THE DEVELOPMENT OF ON-LINE PIPE TO SOIL POTENTIAL MONITORING SYSTEM

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1 THE DEVELOPMENT OF ON-LINE PIPE TO SOIL POTENTIAL MONITORING SYSTEM Sang-Yup Jang*, R&D center of Korea Gas Corporation Jae-Young Jeoun, R&D center of Korea Gas Corporation Kyung-Whan Park, R&D center of Korea Gas Corporation 1. Introduction Network of pipeline were constructed for gas supply in the country. For high pressure pipeline have to operate safely first of all, steel pipe have to qualify for adequate standard were used at high pressure gas transmission pipeline. Therefore, that has the merit for safe gas supply under the high pressure. But, once conditions are satisfied for corrosion, steel pipe could be pitted after all. For leak of gas through local defect have trouble in gas supply, Gas Company have interest in this issue. Measurement of metal to soil potential is a widely used technique to maintain the buried steel pipeline. This is the case that electro-chemical theory is applied to industry field. Measurement and evaluation of the potential are effective inspection method which could find out the possibility of corrosion for steel pipe under cathodic protection. The management of metal to soil potential is a series of activities which are measurement, recording, and inspection whether the potential was located in safe zone or not. Generally, strip-chart recorder or digital data logger which has storage capacity were used for recording the metal to soil potential. But, the existing methods have difficult in continuous monitoring and have troublesome to field worker. In this study, thanks to the development of information technology(it), on-line metal to soil potential monitoring system was developed, which is transmit the collected pipe to soil potential through wireless communication network at field. And manager can receive the data at his computer connected with Internet. 2. Basic function design 2.1 The definition of data communication Data communication is defined as the action of data of between equipments that is a long way off through electric communication line with the binary scale. In the increasing demands, most of works are base on the data communication. Furthermore the technique also developed with rapid speed. Electric switched network is classified as circuit switched network and packet switched network. Circuit switched network is easily understood if we have only to think about telecommunication system. Calling the connection of the two places, socket-board connects demanded 2 points till end of communication time. there is, physical communication path between 2 contact points were maintained. Each data are divided by packet that is called minimum unit of information and send to the receiver in packet switched network. Therefore, It is not necessary to contact synchronically between sender and receiver. Table 1 is shows the difference of each switched network. Table. 1 The comparison of between circuit switched network and packet switched network. Circuit switched network Packet switched network Battery consumption High Low. Multi-receive function Impossible Possible Cost High Low Strong point Tele communication Data communication Extensity Bad Good

2 Technical trend decreased increased Wireless data communication offer perfect mobility to facilities. Therefore without power line and communication line, wireless data communication is defined as technique that is enabled to communicate each equipment in other place. In this study, what we want to develop is on the base of wireless data communication and adequate communication method is adapted. An outline of function of wireless data logger are shown at Fig. 1 CDM Wireless data transmitter Test Box Reference electrode High pressure pipeline Fig. 1. The outline of wireless data logger Basic function of data logger is to measure the potential difference and store the data. But to check the measured data, the manager have collected the installed data logger at field and called the data with an exclusive program at his desk. After a series of work, battery was recharged again and data logger was installed at field. As logger has been used for several years, the capacity of battery is decreased. Furthermore, because real time monitoring is impossible, management of trouble was delayed. So, to solve these problems, we developed an new wireless data logger for online monitoring. Wireless data logger measures the pipe to soil potential at test box where is the right above of high pressure pipeline and yields average, maximum value, minimum value, standard deviation from the measured data. Logger sends these values to manager s computer. 2.2 Basic function and constitution Wireless data logger is composed of signal transformer, filter, 16bit A/D converter, data operation part, memory, CDMA transmission part. Signal process is shown at fig. 2. Inputted data are filtered and transformed to appropriate form before A/D conversion process, so logger can monitor only the interested signal. Because wireless data logger operate by time base, all of operation is controlled by real time clock(rtc). In order to minimize the power consumption, it remains at sleep mode until wake-up time by RTC. Wireless data logger measures the potential difference between pipe and reference electrode 2 times for 10 minutes by 5 seconds periods everyday. Set up time could be change by hand terminal or manager s computer. Logger calculates the average, maximum, minimum, standard deviation value. These values are sent to the manager s computer at set time every day. In case that it is necessary to check the law data, logger conserves measured data in memory for 7 days and then delete it. Transmitted data were supposed to arrive at manager s computer that has fixed IP address.

3 Signal PGA Programmab le Anti-aliasing Filter 16- BIT Low Power Flash- MCU CDMA module Ultra-Super Power Management RTC SRA M SRAM Memor Fig. 2 Operative procedure of wireless data logger Fig. 3 Installed CDMA module at circuit board Fig. 3 is the photo of the CDMA module installed at the back side of circuit board. Two kinds of CDMA module can be used for manager s choice of commercial network at the field. On the results of reasonable design, wireless data logger could be produced with compact size. As mentioned above paragraph, logger have to monitor the pipe to soil potential at least 1 year. Therefore, low electric design should be adapted. If battery is required to change many times due to high power consumption, this system does not have merits any more compared to previous data logger. Many efforts were concentrated on the power save. 3. Performance test Wireless data logger largely could be divided by measurement part, calculation part and transmission part with a point of view of function. Each parts have to verified compared for the measuring device. 3.1 Pipe to soil potential measurement Fig. 4 is the photo of wireless data logger at field. Logger is equipped at cover of test box and antenna for communication inserted into the cover. Performance of projective type is better than inserted type. But projective type antenna could cause the traffic accident, inserted type were selected. Measured data were compared with commercial recorder. At the comparison, the data of logger and recorder are shows the good agreement.

4 Fig. 4 The photo of data logger installed at test box cover at field. 3.2 Power consumption Power consumption is the most important item. Because of high power consumption, if the battery replace is frequently happened, new developed wireless data logger has no merit. Logger is remained sleep mode for normal condition, But time is reaching the set up time, RTC(real time clock) wakes up the circuit to measure the potential data and data transmit is conducted. After scheduled work, logger changes to sleep mode again. A little bit power were consumed for synchronize to the relay station in the beginning of data transmit mode and peak power(maximum 350mA) were required for data transmit. Therefore electric consumption of CDMA module is not constant but different from the communication sensitivity and environment condition. Maximum current consumption time is very short. As mentioned above paragraph, high power is instantaneously need to data transform, lithium ion battery was selected to cope with the power consumption for 1 year. Sleep Wakeup (1Sec) Traffic (5~10 Sec) Time MAX 300mA (t) 150mA 8.9mA Power 75uA 75uA 110mA 75uA 8.9mA 75uA SLEEP IDL TRANSMI (t) Fig. 5 Power consumption of CDMA module Prior to full-scaled data transmit, logger wakes up from the sleep mode. It is considered that a series of data measurement, calculation and transmission is 1cycle. 2cycles are operated in 1 day. 730 cycles correspond to 1 year s operation cycle. In this test, 1500 cycles were conducted to confirm the battery s capacity. It is assumed that logger have no problem in power management. 3.3 data transmit test The purpose of new developed logger is online monitoring of pipe to soil potential for high pressure pipeline. In order to satisfy this purpose, with the ensure of battery capacity, all of data were sent to the manager s computer. For this system transmit the data by wireless, data loss must not be happened on the way of transmission.

5 Fig. 6 Data collection at exclusive program Percentage of data transmit was checked at 3 point. At the results of the test, minimum 98% of receiving percentage was observed. Once data were not transmitted due to unexpected communication problems, previous data were designed to re-transmit at the next transmission time. Even the low sensitivity area, high receiving percentage was observed. As shown at Fig. 7, data from each transmitter at field are collected and stored at manager's computer. With more enforced search function, data management program could be expressed the graphical results in accordance with user's intension. So, manager could find a problem easily. 4. Results In this study, new wireless data logger developed for monitoring of pipe to soil potential of gas pipeline. Through the field test, effectiveness is confirmed. In the field used the electric corrosion protection method, adapting this new developed logger system, rational management could be possible. Through the developing process, the valuable results are summarized as follows. - Use of packet circuit communication enables to save battery consumption and communication fee. - In order to check the data, measured data were stored in memory for 7 days. - Adapting the efficient power management, wireless data logger was used for long time at the field. - Received data were stored and analyzed at exclusive program at manager s computer. So, systematic management could be possible.