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01 Risk analysis and countermeasures for pig operation

1.1 Pig Scraper jamming

Pig Scraper jamming is a serious problem that may occur during pigging. If it is not serious, it will cause the interruption of the oil transportation process. In severe cases, it may cause an abnormal increase in pipeline pressure. This may even lead to serious problems such as pipe leakage. There are various reasons for pig jamming.

In general, it mainly focuses on the following aspects:

  1. The pipe tee is not provided with a bar. The pig is gradient when passing through the tee. This may cause jamming.
  2. The pipeline has severe deformation. This makes it impossible for the pig to pass smoothly, resulting in jamming;
  3. The valve on the main pipeline is not fully opened during ball passing. It is easy to cause pig jamming;
  4. There are large foreign matters in the pipeline that make the pig unable to pass smoothly, causing foreign matters to jam;
  5. There are too many impurities such as oil sludge and wax block in the pipeline. The pig has blockage due to slow sedimentation during pigging.

From the change in pipeline pressure, there are two phenomena of pig jamming.

One is the obvious change of pipeline pressure. The pressure of the service station continues to rise during the pass. The pressure of the receiving station drops obviously or remains unchanged. Finally, the pressure at the service station suddenly rebounded. It indicates that the pig has a blockage at a certain position.

The other is that the change of pipe pressure is not obvious. This is because the pig cup is damaged or blocked by foreign matters. In the process of tracking the pig, we can find that the pig has not reached the predetermined position for a long time. This requires the tracking device to locate the stuck position of the pig. To reduce the risk of pig jamming. Therefore, before pigging, check the early plugging position. This ensures that the blanking plate is normal. Attention shall be paid during ball passing.

pipeline

In case of instant jamming, the first station stops pumping. The personnel of the ball tracking team shall judge the blocking position of the pig according to the pipeline throughput and pressure distribution. After the pigging personnel confirm the blocking position. They shall timely make fixed marks and report to the superior management department. Notify the oil transportation dispatching and rescue team as soon as possible. Then they work out the emergency repair plan according to the site conditions. They conduct plugging operation at the stuck position of the pig.

After the Pig Scraper is taken out, normal oil delivery is resumed. In case of any sign of slow jamming, the pigging team shall communicate with the dispatcher in time. We will promptly inform the station of the site conditions. The rescue personnel shall be prepared for rescue. Once the pig is blocked, the plugging and rescue work shall be done in a timely manner. After the pig is taken out, normal oil delivery is resumed.

1.2 Pig Scraper tracking loss

Pig tracking loss is a condition that is easy to occur during pigging. Although this cannot directly lead to the interruption of pigging process. However, it will pose a certain threat to the safe pigging. There are various reasons that may cause the loss of pig tracking. Failure of tracking receiver or transmitter or negligence of tracking personnel. These may lead to the loss of pig tracking. In addition, it is assumed that temporary changes in pipeline throughput will cause changes in pig operating speed. Pigging personnel did not obtain parameter change information in time.

These may also result in loss of pig tracking. It is assumed that pig tracking is lost during pigging. Pigging personnel shall timely communicate with oil transportation dispatching personnel. According to the latest operating parameters of the pipeline, the approximate position of the pig is calculated. Then the settling personnel will develop the on-site pig positioning work. Confirm whether the pig operates normally. If its main reason is a mechanical failure of the tracker. Pigging personnel shall immediately replace the tracker and pay close attention to the pig operation status. This can avoid losing tracking again.

If its main reason is transmitter failure. Then they should find a special person to monitor the pig passing through the nearest bare pipe section. The oil transportation dispatching shall closely monitor the change of pipeline pressure until the pig arrives at the station safely. If its main reason is the change of conveying parameters. Then communicate with the dispatcher in time. Calculate the current position of the pig. Then reach the designated position in advance. Finally, they re determined the operation position of the pig and continued to follow the ball.

02 Risk analysis and countermeasures of pipeline body

2.1 Pipeline oil leakage

pig scraper

Pipeline oil leakage is a serious risk during pigging. Although there are various reasons for pipeline oil leakage. But generally speaking, it mainly includes the following two aspects:
First, after long-term corrosion of the pipe body, there are thin parts in the severely corroded parts. The thin part of pipe wall may be broken during ball passing. There is also a risk of oil leakage from the pipeline.
Second, it is assumed that the pig is blocked during ball passing. This may cause a transient increase in line pressure. It may then lead to the risk of rupture and oil leakage at the thin pipe wall. When an oil leakage accident occurs, the first thing to do is to determine the cause of the pipeline oil leakage. If its main reason is a Pig Scraper. Then we refer to the measures for handling pig blockage for emergency disposal. If it is confirmed that the pipeline leakage is not caused by pig blockage. Then the oil transportation dispatcher shall timely inform the on-site tracking personnel of the current oil transportation parameters. The pig tracking group locates the pig. The on-site cooperation personnel shall timely confirm the location of oil leakage in the pipeline. The rescue team shall timely develop emergency rescue work.

2.2 Lack of pipeline crossing support strength

When the Pig Scraper passes through the pipeline crossing section, it is likely to resonate with the pipeline and cause the risk of lack of pipeline support strength, which may lead to problems of the effective pipeline crossing section support and leakage at the thin pipe wall. In order to avoid this kind of situation, before pigging, the pipeline operation unit shall check the crossing parts of the pipeline, and add support to the unqualified pipeline section to ensure that the support strength meets the pigging requirements. During pigging, the pipeline operation unit shall arrange personnel to focus on monitoring the pipeline crossings, especially the locations prone to risks, and increase the density of on-site patrol personnel if necessary. The ball tracking personnel shall confirm the passing status of the pig at the crossing of the pipeline in time to ensure the smooth passing of the pig.

2.3 Secondary hazards caused by pipeline leakage in high-risk areas.

For pipelines crossing densely populated areas, rivers and lakes, water bodies, railways, highways, and other transportation facilities, pipe blockage and pipeline leakage may cause secondary hazards in the above areas. Therefore, pigging is developing. We shall formulate detailed countermeasures against possible hazards. Make a disposal plan for dangerous points. The station shall increase the frequency of line patrol during pigging. In case of Pig Scraper blockage and pipeline leakage in the above areas. We should start the corresponding emergency plan in time.

03 Analysis of station operation risk and countermeasures

3.1 Flashing

Flashover is a kind of relatively large risk that may occur during station operation. Severe cases may cause casualties. When the receiver and launcher are turned over, the residual oil and gas in the receiver and launcher will cause flash combustion when reaching a certain concentration. To prevent flashover accidents. We shall carry out pigging operations in strict accordance with relevant standards. The electrostatic discharge device shall be placed at the receiving and launching site and the grounding shall be good. Before receiving and serving, the on-site personnel must discharge static electricity. The fire source and combustibles in the receiving and launching station shall be cleaned in time. Not allowing operators to carry non-explosion-proof tools.

During the process of opening the receiving and launching blind plate, ensure that no personnel are in the dangerous area where the blind plate is opened. After opening the cylinder, the safety supervisor needs to use a combustible gas detector to measure the oil and gas concentration in the cylinder. If the concentration exceeds the standard, use the wet ball collecting method. It is assumed that a flashover accident occurs during receiving and launching. At this time, the on-site personnel shall timely use the fire extinguisher, felt, fire sand and other fire extinguishing devices equipped in the station to extinguish the fire. Avoid further expansion of the fire. If the fire continues to expand beyond the control range, we should call the fire alarm in time. And report to the emergency management department to start the relevant fire emergency plan.

3.2 Hydrogen sulfide poisoning

Hydrogen sulfide is a strong asphyxiant gas. It has many dangers. And it is also extremely flammable. It can form explosive mixture when mixed with air. Although hydrogen sulfide has a foul smell. But it is very easy to make people smell tired and unaware. So it is very harmful. According to the nature of pigging operation of oil pipeline, on-site personnel are in close contact with leaked crude oil. This is very easy to cause hydrogen sulfide poisoning. To prevent the occurrence of hydrogen sulfide poisoning in the process of receiving and sending balls on site. We should establish operation standards for receiving and serving. The on-site personnel shall carry out relevant operations in strict accordance with the operation standards.

In the process of receiving and sending the ball, on-site operators shall be familiar with the hazards, protection knowledge, and emergency plan of hydrogen sulfide gas. Before opening the blind plate, except the operators who open the blind plate, other personnel shall keep a safe distance. And they cannot be in the operation area. Operators who open blind plates shall wear positive pressure respirators. They stand at the upper air outlet and carry hydrogen sulfide gas detectors.

When the blind plate is opened, the safety supervisor shall detect the hydrogen sulfide concentration in the spherical cylinder and at the operation site. At the same time, ensure good ventilation conditions on site. The blind plate shall be left standing for at least 30min after opening. During this period, we will monitor the concentration of hydrogen sulfide in the cylinder at any time. If the hydrogen sulfide concentration exceeds the standard during the ball receiving, evacuate the personnel immediately. After the concentration of hydrogen sulfide is lower than 10mg/m3, continue the ball receiving and launching operation.

04 Conclusion

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In a word, pigging of crude oil pipeline is an effective way to ensure safe operation of pipeline and improve transmission efficiency. The risks in crude oil pipeline pigging operation are mainly concentrated in Pig Scraper operation, pipeline body and station operation. For each risk type identified, we have formulated corresponding countermeasures. This provides an effective guarantee for the safe and smooth operation of the whole pigging operation. During pigging, follow relevant standards strictly. If we have the above risk problems, we can take corresponding measures to deal with them. In addition, the site conditions are varied and different. We should properly adjust the corresponding response measures according to the actual situation on site. Strive to combine theory with practice. Only in this way can the whole pigging process be carried out safely and smoothly.