Engineering Failure Analysis 57 (2015) 434–443

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Engineering Failure Analysis

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Review

Concerns of corrosive effects with respect to lightningprotection systems

Aidin Ghavamian a,⁎, Mohammad Reza Maghami b, Shayan Dehghan c, Chandima Gomes b

a Department of Aerospace Engineering, Universiti Putra Malaysia, Serdang, 43400 Selangor, Malaysiab Department of Electrical and Electronic Engineering, Universiti Putra Malaysia, Serdang, 43400 Selangor, Malaysiac Department of Mechanical and Manufacturing Engineering, Universiti Putra Malaysia, Serdang, 43400 Selangor, Malaysia

a r t i c l e i n f o

⁎ Corresponding author.E-mail address: aidin.gha@gmail.com (A. Ghavamian

http://dx.doi.org/10.1016/j.engfailanal.2015.08.0191350-6307/© 2015 The Authors. Published by Elsevier L

a b s t r a c t

Article history:Received 11 June 2015Accepted 13 August 2015Available online 16 August 2015

Lightning protection system elements need to be selected from materials which are resistant tocorrosion and should be protected from fast degradation. However, over the time corrosion willtake place in the presence of galvanically dissimilarmetals in the sameelectrolyte (moisture). His-torically, copper, aluminium and copper alloys (including bronze and brass) have been used inlightning protection applications as these materials are highly conductive and abundantly avail-able. Corrosive effects on system components are influenced by the environmental factors suchas moisture, soil type and temperature that make the corrosion process highly complex in soil.As per many standards on the installation of lightning protection systems, combinations of mate-rials that naturally form electrolytic couples shall not be used, for example copper and steel, espe-cially in the presence of moisture, inwhich corrosionwill be accelerated. Similarly, the conditionswithin soil will have adverse effects on the ground system elements. Down conductors enteringcorrosive soil must be protected against corrosion by a protective covering. The paper presentsthe causes of corrosion and recent developments in minimising the corrosion associated withlightning protection and grounding systems.

© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license

(http://creativecommons.org/licenses/by/4.0/).

Keywords:Lightning protection system (LPS)Galvanic corrosionDown-conductorAir termination systemEarth termination system

Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4342. Significant factors in a LPS system based on corrosion aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435

2.1. LPS materials and coatings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4352.2. Material selection in a grounding system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4372.3. Environmental aspects of corrosion in LPS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438

3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4394. Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 440Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442

1. Introduction

Lightning is a charge of electricity that travels from a thunder cloud and can produce a very high current that can possibly damageany electrical component that it encounters. Therefore, all electrical components should be protected by a lightning protection system

).

td. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

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(LPS). The aim of a LPS is the transport of lightning current safely to ground [1–3]. An external LPS consists of an air termination sys-tem, a down conductor system and an earth termination system as shown in Fig. 1. The earth-termination system, also known as alightning protection grounding system, is intended to provide a low resistance path to dissipate high current into the soil. The conduc-tors that do this job are called down conductors [1,2,4]. The current passed by a down conductor should be dissipated securely in thesoil without raising the potential of the down conductor to high values that could cause sparks. In other words, the integrity of thissystem is important andworthwhile for consideration [4,5]. The transient nature of lightning produces fast rise times and large mag-nitude currents, meaning the grounding system should perform effectively to limit the voltage imposed by the lightning [6,7].

Corrosion which occurs in the presence of different metals in the same electrolyte or similar metals in various electrolytes or var-ious concentrations of the same electrolyte has causedmany problems in electrical systems [8–11]. Among the different kinds of cor-rosion, galvanic corrosion has a high impact on the performance of a LPS. Galvanic corrosion is the outcome of the interaction ofdissimilarmetalswith each other under specific environmental conditions, such as the same electrolyte. An example of common elec-trolyte would be rainwater [12–17].

Grounding normally refers to the connection of an electrical circuit to earth. A good grounding systemwould be expected to dem-onstrate high electrical conductivity, with the conductors being capable of withstanding large fault currents, have a long life, exhibitlow ground resistance and impedance and have good corrosion resistance. A grounding system is important for human safety, reliabilityof the electrical equipment, fault current return and to limit the transient overvoltage. The grounding system components can be dividedinto a grounding conductor, grounding connector and grounding electrodes. An improper grounding system can lead to a dangeroussituation which could be worse than having no grounding system at all [1,6,18–26].

The electrical engineer that designs the grounding system is often not knowledgeable of the corrosion issues. This subject comesalso under the purview of the chemical engineer. Unfortunately, many practical designs only consider the electrical aspects of the bestlightning protection and grounding systems and ignore possible corrosion effects [1,6,27]. Literature that discusses this issue is scarce,thus, in the work presented the cause of corrosion and recent developments in minimising the corrosion associated with lightningprotection and grounding systems have been discussed. This paper also discusses the problems created by dissimilar metal bases.

2. Significant factors in a LPS system based on corrosion aspects

2.1. LPS materials and coatings

Lightning protection elements are constructed from materials which are resistant to corrosion and should be protected from fastdegradation. Over time, corrosion will occur in the presence of galvanically dissimilar metals in the same electrolyte (typically mois-ture). Historically, copper, aluminium and copper alloys (including bronze and brass) have been used in lightning protection applica-tions as they are conductive [1,3,28]. The grounding rods that are used practically are made from copper bonded steel, galvanizedsteel, solid stainless steel, stainless-clad, solid copper, copper-clad and plain steel. Unfortunately, all of these materials are exposedto the corrosion issue and this reduces the performance of the grounding system [1,3,4,24,25]. Corrosion is one of themost destructivemechanisms in aluminium alloys. Corrosion pits typically start because of some chemical or physical heterogeneity on the surface,such as phase particles, defects, mechanical damage or dislocations [10,11,29–32]. Aluminium alloys include many constituent parti-cles,whichplay an important role in the creation of pitting corrosion [3,32–38]. Other than aluminium, historically, bronze and coppermaterials have been utilised in lightning protection applications for all the surfaces on rooftops, due to their good conductivity,

Fig. 1. Lightning protection system (LPS); transfer the lightning current safely to the ground. This system includes air termination, down conductor and earth termina-tion system which is also known as a lightning protection grounding system that intended to provide a low resistance path to dissipate high current into the soil.

Fig. 2.Amulti-metal contact point (copper, iron and stainless steel)with paint coating layers, a copper conductor attached to painted iron plate with stainless steel nutsand bolts.

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durability and thermal characteristics. It is important that a properly installed LPS will last for a long time and maintain its integritywith only minimum repair. However, the first problem is that bronze and copper materials in contact with external painted steelor galvanized surfaces may create considerable corrosion over time and the effect is only partially alleviated by traditional methodssuch as repainting (Figs. 2 & 3) [12,18,39–42]. Fig. 2 shows a joint of a copper conductor made of painted iron plate with stainlesssteel nuts and bolts used for tightening the components. The coating of white paint of the plate is almost entirely removed by theswelling iron due to extensive corrosion. The stainless steel nuts and bolts are almost unaffected by the presence of both iron and

Fig. 3. Copper-galvanized iron contact point with galvanized iron covered with a coating of paint. A painted galvanized iron box has been partially damaged by thecorrosion.

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copper. Fig. 3 also shows a similar situation where a painted galvanized iron box has been partially damaged by the corrosion. Thecorrosion process may have accelerated due to the galvanic effect between copper and galvanized iron and also the dampness ofthe environment. These cases clearly show that paint coating may not be a proper solution for the rapid corrosion of materials atbi-metal or multi-metal contact points.

With respect to the grounding of down conductors, one of themost important factors is that the ground conductors should not bemade of aluminiumor aluminium alloys and if the soil is corrosive, then a corrosive protection covermust be applied to the groundingelectrodes, including parts of the down conductor close to the ground [43]. Łoboda andMarciniak [3] in 2003 in Poland started a fieldcorrosion test in a long term project of steel earthing rods. In this project several tens of rods, each having total length of 3 m withvarious protective coatings was embedded in various types of soil (Fig. 3). After two years of exposure in soil the rods with zincand copper coating was removed from the soil. Subsequently, the other rods were removed (after four years of exposure in two dif-ferent locations; Mielno and Inowroclaw sites (Figs. 4a, b, and 5a, b). The results depict better corrosion protection of steel earthingrods coated with pure copper compared to zinc coatings having various thicknesses of coating and using different kinds of technolo-gies so that loss of zinc on galvanized steel rods caused extreme corrosion, while copper-bonded steel earth rods revealed little cor-rosion (Fig. 5a–c) [3].

2.2. Material selection in a grounding system

The materials used in the construction of a lightning protection grounding system should possess good electrical conductivity,have sufficient mechanical strength to withstand the electrodynamic stresses and electromagnetic effects of the lightning current,and demonstrate suitable resistance to corrosion in aggressive environments. Table 1 gives a general guide to materials that are nor-mally used in a LPS based on IEC 62305-3 [3,44,45]. Gold and platinum show the best corrosion-resistance; however, the extreme highcost prevents them from using as components of grounding system. Consequently, steel, aluminium and copper are the three mainmetals used in grounding system applications [3]. Aluminium is subject to rapid corrosion attack due to the fact that aluminium is

Fig. 4. (a) Condition of installation and (b) zinc galvanized rod exhumation's picture [3]. After two years of exposure in soil the rods with zinc and copper coating wasremoved from the soil.

Fig. 5. The sample pictures show rods after removing from the soil after four years. (a) Copper-bonded coating. (b) Zinc galvanized coating. (c) Zinc electroplated coat-ing [3]. The results depict better corrosion protection of steel earthing rods coatedwith pure copper compared to zinc coatings having various thicknesses of coating andusing different kinds of technologies so that loss of zinc on galvanized steel rods caused extreme corrosion, while copper-bonded steel earth rods revealed littlecorrosion.

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always anodic in soil relative to othermetals [46–48]. Table 1 provides information about lightning protection systemmaterials usingin different conditions. Referring to the table, the usable material in Earth is copper while aluminium is unsuitable.

2.3. Environmental aspects of corrosion in LPS

In the United States, the National Fire Protection Association (NFPA 780: Standard for the Installation of Lightning Protection Sys-tems [51]), makes it clear that copper should not be used in contact with aluminium surfaces, and vice versa. In other words, combi-nations of the materials should not be used that form electrolyte pairs of such a kind that in the presence of humidity galvaniccorrosion is accelerated [52]. Down conductors entering corrosive soil should be protected against corrosion by a protective coveringbeginning at a point 0.9m (3 ft) above grade level and extending for the entire length belowgrade [1,26,52]. In nature, soil corrosion ofearth electrodes takes place at a rate relying on different environmental factors such as soil resistivity, dissolved salt forming an elec-trolyte, moisture, degree of aeration and temperature that make this situation very complex [3,53,54].

Moreover, Underwriters Laboratories (UL) Inc. says in its standard 96A Standard for Installation Requirements for Lightning Pro-tection Systems, that copper should not be put in contact with any exterior painted steel surface [3,19,55,56]. It is obviouswhere steeland copper are in contact and subject to an electrolyte fluid such as rainwater, galvanic corrosion will take place. Fig. 6 shows a casewhere a copper conductor, fixedwith brass clips to a galvanized steel roofing sheet. The site is located in a regionwith extremely highprecipitation level inMalaysia. Thefigure depicts the seriousness ofmaterial degradation due to corrosionwhich has also been report-ed elsewhere [3,18].

Table 1Lightning protection systemmaterials and condition of use [3,5,44,45,49,50].

Material Use in open air Use in earth Use in concrete Resistance Increased by May be destroyed bygalvanic coupling with

Copper Solid stranded Solid strandedas a coating

Solid strandedas a coating

Good in many environments Sulphur compoundsorganic materials

–

Hot galvanizedsteel

Solid stranded Solid Solid stranded Acceptable in air, concreteand benign soil

High content of chlorides Copper

Stainless steel Solid stranded Solid stranded Solid stranded Good in many environments High content of chlorides –Aluminium Solid stranded Unsuitable Unsuitable When low concentration of

sulphur or chlorideAlkaline solutions Copper

Lead Solid as a coating Unsuitable Unsuitable When high concentration ofsulphate

Acid soils Copper, stainless steel

This table shows a general guide to materials that are normally used in a LPS. Steel, aluminium and copper are the three main metals used in grounding systemapplications.

Fig. 6. Copper conductor in contact with galvanized steel roofing sheet fixed with brass clips in a region with extremely high precipitation level in Malaysia.

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In the selection process of the materials for the design of a lightning protection grounding system, the corrosion effect can beminimised by avoiding the use of unsuitable materials in an aggressive environment [1,3,57]. No combination of materials shall beused that will form an electrolytic junction, although it may be impractical to avoid a junction between dissimilar metals. The corro-sion effect shall be reduced by the use of plating or special connectors, such as stainless steel connectors used between aluminium andcopper or copper alloys [3,5,52].

3. Discussion

The abovementioned corrosion problems often do not constitute any danger to the function of the lightning protection system.Despite the fact that the boundaries to which LPS materials are connected will degrade, copper is considered nobler than aluminiumor steel (Fig. 10). It cannot be avoided that there will be a very small effect on the efficiency of the main conductor. However, a light-ning protection system cannot be presented as an independent system, but as an integral component of thewhole building envelope.The importance of the LPS can only be realised in the event of a direct strike to the building and this may only happen once every fewyears [18]. In 1995, Durham and Durham [6] conducted research to show that variants exist concerning how to protect a tower. Oneapproach is to place a lightning rod on top of the tower then a copper groundwire is run down the building [3,6,58–60]. However thedifferentmetals such as copper and steel cause a corrosion problem. In addition, the inductance of the longwire tends to create a high-impedance path [3,6,61]. Thus the effects of corrosion must be considered as part of the whole LPS.

The deterioration of metals may not pose any immediate danger to the building materials. Roofing layers are usually overlapped,thus giving a layer of waterproofing for the second layer so that any penetration due to corrosion through the substructures will bevery small at worst. On the other hand, for the case of standing-seam roofs, the primary penetration barrier is related to the metal it-self. Fig. 6 showsmetal corrosion on a standing-seam roof after less than 15 years in contactwith a bare copper conductor [3,18,62,63].

Fig. 7. Copper in touch with a metallic standing-seam roof [18]. The suppliers have installed air-terminals grounded by bare copper strips laid on themetal roofing andfacades. It is noted that the aluminium casing of the test joints that are fixed to the facades by nuts and bolts, has caused even worse corrosion problems due to thepresence of various metals together.

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Likewise, sometimes it can be seen that opportunistic suppliersmake unnecessary or sometimes even dangerous choices. Fig. 7 showsthat the suppliers have installed air-terminals grounded by bare copper strips laid on themetal roofing and facades. It is noted that thealuminium casing of the test joints that are fixed to the facades by nuts and bolts, has caused even worse corrosion problems due tothe presence of various metals together. This unnecessary installation of a LPS caused severe corrosion consequences that has dam-aged the building structure As is shown in (Fig. 8a, 8b) [3,4].

It is worth to note that preventativemaintenancemay alleviate a number of problems associatedwith corrosion by using differenttypes of paint to influence the surface of themetals to slowdown the oxidation process. However, as shown in Fig. 9, the prevention ofany type of corrosion will not be permanently effective through painting. Due to the fact that the lightning conductor is normallybraided, absorption of humidity via the spaces is unavoidable. There will always be penetration, and thus there will always be largeamounts of corrosion. Even if the corrosion is very small, in accordance with the UL and LPS standards if galvanized or paintedsteel comes into contact with steel, it is sufficient for a lightning protection system to become non-compliant [3,27,52]. The mainte-nance/replacement cycle and the system life is dependent on the selection of materials and the local environmentmust be coordinat-ed with the structural materials [3,18,52,64].

As mentioned before, in a LPS another fact to be taken into account is the effects of corrosive soil on the ground conductors. Theseconductors should not be made of aluminium and if the soil is corrosive then a corrosive protection cover should be applied to theground rods, including part of the down conductor [18,26,43]. Also prohibited is the attachment of aluminium conductors to a surfacecoated with an alkaline-based paint, embedded in concrete, or set up in a location subject to high humidity [52,65].

Further, the only material allowed to be set up in contact with the earth at very humid locations is copper. Aluminium–copper al-loys (including bronze and brass) and copper are the fundamental system component materials. These materials provide the bestjoining features in terms of weathering and current-carrying capacity. However, aluminiummaterials have reduced current-carryingcapability and mechanical strength compared to the same sized copper products. Moreover, water will oxidise galvanized surfacesand aluminium if thewater cannot run off. So coordination of system design andmaterial selectionmust include consideration of gal-vanic corrosion as one of the problems of installation [3,64]. Since 2007, changes to the UL96A standard means that most lightningprotection firms have taken up the practice of aluminium conductor installation and components on all non-copper external metalsurfaces. As the conductivity of aluminium is less than copper, cables made of aluminium are larger and therefore more visible.This issue has the advantages of using materials that are less noble than the materials to which they are attached (Fig. 10)[3,18,52]. Despite the fact that the aluminium will tend to degrade over time instead of the substructure in practice, the impact ofthe lightning conductor will be minimal and the LPS performance will not be greatly hampered [18].

4. Conclusion

To ensure the integrity of a structure, both the LPS and the structure such as rooftop surfaces are considered as part of the building.In other words, the LPS should not be considered as a separate system so that it can maintain its full capability for as long as possiblein-station. In this case, by improving the lightning protection materials by selecting only those materials suitable for the LPS and

Fig. 8. An all-metal structure (supporting struts, roof, and facades) installed with ESE air terminations and bare copper down conductors in contact with the buildingmaterial. The air termination and painted aluminium test joint could be seen in both pictures a and b. The picture has been taken soon after the installation of the system.

Fig. 9. Corrosion between a painted conductor and a painted unit [18].

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adjusted for the substructure, the risk of galvanic corrosion can be reduced. This will ensure that both systems exceed or meet theiranticipated service life. In this way, the safety of the building contents, its structural integrity, and the residents can be guaranteed.

The importance of the choice of materials by making them a priority to ensure proper maintenance of their performance in theinstalled location is an essential factor. In some cases, persistent vendors insist on installing unnecessary LPS materials which cancause grave corrosion consequences that can damage the building structure and subsequently result in high-cost structural repairs.

Despite the relevant costs, when the opportunity arises it would be beneficial in the long-run for building owners to replace thecopper components on the external steel surfaces with aluminium. It is suggested that the bronze and copper materials that poseno immediate danger can be retained in place to protect the structure, as long as the whole system remains in conformance withthe published standards. However, if substantial roof work is required, it is proposed that the lightning protection system should

Fig. 10. The galvanic series, despite the fact that the boundaries towhich LPSmaterials are connectedwill degrade. Copper is considered nobler than aluminiumor steel.As the conductivity of aluminium is less than copper, cables made of aluminium are larger and therefore more visible. This issue has the advantages of using materialsthat are less noble than the materials to which they are attached.

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be brought into full compliancewhere possible. Itmay be helpful to note that notwithstanding the above, that bronze and copperwillconstantly be the materials of choice in places where corrosion is not possible such as with non-metallic surfaces.

Acknowledgement

The authors would like to acknowledge the Faculty of Engineering at the University Putra Malaysia for placing their excellent re-search facilities at our disposal to complete this work.

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