188bet 88betapp Stray current interference and mitigation for underground pipeline

Summary

Stray currents can have a wide range of interference effects on a pipeline, 188bet 88betapp most harmful being 188bet 88betapp creation of localised electrochemical corrosion cells that attack any buried metallic structure. Stray currents come from different sources, for example, DC rail transit systems and high voltage power transmission systems. It is important for 188bet 88betapp pipeline operators to determine whether stray currents are affecting 188bet 88betapp pipelines, identify 188bet 88betapp possible source(s) of stray currents, evaluate 188bet 88betapp severity of 188bet 88betapp stray current interferences on 188bet 88betapp pipelines and mitigate 188bet 88betapp interference effects. As urbanisation proceeds and more large-scale infrastructures are invested, oil and gas pipelines are threatened by stray current corrosion risks throughout their service life due to interference issues, which are not nuisance but rather major safety hazard that may take much effort to be taken care of. This article introduces two types of DC stray current interferences caused by DC rail transit systems and high voltage direct current transmission systems, and also gives a review on 188bet 88betapp state- of-188bet 88betapp-art of best practices on mitigating these interferences for protection.

Key words: Stray current, corrosion, dynamic interference, high voltage direct current, transit system, mitigation, remote monitoring. 

1. Introduction

Stray currents are caused by sources of current flowing through unintended paths. These can cause electrical interference and have significant effects on buried pipelines and other metallic structures. It is important for 188bet 88betapp pipeline operators to be aware of this as a type of risk as these stray currents can initiate and/or accelerate 188bet 88betapp corrosion of pipelines [1]. In this context, it is also obligated for 188bet 88betapp pipeline operators to determine whether stray currents are affecting 188bet 88betapp pipelines, identify 188bet 88betapp probable source(s) of stray currents, evaluate 188bet 88betapp severity of stray current interferences on 188bet 88betapp pipelines and mitigate 188bet 88betapp interference effects to protect 188bet 88betapp pipelines.

In 188bet 88betapp principle of electrochemistry, stray currents flow at 188bet 88betapp interface between electrolytes and metallic structures sitting in them through charge transfer reactions, governed by Faraday’s Law. Stray currents have varied deleterious effects [2]. At 188bet 88betapp locations 188bet 88betapp current leaves 188bet 88betapp pipeline, oxidation reactions occur to convert electronic current to ionic current. If metallic matrices are involved in 188bet 88betapp oxidation process by releasing electrons directly, they are transformed into metallic ions and dissolved in 188bet 88betapp sitting electrolyte, which is known as corrosion attack. Often this phenomenon is found in close proximity to 188bet 88betapp generation locations of stray currents or a holiday in 188bet 88betapp coating. At 188bet 88betapp locations 188bet 88betapp current flows into 188bet 88betapp pipeline, reduction reactions occur to convert ionic current to electronic current. Depending on what metallic structures are picking up stray currents, there might be different consequences. If 188bet 88betapp structure is coated and has its own cathodie protection (CP) system, stray current pickup, causing additional cathodic polarisation, may result in cathodic disbondment of 188bet 88betapp coating, and meanwhile, threaten 188bet 88betapp structural integrity by increasing 188bet 88betapp susceptibility of hydrogen embrittlement to sporadic hard spots of 188bet 88betapp pipeline (such as girth welds, plastically strained gouges, etc.) and 188bet 88betapp pipeline itself if made of high-strength steels. If 188bet 88betapp structure is made of amphoteric metals, 188bet 88betapp high pH niche developed at 188bet 88betapp structure/electrolyte interface caused by 188bet 88betapp reduction of water molecules can effect “cathodic” corrosion.

2. Sources of stray currents

Stray currents come from different sources and impose impacts on pipelines or other underground structures in varied manners, as summarised in Table 1. There are two types of stray currents, static and dynamic, both of which can be either direct currents or alternating currents. Static stray currents maintain a steady current  flow and are often from other cathodic protection systems on pipelines or other underground structures conducting current flow via soil. Dynamic stray currents fluctuate over time and can come from natural or manmade sources.

Table 1. Categorisation of stray current interferences

Stray currents interfere with underground pipelines as a function of 188bet 88betapp way how they are generated.

a. High voltage direct current (HVDC) transmission can be performed using monopolar earth-return systems for regular inspection or accidental fault for a sustained period of time, during which thousands of amperes of current are injected into 188bet 88betapp earth. 188bet 88betapp monopolar earth- return operation mode causes 188bet 88betapp pipeline segments to be subject to cathodic or anodic interferences at different locations. 188bet 88betapp interference lasts a short term depending on 188bet 88betapp duration of 188bet 88betapp monopolar operation, normally a few hours, and is identified with an abrupt potential excursion on 188bet 88betapp potential-time plot.

b. Long-term interferences are often detected on 188bet 88betapp pipelines that are collocated with other infrastructures, such as DC-electrified transit systems, high voltage AC transmission systems, low voltage AC distribution systems, AC-electrified high-speed railway systems, and foreign cathodic protection systems. Long-term interferences can harm 188bet 88betapp integrity of 188bet 88betapp pipeline due to their accumulative effects throughout their service life. This necessitates not only 188bet 88betapp monitoring of 188bet 88betapp interference status on 188bet 88betapp pipeline but also 188bet 88betapp mitigation of 188bet 88betapp interferences.

c. Welding operations generate DC stray current intermittently as 188bet 88betapp welding machine is normally grounded. This poses 188bet 88betapp underground structures in proximity to 188bet 88betapp welding site in a situation of suffering from accelerating metal loss.

d. Telluric currents, natural stray currents, caused by 188bet 88betapp variations in 188bet 88betapp earth’s magnetic field are well known to present difficulties to pipeline operators. These currents manifest themselves as pipe-to-soil potential fluctuations which are dependent on both location and time. Two mechanisms are generally considered when discussing telluric current effects: classical electromagnetic induction that elucidates local changes in 188bet 88betapp earth’s magnetic field will induce electrical current in stationary conductors such as pipelines; alternately, geomagnetic disturbances may result in large voltage gradients created in 188bet 88betapp earth’s crust in which long metallic conductors such as pipelines merely carry 188bet 88betapp charge [3].

In 188bet 88betapp next paragraphs, this article will focus on two types of 188bet 88betapp above interferences - dynamic DC transit interference and HVDC interference - per 188bet 88betapp authors’ experience in recent years.

3. Dynamic DC transit interference

3.1. Occurrence

Nowadays, 188bet 88betapp construction of electrified DC rail transit systems in modern cities, especially in developing countries, has been a movement to alleviate congested highways and to provide efficient mass transportation. However, dealing with corrosion and its detrimental effects, attributable to stray-current corrosion due to 188bet 88betapp DC rail systems, is, at 188bet 88betapp same time, becoming a challenge in terms of public safety, fortunately, with increasing awareness. 188bet 88betapp operation of DC rail systems causes stray current interference problems to 188bet 88betapp underground pipelines for transporting product oil, natural gas, water, etc.

Figure 1. Generation of stray current from DC rail transit systems [2].

Figure 2. Pipe-to-soil potential vs time plot displaying fluctuations.

188bet 88betapp most common DC rail systems are traction powered by DC current supplied from substations via a positive feeder circuit (e.g., overhead power conductor in Figure 1) and use 188bet 88betapp running rails as 188bet 88betapp negative return circuit to return 188bet 88betapp power current to 188bet 88betapp substation. 188bet 88betapp running rails are in resistive or conductive contact with earth, rather than being ideally isolated from it, causing current leakage problem. Essentially, stray-current leakage is a result of 188bet 88betapp resistance relationship between 188bet 88betapp rail-to-earth return path and 188bet 88betapp running-rail return path. A high resistance of 188bet 88betapp running-rail negative return increases 188bet 88betapp voltage drop along 188bet 88betapp rails and, therefore, makes 188bet 88betapp rail-to- earth return circuit a more favourable path for 188bet 88betapp return current, thus causing stray-current leakage. These leakage currents in 188bet 88betapp earth tend to pick 188bet 88betapp paths like tunnel structure steel bars and underground metallic piping and cables with low resistance and then flow back to 188bet 88betapp substations [4]. 188bet 88betapp current leakage off 188bet 88betapp running rails can be 5 - 10% of 188bet 88betapp power current for railcar running. This may seem a small percentage, but 188bet 88betapp stray currents can be substantial because 188bet 88betapp start-up load current can be several hundred amperes for a single railcar and several thousand amperes for a subway train. If 188bet 88betapp traction power is at 188bet 88betapp level of 2,000 - 3,000 amperes, 188bet 88betapp stray current leaking to 188bet 88betapp earth can reach up to 100 - 300A, which is significantly higher than 188bet 88betapp magnitude of current required by in which 188bet 88betapp cathodic protection systems for 188bet 88betapp underground pipelines, typically, at 188bet 88betapp level of several amperes to tens of amperes.

188bet 88betapp stray current leakage behaves in a fluctuating manner. Not only will 188bet 88betapp magnitude of 188bet 88betapp stray current vary with time of day and whether 188bet 88betapp vehicle is accelerating or decelerating, but 188bet 88betapp location of stray current pick- up on 188bet 88betapp underground pipelines will also change as 188bet 88betapp railcar moves along 188bet 88betapp rails. Thus, a pipe-to-soil potential recording will have a dynamic appearance, as seen in Figure 2 from our team’s project. 188bet 88betapp potential- time recording of stray current effects from a DC transit system has a distinctive pattern. There are considerable potential fluctuations during 188bet 88betapp daytime when 188bet 88betapp transit schedules are busy, while virtually no changes during 188bet 88betapp early morning hours. In Figure 2, 188bet 88betapp potential data was obtained with a data logger from a product pipeline with route intersected with a metro line. 188bet 88betapp plot shows that, from 8:30 am to 11:30 pm November 9 and from 5:30 am to 8:30 am November 10, 188bet 88betapp ON potential (black dots on solid line) and OFF potential (red dots on solid line) readings fluctuated rapidly, and roughly a third of 188bet 88betapp OFF potential readings excursed to 188bet 88betapp positive direction beyond 188bet 88betapp protection criterion -0.85 VCSE (blue solid line), indicating inadequate protection due to dynamic DC interference. While 188bet 88betapp ON potentials and OFF potentials nearly remained stable from 11:30 pm November 9 to 5:30 am November 10, and 188bet 88betapp OFF potential readings were approximately -1.00 VCSE, indicating acceptable protection if 188bet 88betapp dynamic interference was off.

Figure 3. Layouts of different DC drainage systems.

Although 188bet 88betapp stray current pick-up locations change with time, 188bet 88betapp discharge sites are predominately in proximity to 188bet 88betapp substation ground. Therefore, determining 188bet 88betapp impact of transit-caused stray current on metallic facilities in urban areas requires comprehensive detection and evaluation, starting in 188bet 88betapp vicinity of 188bet 88betapp substation grounds and along 188bet 88betapp transit system route.

3.2. Mitigation

It is usually agreed by all parts that mitigating 188bet 88betapp DC transit interference on 188bet 88betapp pipelines is rather a task with challenge. Per 188bet 88betapp lessons 188bet 88betapp industry has learned so far, a committee comprised of local pipeline operators, 188bet 88betapp railway operators and 188bet 88betapp governing organisations is necessary to form to call for collaboration of 188bet 88betapp diagnosis, evaluation and mitigation of interference problems. Forming 188bet 88betapp committee and improving awareness has proved to be an effective and sometimes imperative way for interference control and mitigation.

Mitigation methods for minimising 188bet 88betapp deleterious effects of DC transit system stray currents include: electrical isolation of rails and substations implemented solely by 188bet 88betapp railway operators and regarded as proactive measures, and passive measures implemented in combination by 188bet 88betapp pipeline operators such as cathodic protection (CP), coating repair, drainage bonds, etc.

Figure 4. Comparison of potential excursions monitored on a product pipeline among 188bet 88betapp test durations when 188bet 88betapp innovated bidirectional drainage equipment was on or off.

Drainage measures are often sought for effectively driving stray current out of 188bet 88betapp pipeline in 188bet 88betapp controlled path [5]. 188bet 88betapp principle of drainage measures is to provide an electronic path for 188bet 88betapp stray current to return to its source, thus reducing 188bet 88betapp amount leaking to 188bet 88betapp electrolytic path. In practice, there are four different ways of building up DC drainage arrangements:

a. Grounding drainage

This drainage method (Figure 3a) is achieved by installing a groundbed close to 188bet 88betapp affected pipeline and connecting them together. Independent from 188bet 88betapp interference sources, this method is preferably applicable to 188bet 88betapp scenario 188bet 88betapp anodic areas of 188bet 88betapp pipelines are relatively fixed, where stray currents picked up by 188bet 88betapp pipelines from unknown locations are drained to 188bet 88betapp soil through 188bet 88betapp strategically installed groundbed.

b. Direct drainage

This drainage method is achieved by creating a stray current flow path from 188bet 88betapp pipeline to 188bet 88betapp negative bus of 188bet 88betapp stray current source. 188bet 88betapp execution of this method must ask for an agreement from 188bet 88betapp transit operators. In this method, 188bet 88betapp stray currents entering 188bet 88betapp pipeline from unknown locations are directed back to 188bet 88betapp original source through 188bet 88betapp intentionally established path.

c. Unidirectional drainage

This drainage method is achieved by creating a current flow path from 188bet 88betapp pipeline via a unidirectional device (e.g. diodes) to 188bet 88betapp negative bus of 188bet 88betapp stray current source or a dedicated groundbed. An agreement must be asked from 188bet 88betapp transit operators if stray currents are to flow back to 188bet 88betapp original source. 188bet 88betapp unidirectional device is employed for avoiding stray currents from re-entering 188bet 88betapp pipeline through 188bet 88betapp groundbed or preventing stray currents circulating. In this way, this drainage arrangement is applicable to 188bet 88betapp scenario 188bet 88betapp affected pipeline segments are indefinitely changing between anodic and cathodic.

d. Forced drainage

This method is achieved by substituting 188bet 88betapp unidirectional device for a forced drainage device, for instance, a potential-controlled rectifier. 188bet 88betapp forced drainage device works if 188bet 88betapp pipeline potential is more positive than that of 188bet 88betapp original source or 188bet 88betapp dedicated groundbed. An agreement must be asked from 188bet 88betapp transit operators if stray currents are forced to flow back to 188bet 88betapp original source. To be completely effective, 188bet 88betapp forced drainage arrangement must be located at 188bet 88betapp point of maximum discharge.

Figure 5. HVDC transmission operations [6]: bipolar systems (a), monopolar system (b).

These drainage methods are described in 188bet 88betapp order happening to show 188bet 88betapp evolution course. All these methods are more applicable to mitigating interferences for pipeline sections adjacent to 188bet 88betapp negative return circuit of stray currents and are effective to controlling 188bet 88betapp OFF potential of these pipeline sections within 188bet 88betapp industrially-acknowledged criteria. At locations where anodic and cathodic interferences are mixed, none of 188bet 88betapp above drainage methods demonstrates 188bet 88betapp interference mitigation efficiency as expected. 188bet 88betapp authors’ team has invented a set of potential-controlled bidirectional drainage equipment. This equipment is capable of feeding varied amount of current in both directions in response to 188bet 88betapp interference potential to cancel off 188bet 88betapp interference effects, by which 188bet 88betapp pipe-to-soil potential can be controlled within criteria. 188bet 88betapp equipment has been put into a field test to verify 188bet 88betapp mitigating effect on 188bet 88betapp same product pipeline as related to Figure 2, and 188bet 88betapp results are displayed in a potential-time plot in Figure 4. From 188bet 88betapp plot, it is seen that, 188bet 88betapp OFF potential excursions of 188bet 88betapp pipeline under CP (Rect. on) were significantly reduced below -0.85 VCSE line when 188bet 88betapp bidirectional drainage equipment was in operation at different output modes (in which +/- stands for current output in positive or negative direction; P and I values reflect 188bet 88betapp response time). This invention has proved to be an additional choice for 188bet 88betapp mitigation of interference from DC rail transit systems.

To summarise, stray current corrosion caused by DC rail transit systems has been found on 188bet 88betapp underground pipelines or other structures in many cities all over 188bet 88betapp world. It is ultimately important for 188bet 88betapp pipeline operators to be clear of how severe these dynamic stray currents can cause wall loss of 188bet 88betapp pipelines and how to effectively mitigate 188bet 88betapp interference problems. However, neither evaluating 188bet 88betapp severity of dynamic DC stray current interference nor mitigating 188bet 88betapp corrosion risk is a best- practice-procedure-following task. More efforts are certainly required from engineers, scientists, operators, regulators and officials in order to make informed decisions on improving 188bet 88betapp reliability of 188bet 88betapp pipelines and other underground utilities in 188bet 88betapp cities.

(a) Cathodic HVDC interference

(b) Anodic HVDC interference

Figure 6. Mechanism of HVDC electrode interference [7].

4. HVDC interference

4.1. Occurrence

HVDC transmission networks have been widely implemented globally in recent years. HVDC transmission is used to carry electrical energy over long distances or to interface two AC power systems that might not be synchronised [6].

Figure 7. Pipe-to-soil potential shifts on a pipeline as a result of HVDC interference at different times.

Figure 8. Remote monitoring and control network for HVDC interferences.

HVDC transmission systems may operate in such a manner that continuous (normal operation) or periodic (monopolar operation) direct current follows an earth path between HVDC system terminals [6], as seen in Figure

5. During such operations, a portion of 188bet 88betapp DC current that is flowing between 188bet 88betapp two HVDC electrodes is captured by 188bet 88betapp pipelines and associated grounding systems located in zones where 188bet 88betapp earth potentials are high and are discharged back to 188bet 88betapp soil at locations where 188bet 88betapp earth potentials are lower. More precisely, a pipeline may collect, conduct, or discharge a portion of this current depending on 188bet 88betapp location of 188bet 88betapp pipeline and 188bet 88betapp polarity of 188bet 88betapp HVDC ground electrode. Due to such excessive stray currents, pipe-to-soil potentials are accordingly shifted at different locations, making 188bet 88betapp potential- mileage plot similar to a “hat” shape, as seen in Figure 6. When 188bet 88betapp electrode near 188bet 88betapp pipeline is operating in positive mode, 188bet 88betapp current from 188bet 88betapp electrode is collected by 188bet 88betapp pipeline in 188bet 88betapp region located in 188bet 88betapp vicinity of 188bet 88betapp electrode, and then discharged from 188bet 88betapp pipeline at locations remote from 188bet 88betapp electrode. When 188bet 88betapp HVDC electrode near 188bet 88betapp pipeline is operating in negative mode, 188bet 88betapp current is discharged from 188bet 88betapp pipeline in 188bet 88betapp vicinity of 188bet 88betapp electrode and collected in 188bet 88betapp area far from 188bet 88betapp electrode. 

Figure 9. Intelligent data sampling units installed in test posts along 188bet 88betapp pipeline.

Corrosion of 188bet 88betapp metallic pipelines occurs if DC stray current discharges from 188bet 88betapp metallic structure into 188bet 88betapp soil, namely, in 188bet 88betapp anodic areas in Figure 6. 188bet 88betapp corrosion, causing metal loss, is particularly critical on well-coated pipelines where 188bet 88betapp current discharge is concentrated at holidays in 188bet 88betapp coating. Perforation of 188bet 88betapp pipe wall can occur rapidly at a holiday as a result of 188bet 88betapp high density of current discharge from 188bet 88betapp pipeline to 188bet 88betapp earth. In 188bet 88betapp cathodic areas, pipe-to- soil potential shifts in 188bet 88betapp negative direction in Figure 6. This shift can be beneficial for 188bet 88betapp pipeline, provided that 188bet 88betapp pipe steel is not susceptible to hydrogen embrittlement. Otherwise, sustained high negative voltages can cause coating disbondment and embrittlement of high-strength steels [7]. Figure 7, from our team’s work, depicts 188bet 88betapp potentials of a pipeline continuously monitored with remote monitors for capturing HVDC interference events due to its proximity to a ground electrode in Southern China. 188bet 88betapp potential shifts indicate that, within this period, 188bet 88betapp pipeline at this monitoring location reached nearly 100V when 188bet 88betapp nearby HVDC electrode operated as a negative electrode, and in contrast, -120V when 188bet 88betapp nearby HVDC electrode operated as a positive electrode. Depending on 188bet 88betapp soil condition and 188bet 88betapp relative position relationship between 188bet 88betapp pipeline and electrode (even several tens of kilometres apart), HVDC interference, can have massive impact on 188bet 88betapp pipeline in 188bet 88betapp range of hundreds of kilometres. Therefore, 188bet 88betapp concerns on their possible adverse impact on 188bet 88betapp environment have accelerated 188bet 88betapp need for accurate approaches to analyse HVDC adverse effects on neighbouring buried metallic utilities and development of appropriate effective and economical mitigation measures.

4.2. Mitigation

188bet 88betapp mitigation of HVDC interference relies on comprehensive measures. Similar to 188bet 88betapp mitigation of dynamic DC interference, a collaborative committee should form for problem solving. A proper design based on full engineering analysis and interference prediction is deemed to be 188bet 88betapp most effective method to avoid severe interference issues; however, this article only emphasises 188bet 88betapp possible mitigation measures for existing structures.

Most pipelines are located far from 188bet 88betapp HVDC electrodes, 188bet 88betapp interference sources, to make it not economical to install a bond. Because of 188bet 88betapp large voltage shifts, sacrificial anodes may not adequately compensate thelocalelectricfieldcausedbythe HVDCearthcurrent.188bet 88betapp most practical mitigation method is to use an impressed current system powered by a potential controlled rectifier. Not only would 188bet 88betapp cathodic protection power supply be able to counteract 188bet 88betapp large positive potential shifts, but during 188bet 88betapp negative shift periods it would also shut down, thus minimising 188bet 88betapp stress on 188bet 88betapp coating [8].

Depending on 188bet 88betapp amplitude of HVDC earth current, it is ultimately necessary to divide 188bet 88betapp pipeline into numerous electrically isolated sections to increase 188bet 88betapp effective path resistance for facilitating 188bet 88betapp application of 188bet 88betapp above mitigation measures. In this way, sacrificial anodes can be used for mitigation. Besides, if 188bet 88betapp use of sacrificial anodes is still not adequate, using automatic potential-controlled rectifiers in each section can mitigate HVDC fault currents.

188bet 88betapp author’s team has accomplished to mitigate HVDC interference for 188bet 88betapp pipelines by using 188bet 88betapp abovementioned bidirectional forced drainage equipment. 188bet 88betapp equipment is capable of automatically adjusting 188bet 88betapp magnitudes and directions of 188bet 88betapp current outputs in response to shifts and changes in 188bet 88betapp structure- to-electrolyte potential. 188bet 88betapp HVDC interference case showed in Figure 7 was successfully mitigated at this location with 188bet 88betapp bidirectional forced drainage method. After mitigation measures were taken, 188bet 88betapp potential shifts have been controlled within 188bet 88betapp range between -27V in 188bet 88betapp negative direction and 23V in 188bet 88betapp positive direction.

4.3. Remote monitoring

HVDC interference on 188bet 88betapp underground pipelines has been found with 188bet 88betapp features of inadvertence, unpredictability, and random durations. Therefore, remote monitoring techniques are to seek for continual monitoring of not only 188bet 88betapp HVDC interference incidents but also 188bet 88betapp HVDC mitigation efficiency.

188bet 88betapp continual monitoring of HVDC interferences can be achieved by configuring a remote monitoring and control network, as depicted in Figure 8. 188bet 88betapp network is composed of three main elements:

a. Intelligent data sampling units

These units are installed in 188bet 88betapp test posts at 188bet 88betapp strategic locations along 188bet 88betapp pipeline (Figure 9), and, with 188bet 88betapp aid of buried coupons and permanent reference electrodes, measure 188bet 88betapp required parameters, such as potential, voltage, current and soil resistivity, etc. These data can be ready for automatic transmission or stored for retrieval.

b. Data transmission network

188bet 88betapp data transmission network is 188bet 88betapp core to transmit 188bet 88betapp data measured at 188bet 88betapp test posts with certain protocols to servers for storage. On 188bet 88betapp other hand, commands for adjusting 188bet 88betapp work mode of 188bet 88betapp units are sent over 188bet 88betapp same network and received by 188bet 88betapp units. At present, 188bet 88betapp most popular data transmission network can be cellular communication network, satellite and other wireless techniques.

c. Servers

Servers are used via internet services to receive and store 188bet 88betapp field measurement data from 188bet 88betapp units for processing and analysis. All 188bet 88betapp HVDC monitoring data are managed through specialised software installed on 188bet 88betapp servers. Other than this, 188bet 88betapp management software is also integrated with control functions for changing 188bet 88betapp work mode of 188bet 88betapp units.
In order to effectively monitor HVDC interferences, multiple intelligent data sampling units are to be installed at 188bet 88betapp strategically selected locations along 188bet 88betapp pipeline right-of-way, minimally, at 188bet 88betapp pipeline section close to 188bet 88betapp HVDC electrodes. 188bet 88betapp occurrence of HVDC interference can be ascertained if 188bet 88betapp pipe-to- soil potential shifts are noticed at different monitoring locations at 188bet 88betapp same time.

5. Conclusions

Stray currents can have a wide range of interference effects on a pipeline, 188bet 88betapp most harmful being 188bet 88betapp creation of localised electrochemical corrosion cells that attack any buried metallic structure. Stray currents flow through unintended paths and come from different sources. It is important for 188bet 88betapp pipeline operators to determine whether stray currents are affecting 188bet 88betapp pipelines, identify 188bet 88betapp probable source(s) of stray currents, evaluate 188bet 88betapp severity of 188bet 88betapp stray current interferences on 188bet 88betapp pipelines and mitigate 188bet 88betapp interference effects. DC stray current interferences caused by DC rail transit systems and high voltage direct current transmission systems are becoming more and more severe on 188bet 88betapp pipelines as urbanisation proceeds and more large-scale infrastructures are invested.

Acknowledged by 188bet 88betapp industry, a collaborative committee comprised of at least pipeline operators and 188bet 88betapp parts operating 188bet 88betapp interference sources is necessary to form for 188bet 88betapp diagnosis, evaluation and mitigation of interference problems. Diminishing 188bet 88betapp discharge of stray currents into soil is 188bet 88betapp most effective way; however, pipeline operators are still in need of their own measures for interference mitigation, such as CP. Forced drainage methods are often sought for DC interference mitigation when 188bet 88betapp stray current in 188bet 88betapp pipeline is at a high level. Otherthanconventionalprotectionmethods, bidirectional forced drainage methods have been accomplished by 188bet 88betapp author’s team to mitigate dynamic transit DC and HVDC interferences. In order to evaluate 188bet 88betapp severity of interferences on a pipeline in a timely manner, remote monitoring techniques are recommended for continual monitoring of not only interference incidents but also mitigation efficiency.

 References

1. Elizabeth Nicholson. Stray current detection and correction. Poland Corrosion Conference. 2010.

2. NACE International. CP interference manual. 2012.

3. T.Place, T.Smith. Practical telluric compensation for pipeline close interval survey. NACE International conference. 2000.

4. Thomas J.Barlo, Alan D.Zdunek. Stray current corrosion in electrified rail systems: Final report. 1995.

5. M.Cheng, Q.Tang, D.Wei, P.Zhang, Comprehensive protection of buried steel pipelines at HVDC earthed electrode interference area. Natural Gas Industry. 2015; 35 (9): p. 105 - 111.

6. Walter von Baeckmann, Wilhelm Schwenk, Werner Prinz. Handbook of cathodic corrosion protection. Gulf Professional Publishing. 2011.

7. Yu Gong, Chunlin Xue, Zhilei Yuan, Yexu Li, Farid Paul Dawalibi. Advanced analysis of HVDC electrodes interference on neighboring pipelines. Journal of Power and Energy Engineering. 2015; 3: p. 332 - 341.

8. NACE International. High-voltage direct current interference (24254-SG). 2014.