1

Corrosion problems in specific indoor microclimates

Katerina KREISLOVA1,2

, Hana GEIPLOVA1,2

, Libor TUREK1, Dusan MAJTAS

2

1SVUOM Ltd., Prague, Czech Republic, info@svuom.cz 2ITAM CE, Telc, Czech Republic, majtas@itam.cas.cz

Abstract: Specific indoor microclimates are very corrosive in respect to operation and other factors.

These high corrosivity negatively affected durability and service life of used installations, equipment

and other facilities, mainly electric and electronic ones. The identification of source of pollution and

its level is very important for proper and long-term durability and functionality of these subjects.

There were estimated indoor corrosivity e.g. in some plan storage and operation spaces, in food

industry halls and swimming pools. The serious corrosion problems were identified for such materials

as carbon steel, stainless steel, zinc, copper and aluminium. For estimation of indoor corrosivity the

metallic coupons were exposed in various localities and spaces. In some of indoor localities the

corrosion mass losses of exposed metal coupons were over the classification of indoor corrosivity

according to ISO 11844. The corrosion products has been analysed by EDS method to verify the effect

of specific pollution. Very specific is pollution of chlorine compounds or/and H2S in some indoor

localities.

Keywords: copper corrosion; indoor corrosivity; air pollution;

Introduction

Indoor climates, respectively microclimates, cover very wide type of conditions from very

moderate to strongly aggressive polluted by different chemical compounds.

The corrosion inside buildings – indoor environments dependent upon the internal

environment but in “normal” atmospheres, e.g. dry and heated, it is insignificant. In indoor

atmospheres is a lesser likelihood of extreme values of temperature or RH neither their

variations. Typical pollutants are SO2, NO2, O3, H2S, Cl2, NH3, HCl, HNO3, Cl-, NH4

+,

organic acids, aldehydes and particles. Compared to the pollutants which infiltrate from

outdoors (mainly SO2, NO2, PM10), the indoor environment may contain pollutants in much

higher concentrations. Indoor atmospheres are polluted by the components from internal

sources, too. The ability to predict indoor corrosion rates based on information on only a few

pollutant concentrations is very limited and cannot be performed with high accuracy yet.

Copper as material of electronic and electric products, equipment’s and operation systems, but

also the other products is exposed in all of them. Indoor atmospheric corrosion was first

studied in the 1930s to monitor switchboards.

1 Corrosivity classification for copper

The corrosivity of the indoor location, e.g. control rooms, electric boxes, storage rooms, etc.,

is determined from the corrosion rate calculated from the mass change or resistance change

per unit area of standard specimens of metals after exposure for a certain time period. The

growth of corrosion films on copper coupons gives an excellent indication of the type and

concentration of pollutants, and its measurement was used here to assess and classify the

conditions.

2

There are few classification systems for estimation of the effect of atmospheric environments

onto corrosion of copper:

- Standard EN ISO 9223 [1] covers outdoor and indoor exposure conditions in categories

C1 to CX. Classification is based on yearly average values of temperature, relative

humidity, SO2 and chloride deposition. In Annex B other important pollutions including

H2S are listed not related to classification system. In Annex C there are given some

examples of type of indoor environment.

- The classification in EN ISO 9223 is too broad for some purposes in low-corrosivity

indoor atmospheres, e.g. places where electronic devices, sophisticated technical

products, or works of art and historical objects are stored. Low corrosivity indoor

atmospheres are classified according to EN ISO 11844 [2] which divide the corrosivity

categories C1 (very low) and C2 (low) into indoor corrosivity categories IC1 to IC5 –

Table 1.

Table 1. Classification of indoor corrosivity for copper

Corrosivity category Corrosion rate (rcorr)

(mg.m-2

⋅a-1

) Rate of mass increase (rmi)

(mg.m-2

⋅a-1

)

IC 1 very low indoor rcorr ≤ 50 rmi ≤ 25

IC 2 low indoor 50 < rcorr ≤ 200 25 < rmi ≤ 100

IC 3 medium indoor 200 < rcorr ≤ 900 100 < rmi ≤ 450

IC 4 high indoor 900 < rcorr ≤ 2 000 450 < rmi ≤ 1 000

IC 5 very high indoor 2 000 < rcorr ≤ 5 000 1 000 < rmi ≤ 2 500

- Standard ISA 71.04-1985 [3] provides a classification system using corrosion (or

reactivity) monitoring to determine the corrosive potential of an environment towards

electronic equipment. ISA-S1.04 covers airborne contaminants (solid, liquid, gaseous)

and biological influences that affect industrial process measurement and control

equipment. Classifications have been established according to the type of contaminant.

Contaminants are listed as Class A, Class B, etc., or as special Class X with increasing

Severity Levels 1, 2, 3, and X. From corrosion attack point of view temperature, relative

humidity and gaseous pollutants are evaluated.

Table 2. Visual evaluation of copper coupons according to ISA 71.04-1985

surface appearance class

no visible change G1

light gold-brown in 4 to 6 months, gold-brown in 12 months, or slow change

over a longer period G2

blue or black in any time period G3 or GX

flaking film in 3 to 6 months G3

3

- Standard IEC 60654-4 [4] sets out an air quality classification for industrial process and

measuring devices with the classes C1 to C4 according to each included type of pollution.

For H2S they cover concentrations < 3 ppb; < 50 ppb; < 10 000 ppb; and ≥ 10 000 ppb.

- Standard IEC 60721 [5] only defines environmental classification in terms of atmospheric

conditions including air pollution concentrations. This classification must always be

complemented with product specific amendments or additions. Only then will a

comprehensive picture be formed of most environmental factors having an effect also on

corrosion. Separate groups of classes are given for different product applications.

On Figure 1 there is correlation between classification systems for copper coupons/standard

specimens as only metal included in all these systems.

Figure 1. Copper corrosivity classification according to ISO, IEC and ISA

2 Copper Corrosion Coupon Field Results

Atmospheric corrosion of copper in outdoor exposures in Czech Republic is in corrosivity

category C4 practically on the whole area [6]. Figure 2 shows the Czech Republic map of 1

year copper atmospheric corrosion loss at open atmospheres with studied indoor spaces.

Figure 2. Copper corrosion loss (µm) after 1 year exposure

locality 1

locality 2

locality 3

locality 4

locality 6

locality 5

4

Copper corrosion was dominated by active sulphur contamination. This group includes

hydrogen sulphide, elemental sulphur, and organic sulphur compounds such as the

mercaptans; these compounds presented at low concentrations rapidly attack copper. That

attack still occurs in low relative humidity environments - < 60 %. The presence of moisture

and small amounts of inorganic chlorine compounds greatly accelerates sulphide corrosion.

For a given gas concentration, the corrosivity can be expected to be increased by one level for

each 10% increase in relative humidity above 50%.

Total copper corrosion, and particularly copper sulphide film (Cu2S) formation, is dominated

by H2S. The 1 ppm concentration is sufficient for this corrosion reaction. This corrosion film

can form an insulating layer causing electrical failures. SO2, by itself, produced only a copper

oxide (Cu2O) film.

2.1 Case studies of copper corrosion in typical indoor environments

Copper coupons were placed vertically at each monitored sites for one month, few months or

year according the observed changes. The corrosivity of indoor environments was determined

as the mass loss of corroded copper. The obtained data on corrosion of copper coupons are

interpreted using ISO 11844-1 standard. The visual evaluation of exposed coupons according

to Table 2 had been used too.

The corrosivity of 4 indoor localities of mining open air museums Pribram (locality 1) were

determined – they were indoor (uncontrolled) spaces with yearly average temperature 10.6°C;

relative humidity 72 %; time of wetness 3224 hrs.a-1

and air pollution by 2.6 µg SO2.m-3

. The

average yearly corrosion loss of copper coupons was 250 mg.m-2

.a-1

corresponding to indoor

corrosivity category IC3 (Table 1) and class G1 (Table 2 and Fig. 3a). There were practically

any significant differences among these 4 localities.

The average temperature at National Museum, Prague (locality 2) was 21.7°C and RH 38 %

and 1.8 µg SO2.m-3

, but the H2S level was relative high to cause copper corrosion mass loss

144 mg.m-2

.a-1

corresponding to indoor corrosivity category IC2 (Fig. 3b and 3c – coupons

evaluated after 1 year and after 1 month). The copper Rohrback sensor measurement showed

the corrosivity is middle for this metal - maximum monthly corrosion rate for copper sensor

was 160 Ă. The corrosivity class was G1, too. The effect of H2S pollution is evident from

colour of thin layer of corrosion products which is darker than in indoor atmospheres without

this pollution (localities in Pribram) even the corrosion loss was lower.

The industrial localities in Vamberk (locality 3) and Pardubice (locality 4) represents

unheated production building where the copper products were storaged. The average

temperature was ca 10°C and relative humidity ca 70 – 75 %. The outdoor atmospheric

corrosivity is practically the same at both these localities, but microlocality 4 is more polluted

from traffic pollution. At locality 3 the average corrosion loss was 700 mg.m-2

.a-1

; i.e. indoor

corrosivity was IC4 or G2. At locality 4 the average corrosion loss was 1 800 mg.m-2

.a-1

; i.e.

indoor corrosivity was IC5 or G2. The sulphur content on exposed surface analysed by EDX

was ca 0.5 – 0.6 wt. %.

5

1 year exposure 1 month exposure 5 months exposure

locality 1 locality 2 locality 2 locality 3 locality 4

IC3/G1 IC2/G1 IC4/G2 IC5/G2

Figure 3. The examples of copper coupons after exposure in various indoor environments

with low air pollution and corrosivity

2.2 Case studies of copper corrosion in specific indoor environment

Indoor corrosivity of technical rooms (locality 5a and 5b) was monitored as a result of

premature failure of copper tubes for cooling of installed equipment. The rooms were heated

so the average temperature was 18 – 20 °C and relative humidity was ca 50 – 55 % in room 5a

but high – between 70 - 75 % as the room 5b served as boiler room. According to Table 2 the

corrosivity of these rooms was evaluated as G2 for room 5a and G3 for room 5b. The H2S

source is probably wrong sewage installation in building.

G2 G3

Figure 4. The examples of copper coupons after 3 months exposure in indoor environments

with H2S pollution

6

The extremely significant corrosion problems with different electric products occurred in

indoor spaces of Aquapark (locality 6) where the chlorine is used for disinfection and some

pools are filled by thermal water containing 5 – 12.8 mg H2S .L-1

. In this object the electric

and electronic installations and equipment failed after very short period of exposure (Fig. 5).

The influence of air pollution by hydrogen sulphide and chloride onto corrosion attack of

copper was proved by elementary analysis and x-ray diffraction analysis (Fig. 6). The

identified dominant compound was paratacamite Cu2Cl(OH)3, atacamite Cu2Cl(OH)3,

covellite CuS and cuprite Cu2O. Usually when chlorides are added to sulphides, especially in

the present of high humidity, the combination causes copper reactivity to be worse than the

actual visual indication. The EDX analysis of electric bar corroded surface shows 6.1 wt. % of

sulphur and 16.6 wt. % of chlorine.

new copper electric bar 3 months exposed copper electric bar

Figure 5. Corrosion attack in electric equipment in Aquapark indoor environment

To monitor the corrosivity inside of building the copper coupons were exposed in 26 various

rooms and other place. The temperature was ca 20°C but the relative humidity differs

depending the distance from sources (pools, showers, etc.). In 17 rooms the corrosivity for

copper was at category C3 and average corrosion loss was 7.0 g.m-2

.a-1,

i.e. 0.8 µm.a-1

. Two

rooms had corrosivity category C4 (16.5 g.m-2

.a-1,

i.e. 1.8 µm.a-1

); one room had corrosivity

category C5 (30.9 g.m-2

.a-1

; i.e. 3.5 µm.a

-1) and two rooms had corrosivity category CX (70.3

g.m-2

.a-1

; i.e. 7.8 µm.a

-1). But there were 4 rooms (engine rooms) where the corrosion loss was

over all these categories – ca 170 g.m-2

.a-1

(19 µm.a-1

) and 220 g.m-2

.a-1

(25 µm.a-1

). The

examples of coupons appearance are given on Fig. 6.

The EDX analysis was performed on selected coupons and results of sulphur and chlorine

contents in corrosion product layers are in Table 3. These results show synergetic effect of

both type of pollution on copper corrosion in condition with high humidity. On Fig. 7 there

are shown differences between coupons with similar corrosion mass loss but difference of

corrosion stimulators effect.

7

C3/G2 C4/G3 C5/G3 CX/GX

specific 1/GX specific 2/GX

Figure 6. The examples of copper coupons after 1 month exposure in Aquapark indoor

environments

Table 3. Sulphur and chloride content in corrosion layers by EDX analysis

coupon corrosivity

category

mass loss

(g.m-2

.a-1

)

element content (wt.%)

S Cl

Cu03 C4 17.9 4.3 0.6

Cu19 C5 30.9 1.2 8.7

Cu16 CX 84.0 12.9 0.3

Cu24 special 1 145.6 15.9 0.2

Cu26 special 1 189.3 10.8 0.6

Cu25 special 2 216.7 14.2 1.0

Cu22 special 2 225.5 1.0 15.9

Cu24 Cu25 Cu26 Cu22

8

Cu25

element

analysis:

14 wt. % S

1 wt. % Cl

Cu22

element

analysis:

1 wt. % S

16 wt. % Cl

Fig. 7. Corrosion layer of copper coupons with dominate effect of H2S and Cl-

Conclusion

There were many case studies of corrosion failure of various metallic materials and coatings

in indoor environments with specific effects as high humidity and/or air pollutions. The

classification systems according to ISO 9223 or ISO 11844 cannot be used for such

environments.

Copper and copper alloys are widely used in many environments and applications because of

their excellent corrosion resistance, which is coupled with combinations of other desirable

properties, such as superior electrical and thermal conductivity, ease of fabricating and

joining, wide range of attainable mechanical properties, and resistance to biofouling. Copper

corrosion in the indoor atmosphere has been studied extensively since copper is a typical

material used in electronics. The formation of tarnish films on a copper surface exposed to

environments containing atmospheric pollutants and high humidity results in increasing the

contact resistance leading to electric failures of the electronic devices. Copper sulphidation is

a fast process occurring on the metal-gas phase interface impairing the Cu corrosion

resistance.

The study was elaborated in frame of the project IP 6/2016 financed by Ministry of Industry

and Trade of the Czech Republic.

9

References

1. EN ISO 9223 Corrosion of metals and alloys – Corrosivity of atmospheres -

Classification, determination and estimation

2. EN ISO 11844 Corrosion of metals and alloys - Classification of low corrosivity of indoor

atmospheres

3. ISA-S1.04 Environmental Conditions for Process Measurement and Control Systems:

Airborne Contaminants

4. IEC 60654-4 Operating Conditions for Industrial-Process Measurement and Control

Equipment. Part 4: Corrosive and Erosive Influences

5. IEC 60721 Classification of environmental conditions Classifications of Groups of

environmental parameters and their severities

6. K. Kreislova, H. Geiplova, D. Majtas, Long-term study of structural metals´ atmospheric

corrosion in the Czech Republic, proceedings of conference EUROCORR 2016