CN105678387A - Pipeline cleaning safety assessment method for natural gas pipeline crossing structure - Google Patents

Abstract

The invention discloses a pipeline cleaning safety assessment method for a natural gas pipeline crossing structure. There is no safety check index and check process specially aimed at pipeline cleaning process of a natural gas pipeline crossing structure and it is difficult to assess the pipeline cleaning safety of a natural gas pipeline crossing structure. By use of the provided method, pipeline cleaning safety is assessed and the above problems are solved. The method comprises following steps: collecting basic data such as the length and pipeline steel yield strength of the natural gas pipeline crossing structure according to the design information of the natural gas pipeline crossing structure; calculating the maximum permissible displacement and the maximum permissible stress of the crossing structure; comparing the displacement, stress and permissible values of the crossing structure under different pipeline cleaning speed, sorting a safety checking list for the pipeline cleaning of the natural gas pipeline crossing structure, and determining whether pipeline cleaning is needed or not and the pipeline speed according to the checking result. The method has simple assessment process and clear assessment index and can help determine whether pipeline cleaning is needed or not.

Description

A pigging safety evaluation method for spanning structures of natural gas pipelines

technical field

The invention belongs to the field of design and safety assurance of natural gas pipelines, and in particular relates to a pigging safety evaluation method for spanning structures of natural gas pipelines.

Background technique

The pipeline spanning structure is a construction project in which the transmission pipeline passes through the upper part of natural or artificial obstacles. my country has started to build natural gas pipeline spanning structures since the 1970s, and there are more than 30 large and medium-sized pipeline spanning structures in service so far. . After the natural gas pipeline is newly built and put into operation and during the normal operation cycle, it needs to be pigged to remove debris and accumulated water in the pipeline to ensure its transmission capacity. However, for natural gas pipeline spanning structures, the dynamic load during pigging may cause extremely serious consequences and losses. Because the main load-bearing parts of the spanning structure are steel cables, it is a flexible constraint on the pipeline. During the pigging process, the local slug flow formed by the pig pushing the accumulated water in the pipe will also change the flow state when passing through the bends and undulating terrain of the upper bridge of the spanning structure, which will easily cause the spanning structure to vibrate and Displacement; and pipeline vibration will affect the flow state of the two-phase flow in the pipeline, forming fluid-solid coupling vibration under the condition of two-phase flow, which will further aggravate the vibration and displacement of the spanning structure. For example, when the spanning structure of the cable-stayed pipeline in Nanguang River, Sichuan Province was pigged, the maximum displacement of the pipeline reached 2m. Substantial displacement and vibration will not only cause the instability of the spanning structure, but also easily cause its stress to exceed the limit, which will lead to the destruction of the overall structure. The leaked natural gas after the destruction may cause fire and explosion accidents, seriously threatening the lives and property safety of residents around the spanning structure. Therefore, it is extremely necessary to conduct a safety assessment of the pigging plan before pigging across the structure to ensure the safety of the spanning structure and the stability of the pigging process.

Many scholars at home and abroad have studied the displacement and stress calculation methods of the spanning structure of the natural gas pipeline during the pigging process, but a complete pigging safety evaluation process has not been formed. As for the relevant standards for spanning structures of natural gas pipelines, GB50459-2009 "Code for Design of Crossing Projects for Oil and Gas Transmission Pipelines" only stipulates the allowable stress and allowable displacement of spanning structures under all load-bearing conditions, and does not propose special requirements for the pigging process. It is also difficult to evaluate the pigging safety across structures.

To sum up, the large displacement and strong vibration of the spanning structure of the natural gas pipeline during the pigging process are major safety threats it faces. However, at present, there is no evaluation method and evaluation process for the safety of the pigging process of the natural gas pipeline spanning the structure, and there are defects in the production and operation of the pipeline.

Contents of the invention

The present invention provides a pigging safety evaluation method for a natural gas pipeline crossing structure to solve various defects and deficiencies in the prior art. The technical solution adopted by the present invention is as follows: Provide a pigging safety evaluation for a natural gas pipeline spanning structure method, the method includes the following steps:

Step 1. According to the design data of the spanning structure of the natural gas pipeline, site survey and the proposed pigging operation plan, collect the length of the spanning structure of the natural gas pipeline and the yield strength of the steel used for the pipeline, and collect the spanning structure at different pigging speeds according to Table 1. displacement and stress values;

Table 1 Displacement and stress values of natural gas pipeline spanning structure at different pigging speeds

Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Pipeline maximum stress/MPa Pipeline maximum displacement/m

Step 2, according to the collected basic parameters, in combination with Table 2, calculate the maximum allowable displacement and maximum allowable stress of the spanning structure, which is called the displacement and stress allowable value of the spanning structure of the pipeline;

Table 2 The maximum allowable displacement and maximum allowable stress of the natural gas pipeline spanning structure

Step 3: Comparing the displacement, stress and allowable value of the crossing structure at different pigging speeds, sorting out and forming the pigging safety checklist for the crossing structure of the natural gas pipeline, and deciding whether to pigge and a reasonable pigging rate based on the check results , the specific implementation steps are:

(1) Compare the displacement and stress values at different pigging speeds with the allowable value, if the displacement value or stress value is less than the comparative allowable value, it is called "safe state"; if the displacement value or stress value is greater than the comparison The allowable value is called "over limit state", and all the check results are summarized to form Table 3;

Table 3 Checklist of safety status of natural gas pipeline spanning structure

Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Displacement calibration allowable strength check Limit allowable strength check

(2) If in Table 3, under the condition of a pigging speed, the displacement check, the allowable strength check and the limit allowable strength check are all in the "safe state", then the spanning structure is said to be "safe by pigging". check, pigging can be implemented”; if in Table 3, there is a pigging speed that makes the displacement check and the limit allowable strength check a “safe state”, but the allowable strength checks at all pigging speeds are If the crossing structure is "out of limit", it is said that the crossing structure "passes the pigging safety check, but the pigging speed must be carefully selected to ensure the safety of the crossing structure"; if in Table 3, under all pigging speed conditions, the displacement If the check, allowable strength check, and limit allowable strength check are all "over limit", it is said that the spanning structure "failed to pass the pigging safety check, and pigging cannot be carried out under the existing conditions";

(3) If the spanning structure is judged as "passing the pigging safety check, pigging can be carried out", then the pigging can be selected in which the displacement check, allowable strength check and limit allowable strength check are all in a "safe state". The pigging speed shall be carried out at a certain speed; if the crossing structure is judged as "passing the pigging safety check, but the pigging speed must be carefully selected to ensure the safety of the crossing structure", a pigging speed of 3m/s shall be selected for pigging.

The pigging safety evaluation method of the spanning structure of the natural gas pipeline provided by the present invention is based on the design parameters and the pigging scheme of the spanning structure of the natural gas pipeline, combined with the principles of material mechanics and the safety check standard of the spanning structure, and researches and establishes the safety of the spanning structure of the pipeline A new method for pigging evaluation process. The evaluation process is simple, the evaluation index is clear, and the final result obtained by using the evaluation method can assist in decision-making whether to implement pigging on the crossing structure of the natural gas pipeline, and can determine a reasonable pigging rate, which provides guidance for the pigging safety of the crossing structure of the natural gas pipeline. Governance basis.

Description of drawings

Fig. 1 Flowchart of pigging safety assessment method for natural gas pipeline spanning structure.

detailed description

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The invention provides a method for calculating the maximum displacement and bending stress in the pigging process of a natural gas pipeline spanning a structure. The method includes the following steps:

Step 1. According to the design data of the spanning structure of the natural gas pipeline, site survey and the proposed pigging operation plan, collect the length of the spanning structure of the natural gas pipeline, the yield strength of the steel for the pipeline, and the displacement and stress values of the spanning structure at different pigging speeds and other basic data;

Step 2, calculate the maximum allowable displacement and maximum allowable stress of the spanning structure according to the collected foundation parameters;

Step 3: Comparing the displacement, stress and allowable value of the crossing structure at different pigging speeds, sorting out and forming the pigging safety checklist for the crossing structure of the natural gas pipeline, and deciding whether to pigge and a reasonable pigging rate based on the check results .

In step 1, the basic parameters that need to be collected include the length of the spanning structure of the natural gas pipeline and the yield strength of the steel used for the pipeline, and the displacement and stress values of the spanning structure at different pigging speeds are collected according to Table 1;

Table 1 Displacement and stress values of natural gas pipeline spanning structure at different pigging speeds

Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Pipeline maximum stress/MPa Pipeline maximum displacement/m

In step 2, calculate the maximum allowable displacement and maximum allowable stress of the spanning structure according to the collected basic parameters in combination with Table 2, which is called the allowable value of displacement and stress of the spanning structure of the pipeline;

Table 2 The maximum allowable displacement and maximum allowable stress of the natural gas pipeline spanning structure

In step 3, compare the displacement, stress and allowable value of the spanning structure at different pigging speeds, sort out and form the pigging safety checklist for the spanning structure of the natural gas pipeline, and decide whether to pig and a reasonable cleaning method according to the check results. Tube rate, the specific implementation steps are:

(1) Compare the displacement and stress values at different pigging speeds with the allowable value, if the displacement value or stress value is less than the comparative allowable value, it is called "safe state"; if the displacement value or stress value is greater than the comparison The allowable value is called "over limit state", and all the check results are summarized to form Table 3;

Table 3 Checklist of safety status of natural gas pipeline spanning structure

Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Displacement calibration allowable strength check Limit allowable strength check

(2) If in Table 3, under the condition of a pigging speed, the displacement check, the allowable strength check and the limit allowable strength check are all in the "safe state", then the spanning structure is said to be "safe by pigging". check, pigging can be implemented”; if in Table 3, there is a pigging speed that makes the displacement check and the limit allowable strength check a “safe state”, but the allowable strength checks at all pigging speeds are If the crossing structure is "out of limit", it is said that the crossing structure "passes the pigging safety check, but the pigging speed must be carefully selected to ensure the safety of the crossing structure"; if in Table 3, under all pigging speed conditions, the displacement If the check, allowable strength check, and limit allowable strength check are all "over limit", it is said that the spanning structure "failed to pass the pigging safety check, and pigging cannot be carried out under the existing conditions";

(3) If the spanning structure is judged as "passing the pigging safety check, pigging can be carried out", then the pigging can be selected in which the displacement check, allowable strength check and limit allowable strength check are all in a "safe state". The pigging speed shall be carried out at a certain speed; if the crossing structure is judged as "passing the pigging safety check, but the pigging speed must be carefully selected to ensure the safety of the crossing structure", a pigging speed of 3m/s shall be selected for pigging.

The application principle of the present invention will be further described below in conjunction with specific examples.

Example 1: The length of a natural gas suspension cable spanning structure is 320m, and the yield strength of the pipeline steel is 552MPa. Try to evaluate the pigging safety of the spanning structure.

Step 1: The collected basic parameters include the span length L _p of the natural gas pipeline spanning structure = 320m, the yield strength of the pipeline steel σ = 552MPa, and the displacement and stress values at different pigging speeds are shown in Table 4.

Table 4 Displacement and stress values of the example pipeline spanning structure at different pigging speeds

Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Pipeline maximum stress/MPa 291 295 299 301 303 306 Pipeline maximum displacement/m 0.2495 0.2527 0.2753 0.2886 0.2968 0.3152

Step 2: Calculate the maximum allowable displacement and maximum allowable stress of the spanning structure based on the collected basic parameters in combination with Table 5, which is called the allowable value of displacement and stress of the spanning structure of the pipeline.

Table 5 The maximum allowable displacement and maximum allowable stress of the spanning structure of the pipe in the example

Step 3: Comparing the displacement, stress and allowable value of the spanning structure at different pigging speeds, sorting out and forming the pigging safety checklist of the spanning structure of the natural gas pipeline, and deciding whether to pigge and a reasonable pigging according to the check results The specific implementation steps are as follows:

(1) Compare the displacement and stress values at different pigging speeds with the allowable values to form a checklist for the safety state of the spanning structure as shown in Table 6;

Table 6 The safety status check list of the pipeline spanning structure of the example

(2) According to Table 6, at all pigging speeds, the displacement check and the limit allowable strength check are both "safe state", but the allowable strength check is "over limit state", so the span structure The conclusion of the safety evaluation is: pass the pigging safety check, but the pigging speed needs to be carefully selected to ensure the safety of the crossing structure;

(3) Based on the safety assessment conclusion, a pigging speed of 3m/s should be selected for pigging.

From the above calculation example, it can be found that the evaluation process of the present invention is simple, the evaluation index is clear, and it can make a decision for the pigging scheme of the natural gas pipeline crossing structure. Therefore, the present invention clearly has its necessity and practicality.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (4)

1. A pigging safety evaluation method of a natural gas pipeline spanning structure, comprising the following steps: Step 1. Based on the design data of the natural gas pipeline crossing structure, site survey and the proposed pigging operation plan, collect the basic data of the natural gas pipeline spanning structure, including the length of the pipeline, the yield strength of the steel used for the pipeline, and the spanning structure at different pigging speeds. Displacement and stress values under; Step 2, calculate the maximum allowable displacement and maximum allowable stress of the spanning structure according to the collected foundation parameters; Step 3: Comparing the displacement, stress and allowable value of the crossing structure at different pigging speeds, sorting out and forming the pigging safety checklist for the crossing structure of the natural gas pipeline, and deciding whether to pigge and a reasonable pigging rate based on the check results . 2. the pigging safety evaluation method of natural gas pipeline spanning structure as claimed in claim 1, is characterized in that, collects the length of natural gas pipeline spanning structure, the yield strength of pipeline steel, and according to table 1 collect spanning structure in different pigging Displacement and stress values at velocity. Table 1 Displacement and stress values of natural gas pipeline spanning structure at different pigging speeds Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Pipeline maximum stress/MPa Pipeline maximum displacement/m 3. the pigging safety evaluation method of natural gas pipeline crossing structure as claimed in claim 1, is characterized in that, according to the basic parameter collected, in conjunction with table 2, calculates the maximum allowable displacement and the maximum allowable stress of crossing structure, referred to as the Displacement and stress allowable values for pipe spanning structures. Table 2 The maximum allowable displacement and maximum allowable stress of the natural gas pipeline spanning structure 4. the pigging safety evaluation method of natural gas pipeline crossing structure as claimed in claim 1, is characterized in that, compares the displacement, stress and allowable value thereof of crossing structure at different pigging speeds, sorts out and forms natural gas pipeline crossing structure cleaning. Check the management safety checklist, and decide whether to piggage and the reasonable pigging rate according to the check results. The specific implementation steps are: (1) Compare the displacement and stress values at different pigging speeds with the allowable value, if the displacement value or stress value is less than the comparative allowable value, it is called "safe state"; if the displacement value or stress value is greater than the comparison The allowable value is called "over limit state", and all the check results are summarized to form Table 3; Table 3 Checklist of safety status of natural gas pipeline spanning structure Pigging speed/(m/s) 3 3.2 3.4 3.6 3.8 4 Displacement calibration allowable strength check Limit allowable strength check (2) If in Table 3, under the condition of a pigging speed, the displacement check, the allowable strength check and the limit allowable strength check are all in the "safe state", then the spanning structure is said to be "safe by pigging". check, pigging can be implemented”; if in Table 3, there is a pigging speed that makes the displacement check and the limit allowable strength check a “safe state”, but the allowable strength checks at all pigging speeds are If the crossing structure is "out of limit", it is said that the crossing structure "passes the pigging safety check, but the pigging speed must be carefully selected to ensure the safety of the crossing structure"; if in Table 3, under all pigging speed conditions, the displacement If the check, allowable strength check, and limit allowable strength check are all "over limit", it is said that the spanning structure "failed to pass the pigging safety check, and pigging cannot be carried out under the existing conditions"; (3) If the spanning structure is judged as "passing the pigging safety check, pigging can be carried out", then the pigging can be selected in which the displacement check, allowable strength check and limit allowable strength check are all in a "safe state". The pigging speed shall be carried out at a certain speed; if the crossing structure is judged as "passing the pigging safety check, but the pigging speed must be carefully selected to ensure the safety of the crossing structure", a pigging speed of 3m/s shall be selected for pigging.