloading stresses in the defective pipe will not allow to eliminate the development of the defect. If the compression pressure is higher than the permissible value, the entire load will be transferred to the coupling, which will lead to its destruction, and then to the destruction of the pipeline itself.

 The claimed invention solves the problem of increasing the strength and stability of the repaired section of the pipeline by increasing the accuracy of determining the compressive clutch load.

где P_раб - рабочее давление в трубопроводе, МПа;
P_ост - остаточное давление в ремонтируемом трубопроводе, МПа;
t₁ - эквивалентная остаточная толщина ремонтируемого трубопровода, мм;
t₂ - толщина муфты, мм;
R_н - наружный радиус трубопровода, мм;
R_в - внутренний радиус трубопровода, мм;
E - модуль упругости материала трубопровода, МПа;
L' - длина распространения зоны "краевого эффекта", мм;
a - длина участка приложения обжимающей нагрузки на муфту вдоль оси трубопровода, мм;
f - коэффициент трения при скольжении муфты по трубопроводу;
ε_св - средние относительные деформации трубопровода от тепловой усадки сварного шва муфты;
σ_рез - результирующие кольцевые напряжения в стенке трубопровода после установки муфты, МПа.The problem is achieved in that in a method of repairing a pipeline using a sleeve installed on a repaired section of the pipeline, including creating an adjustable compressive load sleeve using an elastic chamber filled with liquid or gas under pressure, the residual pressure in the pipeline and the residual thickness of the area being repaired are pre-measured, and the value of the squeezing pressure in the elastic chamber is determined based on the dependence

where P _slave is the working pressure in the pipeline, MPa;
P _OST - residual pressure in the repaired pipeline, MPa;
t ₁ - equivalent residual thickness of the pipeline being repaired, mm;
t ₂ is the thickness of the coupling, mm;
R _n - the outer radius of the pipeline, mm;
R _in - the inner radius of the pipeline, mm;
E is the elastic modulus of the pipeline material, MPa;
L 'is the propagation length of the zone of "edge effect", mm;
a is the length of the area of application of the crimping load on the sleeve along the axis of the pipeline, mm;
f is the coefficient of friction when sliding the coupling through the pipeline;
ε _St - average relative strain of the pipeline from heat shrinkage of the weld of the coupling;
σ _rez - resulting ring stresses in the pipe wall after installation of the coupling, MPa.

 From the scientific and technical literature and patent documentation it is not known to use the claimed dependence to determine the optimal value of the squeezing pressure, ensuring a uniform fit of the coupling along the entire circumference and reducing the annular stresses in the pipeline wall to the required value.

 The technical result consists in reducing the ring stresses in the pipe wall to the required value by ensuring the accuracy of determining the compression of the coupling sleeve, which helps to restore the bearing capacity of the defective sections not lower than the bearing capacity of the defect-free part of the pipeline. This provides increased strength and stability of the repaired section of the pipeline.

 The method is as follows.

 Repair of pipelines is carried out both with the termination, and without interruption of supply of the transported product. A pipeline with through defects is repaired after depressurization in a given section of the pipeline. In the case where the length of the defective section is large enough, the repair is carried out step by step, moving the structure with the elastic chamber in stages to the adjacent section, until the defective section of the pipeline is completely repaired.

 A preliminary assessment of the technical condition of the pipeline (the nature and size of the defects) is carried out using known methods of external or in-line diagnostics - ultrasonic, acoustic, etc.

 The pipeline section with local non-through defects is cleaned of corrosion products, anticorrosion coating, dust, dirt, then the defective pipeline sections are degreased with acetone or another organic solvent and the defects are puttied with epoxy resin or putty. With through defects (fistulas), the ends of the fistula are drilled and conical steel plugs lubricated with epoxy are inserted into the holes obtained. The fistula area is degreased and greased with epoxy.

 The longitudinal halves of the coupling are installed on the pipeline, the thickness of which should not differ from the wall thickness of the pipeline being repaired by more than 20%. An elastic chamber is mounted on the clutch using a device made, for example, in the form of two half-hollows connected by studs. In the elastic chamber through the nozzle serves liquid or gas under pressure, the value of which is previously calculated according to the proposed dependence. Then half of the coupling is welded with longitudinal seams.

 The selection of the compression clutch pressure is as follows.

 In FIG. 1 shows a diagram of the application of a crimping load on the coupling; FIG. 2 is a section along A-A in FIG. 1. In FIG. 3 and FIG. 4 shows the projection of defects on the compression length in the axial section of the pipe wall.

где А_пот - площадь потери металла в дефектной стенке оболочки на длине обжатия a+L', мм²;
a - длина участка приложения обжимающей нагрузки на муфту вдоль оси трубопровода, мм;
L' - длина распространения зоны "краевого эффекта", мм.Measure the residual pressure in the pipeline being repaired. Using one of the methods of non-destructive testing, for example, ultrasonic testing, throughout the entire defective section, the residual thickness of the pipeline is pointwise measured, based on which the configuration of the defects of the pipeline being repaired emerges. Then, by well-known methods, the area of metal loss in the defective zone of the pipeline along the compression length is calculated. Then determine the equivalent residual thickness of the defective section of the pipeline according to the formula

where A _sweat is the area of metal loss in the defective shell wall along the compression length a + L ', mm ² ;
a is the length of the area of application of the crimping load on the sleeve along the axis of the pipeline, mm;
L 'is the propagation length of the "edge effect" zone, mm.

где R_н - наружный радиус трубопровода, мм;
t_тр - толщина трубопровода, мм.The propagation length of the "edge effect" zone is

where R _n - the outer radius of the pipeline, mm;
t _Tr - the thickness of the pipeline, mm

 The average relative deformation of the pipeline being repaired from the heat shrinkage of the coupling weld is determined by the empirical dependence.

ε _sv = (2 ... 2.5) • 10 ^-6 • σ _t ,
where σ _t - yield strength of the coupling material, MPa.

Необходимый уровень результирующих кольцевых напряжений в дефектной стенке трубопровода, транспортирующего сероводородсодержащий продукт, в результате установки муфты определяют исходя из того, что напряжения в стенке трубопровода должны быть в два раза меньше, чем в стенке муфты

После этого по заявляемой формуле вычисляется конкретное значение обжимающего муфту давления для данного участка трубопровода. При этом обжимающее давление в упругой камере должно быть больше 2 МПа, так как при меньшем давлении не обеспечивается плотное прижатие муфты к трубопроводу.The required level of the resulting ring stresses in the defective wall of the pipeline transporting the purified gas, as a result of the installation of the coupling, is determined on the basis of the equal strength of the resulting structure

The required level of resulting ring stresses in the defective wall of the pipeline transporting the hydrogen sulfide-containing product, as a result of the coupling installation, is determined on the basis that the stresses in the pipeline wall should be half as much as in the wall of the coupling

After that, according to the claimed formula, the specific value of the compression sleeve is calculated for this section of the pipeline. In this case, the compressive pressure in the elastic chamber should be greater than 2 MPa, since at a lower pressure, the clutch is pressed tightly against the pipeline.

 Thus, when applying to the elastic chamber a compression pressure calculated by the claimed formula after the necessary measurements, the stresses in the pipeline wall will be reduced to the required level, which ensures the strengthening of the defective section, which leads to greater efficiency of the proposed method of repairing the pipeline compared to previously published .

 Using the proposed method will improve the strength and stability of the repaired section of the pipeline due to the accuracy of determining the compression of the coupling load, which leads to the restoration of the bearing capacity of the defective sections is not lower than the bearing capacity of the defect-free part of the pipeline.

Sources of information
1. Application N 96/19694. PCT, 6 IPC F 16 L 55/175, claimed 12/22/94, publ. 06/27/96.

 2. RF patent N 2140600, 6 IPC F 16 L 55/172, publ. 10.27.99, BI N 30, 1999 (prototype).

Claims (1)

A method of repairing a pipeline using a sleeve installed on a repaired area, including the creation of an adjustable compression sleeve load using an elastic chamber filled with liquid or gas under pressure, characterized in that the residual pressure in the pipeline and the residual thickness of the area being repaired are pre-measured, and the amount of compression pressure is the elastic chamber is determined based on the dependence

where R _slave is the working pressure in the pipeline, MPa;
R _OST - residual pressure in the repaired pipeline, MPa;
t ₁ - equivalent residual thickness of the pipeline being repaired, mm;
t ₂ is the thickness of the coupling, mm;
R _n - the outer radius of the pipeline, mm;
R _in - the inner radius of the pipeline, mm;
E - modulus of elasticity of the material of the pipeline, MPa;
L 'is the propagation length of the zone of "edge effect", mm;
a is the length of the application of the crimping load on the sleeve along the axis of the pipeline, mm;
f is the coefficient of friction when sliding the coupling through the pipeline;
ε _St - average relative strain of the pipeline from heat shrinkage of the weld of the coupling;
σ _rez - resulting ring stresses in the pipe wall after installation of the coupling, MPa.

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