No fear of thunder and lightning
Protection against lightning and surges on a crude oil pipeline

Pipelines are an essential element in the network which supplies crude oil to refineries. Millions of tons of crude oil are pumped through the German segments of the pipeline networks alone. Statistically, pipelines are the safest way of transporting crude oil and petroleum products. They are nevertheless a potential hazard that must not be underestimated. This article explains how lightning and surge protection helps keep pipelines operating safely.



Just protecting the family home against lightning strikes is not a simple task. Protecting an entire crude oil pipeline is a mammoth project. Besides the actual pipeline itself, there is a range of equipment associated with the pipeline. Petroleum products are segregated by type and stored in tank farms. From there, the products are pumped to their destinations. Pumping and pressure relief stations are needed to maintain stable pressure in the pipeline. The pipelines also have to be subdivided into segments using valve stations which are used to partially open and close sections of the pipeline. Pipelines also
have transfer stations which are used to move the oil along and deliver it to the various refineries. All of this equipment, together with the associated instrumentation, must be covered by a comprehensive protection strategy. The following example illustrates how the appropriate measures can be implemented.
Lightning protection of the Transalpine Pipeline
Deutsche Transalpine Ölleitung GmbH has been operating Europe’s most important pipeline between Triest in Italy and Ingolstadt in Germany since 1967. The crude oil must be pumped more than 465 km to the central station in Ingolstadt. A 270 km branch line connects the German city of Karlsruhe with the central storage facilities. The difference in elevation along the length of the pipeline, which crosses the Italian and Austrian Alps, is nearly 1,600 m. TAL supplies 100% of the crude oil needed by the German state of Bavaria, 75% of Austria’s requirements and 55% of the crude oil used in the state of Baden-Württemberg. TAL operates 2 tank farms in Triest, 25 pumping stations, 4 pressure compensation stations, 3 transfer stations and 73 valve stations. The pipeline has a capacity of 6,000 cubic meters per hour. 386 ships were unloaded in Triest in 2002, and 34.8 million tons of oil were supplied to the transfer stations.
The closure of the Central European Line (CEL) in 1996 due to environmental problems and the need for significant upgrading of the line has increased the importance of the TAL pipeline in Germany’s crude oil distribution system. Back in 1994, the operating company, which includes all of the well known oil companies, awarded contracts for project TAL-C94. The purpose of the project was to retrofit all of the communications and control equipment on the pipeline and to provide fully automatic operation of the pipeline from central control stations in Triest and Ingolstadt. The TAL line had to continue to operate at full load without interruption. The engineering firm which was responsible for project management carried out design and request for quotation planning for station automation and field instrumentation as well as planning for lightning and surge protection based on a IEC 61312-1 compliant lightning protection
design. This standard will be replaced by IEC 62305-4 (current status IEC 81/238/CDV).
Protection strategy
Implementation of the Lightning Protection Zone Concept was preceded by a risk assessment. The assessment identified the need for class I lightning protection. The protection strategy was based on reduction of conducted and emitted interference caused by lightning discharge or switching events. The magnitude of the interference had to be reduced to a level which was compatible with the EMC characteristics of the equipment and systems. Structures were divided into lightning protection zones. Lightning striking in protection zone 0 (LPZ 0) outside of a protected structure acts as an unimpeded source of interference.
Lightning protection zone 0A (LPZ 0A) includes all areas that are susceptible to direct lightning strikes and are exposed to unattenuated electromagnetic fields caused by lightning. Direct lightning strikes cannot occur in LPZ 0B, but the zone is susceptible to field-borne interference from the lightning’s electromagnetic field. Air termination systems were installed to ensure that protected assets were located in LPZ 0B. Other protection zones were then defined based on engineering and economic considerations. Room and building shielding made up of connected reinforcing iron was installed to enclose the protection zones. Metal equipment housings can provide additional protection zones. Older buildings often offer no shielding, because this feature was not taken into consideration in the original design and previous use. Especially when older buildings are used, it is important that shielding is installed to protect automation equipment. One solution is to place automation systems in cabinets that have good shielding characteristics.
External lightning protection
The control center building in Ingolstadt is located about 200 meters from the oil tanks. The entire building has external class I lightning protection, safeguarding the structure and the persons inside against the effects of a direct lightning strike. The central control station is housed in an annex that has a roof sprinkler system to prevent the control center from exposure to excessive heat in case of a fire at the tank farm and to guarantee that the center remains operational in that critical situation. The sprinkler system is integrated via air terminators into lightning protection zone 0B (LPZ 0B) to prevent lightning from directly striking this safety system.

Meshed grounding system
The protective grounding system connects electrical equipment with the earth and protects persons and property in case an electrical fault occurs. The grounding system fulfills a functional grounding function to ensure that electrical and electronic equipment operates safely and if possible fault free.
Lightning strike current is ultimately conducted to earth through the grounding system acting as lightning protection ground. In practice, grounding systems were often implemented separately (lightning protection and protective ground separate from functional ground). This approach has proven to be unsuitable and can even be dangerous. When lightning strikes, voltage differentials in the range of several hundred kilovolts can be generated, which can result in the destruction of electronic components, place persons at risk and cause sparking that can trigger explosions in hazardous zones. To avoid these risks, every single building in the TAL system and every subsystem has its own grounding system, which is meshed with all the others. This reduces the differences in potential between buildings as well as the amplitude of conducted partial lightning strike currents. Increasing the density of the mesh decreases the differences in electrical potential between the parts of the system that occur as a result of a lightning strike. A mesh spacing of 10 x 20 m has proven to be an economical solution. During selection of grounding materials, it is important to choose pipes that resists corrosion when it is installed underground.
Equipotential bonding
Over the length of the TAL pipeline, there are segments and subsystems that are located in potentially explosive areas. Equipotential bonding was installed in these area in particular. Building supports and structural elements, conduit, storage tanks etc. were integrated into the equipotential bonding system to make it very unlikely that a dangerous difference in potential will occur (even when there is a fault condition).
Surge protection of the low voltage
Consumer’s Installation
In accordance with the subdivision of the lightning protection zones it was important to also include the conducting and energized lines into the lightning protection equipotential bonding at zone boundary from LPZ 0A to LPZ 1. Powerful lightning current arresters ensure these conditions at the service entry of the power suppy line. Power subdistribution boards are used for supplying the control cabinets. These are integrated into LPZ 2 together with the main automation equipment and are therefore equipped with surge arresters. Important was the use of (energy-) coordinated surge protective devices (SPDs). This can only be ensured by using products made by one manufacturer.
Surge protection for
automation equipment
Following an upgrade of the instrumentation used to monitor pressure, flow rates, temperature and fill levels and after the changeover to the new control station design, nearly 18,000 inputs and outputs had to be integrated into the new protection strategy. It was important to make sure that protective measures for equipment in buildings and stations as well as for local transducers were included in the overall lightning protection strategy. Given the existing space available and the desire to connect 0/4–20 mA signals as well as signals from intrinsically safe measurement loops to protective devices that all have the same mechanical design, the decision was made to choose a universal protection device. To ensure visual identification and quick recognition, the protective devices for EEx(i) measurement loops are blue and devices used to protect binary and analogue signals are yellow.
During the planning of surge protection for explosion protection zones, lightning protection and explosion protection zones were harmonized. The consequence of this approach is that requirements which apply to the use of surge protection devices in Ex zones as well as the lightning protection zone boundaries had to be adhered to. This determined the position of the surge arrester, which is located at the transition between LPZ 0B and LPZ 1. The arrester discharges interference voltage, thus preventing dangerous surges from penetrating into Ex 0 zone. This also increases the availability of the traducers which play such an important part in the process.
The system must also comply with the requirements defined in EN 60079-14 (DIN VDE 0165-1):
The surge protector must be capable of diverting a minimum peak discharge current of 10 kA (ten 8/20 µs impulse events) with no defect or degradation of the surge protection function.
-The protective device must be installed in a housing with metal shielding, and grounding must have a cross-sectional area of at least 4 mm2 of copper.
-The cables between the protective device and the operating equipment must be installed in metal conduit which is grounded at both ends, or shielded cable must be used that has a maximum length of
one meter.
As defined in the protection strategy, central control equipment in the control center is defined as LPZ 2. The intrinsically safe measurement leads connected to the transducers are also fed through surge protectors at the transition between LPZ 0B and LPZ 1. A protective device at the
other end of a field line which leaves the building must have the same discharge capacity as the device which is installed at the tank.
On the other side of the surge protector, the intrinsically safe cable is routed to an isolation amplifier. From there, a shielded cable is connected to the control equipment in LPZ 2. Installation of shielding at both ends reduces the need for a protective device, because the expected residual electromagnetic interference is highly attenuated by the cable shielding which is grounded at both ends.
When surge protectors are used in intrinsically safe measurement loops, it is important to consider whether the measurement circuit is grounded or floating. The circuit is considered to be grounded if the insulation resistance of the operating device is <500 V AC. If this is the case, the protection level Up of the protective devices must be less than the insulation resistance of the “grounded” operating equipment at a nominal discharge current of
10 kA (8/20 µs), for example Up (core/PG) #35 V. Installing the protective device in the field in Ex Zone 1 is sufficient for “ib” type of protection. Since the surge protector being used is certified to “ia”, it meets the most stringent requirements and is suitable for “ib” applications.
Before EEx(i) measurement loops are commissioned, evidence of intrinsic safety must be provided for the circuits. The supply device, the transducer, the cable and the surge protectors must meet the interconnect requirements. The inductance and capacitance of the protective devices may have to be taken into account. According to the EU Type Examination Certificate (PTB 99 Atex 2092), the inner capacitance and inductance of the surge protectors used on the TAL line are negligible and may be ignored during an review of interconnect requirements.