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IS 14191 (1996): Corrosion of Metals and alloys -classification of corrosivity of atmosphere [MTD 7: LightMetals and their Alloys]

IS 14191 : 1996

*m

CORROSION OF METALS AND ALLOYS - CLASSIFICATION OF CORROSIVITY OF

ATMOSPHERES

UDC 669 : 620.193.2

0 BIS 1996

BUREAU OF INDIAN STANDARDS MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

June 1996 Price Group 6

Corrosion Protection Sectional Committee, MTD 24

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Corrosion Protection Sectional Committee had been approved by the Metallurgical Engineering Division Council.

Metals, alloys and metallic coatings may suffer atmospheric corrosion when their surfaces are wetted. The nature and rate of the attack will depend upon the-properties of surface formed electrolytes, particularly with regard to the level and type of gaseous and particulate pollutants in the atmosphere and to the duration of their action on the metallic surface.

Data on the corrosivity of the atmosphere are an essential requirement for the development and specification of optimized corrosion resistance for manufactured products.

There are two ways to determine the corrosivity category of a given location according to this standard as given in Annex C.

The corrosivity categories are defined by the corrosion effects on standard specimens as specified in IS 14297 : 1995 ‘Corrosion of metals and~alloys - Corrosivity of atmosphere - Method of determination of corrosion rate of standard specimens for the evaluation of corrosivity’. The corrosivity categories may be assessed in terms of the most significant atmospheric factors influencing the corrosion of metals and alloys, that is, time of wetness and pollution level.

The corrosivity category is a technical characteristic which provides a-basis for the selection of materials and protective measures in atmospheric environments subject to the demands of thespecific application, particularly with regard to service life.

The standard does not take into consideration the design and mode of operation of the product which can influence its corrosion resistance since these effects are highly specific and cannot be considered on a general level.

The standard is based on IS0 9223 Corrosion of metals and alloys - Classification of corrosivity of atmospheres prepared by International Organization for Standardization.

In reporting the results of a test or analysis made in accordance with this standard, if the final value, observed or calculated, is to be rounded off, it shall be done in accordance with IS 2 : 1960 ‘Rules for rounding off numerical values (revised)‘.

IS 14191: 1996

Indian Standard

CORROSIONOFMETALSANDALLOYS- CLASSIFICATIONOFCORROSIVITYOF

ATMOSPHERES 1 SCOPE

1.1 This standard specifies key factors in the at- mospheric corrosion of metals and~alloys, classifies categories for time of wetness and pollution by SO2 and airborne salinity and defines corrosivity categories on the basis of corrosion classification data.

1.2 The classification given in this standard can be used directly to evaluate the corrosivity of atmos- pheres for metals and alloys under known condi- tions of time of wetness and pollution by SO2 and/or airborne chlorides within classified ranges.

1.2.1 This standard does not characterize the cor- rosivity of specific service atmospheres, for ex- ample, the atmospheres of chemical or metallurgical industries because the pollution and time of wetness characterization of these environ- ments cannot be generalized.

1.2.2 The classified pollution and corrosivity categories can be directly used for technical and economical analysis of corrosion damage and for rational choice of protection measures.

1.3 Annex A represents the technical content of this standard in form, easy to survey.

2 REFERENCRS

The Indian Standards listed below are necessary adjuncts to this standard:

IS No.

3531 : 1983

14297 : 1995

14321: 1995

Title

Glossary of terms relating to cor- rosion of metals (first revision)

Conventionally determined quantitativeor qualita- tive characteristics showing the amount of chemi- cally active substances, corrosive gases or suspended particles in the air, both natural and man-made, which are different from the ordinary components of the air.

Corrosion of metals and alloys - Corrosivity of atmosphere - Method of determination of corrosion rate of standard specimens for the evaluation of corrosivi ty

3.4 Type of Atmosphere

Characterization of the atmosphere on the basis of appropriate classification criteria other than cor- rosivity (industrial, marine, etc) or of complemen- tary operational factors (chemical, etc).

3.5 Temperature-IIumidity Complex

Corrosion of metals and alloys - Recommended values for the cor-

The joint effect of temperature and relative

rosivity categories of atmosphere humidity relevant to the corrosivity of the atmos- phere.

IS No.

14322 : 1995

Title

Corrosion of metals and alloys - Corrosivity of atmospheres - Methods of measurement of pal; lution

3 TERMINOLOGY

For the purpose of this standard, the following definitions shall apply.

3.1 Cocrosivity of the Atmosphere

The ability of the atmosphere to cause corrosion in a given corrosion system (for example, atmospheric corrosion of a given metal or alloy).

3.2 Time of Wetness

The period during which a metallic surface is covered by absorptive and/or phase films of electrolyte that are capable of causing atmospheric corrosion.

3.2.1 Calculated Time of Wetness

The time of wetness estimated from the tempera- ture-humidity complex (see 5.2).

3.2.2 Experimental The of Wetness

Time of wetness indicated directly by various measuring systems (see 5.3).

3.3 Pollution Category

1

IS 14191: 1996

3.8 Category of Location

Conventionally defined typical exposure condi- tions of a component or structure, for example, in open air, under shelter, in closed space, etc.

4 SYMBOLS AND ABBREVIATIONS

T - time of wetness, P - pollution category with sulphur

compounds based on SO2 levels, S - pollution category based on airborne

salinity contamination, and c - atmospheric corrosivity category.

5 CIIARACTERIZATION OF TIIE ATMOSPHERE IN RELATION TO ITS CORROSMTY

5.1 For the purpose of this standard the key cor- rosion factors of the atmosphere for metals and alloys are time of wetness, and SO2 and chloride pollution levels.

5.2 The wetting of surfaces is caused by many fac- tors, for example, dew, rainfall, melting snow and high humidity. The length of time when the relative humidity RH > 80% at > 0°C is used to estimate the calculated time of wetness (T) of corroding surfaces.

5.3 The experimental time ofwetness can be deter- mined directly by various measuring systems.

5.4 The most important factor within a particular category of time of wetness is~the pollution level by sulphur dioxide or airborne salinity.

5.5 Pollution level must be measured in accord- ance with IS 14322 : 1995

operational one (for example, vapours of acids in the operational microclimates).

NOTES

1 The time of wetness calculated by this method does not necessarily correspond with the actual time of wetneas be- cause wetness is influenced by the type of metal, the shape, mass and orientation of the object, the quantity of corrosion product, the nature of pollutants on the surface and other factors. These considerations may increase or decrease the actual time of wetness. However, this criterion is usually sufficiently accurate for the characterization of atmospheres. The relevance of the time of wetness defined in the prescribed manner decreases with the degreeof sheltering.

2 The indicated time can depend upon the type of instru- ment and sensor. Wetting times indicated by various systems are not directly comparable and-are convertible only within a limited extent of temperature-humidity characteristics

6 CLASSIFICATION OF TIME OF WETNESS

6.1 Time of wetness (see 5.2 and 5.3) depends upon the macroclimatic zone and the category of the location.

6.2 The classification of time of wetness for atmos- pheres is givenin Table 1. The classified values are based on the long term characteristics of macro- climatic zones for typical conditions of the location categories.

6.3 The calculated times of wetness and selected climatological characteristics of the macroclimatic zones of the earth are informative shown in Annex B.

6.4 For time ofwetnesrt, almost no condensation is expected. For r2 the probability of liquid forming ,on the metallic surface islow. Wetness times 73 to 7s include periods of condensation and precipita- tion.

5.6 Other kinds of pollution can also exert an ef- fect (NOx, and industrial dust in populated and 7 CLASSIFICATION 0-F POLLUTION

industrial zones) or the specific operational and CATEGORIES

technological pollution of microclimates (Ch,H2S, organic acids, de-iceing agents). These types of pol- 7.1 Pollution categories are defined for pollution

lution have not been taken as the classification of the atmosphere by SO2 and for airborne salinity.

criteria. These two kinds of pollution are representative for

According to this standard the other kinds of pol- ruraLurban, industrial and marine atmospheres.

Jution should be considered accompanying ones 7.2 The classification of pollution by SO2 for (for example, NOx in urban atmosphere) or specific standard outdoor atmospheres is given in Table 2

Category

71

72

73

74

75

T _

-

IS 14191: 1996

Table 1 Classification of Time-of Wetness (Clause-6.2)

h/a

7510

10 < 7 5 250

250<r 5;2 500

25OO<r<5500

5500<7

percent

750.1

0.1-C 7 13

3<7530

30<?$60

Internal microclimates with climatic control

Internal microclimates without climatic control except for internal

non-air conditioned spaces in damp climates

Outdoor atmospheres in dry, cold and part of temperate climates,

properly ventilated sheds in temperate climate

Outdoor atmospheres in all climates (except for the dry and cold

climates), ventilated sheds in humid conditions, un-ventilated sheds in temperate climate

60<7 Part of damp climates, unventilated sheds in humid conditions

Example of Occurrence

NOTES 1 The time of wetness of a given locality depends on the temperature-humidity complex of the open air atmosphere and the categoty of the location and is expressed in hours per year or as part of exposure time (in %).

2 The values of time of wetness in % are rounded and informative only.

3 The column indicating the occurrence does not include all possibilities following from the degree of sheltering.

4 Sheltered surfaces in marine atmospheres where chlorides are deposited may experience substantially increased time of wetness due to the presence of hydroscopic salts and should be classified in the category TV.

5 In indoor atmospheres without climate control wetted by operational sources of vapour times of wetness t3 - 75 can be attained.

6 For time of wetness 7t and t2, the corrosion proceeds according to probability laws (probability and frequency of critical values affecting environmental factors). The probability of corrosion is higher for surfaces on which dust may settle.

Table 2 Classification of Pollution by Sulphur- Containing Substances Represented by SO2

(Clause 7.2)

Deposition Rate of SO2 Concentration of SO2

mg/(m’. d) /m/m3

Category

Pd 5 10

10 < Pd 5 35

35 < P,, 5 80

80 < Pd 5 200

PC 112

12 < P, zz 40

40 < P, 5 90

90 < P, 5 250

PO

Pl

P2

P3

NOTES

1 Methods of determination of SO2 are specified in IS 14322 : 1995.

2 The SO2 values determined by the deposition (Pd) and volumetric (PC) methods are equivalent for the purpose of classification. The relationship between measure- ments using both methods could be approximately for- mulated as Pd = 0.8 PC.

3 For the purposes of this standard, the SO2 deposition rate and concentration are calculated from continuous measurements during at least one year and are expressed as the annual average. The result of short term measure- ments may differ considerably from long term averages. Such results serve for guidance only.

4 Any concentration of SO2 within PO is considered to the background concentration and is insignificant from the point of view of corrosive attack.

5 Pollution by SO2 over P3 is considered extreme and is typical of operational microclimates beyond the scope of this standard.

6 In shed-type atmospheres and, especially, in indoor atmospheres, the concentration of the pollutants is reduced depending upon the degree of sheltering.

7.3 The classification of pollution by chloride (Cl-) relates to outdoor atmospheres which are polluted by airborne salinity in marine environments. The classification is given in Table 3.

Table 3 Classification of Pollution by Airborne Salinity Represented by Chloride

Deposition Rate of Chloride

mgl(m’. 4 Category

s?z3 So 3<S 560 ,Sl

6OcS 5300 S2 300 c s 5 1500 S3

NOTES 1 The classification of airborne salinity according to this

standard is based on the wet candle method specified in IS 14322 : 1995.

2 The results obtained by the application of various mefhods for the determination of the salt content in the atmosphere are not always directly comparable and con- vertible.

3 For the purpose of this standard, the chloride deposi- tion rate is “pressed as the annual average. The results of short-term measurements are very variable and the dependence upon weather effects is very strong.

4 AnychloridedepositionrateofwithinSois takenas the background concentration and is insignificant from the point of view of corrosive attack.

5 Extreme pollution by chloride, being typical of marine splash and spray is beyond the scope of the standard.

6 The airborne salinity is strongly dependent on the variables influencing the transport of sea-salt to inland, such as wind direction, wind velocity, local topography, distance of the exposure site from the sea, etc.

IS 14191: 1996

8 CATEGORIES OF CORROSIVITY OF THE ATMOSPHERE

8.1 The corrosivity of the atmosphere is divided into five categories (see Table 4).

Table 4 Categories of Corrosivity of the Atmosphere

Caleg0l.y

Cl . Ci c3 c4

Corrosivity

Very low LOW

Medium

i_____ 1

High C5

I Very high

__..~ ~~~__

9 CLASSIFICATION OF CORROSIVITY BASED ON CORROSION RATE MEASUREMENTS OF STANDARD SPECIMENS

Numerical values of the first year corrosion rate for stanc&rrd metals (carbon steel, zinc, copper,

aluminium) are given in Table 5 for each of the corrosivity categories. The values cannot bc cx- trapolated for prediction of long term corrosion behaviour. Guiding corrosion values and addition- al information are given in 1s 14297 : 1995.

10 CLASSIFICATION OF CORROSIVITY BASED ON ENVIRONMENTAL DATA

10.1 The pollution and time of wetness categories are used for the determination of the corrosivity category for the individual metals.

10.2 Corrosivity categories corresponding to the classified time of wetness and poll&in categories are given in Table 6.

10.3 In the case of the time of wetnessrcatcgory rr, the corrosivity category is always 1 except in highly polluted indoor atmosphcrcs.

Table 5 Corrosion Rates for the First Year of Exposure for the Different Corrosivity Categories

I_ --- ___-__----- 1

Corrosion Rales of Metals Corrosivily

Calegory Units

g/(m' a)

lcmla

g/(n? a)

pm/a

s/(m’ . a) lcmla

g/(m* a) [cmla

s/(m’ a> ttmla

i

Carbon Steel

_~____ Zinc

rcorr 510 rcorr SO.7

rWrr 5 1.3 rcrJrr IO. 1

lo< rwrr 1200 0.7-z rcorr s.(

1.3< rarr s25 O.l< r x07 carr-

200< rcorr 1400 5-z rcorr 515

25< rcorr 550 0.7< r <21 corr- .

400~ rWrr 1650 15< rcorr 530

50~ rcorr 580 2.1~ rcorr ~4.2

650-z rWrr 11500 30< rcorr160

80~ rcorr 1200 4.2~ rcorr 18.4

T

1 The classification criterion IS based on the methods of~determination of corrosion rate of standard specimens (flat plate or helix) for the evaluation of corrosivity [see IS 14297 : 19951. 2 The corrosion rates expressed in g/(n? a) have been recalculated inltm/a and rounded. 3 The materials are characterized in IS 14297 : 1995. 4 Aluminium experiences localized corrosion but the corrosion rates shown in Table 5 are calculated as uniform corrosion. Therefore, values for corrosion depth per unit time are no! meaningful. 5 Corrosion rates exceeding the upper limits in C 5 represent environments behind the scope of this standard.

-r

-

_____.

Copper rwrr 60:9

rcorr 10.1

0.9r rcorr 55

O.l< r -=06 Eorr - . 5< rcorr 512

0.6~ rWn. 11.3

12~ rWrr 525

1.3~ rCOrr 62.8

25< rcorr 150

2.8~ rcorr 15.6

r _ Aluminium

negligible

-

rcorr (0.6

-

0.6-c rcorr 12

-

2c rcorrs5 -

SC roorr510 -

4

Table 6 Estimated Corrosivity Categories of the Atmosphere (Clause 10.2)

Unalloyed Carbon Steel:

I I

So-S1 SZ s3 So-St s2 s3 so-s1 j s2 s3 so-s1 Sl S3 so-s1 542 s3

t ! b PO-PI p3 P7 1 or2 1 1 or 1 1 1 1 or2 or 2 2 1 or 2 1 2 2;3 I 1 2 :;I :,:

L

;;I

Zinc and Copper:

so-s1 s2 s3 so-s1 s2 s3 so-s1 s2 s3 so-s1 s2 s3 So-S1 s2 s3

‘VI PO- PI 1 1 1 1 1 or2 3 3 3 3 or4 3 4 5 3 or 4 5 5

P2 1 1 1 or2 1 or2 2 3 3 3 or4 4 3 or 4 4 5 4 or 5 5 5

P3 1 1 or2 2 2 3 3 or4 3 3 or 4 4 4 or 5 5 5 5 5 5

I I

Aluminium:

so-s1 s2 s3 so-s1 s2 s3 so- s1 s2 s3 so-SI s2 S3 so-s1 s2 s3

PO-PI 1 2 2 1 2 or 3 4 3 3 or4 4 3 3 or4 5 4 5 5

P2 1 2 2 or 3 1 or2 3 or 4 4 3 4 4 or 5 3 or 4

P3 1 2 or 3 3 3 or4 4 4 3 or4 4 or 5 -7+

E

NOTE 1 Corrositity is expressed as the number part of corrosivity category code (example 1 instead c 1). z CI rD I

ANNEX A (Clause 1.3)

DERIVATION OF CORROSIVITY OF ATMOSPHERES FOR VARIOUS METALS

TPB-JP 7 nnvivntinn nf Pmw,.;v;tv nf Atmncnhnm. fnc Pnchnn Ctnal

Corrosivity Corrosion Rate Time of WetnessI) Calculated as Hours RH < 80 percent, 8 > 0°C (NB)

IO<TS 250 250< rSisO0 2500< r15500 r>5500 (class 72) (class ?j) (class u) (class rs)

Outdoors in Dry and , Outdoors in Temperate Outdoors in Damp Cold Climates, Climates, Unventilated Climates, Humid Ventilated Sheds in Sheds in Temperate Unventilated Sheds

Climates Temperate Climates Climates. Ventilated Sheds in Damp Climates

Cl rcorr 5 10 rlin S 0.1

c2 lo< rcorr S 200 O.l< flit! s 1.5

c3 200< rcorr S 400 1.5-cr~16

c4 400~ rcorr S 650 6crli.S20 Airborne Salinity 4’

c5 6.50~ rcOrr S 1 500 20< rb 6 90 Chloride Deposition Rate, mg/(m’.d)

So Sl sz s3 so Sl sz s3 so Sl s2 s3 so Sl s2 s3

Industrial Pollution’) by SOz

Concentration Category Deposition rate

Wm3 mg/(m’.d) ,g VI ,I;

m *

VI V 0) m

P,< 12 PO Pd-< 10 1 1 lor2 1 2 3 or 4 2 or 3 3 or4 14 3 4 5 3or4 5 5 12<P,S40 PI lo<Pds35

40-c I 90 P, p2 35< I 80 Pd 1 1 1 or2 1 or2 3 or 4 3 or 4 3 or4 3 or 4 4or5 4 4 5 4or5 5 5

90-z P, I 250 P3 60~ Pj < 200 1 or2 1or2 2 2 3 4 4 4 or 5 5 5 5 5 5 5 5

NOTE - Corrosivity is expressed as the number part of the corrosivity category code (example 1 instead C 1) according to Table 6.

‘)According to Table 1 *)According to ‘Table 5

4)According to Table 3

3)According to IS 14321 : 1995 ‘)According to Table 2

(Steady state corrosion rate derived from long term exposure)

onnn

o ‘A

4

w

,J

e

6 ,: ‘E 1 E

n

s13

B

3 <

s S

60

c”

N z w

N

--

h)

-.

w

--

w 2 4

60

< s

$ 30

0 x

300

< s

I 15

00

2

s13

i?

3 <

s 2

60

”

60

c s

I300

,%

=

w

3<s1

60

c”

60

< s

I 30

0 B

w

g 4 4 4 2 VI

300

< s

2 I.5

00

E

s13

F

3<

sS60

F

60

< s

$ 30

0 .?

=

300

< s

I 15

00

F I

3 <

s 2

60

”

60<

s.13

00

eY

300

< s

I 15

00

v:

w

9661

: 16

IPT

S

I

00

Cl

c2

c3

c4

C5

=F

Corrosivity Category

Corrosion Rate

1st Yca2) Steady Stab? g/(m2.a) @a

rc.,,rr < 0.9 rlin 5 0.01

0.9< ralrr < 5 O.Ol< rlin _< 0.1

5< rcorr 5 12 O.l< rrin < 1

12~ rcorr s 25 I<rbi,3

25< rcorr 2 50 3<rb<5

Table 9 Derivation of Corrosivity of Atmospheres for Copper

7 !G-io

Time of WetnessI) Calculated as Hours RH > 80 percent, 6 > 0°C (h/a)

lO<T5250 250<5~2500 - 2500<~<5500 7>5500 (class q) (class 72) (class 73) (class 74) (class 7s) Indoors, Climatic Indoors, No Climatic Outdoors in Dry and Control

Outdoors in Temperate Outdoors in damp Control Except in Cold Climates, Climates, Unventilated Climates, Humid Damp Climates Ventilated Sheds in. Sheds in Temperate Uliventilated Sheds

Temperate Climates Climates, Ventilated Sheds in Damp Climates

.

Airborne Salinity ”

Chloride Deposition Rate, mg/(m2.d)

J

Industrial Pollution’) by SO2 So s1 sz s3 so Sl s2 s3 so Sl s2 s3 so SI s2 s3 so Sl s2 s3

Concentration Category Deposition Rate Wm3 mgl(m’.d)

8 8 ”

% g g 8 8 8 -

1

8 “’

v’

8 E 3 VI s

g “, c:

VI 8

8 ” VI

VI VI * VI vi VI y1 VI

I

z VI VI “,’ v1 y. VI w VI s

m =

jm;

v m * w.

Lx;

v mV’ V m = V cr. Ifa V

VI V

* 5 : ::; g “,‘::; gv,I 5 5

P,< 12 PI7 P,,< 10 12<P,<40 PI lO<Pd<35 1 1 1 1 lor2 3 3 3 3or4 3 , 4 5 3or4 5 5

40< P, < 90 PZ 35< Pd 5 80 1 1 1or2 1or2 2 , 3 3 3or4 4 3or4 4 5 5 40;5 5

9Oc PC s 250 P, 8o<Pdz;2@, 1 lor2 2 2 3 3or4 3 3or4 4 4or5 5 5 5 5 5

L

NOTE - Corrosivity is expressed as tht number part of the corrosi\ity category code (exampIe 1 instead C 1) according to Table 6.

‘)According to Table 1 *‘According to Table 5

4’According to Table 3

3)According to IS 14321 : 1995 ‘)According to Table 2

(Steady state corrosion rate derived from long term exposure)

\

Table 10 Derivation of Corrosivity of Atmospheres for Aluminium

Com~~ion Rate

1st Yea? -

Time of WetnessI) Calculated as Hours RH > 80 percent, f3 > dT (h/a)

g/(m*.a)

Steady State3’

pm/a

Negligible Negligible

Corrosivity Category

Cl

.c 2

c3

c4

C5

rcorr 5 0.6 0.01-c rsrj 5 0.02

0.6< rcorr < 2 0.02< rh < 0.2

2< ruorr 2 5 See Note ’

3-c rcorr < 10 See Note .4irborne Salinity ‘!

Chloride Deposition Rate, mg/(m’.d)

s2

8 m

VI Y;

V

s

3 or4

4

5

s2 s3

3 5 0 T CCI

VI VI cz

v:

V V

5; is

z or 3 4

3

3or4 4

4!4

L t t L

- So

c”.

“I

v. -

- Sl

53 VI %

V

(r. -

so

t-c

VI (I:

-

- Sl

8 VI CA

V

m -

-

I t t I t t 1

1 or2

2 or 3

T

-

s2

i?

VI Y;

”

%

3 or 4

4

4 or 5

4or5.

Industrial Pollution” by SO2

Concentration Category Deposition Rate

pg/m3 mg/(m’.d)

4 or 5

P,< 12 Pi, Pd< 10 12< P, I40 PI to<Pd<35

3

3

3 or4

3 or 4 4o<P,190 Pt 35-c Pd < 80

90< P, < 250 P3 8kP.j<200 4 or 5

NOTE - Corrosivity is expressed as the number part of the corrosivity category code (example 1 instead C 1) according to Table 6

“According to Table 1 ‘)According to Table 5

“According to Table 3

‘)According to IS 14321 : 1995 ‘)According to Table 2

(Steady state corrosion rate derived from long term exposure) In corrosivity categories C 4 and C 5 marked increase of corrosion rate may be expected, local corrosion effects become important.

ANNEXB &5 !z

(Clause 6.3) E Table 11 Calculated ‘IIme of Wetness and Selected Climatological Characteristics of the Macroclimatiiz Zones of the Earth

. . CI

3

I Type of Open-Air Climate I Mean Value of the Annual Extreme Values Calculated Tie of Wetness

(Hours at RH > 80 percent and e > O”c,

category Time of Wetness

Extremely cold -65 +32

Cold - so +32

Cold temperate Warm temperate

Warm dry Mild warm dry Extremely warm dry

- 33 +34 - 20 +35

- 20 +40 -5 +40 +3 +55

Warm damp Warm damp, equable

+5 +40 +I3 +35

L

Highest Temperature

with RH L 95 % T

+20

+20

+23 +25

+27 +27 +28

+31 +33

h/a

o- 100

ISO- 2500

2 SOO- 4200

10-1600

4200-6OGU

‘II or g

72 or T3

T4

52 or 53

q or 7s

-IS14191:1996

ANNEX C (Foreword )

CLASSIFICATION OF ATMOSPHERIC CORROSMTY

Classification of atmospheric corrosivity (two approaches)

Corrosivity categories .

(IS 14191)

Guiding values of corrosion rate for each category for specific metals

(IS 14321)

11

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Review of Indian Standards

Amendments are issued to standards as theneed arises on the basis of comments. Standards are also reviewed periodically; a standard along with amendments is reaffirmed when such review indicates that no changes arc needed; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standards should ascertain that they are in possession of the latest amendments or edition by referring to the latest issue of ‘BIS Handbook’ and ‘Standards Monthly Additions’.

This Indian Standard has been developed from Dot : No. MTD 24 ( 3767 ).

Amendments Issued Since Publication

Amend No. Date of Issue Text Affected

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Eastern :

Northern :

Manak Bhavan, 9 Bahadur Shah Zafar Marg NEW DELHI 110002

1114 C. LT. Scheme VII M, V. 1. P. Road, Maniktola CALCUTTA 700054

SC0 335-336, Sector 34-A, CHANDIGARH 160022

Southern : C. I. T. Campus, IV Cross Road, MADRAS 600113

Western :

Branches :

Manakalaya, E9 MIDC, Marol, Andheri (East)

(

832 92 95,832 78 58 MUMBAI 400093 832 78 91,832 78 92

AHMADABAD. BANGALORE. BHOPAL. BHUBANESHWAR. COIMBATORE. FARIDABAD. GHAZIABAD. GUWAHATI. HYDERABAD. JAIPUR. KANPUR. LUCKNOW. PATNA. THIRUVANANTHAPURAM.

323 76 17 323 38 41

337 84 99,337 85 61 337 86 26,337 9120

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60 38 43 60 20 25

{

235 02 16,235 04 42 235 15 19,235 23 15

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