Study improves lightning protection of remote monitoring devices

Oct. 4, 2010
Characterization studies including destructive testing have improved protection of remote corrosion-monitoring devices in use on hydrocarbon pipelines against high-energy surges.

Characterization studies including destructive testing have improved protection of remote corrosion-monitoring devices in use on hydrocarbon pipelines against high-energy surges. Cobham Technical Services, Abingdon, UK, used Abriox's Merlin cathodic protection monitor for the tests (Fig. 1).

The Merlin monitor remotely monitors cathodic protection on pipelines, storage tanks, and other buried metal infrastructure (Fig. 1).


An initial review considered the particular installation conditions and environments of the Merlin CP monitor and a typical catastrophic field failure. A destructive test at Cobham's test facility in Abingdon (Fig. 2) made clear the corrosion monitor was most likely dealing with power surges from direct strikes on the pipeline itself or the supply to the electrical rectifiers that provide the impressed-current cathodic protection system. There are no standard lightning test waveforms for this type of nearby strike to ground-based equipment, according to Cobham, which instead created a representative waveform specifically for this testing.

Cobham Technical Services' lightning testing lab offers a range of generators capable of simulating most forms and intensities of lightning strikes (Fig. 2).

Abriox used the results of this testing to up-rate Merlin's surge-protection circuitry, replace some components and change the physical layout of parts of the embedded electronics system, performing low-power, high-voltage tests at its own facilities to test switching times and clamping characteristics.

Cobham then subjected the equipment to increasing levels of lightning strikes using a range of pulse shapes and durations representing the kind of surges experienced in typical installation scenarios. The revised protection continued to operate successfully beyond its target energy level protection rating of a 12 kiloamp (kA) transient waveform.

Cobham used a 30 kA-rated generator to test the equipment and, in the final test step, increased the strike energy to maximum. This destroyed the frontend protection circuitry, but the Merlin monitor itself survived and continued to function.


Malaysia's Petronas Gas Berhad began a total mitigation effort against lightning's effects on its 2,600-km onshore natural gas pipeline network in 2002, citing lightning as the primary cause of reliability issues on the network's supervisory control and data acquisition system. Petronas Gas Control Centre used 107 SCADA-linked remote stations as of 2005.

Lightning flashes along Petronas' network reached more than 1.3 million/year during the 6 years 1995-2000 (table), with densities in some areas of >20/sq km and positive-flash percentages peaking at 4.53%.1

Positive-charge lightning starts at the upper parts of thunderstorms, the longer path typically producing an electric field much stronger than lower-originating negative strikes. A positive strike's flash duration is longer and its peak charge and potential can reach as high as 300,000 amp and 1 billion v, respectively. Positive flashes cause more lightning-related damage than negative flashes despite the 5% sample of all strikes they comprise.2

Similarly high strike frequencies occur in Chad's Doha basin, which experiences 41 strikes/sq mile/year (OGJ, July 16, 2007, p. 44). OGJ


1. Saat, R.M., and Ayub, Z., "Managing Total Solution for Lightning Protection—Petronas Gas Berhad Experience," Asian Pipeline Conference, Kuala Lumpur, Sept. 27-28, 2005.

2. National Weather Service, NWS JetStream, "The Positive and Negative Side of Lightning," Southern Region Headquarters, Fort Worth, Jan. 5, 2010.

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