The high consequence area of oil and gas transmission pipeline is characterized by high risk, difficult management and great injury. Its management requires joint efforts of local governments and pipeline enterprises. To address this issue, find a way to effectively control the high consequences area, Based on the experience of the forefathers, this paper summarizes the corresponding risk management measures, in order to ensure that the high-pressure natural gas pipeline transportation task can be completed safely and efficiently.
Definition and Control Significance of High Consequence Area of Gas Transmission Pipeline
1.1 Definition of High Consequence Zone for Gas Transmission Pipelines
High Consequence Areas (HCAs) are areas where leakage of pipelines will seriously endanger public safety and / or cause environmental damage. The typical high-consequence areas are densely populated areas and sensitive environmental areas. Gas pipelines do relatively little harm to sensitive areas such as rivers, lakes and nature reserves. Therefore, the environmental sensitive high-consequence zones are mainly for oil pipelines.
High consequence area is the key point of pipeline management. It is the consensus of the pipeline management units to identify high consequence areas. On the one hand, the degree of pipeline leakage accident is different from that of non-high-consequence area. Pipeline leakage accidents in high-consequence areas may cause great harm to the safety of people and environment around the pipeline, and then have great social impact. The influence of pipeline leakage accident in non-high consequence area is mainly directed to the interior of pipeline enterprise. We should avoid pipeline leakage and secondary disaster caused by pipeline leakage.1.2 Gas pipeline high consequence area control significance
High consequence area is the focus of pipeline management. It is the consensus of domestic and foreign pipeline operators to identify and control high consequence areas. Oil and gas pipeline accidents at home and abroad in recent years, especially the Qingdao “11 · 22” Sinopec Donghuang oil pipeline accident, It caused great damage to the pipeline enterprises and the surrounding personnel. At the same time, the competent authorities of gas pipeline protection pay more and more attention to the control and inspection of the high-consequence areas of oil and gas transmission pipelines. In 2017, the State Administration of Work Safety (SAWS) and other departments issued the Circular on Strengthening Safety Management of High Consequence Areas in Crowded Places Along Oil and Gas Transmission Pipelines (No. 138 [2017], General Manager III), It explicitly requires pipeline enterprises to take primary responsibility, identify and control the high-consequence areas of oil and gas pipelines. GB 32167-2015 “Integrity Management Code for Oil and Gas Transmission Pipelines” implemented in March 2016 [1] There are six mandatory provisions, three of which relate to high-consequence zones: Article 4.4 “During the construction period, high consequence area identification is carried out and routing is optimized. Safety precautions should be taken when avoiding high-consequence areas ” ； Article4.5 “High consequence zone identification shall be carried out periodically during the operation period of the pipeline, and the longest interval shall not exceed 18 months. When the pipeline and surrounding environment change, high consequence zones shall be renewed in time.” Article 4.6 “Risk assessment of pipelines in high consequence zones.”
2 High consequence zone recognition
2.1 High Consequence Area Identification Guidelines
High-consequence areas are areas where a pipeline leak may cause significant adverse effects on the public and the environment. According to GB32167-2015 “Management Code of Integrity of Oil and Gas Transmission Pipelines,” high consequence areas along gas transmission pipelines mainly include the following areas [1] ：
(1) The third and fourth grade areas where the pipeline passes.
There are hospitals, markets, schools, nurseries and kindergartens in the pipeline’s potential impact area.
(3) There are chemical plants, gas stations, oil depots and other inflammable and explosive sites within 200m on both sides of the pipeline center line. It is divided into three grades: I, II and III. Grade I is the least severe and grade III is the greatest.
(4) Specific places, specific places I: hospitals, schools, nurseries, kindergartens, nursing homes, prisons, shopping malls and other construction areas where people evacuation is difficult; Site-specific II: An area of at least 30 or more people for at least 50 days a year. Such as bazaars, temples, sports grounds, squares, recreational areas, theaters, campgrounds, etc. For the identification of high consequence zone of specific site type, the distance from pipeline center line should be determined according to the formula of potential impact radius.
2.2 High Consequence Area Identification Workflow
According to the requirements of GB32167-2015 “Management Code for the Integrity of Oil and Gas Long-Distance Pipelines,” the identification of high-consequence areas should be carried out according to following procedures:
2.2.1 Collection of materials and data
First, collect the related information about rectified pipeline and pipeline periphery, including not limited to the remaining information:
1 Basic parameters of pipeline, pipeline operating life, pipe diameter, wall thickness, pipe grade, etc.
Preliminary design report and completed data of pipeline;
The remote sensing or aerial image of the pipeline and the line as built drawings;
Pipe crossing, valve room and other facilities information;
Statistics of key section, distribution of population around pipeline;
Pipeline safety hidden trouble identification list;
Pipeline construction operations;
Third party cross construction information.
2.2.2 Initial Identification of High Consequence Areas
Through the map function of GIS, the electronic map processing of the long pipeline and the surrounding environment is vectored to form a visual information system which integrates the attribute information and spatial information of the natural gas pipeline. Through spatial query, location and analysis, the sensitive area along the pipeline and the densely populated area are determined, and the location of the high consequence area is initially identified, and a preliminary summary table is formed.
2.2.3 On-site review
Natural gas transmission pipelines have longer routes, passing through hilly basins, mountainous regions and plain areas with dense water networks, Many sections of pipeline have large drop and complicated crossing engineering, so it is difficult to achieve the accuracy and integrity of identifying the high consequence area of pipeline only by using pipeline location image. It is necessary to survey the field situation along the pipeline, analyze the key pipeline sections in detail, and modify and improve the preliminary summary table of high consequence areas.
2.2.4 Reporting
The HRA identification report shall include at least the following:
1 Overview: High consequence area identification work situation and pipeline situation overview;
High consequence area identification result;
Result analysis and suggestion.
3 Reasons for the Formation of High Consequence Zone in Gas Transmission Pipeline
3.1 Legacy of the Construction Period
During the construction period of pipeline, high consequence zone was not identified sufficiently and densely populated area was not avoided effectively, which led to the formation of high consequence area after pipeline put into operation.
3.2 Pipeline and Urban-Rural Development Planning Contradiction
With the development of social economy, the contradiction between urban and rural planning and land planning around the pipeline is becoming more and more prominent. The main performance is the large-scale development and construction around the pipeline, resulting in changes in the level of the area where the pipeline is located, the number of densely populated high-consequence areas is on the rise, forming new high-consequence area.
- Control and control measures and countermeasures in high consequence area of gas pipeline
4.1 New projects do a good job of identifying high consequence areas in advance
In the early stage of construction, the identification of high consequence area of gas pipeline should be carried out, the routing selection should be optimized, and the stock of high consequence area should be reduced as far as possible. If it can not avoid circumventing, safety protection measures should be taken to improve the essential safety of pipeline.
4.2 do a good job of identifying high consequence areas on a regular basis
The high consequence area is not immutable, it changes with the change of time and environment, the re-identification cycle of the high consequence area should not exceed 18 months, and the “one area case” should be updated on a regular basis. We should conscientiously study the criteria for identifying high-consequence areas, unify standards, and avoid artificially increasing or reducing the number and level of high-consequence areas.
4.3 regular risk identification
According to the requirements of national standards, regular personnel should be organized to carry out risk assessment of pipelines in high-consequence areas, at the same time, it is necessary to formulate targeted risk reduction measures strictly according to the results of risk assessment and implement them one by one, and priority should be given to the management of geological hazard risk points.
4.4 do a good job of integrity evaluation
According to the requirements of the code, the integrity evaluation of the pipeline in the high consequence area can identify the defects of the pipeline body and predict the residual strength and remaining life of the pipeline, which provides the scientific basis for the pipeline operation and arranges the repair of the abnormal points of the pipeline body.
4.5 strengthen pipeline corrosion control
Pipeline corrosion control should be strengthened in high consequence area, internal and external inspection and cathodic protection potential test should be carried out regularly, and the corresponding work implementation plan should be worked out. Whether the cathodic protection potential of the pipeline in the high consequence area is normal or not is detected regularly. The stray current interference is checked by pile-by-pile test, electrification point (confluence point) potential test and natural potential test along the pipeline. According to the test data, the status of line protection is analyzed. Effective measures are taken to ensure the normal operation of the pipeline cathodic protection system and to ensure the essential safety of the pipeline. When making the annual maintenance plan, priority should be given to rectifying the leakage point of pipeline anticorrosion coating, stray current interference, pipeline body defects and other abnormal points in the high consequence section.
4.6 strengthening monitoring of buried depth of pipelines
The buried depth of the pipeline in the high consequence section is detected regularly, and the shallow buried pipeline in the high consequence section is dealt with in time. On the one hand, the qualified buried depth can prevent the pipeline from scouring, on the other hand, the external third party can effectively avoid the accidental injury of the pipeline. It is suggested that a buried depth test should be organized before and after the flood season.
4.7 strengthen third-party construction management
The third party construction control is the key point of pipeline safety in high consequence area, establish the corresponding enterprise and land contact mechanism, grasp the pipeline safety information in high consequence area in time, strictly carry out the cross construction management procedure, arrange the special person to be responsible for the whole process supervision and management of the third party construction, introduce the technical prevention measures of optical fiber early warning system conditional, and identify the construction situation of the third party around the pipeline in advance.
4.8 strengthen pipeline inspection in high consequence section
Strengthening the inspection is an effective guarantee for the control and control of the high consequence area. In the daily hiking inspection, priority should be given to the inspection of the high consequence area, the route of inspection should be optimized for the local patrol workers, and the frequency of inspection should be properly encrypted, and the inspection frequency should not be checked or bypassed from a long distance. Improve the “three piles and one brand” to ensure that the handwriting is clear and the pipeline direction is clear and correct. Clean up weeds regularly to ensure access to the line.
4.9 Collection and detection of closed space information
Regularly collect and update the underground facilities information of drainage, sewerage pipeline and pipeline trench, pipe culvert and other possible oil and gas accumulation space around the pipeline, regularly detect the existence of flammable gas, and strictly prevent the leakage of combustible pressure to the closed space.
4.10 rely closely on the government to do a good job in the control of fruit areas
Actively contact with local government planning, land departments, development and reform commission, safety supervision, etc., actively report pipeline completion survey map, emergency plan and site disposal plan and identification results of high consequence area, manage the stock of high consequence area and strictly control the increment.
4.11 do a good job of emergency work
Combing and perfecting the emergency plan and on-site disposal plan in the high consequence area, ensuring the enforceability of the emergency plan, mastering the distribution of emergency repair resources around the pipeline and the situation of the approach road, strengthening the training of personnel, organizing all kinds of typical emergency exercises on a regular basis, and improving the ability of emergency disposal.
