阅读说明：本技术 一种lng管道保冷结构在线修复方法 (Online repair method for cold insulation structure of LNG pipeline ) 是由 杨玉霞 付子航 刘艳平 张由素 刘方 冯亮 殷德庚 吴然 杨宏伟 黄洁馨 于 2019-10-14 设计创作，主要内容包括：本发明公开了一种LNG管道保冷结构在线修复方法。所述在线修复方法包括如下步骤：1)对LNG管道的保冷结构进行保冷性能评估：2)对不符合保冷设计要求的保冷结构,重新进行保冷设计；3)对待修复部位的保冷结构进行拆除并借助修复工具更换新的保冷结构；4)修复作业完成后对修复部位保冷结构的保冷性能进行检测评价。利用本发明修复方法对LNG管道保冷结构进行修复时,可实现整个修复过程不停车。本发明修复方法利用一种专用修复工具,保证修复过程管道表面不结霜,不会造成人员冻伤,修复后保冷效果显著。本发明不仅适用于LNG管道,其他低温管道、装置同样适用,可在其他低温深冷领域推广使用。(The invention discloses an on-line repair method for a cold insulation structure of an LNG pipeline. The online repair method comprises the following steps: 1) and (3) carrying out cold insulation performance evaluation on the cold insulation structure of the LNG pipeline: 2) carrying out cold insulation design again on the cold insulation structure which does not meet the cold insulation design requirement; 3) dismantling the cold insulation structure of the part to be repaired and replacing the new cold insulation structure by a repairing tool; 4) and after the repairing operation is finished, detecting and evaluating the cold insulation performance of the cold insulation structure of the repaired part. When the LNG pipeline cold insulation structure is repaired by the repairing method, the whole repairing process can be realized without stopping. The repairing method of the invention utilizes a special repairing tool to ensure that the surface of the pipeline does not frost in the repairing process, does not cause personnel frostbite, and has obvious cold insulation effect after repairing. The invention is not only suitable for LNG pipelines, but also suitable for other low-temperature pipelines and devices, and can be popularized and used in other low-temperature cryogenic fields.)

1. An LNG pipeline cold insulation structure on-line repairing method comprises the following steps:

1) and (3) carrying out cold insulation performance evaluation on the cold insulation structure of the LNG pipeline: 2) carrying out cold insulation design again on the cold insulation structure which does not meet the cold insulation design requirement; 3) dismantling the cold insulation structure of the part to be repaired and replacing the new cold insulation structure by a repairing tool; 4) and after the repairing operation is finished, detecting and evaluating the cold insulation performance of the cold insulation structure of the repaired part.

2. The on-line repair method of claim 1, wherein: in the step 1), the following parameters are collected and detected, and whether a cold insulation structure is repaired is determined according to GB/T8174-2008 'test and evaluation of equipment and pipeline heat insulation effect';

the parameters include the following a) -d):

a) original design parameters of the pipeline to be repaired;

b) operating parameters of a conveying medium in a pipeline to be repaired;

c) the temperature of the outer surface of the pipe cold insulation structure to be repaired;

d) the temperature, dew point temperature, ambient humidity and wind speed of the environment surrounding the pipeline to be repaired.

3. The online repair method according to claim 1 or 2, characterized in that: and 2) designing a cold insulation structure and cold insulation thickness according to GB/T8175-2008 'Equipment and pipeline thermal insulation design guide rules'.

4. The online repair method according to any one of claims 1 to 3, characterized in that: in the step 3), at the moment of dismantling the cold insulation structure to be repaired, purging the surface of the pipeline to be repaired by using the repairing tool;

the repair tool uses nitrogen as a gas source.

5. The online repair method according to any one of claims 1 to 4, wherein: and 3) removing the cold insulation structure to be repaired in a segmented, layered and sequential manner, wherein the length of the inner cold insulation structure removed each time is 1-1.2 m.

6. The online repair method according to any one of claims 1 to 5, wherein: in the step 3), when the cold insulation structure is a special-shaped cold insulation structure, measuring the size of the special-shaped part after the old cold insulation structure is removed and surface purging is completed, and temporarily adopting a flexible cold insulation material for secondary cold insulation; and simultaneously, a cold insulation structure capable of being rapidly installed is prefabricated according to the measured size of the special-shaped piece.

7. The online repair method according to any one of claims 1 to 6, wherein: in the step 3), the main moisture-proof layer of the new cold insulation structure is a self-adhesive composite moisture-proof layer.

8. The online repair method according to any one of claims 1 to 7, characterized in that: and 4) in the step 4), the cold insulation structure normally runs for at least 240 hours after being repaired and replaced, and the cold insulation performance of the repaired and replaced cold insulation structure is detected and evaluated according to the method in the step 1).

Technical Field

The invention relates to an on-line repair method for a cold insulation structure of an LNG pipeline, and belongs to the technical field of low-temperature deep cooling.

Background

The development of LNG cold insulation engineering in China is rapid, hard polyurethane foam is mostly adopted as a cold insulation structure, and the cold insulation structure can crack, shrink and deform after long-term use, and the phenomena are mainly shown as follows: the contact surface of the cold insulation layer and the metal pipeline is dry initially, and when a temperature difference exists between the low-temperature medium and an external cold insulation structure, moisture exists between the steel pipe and the cold insulation structure, and the moisture adheres to the surface of the metal pipeline system in the form of frost particles. During maintenance, the low-temperature system stops working, the temperature of the pipeline system begins to rise, frost particles on the surface of the pipeline system can be condensed into water vapor, the water vapor is collected to the bottom of the pipeline system, and the water vapor flows out from the joint of the cold insulation structure. This is more evident in summer. And after the overhaul is finished, the refrigerating system is restarted, and the condensed water accumulated at the bottom of the pipeline begins to freeze, so that the heat-insulating layer structure is subjected to expansion deformation and cracks.

Especially, in the low-temperature LNG industry, LNG pipelines of a plurality of LNG receiving stations which are put into operation in China are damaged in cold insulation layers in different degrees, partial equipment and pipelines have the phenomena of frost formation, condensation, icing, deformation and cracking of the cold insulation layers, so that the energy consumption is increased, the corrosion of the pipelines of the equipment is increased, and the cold insulation structure repair is urgently needed. Meanwhile, the traditional parking repair has great influence on the capacity and the economic benefit of the receiving station. Therefore, it is important to develop a safe, reliable and economical online repair technology.

Disclosure of Invention

The invention aims to provide an on-line repair method for an LNG (liquefied natural gas) pipeline cold insulation structure, which solves the problems of damage, aging and failure of the LNG low-temperature pipeline cold insulation structure in an LNG receiving station and realizes on-line repair and reconstruction of the low-temperature pipeline cold insulation structure on the premise of ensuring safe and stable on-site operation.

The LNG pipeline cold insulation structure on-line repairing method provided by the invention comprises the following steps:

1) evaluating the cold insulation performance of the cold insulation structure of the LNG pipeline; 2) carrying out cold insulation design again on the cold insulation structure which does not meet the cold insulation design requirement; 3) dismantling the cold insulation structure of the part to be repaired and replacing the new cold insulation structure by a repairing tool; 4) and after the repairing operation is finished, detecting and evaluating the cold insulation performance of the cold insulation structure of the repaired part.

In the online repair method, in the step 1), the following parameters are collected and detected, and then whether the cold insulation structure is repaired is determined according to GB/T8174-2008 test and evaluation of heat insulation effect of equipment and pipeline;

the parameters include the following a) -d):

a) original design parameters of the pipeline to be repaired;

the original design parameters comprise average wind speed, environment temperature, relative humidity, medium temperature, outer surface temperature, dew point temperature, surface heat exchange coefficient, allowable cold loss and the like under the design working condition;

b) operating parameters of a conveying medium in a pipeline to be repaired;

the operating parameters include temperature, flow, pressure, etc.;

c) the temperature of the outer surface of the pipe cold insulation structure to be repaired;

specifically, an infrared thermal imager and a contact thermometer can be adopted for measurement;

d) the temperature, the dew point temperature, the environmental humidity and the wind speed of the environment around the pipeline to be repaired;

the temperature and humidity detector and the anemometer can be used for measurement.

Through analysis, if the following requirements are not met, the cold insulation structure needs to be repaired for reducing cold loss:

i) adopting an economic thickness method to design a cold insulation structure, wherein the temperature of the outer surface of the cold insulation structure is higher than the dew point temperature under the design working condition;

II) a cold insulation structure designed for preventing the condensation of the outer surface, wherein the temperature of the outer surface is higher than the dew point temperature under the design working condition;

III) the cold insulation structure designed according to the allowable cold loss amount has the outer surface temperature higher than the dew point temperature under the design working condition, and meanwhile, the cold loss amount is smaller than the allowable cold loss amount under the design working condition.

In the online repair method, in the step 2), the cold insulation structure and the cold insulation thickness are designed according to GB/T8175-2008 'guide rule for designing heat insulation of equipment and pipelines'; the calculation principle is as follows:

a) in order to reduce cold loss (heat absorption) and prevent cold insulation of external surface condensation, the cold insulation thickness is calculated by adopting an economic thickness method, the external surface temperature is checked by a thermal balance method, and the temperature is higher than the environmental dew point temperature, otherwise, the temperature is thickened and recalculated;

b) in order to prevent the cold insulation of the condensation on the outer surface, the thickness of the cold insulation layer is calculated by adopting a surface temperature method;

c) cold insulation of cold loss amount is allowed in the process, the thickness of the cold insulation layer is calculated by adopting a thermal balance method, the temperature of the outer surface of the cold insulation layer is checked, the temperature is higher than the dew point temperature of the environment, and otherwise, the cold insulation layer is thickened and recalculated;

d) the pipeline and the cylindrical equipment with the nominal diameter larger than 1000mm are calculated according to a plane heat insulation calculation formula, when the nominal diameter is equal to or smaller than 1000mm, the pipeline and the cylindrical equipment are calculated according to a cylindrical surface heat insulation calculation formula, and the spherical equipment is calculated according to a spherical equipment heat insulation calculation formula;

e) when the same cold insulation material is adopted for cold insulation on the same equipment or pipeline, the calculation is carried out according to a single-layer heat insulation calculation formula, when two different cold insulation materials are adopted for cold insulation, the calculation is carried out according to a double-layer heat insulation calculation formula (except for a composite prefabricated product), and the interlayer temperature of the double-layer cold insulation layer is not lower than the lowest safe use temperature of the adjacent outer cold insulation material.

In the on-line repairing method, in the step 3), a special repairing tool is needed in the construction process of replacing the new and old cold insulation structure of the part to be repaired, nitrogen is used as an air source, and the air flow blown out meets the set air pressure by means of the air distributing piece with a specific shape, so that the surface of the pipeline is prevented from frosting in the repairing process.

Specifically, when the old cold insulation structure is dismantled, the old cold insulation structure is dismantled in a segmented, layered and sequential manner; meanwhile, the length of the inner-layer cold insulation structure is guaranteed to be 1-1.2 meters each time;

at the moment of dismantling the old cold insulation structure, a special repair tool is started synchronously to blow the surface of the pipeline to be repaired, so that the requirements of zero icing and zero frosting on the surface of the pipeline to be repaired are met.

The adopted repair tool can be an online repair special purging system for the cold insulation structure of the LNG pipeline with the following structure: the purge system includes a purge tool;

the purging tool comprises a plurality of annular gas distributing piece structures;

the annular gas distributing part structure comprises an arc-shaped pipe formed by circular pipes, a plurality of air outlet pipes are arranged on the arc-shaped pipe, and the air outlet pipes are connected with the blowing nozzle;

the arc-shaped pipe fitting is communicated with a pipeline through a handle, and the pipeline is communicated with an air source.

In the online repair purging system, the annular gas distributing part structures are connected through the short joint structures and then connected with the handle.

In particular, the line is a hose.

Specifically, a valve is arranged on the handle and used for adjusting the scavenging air flow.

Specifically, the air supply is a nitrogen air supply and is used for blocking wet air from contacting with the pipeline to be repaired in a short time, so that the air is prevented from being rapidly condensed into frost on the surface of the LNG pipeline due to too heavy moisture, the surface of the pipeline to be repaired is further protected, and the purging effect is enhanced.

Specifically, the air outlet pipes are uniformly arranged.

Specifically, the air outlet pipe passes through metal collapsible tube with the nozzle that sweeps is connected, metal collapsible tube has certain pliability, and the temporary adjustment of being convenient for sweeps the distance, and the air-out direction makes it can use with the work steel pipe phase-match of different pipe diameters.

Specifically, the material of the blowing nozzle is an organic composite material or an aluminum alloy material;

the blowing nozzle is flat, and the specifications of the blowing nozzle can be as follows: the air outlet structure is 40-60 mm long, 30-50 mm wide and 10-20 mm thick, 1-3 air outlets are arranged at the bottom of the air outlet structure, and each air outlet comprises 5-15 air outlets.

Specifically, the central angle corresponding to the circular arc-shaped pipe fitting is 270 degrees.

In the step 3), cold insulation materials are prefabricated in advance according to the size specifications of the pipeline to be repaired and the conventional pipe fitting;

the repair of the special-shaped cold insulation structure is to accurately measure the size of the special-shaped part after the old cold insulation structure is removed and the surface purging is completed, and temporarily adopt a flexible cold insulation material for secondary cold insulation; and prefabricating a cold insulation structure capable of being quickly installed according to the measured size of the special-shaped piece.

The main dampproof layer of the new cold insulation structure is a self-adhesive composite dampproof layer, particularly a composite dampproof material consisting of dampproof glue, a polyester film and an aluminum foil, and can be integrally constructed at one time, so that the repair operation time is shortened.

The construction process of replacing a cold insulation layer, a moisture-proof layer and a protective layer of a part to be repaired conforms to GB50126-2008 construction Specifications for industrial equipment and pipeline heat insulation engineering.

In the online repair method, in the step 4), the low-temperature pipeline cold insulation structure normally runs for at least 240 hours after being repaired and replaced, the cold insulation performance of the repaired and replaced cold insulation structure is detected and evaluated according to the method in the step 1), and the repaired cold insulation effect meets the design requirement.

The invention has the following beneficial effects:

1. when the LNG pipeline cold insulation structure is repaired by the repairing method, the whole repairing process can be realized without stopping.

2. The repairing method of the invention utilizes a special repairing tool to ensure that the surface of the pipeline does not frost in the repairing process, does not cause personnel frostbite, and has obvious cold insulation effect after repairing.

3. The invention is not only suitable for LNG pipelines, but also suitable for other low-temperature pipelines and devices, and can be popularized and used in other low-temperature cryogenic fields.

Drawings

FIG. 1 is an operational flow diagram of an online repair method.

FIG. 2 is a general schematic view of a repair tool used in the repair method of the present invention.

FIG. 3 is a front view of a purge tool in a repair tool used in the repair method of the present invention.

FIG. 4 is a top view of a purge tool in a repair tool used in the repair method of the present invention.

FIG. 5 is a left side view of a purge tool in a repair tool used in the repair method of the present invention.

The respective symbols in the figure are as follows:

1 purging the tool; 2, a valve; 3, a hose; 4, a nitrogen source; 5, repairing the pipeline; 6, a gas distributing part structure; 7, short connecting pipes; 8, a handle; 9 air outlet pipe; 10 a metal hose; 11 purge the nozzle.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

The flow chart of the online repair method of the invention is shown in fig. 1, and the method of the invention is explained by taking a low-temperature pipeline cold insulation structure with the pipe diameter of DN100 as an example:

1. when cold insulation performance evaluation is carried out on a cold insulation structure of an LNG pipeline, as an old cold insulation scheme is designed by referring to an anti-condensation cold insulation layer thickness method in GB/T8174-2008 test and evaluation of equipment and pipeline heat insulation effect, according to original design parameters of the pipeline, operation parameters of temperature, flow, pressure and the like of a conveying medium in the pipeline to be repaired and parameters of the environment around the pipeline, the measured surface temperature is converted to 25.2 ℃ of the surface temperature under a design working condition and is about 3 ℃ lower than 28.3 ℃ of the dew point temperature under the design working condition (see tables 1 and 2 for details), the cold insulation performance of the cold insulation structure at the part of the pipeline does not meet the design requirements, and the cold insulation structure needs to be repaired.

TABLE 1 original design parameters

TABLE 2 pipe media and environmental parameters

Project parameters	Data of	Project parameters	Data of
				Wind speed m/s	3.0	Ambient air temperature deg.C	20.9
Dew point temperature deg.C	14.8	Humidity of ambient air%	67.6
				Temperature of conveying medium	-196	Pressure of the conveying medium KPa	450
Flow rate m of transport medium3/h	6	Conversion design Condition surface temperature ts	25.2

2. When the cold insulation design is carried out on the part again, the selection of cold insulation materials and the design of cold insulation thickness are carried out according to GB/T8175-2008 'Heat insulation design guide rules of equipment and pipelines':

1) selecting cold insulation materials: hard polyurethane (PIR for short) is selected as the cold insulation material, the heat conductivity coefficient of the PIR material is 0.029W/(m x k) @25 ℃, and the use density is 50kg/m³The compressive strength is more than or equal to 0.22MPa, and the oxygen index is more than 28.

2) Design of cold insulation thickness: the cold insulation thickness is calculated by adopting an anti-condensation cold insulation thickness method, and the method comprises the following steps:

in the formula: d0-outside diameter of the pipe, m; d1-outer diameter of cold insulation layer, m; lambda is the thermal conductivity of the cold-retention material, W/(m × k); t is t_s-temperature of outer surface of cold insulation layer, degree centigrade; t is t_a-ambient temperature, ° c; t-medium temperature, DEG C; delta-cold insulation layer thickness, m; a is_sOuter surface of cold insulation layerCoefficient of heat transfer with the atmosphere, W/(m)²*K)。

The specification of the pipeline to be repaired is phi 108 x 4, the medium temperature is-196 ℃, and the surface heat dissipation coefficient is 8.141W/(m)²K), the dew point temperature value under the design working condition is 28.3 ℃, and the thickness of the required PIR material is calculated to be 110mm according to the principle that the surface temperature is 1.5-3 ℃ higher than the dew point temperature under the design state.

Particularly, for convenient construction, the required cold insulation material PIR is prefabricated into a tube shell shape, the cylindrical tube shell is symmetrically divided into two sections along the center, each section of PIR is processed into a step shape along the axial direction and the radial direction, and the cold insulation material with the thickness larger than 100mm is required to be processed in two layers according to the standard. The design thickness of the cold insulation layer in the cold insulation scheme is 110mm, the cold insulation layer is divided into 2 layers, and the thickness of each layer is 55 mm.

3. In the process of dismantling the old cold insulation structure at the part, when the old cold insulation structure is dismantled, the old cold insulation structure is dismantled in a segmented, layered and sequential manner; meanwhile, the inner-layer cold insulation structure is guaranteed to be detached 1-1.2 meters in length every time, and more outer-layer cold insulation structures can be detached to facilitate the construction of the inner-layer PIRs, and the inner-layer PIRs are still connected in a staggered mode.

And coating the prefabricated new cold insulation structure with cold insulation glue before the old cold insulation structure is dismantled, and preparing.

At the moment of dismantling the old cold insulation structure, a special repair tool connected with a nitrogen source in advance is started synchronously to blow the surface of the pipeline to be repaired, so that the requirements of zero icing and zero frosting on the surface of the pipeline to be repaired are met, and the upper-layer PIR cold insulation structure is installed immediately.

Specifically, the repair tool shown in fig. 2 is adopted in this embodiment, and includes four structures, namely, a purge tool 1, a valve 2, a hose 3, and a nitrogen gas source 4.

Wherein, the instrument of sweeping includes 2 annular gas distribution spare structures 6, and it is the circular arc pipe fitting (as shown in fig. 5, its central angle is 270 degrees) that is formed by the pipe, evenly arranges 5 air-out pipes 9 on every annular gas distribution spare structure 6, and air-out pipe 9 passes through metal collapsible tube and sweeps nozzle 11 and is connected, as shown in fig. 3 and fig. 4, because metal collapsible tube 10 has certain pliability, be convenient for adjust temporarily and sweep distance, air-out direction, make it can use with the work steel pipe phase-match of different pipe diameters. As shown in figure 3, the annular gas distributing part structures 6 are connected through the short joint structures 7 and then connected with the handle 8, the handle 8 is connected with the nitrogen gas source 4 through the hose 3, and the handle 8 is provided with the valve 2 for adjusting the gas blowing amount.

In this embodiment, 2 divide gas spare structures, handle, play tuber pipe all adopt light seamless stainless steel tube to process and form.

In this embodiment, in the purging tool 1, the distance between the two annular gas distributing structures 6 is 200mm, and the number of the annular gas distributing structures can be increased or decreased appropriately according to the length of the pipe section to be repaired.

In this embodiment, the size of the purge nozzle 11 is different, the purge cross section is different, the areas that can be blown are also different, and reference is required when designing the number of the air outlets and the number of the annular air distributing pieces.

In the step 3), the main moisture-proof layer of the new cold insulation structure adopts a self-adhesive composite moisture-proof layer so as to shorten the repairing operation time.

In the construction process of replacing a cold insulation layer, a moisture-proof layer and a protective layer of a part to be repaired with a new one, GB50126-2008 construction specifications of industrial equipment and pipeline heat insulation engineering are strictly executed.

Particularly, after the replacement of the upper cold insulation layer is finished, the next cold insulation layer can be sequentially detached, the expansion joint, the damp-proof layer and the protective layer are processed, and all processes in the whole repairing process are reasonable and compact.

4. After the pipeline is repaired and replaced and normally runs for 240 hours, the cold insulation performance of the repaired cold insulation structure is detected and evaluated. When the cold insulation effect of the part is verified, the cold insulation effect of the repaired cold insulation structure is reevaluated according to the detection and evaluation method in the step 1), the surface temperature under the test working condition is converted to the surface temperature under the design working condition to be 30 ℃, the dew point temperature under the design working condition is 28.3 ℃, and the cold insulation effect is obviously improved.

The LNG pipeline cold insulation structure on-line repairing technology provided by the invention can be applied to the repairing process of low-temperature equipment such as an LNG station and a pipeline system cold insulation structure, the whole repairing process is not stopped, the phenomena of frosting, condensation, icing and the like are avoided by means of a special repairing tool, and the cold insulation performance of the repaired LNG pipeline is ensured.

The above description is only one embodiment of the present invention, and all modifications, equivalents, improvements and the like that are made within the spirit and principle of the present invention are included in the protection scope of the present invention.