ASTM G46-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G46 − 94 (Reapproved 2018) G46 − 21
Standard Guide for
Examination and Evaluation of Pitting Corrosion
This standard is issued under the fixed designation G46; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This guide covers the selection of procedures that can be used in the identification and examination of pits and in the evaluation
of pitting (See Terminologyexamination and evaluation of pitted metals. These G15) corrosion to determine the extent of its
effect.procedures include both nondestructive and destructive approaches.
1.2 The procedures covered in this guide include those that may be used in laboratory evaluations of corroded metal specimens
and field examinations and inspections.
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for
information only and are not considered standard.
1.3.1 Exception—In X1.2.1, mils per year (MPY) are regarded as standard for the target corrosion rate.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E3 Guide for Preparation of Metallographic Specimens
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
G16 Guide for Applying Statistics to Analysis of Corrosion Data
G61 Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of
Iron-, Nickel-, or Cobalt-Based Alloys
G193 Terminology and Acronyms Relating to Corrosion
This guide is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.05 on Laboratory Corrosion
Tests.
Current edition approved Oct. 1, 2018Aug. 1, 2021. Published November 2018October 2021. Originally approved in 1976. Last previous edition approved in 20132018
as G46 – 94 (2013).G46-94 (2018). DOI: 10.1520/G0046-94R18.10.1520/G0046-21.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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2.2 ISO Standard:
ISO 25178-604:2013(E) Geometrical product specifications (GPS) — Surface texture: Areal — Part 604: Nominal character-
istics of non-contact (coherence scanning interferometry) instruments
2.3 National Association of Corrosion Engineers Standard:NACE Standards:
NACE RP-01-73 Collection and Identification of Corrosion Products
NACE SP0775 Preparation, Installation, Analysis, and Interpretation of Corrosion Coupons in Oilfield Operations
3. Terminology
3.1 Terms and acronyms used in this guide are defined in Terminology G193.
4. Significance and Use
4.1 It is important to be able to determine the extent of pitting, either in a service application where in which it is necessary to
predict the remaining life in a metal structure, or in laboratory test programs that are used to select the most pitting-resistant
materials for service. The purpose of the study is crucial in determining the appropriate examination and evaluation steps.
4.2 Some typical purposes of laboratory tests include, but are not limited to, evaluating performance of alloys, determining
whether an alloy is resistant to the environment, evaluating how environmental conditions including corrosion inhibitor affect or
prevent pitting, and evaluating whether a lot of metal is sufficiently resistant for its use in a particular application or environment.
FIG. 1 Variations in the Cross-Sectional Shape of Pits
The last approved version of this historical standard is referenced on www.astm.org.Available from International Organization for Standardization (ISO), ISO Central
Secretariat, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva, Switzerland, https://www.iso.org.
Available from Association for Materials Protection and Performance (AMPP), 15835 Park Ten Pl., Houston, TX 77084, http://www.ampp.org.
Insert in Materials Protection and Performance,Vol 12, June 1973, p. 65.
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4.3 Some typical purposes of field studies include, but are not limited to, determining if pits are likely to grow and cause leak or
release of process fluid, and assisting a determination of whether to replace or repair damage from pits (remaining life assessment).
5. Identification and Examination of Pits
5.1 Preliminary Visual Inspection—An initial visual examination of the corroded metal surface is usually conducted in an
as-received condition before any cleaning or destructive inspection.
5.1.1 It is important to distinguish between as-received, precorroded surfaces, post-hydrotest surfaces, and other surface
conditioning, such as nitriding and nano coatings.
5.1.2 It is often advisable to photograph the corroded surface so that it can be compared with the clean surface after the removal
of corrosion products.
5.1.3 The composition of the corrosion products may be of value in determining the cause of corrosion, especially if the specimen
has been exposed to an unknown environment. Where analysis of corrosion products is desired, follow recommended procedures
for the removal of particulate corrosion products (for example, NACE RP-01-73 ) and preserve them for future identification.
5.1.4 Examine the corroded surface to determine the extent of corrosion and the apparent location of pits as well as identify areas
of interest for further examination.
5.1.4.1 It is often advisable to perform a more detailed examination through a microscope using low-magnification (20×) to
photograph the corroded surface at this point, so that it can be compared with the clean surface after the removal of corrosion
products.
5.1.4.2 This preliminary visual inspection is typically performed under ambient light, with or without the use of a low-power
magnifying glass or additional light source.
5.2 Cleaning/Pit Exposure:
5.2.1 Exposing the pits fully using recommended cleaning procedures to remove the corrosion products (see Practice G1).
5.2.1.1 Avoid solutions that attack the base metal excessively.
5.2.1.2 Scrubbing with a stiff, nonmetallic bristle brush will often enlarge the pit openings sufficiently by removal of corrosion
products or undercut metal, or both, making the pits easier to evaluate;
5.2.1.3 It may be advisable during cleaning to probe the pits with a pointed tool to determine the extent of undercutting, tunneling,
or other subsurface corrosion (Fig. 1).
5.3 Post-Cleaning Visual Inspection—Inspection: A visual examination of the corroded metal surface is usually beneficial, and this
is done under ordinary light, with or without the use of a low-power magnifying glass, to determine the extent of corrosion and
the apparent location of pits. It is often advisable to photograph the corroded surface at this point so that it can be compared with
the clean surface after the removal of corrosion products.
4.1.1 If the metal specimen has been exposed to an unknown environment, the composition of the corrosion products may be of
value in determining the cause of corrosion. Follow recommended procedures in the removal of particulate corrosion products and
reserve them for future identification (see NACE RP-01-73).
4.1.2 To expose the pits fully, use recommended cleaning procedures to remove the corrosion products and avoid solutions that
attack the base metal excessively (see Practice G1). It may be advisable during cleaning to probe the pits with a pointed tool to
determine the extent of undercutting or subsurface corrosion (Fig. 1). However, scrubbing with a stiff bristle brush will often
enlarge the pit openings sufficiently by removal of corrosion products, or undercut metal to make the pits easier to evaluate.
NACE has been changed to AMPP, which may impact how this standard is labeled in the future.
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5.3.1 Examine the cleaned metal surface under ordinary light to determine the approximate size and distribution of pits. Follow
this procedure by a more detailed examination through a microscope using low magnification (20×).extent of corrosion and the
apparent location of pits as well as to identify areas of interest for further examination.
5.3.2 Determine and note the size, shape (1, 2), aspect ratio (diameter/depth) (3), uniformity, and density of pits (corroded
area/total surface area) (1, 2), as needed. Pit size is often defined as the diameter of the pit mouth for hemispherical pits or
equivalent diameter, [2×sqrt(area/π)], or at times it can refer to the depth, length, or width of the pit. It is important to record which
parameter is being measured when reporting the pit size.
5.3.2.1 Pits may have various sizes and shapes, be distributed in a uniform or nonuniform manner, and be arranged in a dense or
sparse pattern. All of these traits may be relevant to the evaluation of the corrosion process.
5.3.2.2 The diverse nature of internal and external standards and specifications for evaluating pitting corrosion may mean that the
level of importance on each of the above criterion may be different for each document.
5.3.3 Determine the size, shape, and density of pits.Evaluation of pit density or the number of pits per given area can be made
easier by the use of a plastic grid. Place the grid, containing 3 mm to 6 mm squares, on the surface. Count and record the number
of pits in each square and move across the grid in a systematic manner until the desired surface area has been covered. Obtain the
average from all the measurements from each square for a final measurement value.
4.1.4.1 Pits may have various sizes and shapes. A visual examination of the metal surface may show a round, elongated, or
irregular opening, but it seldom provides an accurate indication of corrosion beneath the surface. Thus, it is often necessary to cross
section the pit to see its actual shape and to determine its true depth. Several variations in the cross-sectioned shape of pits are
shown in Fig. 1.
5.3.3.1 It is a tedious job to determine pit density by counting pits through a microscope eyepiece, but the task can be made easier
by the use of a plastic grid. Place the grid, containing 3 to 6-mm squares, on the metal surface. Count and record the number of
pits in each square, and move across the grid in a systematic manner until all the surface has been covered. This approach
minimizes eyestrain because the eyes can be taken from the field of view without fear of losing the area of interest.
5.3.3.2 Pit density will be affected if pit clusters, interconnected pits, or the occurrence of pits within pits are treated as one or
multiple pits. In some cases, the fraction of the total area covered by pits can be considered as a parameter more relevant than pit
density.
5.3.4 Metallographic Examination—Select and cut out a representative portion of the metal surface containing the pits and prepare
a metallographic specimen in accordance with the recommended procedures given Evaluation of pit density can also be
accomplished using available software that can post-process electronic images of the corroded surface. Electronic images can be
set to a contrast threshold to delineate the corrosion pits from the noncorroded specimen surface. The number of pits can be counted
and divided by the actual area of specimen in the electronic image (4in Methods ).E3. Examine microscopically to determine
whether there is a relation between pits and inclusions or microstructure, or whether the cavities are true pits or might have resulted
from metal dropout caused by intergranular corrosion, dealloying, and so forth.
5.3.5 Other available software commonly used in profilometry and topography measurements with built-in function of pit
measurement can also be used to determine the pit density.
5.4 Metallographic Examination—A visual examination of the metal surface may show a round, elongated, or irregular opening,
but it seldom provides an accurate indication of the nature of any corrosion beneath the surface. Thus, it is often necessary to cross
section the pit to see its actual shape and to determine its true depth and size. Several variations in the cross-sectioned shape of
pits are shown in Fig. 1.
5.4.1 Select and cut out a representative portion of the metal surface containing the pits and prepare a metallographic specimen
in accordance with the recommended procedures given in Guide E3.
5.4.2 Examine the cross section microscopically.
The boldface numbers in parentheses refer to the list of references at the end of this practice.
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5.4.2.1 Determine whether there is a relation between pits and inclusions/microstructure.
5.4.2.2 Determine whether the cavities might have resulted from metal dropout caused by intergranular corrosion, dealloying, and
so forth.
(1) The diverse nature of internal and external standards for evaluating pitting corrosion may mean that there is an importance
in measuring features related only to a specific form of attack. This means that there is a high level of importance in discerning
the characteristics of the attack observed to prevent incorrectly weighting results. Determination and recordkeeping should follow
standard requirements.
(2) High levels of magnification (200× to 500×) may be required to identify dropout of fine grains because of intergranular
corrosion
5.5 Nondestructive Inspection—A number of techniques have been developed to assist in the detection of cracks or cavities in a
metal surface without destroying the material (15). These methods are less effective for locating and defining the shape of pits than
some of those previously discussed, but they merit consideration because they are often used in situ, and thus are more applicable
to field applications.
5.5.1 Radiographic—Radiation, such as X rays, X-rays, are passed through the object. The intensity of the emergent rays varies
with the thickness of the material. Imperfections may be detected if they cause a change in the absorption of X rays. X-rays.
Detectors or films are used to provide an image of interior imperfections. The metal thickness that can be inspected is dependent
on the available energy output. Pores or pits must be as large as ⁄2 % % of the metal thickness to be detected. This technique has
only slight application to pitting detection, but it might be a useful means to compare specimens before and after corrosion to
determine whether pitting has occurred and whether it is associated with previous porosity. It may also be useful to determine the
extent of subsurface and undercutting pitting (Fig. 1).
5.5.2 Electromagnetic:
5.5.2.1 Eddy currents can be used to detect defects or irregularities in the structure of electrically conducting materials. When a
specimen is exposed to a varying magnetic field, produced by connecting an alternating current to a coil, eddy currents are induced
in the specimen, and they in turn produce a magnetic field of their own. Materials with defects will produce a magnetic field that
is different from that of a reference material without defects, and an appropriate detection instrument is required to determine these
differences. This method is typically not used on ferromagnetic materials.
5.5.2.2 The induction of a magnetic field in ferromagnetic materials is another approach that is used. Discontinuities that are
transverse to the direction of the magnetic field cause a leakage field to form above the surface of the part. Ferromagnetic particles
are placed on the surface to detect the leakage field and to outline the size and shape of the discontinuities. Rather small
imperfections can be detected by this method. However, the method is limited by the required directionality of defects to the
magnetic field, by the possible need for demagnetization of the material, and by the limited shape of parts that can be examined.
5.5.3 Sonics:Sonic:
5.5.3.1 In the use of ultrasonics, pulses of sound energy are transmitted through a couplant, such as oil or water, onto the metal
surface where waves are generated. The reflected echoes are converted to electrical signals that can be interpreted to show the
location of flaws or pits. Both contact and immersion methods are used. The test has good sensitivity and provides instantaneous
information about the size and location of flaws. However, reference standards are required for comparison, and training is needed
to interpret the results properly.
5.5.3.2 An alternative approach is to use acoustic emissions in detecting flaws in metals. Imperfections, such as pits, generate
high-frequency emissions under thermal or mechanical stress. The frequency of emission and the number of occurrences per unit
time determine the presence of defects.
5.5.4 Penetrants—Penetrant—Defects opening to the surface can be detected by the application of a penetrating liquid that
subsequently exudes from the surface after the excess penetrant has been removed. Defects are located by spraying the surface with
a developer that reacts with a dye in the penetrant, or the penetrant may contain a fluorescent material that is viewed under black
light. The size of the defect is shown by the intensity of the color and the rate of bleed-out. This technique provides only an
approximation of the depth and size of pits.
5.5.5 Other Profilometry and Topography Tools:
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5.5.5.1 Different noncontact inspection tools (for example, laser scanner, white-light interferometer, and digital three-dimensional
(3-D) microscope) are available to determine the profile of the corrosion pit without having to cross section the specimen.
NOTE 1—To capture the true shape and size of the corrosion pit using the noncontact inspection tools, the corrosion products need to be removed.
5.5.5.2 The laser scanner uses sticker targets placed on the surface of the specimen as reference for the 3-D reconstruction. As the
sample is being scanned, the laser scanner records the real surface points in relation to the sticker target position. The collected
data can be reconstructed to form the 3-D rendering of the corrosion pits using compatible laser scan software.
5.5.5.3 White light interferometry uses the light interference produced by the surface roughness of the specimen. The source emits
white light that is separated by the beam splitter into measurement and reference beams. The reference beam is reflected from the
reference plane using a mirror, and the measurement beam is incident to the specimen surface. The interference pattern in the
charged-coupled device (CCD) image sensor is formed by the reflected beam that passed through the reference mirror. The data
can be reconstructed to form the 3-D rendering of the corrosion pits using compatible interferometry software (4, 6).
5.5.5.4 A digital 3-D optical microscope can be used to form the profile of the corrosion pit by stacking two-dimensional (2-D)
images taken at different vertical heights (along z-axis). The optical microscope captures the data in the 2-D plane (x-axis and
y-axis) with single- image acquisition at each step along the vertical height (z-axis). A digital 3-D rendered image is reconstructed
using compatible software.
5.5.5.5 Results from 3-D rendering can often be useful in analyzing pit size, pit shape, and pit density.
5.5.6 Caveats—NoneSome of these nondestructive test methods may not provide satisfactory detailed information about pitting.
They can be used to locate pits and to provide some information about the size of pits, but they generally are not some may not
be able to detect small pits, and confusion may arise in attempting to differentiate between pits and other surface blemishes. Most
of these methods were developed to detect cracks or flaws in metals, but with more refined development they may become more
applicable to pitting measurements.
6. Extent of Pitting
6.1 Mass Loss—Metal mass loss is not ordinarily recommended for use as a measure of the extent of pitting unless general
corrosion is slight and pitting is fairly severe. If uniform corrosion is significant, the contribution of pitting to total metal loss is
small, and pitting damage cannot be determined accurately from mass loss. In any case, mass loss can only provide information
about total metal loss due to pitting but nothing about depth of penetration. However, mass loss should not be neglected in every
case because it may be of value; for example, mass loss along with a visual comparison of pitted surfaces may be adequate to
evaluate the pitting resistance of alloys in laboratory tests.
6.2 Pit Depth Measurement:
6.2.1 Metallographic—Pit depth can be determined by sectioning vertically through a pre-selected pit, mounting the cross-
sectioned pit metallographically, and polishing the surface. The depth of the pit is measured on the flat, polished surface by the
use of a microscope with a calibrated eyepiece. measurement system (for example, eyepiece reticle or digital imaging. The method
is very accurate, but it requires good judgment in the selection of the pit and good technique in cutting through the pit. Its
limitations are that it is time consuming, the deepest pit may not have been selected, and the pit may not have been sectioned at
the deepest point of penetration.
6.2.2 Machining (7, 8): (2, 3):
6.2.2.1 This method requires a sample that is fairly regular in shape, and it involves the destruction of the specimen. Measure the
thickness of the specimen between two areas that have not been affected by general corrosion. Select a portion of the surface on
one side of the specimen that is relatively unaffected; then machine the opposite surface where the pits are located on a precision
lathe, grinder, or mill until all signs of corrosion have disappeared. (Some difficulty from galling and smearing may be encountered
with soft metals, and pits may be obliterated.) Measure the thickness of the specimen between the unaffected surface and subtract
from the original thickness to give the maximum depth of pitting. Repeat this procedure on the unmachined surface unless the
thickness has been reduced by 50 % or more during the machining of the first side.
6.2.2.2 This method is equally suitable for determining the number of pits with specific depths. Count the visible pits; then
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machine away the surface of the metal in measured stages and count the number of visible pits remaining at each stage. Subtract
the number of pits at each stage from the count at the previous stage to obtain the number of pits at each depth of cut.
6.2.3 Micrometer or Depth Gage:
6.2.3.1 This method is based on the use of a pointed needle attached to a micrometer or calibrated depth gage to penetrate the pit
cavity. Zero the instrument on an unaffected area at the lip of the pit. Insert the needle in the pit until it reaches the base where
a new measurement is taken. The distance traveled by the needle is the depth of the pit. It is best to use constant-tension instruments
to minimize metal penetration at the base of the pit. It can be advantageous to use a stereomicroscope in conjunction with this
technique so that the pit can be magnified to ensure that the needle point is at the bottom of the pit. The method is limited to pits
that have a sufficiently large opening to accommodate the needle without obstruction; this eliminates those pits where undercutting
or directional orientation has occurred.
6.2.3.2 In a variation of this method, attach the probe to a spherometer and connect through a microammeter and battery to the
specimen (38, 49). When the probe touches the bottom of the pit, it completes the electrical circuit, and the probe movement is
a measurement of pit depth. This method is limited to very regularly shaped pits because contact with the side of the pit would
give a false reading.
6.2.4 Microscopical—This method is particularly valuable when pits are too narrow or difficult to penetrate with a probe type of
instrument. The method is amenable to use as long as light can be focused on the base of the pit, which would not be possible in
the case of example (e) in Fig. 1.
6.2.4.1 Use a metallurgical microscope with a magnification range from 5050× to 500× and a calibrated fine-focus knob (for
example, 1 division = 0.001 mm). If the latter is not available, a dial micrometer can be attached to the microscope in such a way
that it will show movement of the stage relative to the microscope body.
6.2.4.2 Locate a single pit on the metal surface and center under the objective lens of the microscope at low magnification (for
example, 50×). Increase the objective lens magnification until the pit area covers most of the field under view. Focus the specimen
surface at the lip of the pit, using first the coarse and then the fine-focusing knobs of the microscope. Record the initial reading
from the fine-focusing knob. Refocus on the bottom of the pit with the fine-focusing knob and record the reading. The difference
between the initial and the final readings on the fine-focusing knob is the pit depth.
6.2.4.3 Repeat the steps in 5.2.4.26.2.4.2 to obtain additional measurements or until satisfactory duplication has been obtained.
The repeatability of pit depth measurements on a single pit at four magnifications is shown in Annex A1.
6.2.4.4 A variation of the microscopical technique employsinvolves the use of an interference microscope. A beam of light is split,
and one portion is projected on the specimen and the other on a reference mirror surface. The reflected light from these two surfaces
is recombined, and interference fringes are formed that provide a topographical map of the specimen surface. These fringes can
be used to measure vertical deviations on the metal surface. However, the method is limited to the shallower pits, that is, less than
25 μm, because the number of fringes increases to the point where they are difficult to count.
6.2.5 3-D Optical Microscopy Method—This method is distinguishable from 6.2.4.2 in that analysis does not require manual use
of the fine focus of a microscope. Rather, microscopes with computer-controlled capabilities are commercially available with
corrosion pit measurement as an intended application. There are numerous advantages to this type of analysis, including the
reduction in time of analysis and the ability to scan larger surfaces. Such digital equipment has the additional advantage that it
allows quantification of pitted surface areas and pit diameters as well as provides depths and pit shapes. Asymmetric pits and
tunneling processes that distort the pit shape will be as difficult to detect using this method as the manual method above. As with
standard optical microscopy, one needs to: (1) use sufficient magnification to observe pit features, and (2) check the validity of the
equipment using pits with depths validated by independent means. Care should be taken to ensure the system is properly calibrated
and attention should be paid to the influence of sample type and surface condition on how accurately and reproducibly the system
detects the correct number of pits, pit depths, areas, volumes, and so forth.
6.2.6 Laser Scanning Methods (see ISO 25178-604:2013(E))—This profilometry method uses lasers to scan the metal surface and
measure pit depth relative to the metal surface. The use of lasers allows the user to scan large areas for inspection. However, the
resolution required for pit depth measurement may require parameter optimization (for example, scan speed/scan interval). In
addition to ensuring proper calibration of the system, attention should be paid to the reproducibility of measurements within a given
sample, and the validity of the equipment should be confirmed using pits with depths evaluated using independent means. While
this technology has been used successfully to evaluate surface roughness/topography (10), real-world users have communicated
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significant under-reporting of pit depth (<50 % of actual) when compared to analysis using 3-D optical methods. It is recommended
that pitting measurements (particularly depth) from laser-scanning methods be reported as semiquantitative unless verification
procedures using independent methods are included to demonstrate accuracy
7. Evaluation of Pitting
7.1 There are several ways in which pitting can be described, given a quantitative expression to indicate its significance, or used
to predict the life of a material. Some of the more commonly used methods are described in this section, although it is often found
that no single method is sufficient by itself.
7.2 Standard Charts (8): (3):
7.2.1 Rate the pits in terms of density, size, and depth on the basis of standard charts, such as those shown in Fig. 2. Columns
A and B relate to the extent of pitting at the surface of the metal (that is, Column A is a means for rating the number of sites per
unit area and Column B is a means for showing the average size of these sites). Column C rates the intensity or average depth of
4 2 2
attack. A typical rating might be A-3, B-2, C-3, representing a density of 5 × 10 pits/m , an average pit opening of 2.0 mm , and
an average pit depth of 1.6 mm.
FIG. 2 Standard Rating Charts for Pits
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7.2.2 This method offers an effective means of communication between those who are familiar with the charts, and it is a simple
means for storing data for comparison with other test results. However, it is can be tedious and time consuming to measure all pits,
pits manually, and the time is usually not justified if doing so by hand because maximum values (for example, pit depths) usually
have more significance than average values. With the advent of automated surface scanners, profilometers, and so forth, a large
amount of detailed information regarding the number of pits, pit densities, depths, diameters, surface areas, volumes, and so forth,
can now be obtained in a more time-efficient manner making this process and analysis much easier.
7.3 Automated Profilometers (AP)—There are a variety of commercially available systems that harness interferometry or laser
technology to provide automated assessment of pitting corrosion. These methods (discussed in 6.2.5 and 6.2.6) have a number of
advantages and limitations and can be a useful tool in assessing the size, distribution, and depth of corrosion pits if properly
calibrated and verified. Large areas of samples can be scanned using these methods, and a large number of pits can be evaluated
much faster than is possible using manual methods. However, note that the automation that makes these techniques attractive to
the end user is not a substitute for the interpretation of the collected data by an experienced corrosion professional. Care should
be taken when reporting quantitative results from these methods including providing statistical context for measurements,
mea
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