ISO 21055:2026

International
Standard
ISO 21055
First edition
Corrosion of metals and alloys —
2026-04
Test method for microbiologically
influenced corrosion of oil and gas
transmission pipelines
Corrosion des métaux et alliages — Méthode d'essai pour la
corrosion microbiologique des canalisations de transport de
pétrole et de gaz
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 5
5 Apparatus . 6
5.1 Vessel .6
5.2 Biological equipment . .6
5.3 Other equipment .6
6 Strain source . 7
6.1 General .7
6.2 Strains from on-site pipelines .7
6.2.1 Collection of on-site strains .7
6.2.2 Environmental metagenomic analysis .8
6.2.3 Enrichment of target microorganisms .8
6.2.4 Isolation of target microorganisms .8
6.3 Commercial standard strains.8
6.4 Microbial culture for test .9
7 Test solutions . 9
7.1 General .9
7.2 Natural solutions .9
7.3 Artificial solutions .9
7.4 Introduction of target microorganisms .9
8 Test specimens . 10
8.1 General .10
8.2 Shape and size of specimens .10
8.3 Preparation of specimens .10
9 Sterilization .11
9.1 Sterilization of glassware .11
9.2 Sterilization of aqueous solution .11
9.3 Sterilization of other devices .11
10 Procedure .11
10.1 General .11
10.2 Specimen assembly .11
10.3 Introduction of solution . .11
10.4 Deaeration . 12
10.5 Test conditions . 12
10.6 Detection of planktonic and sessile microorganisms . 12
10.7 Cleaning specimens after test . 13
10.8 Pitting evaluation . . 13
10.9 Calculating corrosion rates . 13
10.10 Quantitative comparison of abiotic and biotic tests .14
11 Test results . 14
12 Test report . 14
Annex A (informative) Measurement of microbial growth curves .16
Annex B (informative) Corrosivity of culture media .18
Bibliography . 19

iii
Foreword
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The procedures used to develop this document and those intended for its further maintenance are described
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of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
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This document was prepared by Technical Committee ISO/TC156, Corrosion of metals and alloys.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Microbiologically influenced corrosion (MIC) refers to corrosion caused by the presence and activities of
microorganisms (e.g. bacteria, archaea and fungi). Although microorganisms do not produce unique types of
corrosion, they can accelerate corrosion reactions and increase the susceptibility of materials to corrosion
processes such as pitting, embrittlement and under deposit corrosion (UDC). MIC has been identified as a
contributor to rapid corrosion of metals and alloys exposed to seawater, crude oil, hydrocarbon fuels, soils
and sewage. In recent years, the oil and gas industry, especially pipelines, are suffering from severe MIC
threats. It is estimated that approximately 20 % of pipeline incidents are related to MIC.
This document establishes a microbiological corrosion test method applicable to oil and gas transmission
pipelines to facilitate microbiological corrosion test evaluation by oil and gas industry users and product
suppliers. In this document, the total immersion corrosion test is used to determine the corrosion rate
(including uniform corrosion rate and pitting corrosion) of metals and alloys. In particular, the test
conditions (e.g. strain source, test solution and corrosive gas), procedures and results are regulated in
detail. This document focuses on the internal microbial corrosion environment of oil and gas transmission
pipelines, but it also applies to environments involving microbial corrosion risks such as water injection and
downhole in the oil and gas industry.

v
International Standard ISO 21055:2026(en)
Corrosion of metals and alloys — Test method for
microbiologically influenced corrosion of oil and gas
transmission pipelines
1 Scope
This document specifies a laboratory test method for microbiologically influenced corrosion (MIC) of oil
and gas transmission pipelines, including the principle, apparatus, sources of strains, solutions, specimens,
sterilization, procedure, results and report.
This document applies to the MIC test of metals and alloys for internal surfaces of oil and gas transmission
pipelines.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 8199, Water quality — General requirements and guidance for microbiological examinations by culture
ISO 8407, Corrosion of metals and alloys — Removal of corrosion products from corrosion test specimens
ISO 11463, Corrosion of metals and alloys — Guidelines for the evaluation of pitting corrosion
ISO 20391-1, Biotechnology — Cell counting — Part 1: General guidance on cell counting methods
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
abiotic
test solution without living organisms, their biological components or the metabolic activities of living
organisms
3.2
archaea
prokaryotic single celled organisms which lack cell nuclei and are morphologically similar to bacteria (3.3)
but radically different in molecular organization, with eukaryote-like metabolic pathways and enzyme
production
EXAMPLE 1 Methanogens are a group of archaea which are involved in microbiologically influenced corrosion
(MIC)by consuming hydrogen at the metal surface and, hereby, creating a depolarization process. Methanogens are
common in oil production systems, but they are normally not measured with current culturing techniques.
EXAMPLE 2 Sulfate-reducing archaea is a group of anaerobic archaea that reduce sulfate and result in sulphide
formation. They are most likely to grow at reservoir conditions (60 °C to 95 °C).

Note 1 to entry: Halophiles (microorganisms that can inhabit extremely salty environments) and thermophiles
(microorganisms that can thrive in extremely hot environments) are also classified as archaea.
[SOURCE: ISO 6107:2021, 3.43, modified — EXAMPLES 1 to 2 and Note 1 to entry have been added.]
3.3
bacteria
large group of microscopic, metabolically active, single-cell prokaryotic microorganisms (3.12), with
dispersed (not discrete) nucleus, mostly free-living, and usually multiplying by binary fission
EXAMPLE 1 Acid-producing bacteria is a group of aerobic or anaerobic bacteria that produce organic acids as a
product of their metabolism. A few organisms (e.g. Thiobacillus), can also produce mineral acids (typically under
aerobic conditions).
EXAMPLE 2 Sulfate-reducing bacteria (SRB) is a group of bacteria that are commonly found in oil and gas
industry. They are active only in conditions of near neutrality and absence of oxygen, which reduce sulphates in their
environment, with the production of sulphides, and accelerate the corrosion of structural materials.
EXAMPLE 3 Iron bacteria is a group of bacteria which is able to derive energy by oxidizing iron (II) and result in the
precipitation of iron (III) hydroxide inside or outside the bacterial sheaths.
EXAMPLE 4 Metal-reducing bacteria is a group of bacteria which is able to use oxidized metal ions (e.g. Fe(III),
Mn(IV), Cr(VI), U(VI)) as terminal electron acceptors during anaerobic respiration.
[SOURCE: ISO 6107:2021, 3.53, modified — EXAMPLEs 1 to 4 have been added.]
3.4
biofilm
layer of microscopic organisms such as bacteria, diatoms and the slimy extracellular polymeric substances
they produce on the test surface
Note 1 to entry: In corrosive environments, both biofilms and corrosion products are usually present on the surfaces
of metals and alloys, and the two are often mixed.
[SOURCE: ISO 21716-1:2020, 3.5, modified — Note 1 to entry has been added.]
3.5
biotic
involving the presence or metabolic activities of living microorganisms (3.12)
3.6
corrosion product
substance formed as a result of chemical or electrochemical interaction between a material, usually a metal,
and its environment
3.7
count
observed number of objects such as colonies or cells determined by direct counting, or most
probable number (MPN) (3.13) estimation based on statistical calculation using the number of positive units
or presumptive positive units in a dilution series of a test sample
[SOURCE: ISO 8199:2018, 3.4]
3.8
culture medium
mixture of ingredients, in liquid or solid form, prepared according to a formula and intended to support the
growth of microorganisms (3.12) under specific conditions
EXAMPLE 1 Postgate’s medium B (Postgate medium B) is a specific medium designed for culturing SRB
characterized by the use of lactate as a carbon source and sulfate as the terminal electron acceptor required for SRB
metabolism.
EXAMPLE 2 Sodium lactate SRB medium is a medium for culturing SRB, which is derived from the original Postgate
B medium and provides similar nutrients and salts but in a slightly different formulation.

Note 1 to entry: There are different types of culture media suitable for growing different types of microorganisms
depending on different included nutrients and chemicals present in the formulation.
[SOURCE: ISO 4973:2023, 3.1, modified — EXAMPLES 1 and 2 have been added.]
3.9
liquid culture medium
culture medium (3.8) consisting of aqueous solution of one or more constituents, such as peptone water or
nutrient broth
Note 1 to entry: Liquid culture media in tubes, flasks or bottles are commonly called “broths”.
Note 2 to entry: Enrichment culture media are generally liquid media which, due to their composition, provide
favourable conditions for microorganisms’ multiplication.
[SOURCE: ISO 4973:2023, 3.1.3]
3.10
metagenomics
study of genetic material (e.g. Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA)), recovered directly
from an environment (e.g. microbiome)
[SOURCE: ISO 16577:2022, 3.7.11, modified — The abbreviated terms DNA and RNA have been written in full
in the definition.]
3.11
microbiologically influenced corrosion
MIC
microbial corrosion
corrosion influenced by the action of microorganisms (3.12)
Note 1 to entry: Bacterial corrosion is MIC due to the action of bacteria.
Note 2 to entry: MIC can occur in biofilms on the surface of the corroding material, and many materials, including most
metals and some nonmetals, can be degraded in this manner.
[SOURCE: ISO 8044:2024, 4.37, modified —The admitted term "microbial corrosion" and Notes 1 to 2 to
entry have been added.]
3.12
microorganism
microbes
group of tiny unicellular or multicellular primary organisms with simple structures and a variety of
physiological characters
EXAMPLE 1 Prokaryotes, such as bacteria and archaea.
EXAMPLE 2 Eukaryotes, such as fungi (e.g. yeasts and moulds), protozoa and microscopic algae.
Note 1 to entry: Oilfield bacteria and archaea, generally recognized as harmful in oilfield systems, should be
considered in MIC testing, while other organisms such as phytoplankton (e.g. algae), protozoa or marine organisms
such as zooplankton (e.g. copepods) should not be considered.
[SOURCE: ISO 22787:2023, 3.6, modified — The admitted term "microbes" has been added, EXAMPLE 3 has
been deleted, and Note 1 to entry has been added.]
3.13
most probable number
MPN
maximum likelihood estimate of the number of microorganisms (3.12) in a specified volume of water, derived
from the combination of positive and negative results in a series of volumes of the sample examined by
standard tests
Note 1 to entry: The multiple tube or wells in a tray method are a set of these standard tests for determining the MPN.

[SOURCE: ISO 6107:2021, 3.350]
3.14
next generation sequencing
NGS
massively parallel nucleotide sequencing
whole genome sequencing
WGS
high throughput nucleotide sequencing method capable of determining multiple DNA sequences
simultaneously and in parallel
Note 1 to entry: The data from a single massively parallel sequencing analysis comprise millions of sequences and the
output is a file containing all sequences.
Note 2 to entry: The output of this test provides details of the microbial populations present, usually family, genus, or
species levels.
Note 3 to entry: This test can aid in defining the potential risk for MIC in a pipeline system, provide insight into
microbial control strategy, and identify key points in a system that requires continued monitoring.
Note 4 to entry: This test can be performed on any liquid or solid sample, as well as bacteria collected via membrane
filter or swab.
[SOURCE: ISO 16577:2022, 3.7.10, modified — The preferred term "massively parallel nucleotide sequencing"
has been reclassified as an admitted term and the admitted term "next generation sequencing (NGS)" has
been reclassified as the preferred term. Notes 2 to 4 to entry have been added.]
3.15
planktonic microorganisms
live microbial particles suspended in a liquid.
Note 1 to entry: These microbial particles can be propagated to a visible number of colonies by means of specialized
media under suitable growth conditions.
Note 2 to entry: Planktonic microorganisms can become sessile microorganisms (3.20) by adhering to a surface.
3.16
polymerase chain reaction
PCR
method allowing the amplification of a specific DNA sequence using a specific pair of oligonucleotide primers
Note 1 to entry: A quantitative version of PCR is called Quantitative Polymerase Chain Reaction (qPCR) (3.17).
Note 2 to entry: While the PCR is producing copies of the relevant DNA sequence, the fluorescent marker fluoresces
in direct proportion to the amount of DNA present (which can, theoretically, be back-calculated to infer the original
amount of that particular DNA present in a sample prior to initiation of PCR).
[SOURCE: ISO 11074:2025, 3.330, modified — Notes 1 to 2 to entry have been added.]
3.17
quantitative polymerase chain reaction
qPCR
method allowing the amplification of a specific DNA sequence using a specific pair of oligonucleotide primers
Note 1 to entry: qPCR is used to quantify the total number of microorganisms (including dead and alive) or a specific
genus/species of microorganisms in nearly any type of sample.
Note 2 to entry: qPCR can be used for both liquid and solid samples, as well as microorganisms collected via membrane
filtration.
Note 3 to entry: qPCR can detect microorganisms that do not grow in culture.
Note 4 to entry: qPCR can enumerate a very general (i.e. total bacteria or archaea) or very specific (i.e. Desulfovibrio
desulfuricans) population.
[SOURCE: ISO 17601:2025, 3.3, modified — Notes 1 to 4 to entry have been added.]
3.18
relative abundance
fraction of a single microorganism operational taxonomic unit in the total microbial community of a defined
environment
Note 1 to entry: It is usually represented as a percentage.
[SOURCE: ISO/TS 24420:2023, 3.19]
3.19
selective culture medium
culture medium (3.8) which allows specifically the growth of selected microorganisms (3.12) or a group of
microorganisms while inhibiting partially or totally the growth of different, non-target microorganisms
which can be in the product to be tested
Note 1 to entry: It can have indicative properties with growth of characteristic aspect of colonies if this is a solid
culture medium.
[SOURCE: ISO 4973:2023, 3.1.5, modified — The subject, “liquid culture medium or solid culture medium”,
has been changed to “culture medium”; “growth of a selected microorganism” has been changed to “growth
of selected microorganisms or a group of microorganisms”.]
3.20
sessile microorganisms
microorganisms (3.12) attached to surfaces and forming a biofilm
Note 1 to entry: These microorganisms are not able to move freely but are anchored to the surface of the pipe by
secreting a sticky substance that forms a protective biofilm.
3.21
sterile
free from viable microorganisms (3.12)
Note 1 to entry: Microorganisms that are foreign to the host body or subject under study should not be introduced.
Note 2 to entry: To sterilize a medium or materials is to kill all microorganisms that are present.
[SOURCE: ISO 20417:2021, 3.28, modified — Notes 1 and 2 to entry have been added.]
4 Principle
MIC tests are carried out as comparative tests, where a number of materials or corrosive media are
compared under the given test conditions. The corrosion is evaluated in terms of general corrosion rate and
pitting assessment. Based on the purpose of the experiment, the strains should be collected from the oil
and gas production site, which is more representative of the application environment. To promote biofilm
formation and thus ensure microbial corrosion, enrichment is performed so that the test solution contains
a high concentration of microorganisms (e.g. 10 cells/mL or more). The contribution of microorganisms to
the corrosion of metals and alloys is reflected by the comparison of biotic and abiotic tests (e.g. influence
factor on uniform corrosion f , and influence factor on pitting corrosion f ). In addition, the role of
ave pit
microorganisms is further demonstrated by measuring the count of planktonic microorganisms in the
test solution before and after the test, as well as the count of sessile microorganisms on the surface of the
corroded specimen.
5 Apparatus
5.1 Vessel
The vessel should be made of materials that are inert to corrosive media (e.g. glass, ceramics) and can meet
the requirements of sealing and injecting gas.
For tests under high temperature and pressure conditions, the vessel should be made of corrosion-resistant
materials (e.g. nickel-based alloys) that can resist the corrosion of corrosive media and maintain a constant
temperature and pressure inside the vessel.
A suitable temperature and pressure control system should be selected so that the temperature and pressure
in the vessel can be maintained within the test requirements.
The specimen support system should be used to support the specimen in the test solution. The support
system should be made of materials that are inert to the specimen and the test solution and have the smallest
possible contact area with the specimen.
According to the purpose of the test, other stirring devices can also be added to achieve the relative
movement of the specimen and the test solution.
For tests requiring aeration, the aeration port should be fitted with a suitable microporous filter membrane
to avoid the introduction of other microorganisms. If the test is done under the aeration condition, the
oxygen corrosion is probably more severe than MIC. A negative control (without microorganisms) shall be
included in the test.
5.2 Biological equipment
Sterilization shall be used to avoid cross contamination. An autoclave capable of maintaining a temperature
and pressure up to 123 °C and 0,2 MPa respectively should be used for sterilizing glass containers or aqueous
solution.
Incubators capable of controlling the temperature up to 60 °C ± 1 °C should be used for microbial culture. For
anaerobic microorganisms, anaerobic conditions should be maintained during growth by proper techniques.
Ultraviolet (UV) lamps with radiation illumination of a value no less than 70 μW/cm should be used for UV
sterilization.
The drying oven should be used for dry heat sterilization of experimental vessels and drying of Petri dishes,
conical flasks and beakers. The temperature is typically controlled to within ± 2 °C.
An ultra-clean bench shall be used for aseptic operation of inoculation and handling of microorganisms.
Pipettes and syringes should be used for the transfer of liquids, and their capacity should be determined
according to the needs of the test. In some cases, automatic pipettes can be used. In either case, they shall be
sterile before use.
Refrigerators should be used for the preservation of strains, culture media, microbial samples and low
concentration reagents.
5.3 Other equipment
Analytical balances to an accuracy of 0,000 1 g or better should be used to weigh the specimens.
The size of the specimen should be measured by using the digital callipers with an accuracy of no less than
0,02 mm.
An optical microscope that can be magnified at least 10X can be applied to the observation of localized
corrosion on the surface of the specimen after the test. For the depth measurement of corrosion pits, a
profilometer or other microscope with a surface roughness analysis function can be used.

[1]
The rotating cage and its appurtenances can be used if a flow rate is considered to be applied in the test.
The rotating cage and its appurtenances should be made of materials that are inert to corrosive media.
6 Strain source
6.1 General
On-site strains can be obtained by collecting either liquids (e.g. produced water, injection water, water from
water-transporting pipelines, water from gas-transporting pipelines) or solids (e.g. corrosion products,
sediments from the internal surface of pipelines, biofilms on the surface of corrosion monitoring specimens
and pigging residue), or both. The collected strains should be representative of the typical environment of
the application scenario.
Depending on the purpose of the test, commercial standard stains can be used in the following cases, if:
a) on-site strains are not available;
b) corrosion of a particular strain is of particular concern.
However, in all cases, the commercial standard strains used shall be representative of the application
scenario.
6.2 Strains from on-site pipelines
6.2.1 Collection of on-site strains
6.2.1.1 Collection of liquid samples
Liquid samples are used to collect planktonic microorganisms.
Liquid samples containing water can include produced water, injection water, water from water-transporting
pipelines, and water from gas-transporting pipelines.
For pipelines transporting a mixture of water and hydrocarbon, gravity or centrifugation should be used to
separate the water and hydrocarbon phases. Tight emulsions can require the addition of a filter-sterilized
emulsion breaker. Heating the fluids at 35 °C to 40 °C for 10 min to 30 min can also be used to facilitate the
separation. Only the water phase of the liquid sample should be collected.
Sterile sample collection containers should be used to collect liquid samples. The container should be
completely filled and as little air as possible left in the container. When liquid samples are used as test
solutions, they should be collected in the amount required for the test. For the DNA-based analysis in 6.2.2, a
minimum of 500 mL shall be collected.
Samples treated with a preservation solution can be transported on ice, while samples not chemically
preserved shall be kept refrigerated (at temperatures of 4 °C or below) at all times after collection.
6.2.1.2 Collection of solid samples
Any removable field system components (e.g. pipe sections, corrosion monitoring pegs) can be used to
sample for sessile microorganisms. Debris from clean pipes and corrosion products on the pipe wall can also
[2]
be used for biofilm analysis .
Solid samples should be collected by using a sterile spatula, scoop, or scalpel. During sampling, enough
chemical preservative should be added to cover the collected material. The sample container should be
sealed, labelled correctly and placed on ice or with ice packs in a cooler box for shipment. A minimum of 10 g
of sample should be collected for DNA-based analysis.

6.2.2 Environmental metagenomic analysis
DNA-based analysis (or molecular microbiological methods) has been applied in sectors beyond the human
microbiome and medicine, to investigate the diversity, number and distribution of microorganisms in a
given environment.
An environmental metagenomic analysis can be performed using the NGS technique to acquire the
abundance and diversity of microbial communities. It should be noted that the relationship between
metagenomic sequences and corrosion-associated microorganisms of interest should be carefully identified
by referencing professional databases and incorporating domain-specific research knowledge.
To characterize the bacterial and archaeal community structures of on-site samples, 16S rRNA gene
sequencing should be used. Based on liquid samples or solid samples collected, according to 6.2.1, taxonomic
identification should be achieved through 16S rRNA gene sequencing, while absolute quantification of
marker gene copy numbers in target microorganisms should be performed using qPCR technology.
DNA extraction, enumeration and taxonomic identification, and data interpretation should follow the
[3]
guidelines in another document .
This provides guidance for subsequent identification, isolation or enrichment of target microorganisms.
6.2.3 Enrichment of target microorganisms
After selecting a suitable medium for enrichment culture of field strains (collected water samples and solid
samples), the enriched strains are used directly in the test.
Microbial enrichment cultures can be prepared from on-site water samples. For example, filter the water
through 0,25 μm hydrophilic membranes to retain microbial biomass, resuspend the concentrated biomass
in sterile basal medium at a 1:1 (v/v) ratio, transfer the suspension to selective liquid culture medium;
incubating at 37 °C for three to five days with three serial subcultures using 10 % (v/v) inocula, and
ultimately yield targeted microbial enrichment cultures. The temperature depends on the site temperature,
and the incubation duration can be different.
6.2.4 Isolation of target microorganisms
Among identified microorganisms, corrosion-associated microorganisms should be ranked by relative
abundance. The microorganism with the highest abundance is typically designated the primary priority
target. When the relative abundance difference between top-ranked microorganisms is statistically
insignificant (e.g. ≤ 10 % based on analysis of variance (ANOVA), p > 0,05) or functionally equivalent, they
should be classified as secondary or tertiary priority targets with corrosion potential validation.
The target strains (e.g. SRB, iron bacteria) can be obtained by using selective culture media (e.g. the
[4]
American Type Culture Collection (ATCC) 1249 medium anda modified Baar’s medium ) for the isolation
of field strains (either liquid or solid, or both, as described in 6.2.1 and 6.2.2) based on the corrosion analysis
and microbial community analysis of the application scenario. Isolated and purified strains should be re-
identified by sequencing techniques as mentioned in 6.2.2.
For the isolated strain, its growth curve in the proposed or alternate medium should be measured in
accordance with Annex A.
6.3 Commercial standard strains
Commercial standard strains shall be used only in the cases described in 6.1.
Commercial standard strains shall be purchased based on the identification by the environmental
metagenomics analysis in 6.2.2.
Standard strains shall be revived and activated according to the supplier's requirements.
The growth curve in the given medium should be determined in accordance with Annex A.

Mix the microorganisms stock culture at the logarithmic growth phase with fresh medium, then continue to
cultivate to logarithmic growth period and repeat two to three times.
6.4 Microbial culture for test
The growth curve of microorganisms in the test solution with different volumes of microbial seed culture
added should be measured in accordance with Annex A to clarify the growth of microorganisms during the
MIC test.
The corrosivity of the test solution with different volumes of sterile medium (without microorganisms)
should be measured in accordance with Annex B. Nutrients in the test solution (from the medium) should
not significantly alter the degree of corrosion, compared to the test without medium.
The microbial seed medium should be prepared before each test. Test solutions with microbial seeds shall
be used within 24 h.
7 Test solutions
7.1 General
The source of the test solution should be determined according to the purpose of the test, which can be
divided into two categories: natural and artificial.
For each test, the minimum ratio of test solution volume to test specimen surface area should be 20 mL/cm .
7.2 Natural solutions
The oil and gas pipeline transmission fluid collected on site is the natural medium, and its main components
should be determined. The natural medium shall not contain chemicals that can have a significant effect on
microbial corrosion, such as corrosion inhibitors and biocides. Otherwise, they shall not be used.
For the abiotic test, the natural solutions shall be sterilized before use, according to 9.2. The sterilization
shall not modify the physical and chemical properties. When the enrichment solution is used in biotic test,
the same solution shall be sterilized and then used for the abiotic test.
For the biotic test, there are two options:
— The enrichment solution as described in 6.2.3 can be directly used in the test.
— The sterilized natural solution should be used after adding target stains (either isolated strains or
commercial strains).
7.3 Artificial solutions
Artificial solutions are generally configured to highlight a specific solution environment or simulate the
main environmental factors in the material service environment. Artificial solutions should be prepared in
accordance with on-site water analysis data (e.g. including ion concentrations, pH), using deionized water
and chemicals of analytical grade or equivalent purity.
For the abiotic test, the artificial solutions shall be sterilized before use, according to 9.2.
For the biotic test, the sterilized artificial solution should be used after adding target stains (either isolated
strains or commercial strains).
7.4 Introduction of target microorganisms
The count of target microbes in the biotic test solution shall be determined by cell counting methods, e.g.
manual counting chamber, plating and colony forming unit (CFU) counting, spectrophotometry, and MPN
method, according to ISO 20391-1 and ISO 8199.

The initial count of target microbes in the biotic test solution should exceed 10 cells/mL.
As the nutrients in the microbial enrichment solution can have effects on the corrosion process (some can
promote corrosion, and some can inhibit corrosion), the degree of impact of sterile nutrient solution on
corrosion should be verified in accordance with Annex B.
8 Test specimens
8.1 General
The test material, usually metallic materials (e.g. carbon steels, stainless steels and corrosion-resistant
alloys), should be determined according to the purpose of the test. Materials that are used, planned or have
the potential to be applied in the oil and gas transmission pipelines should be used. Since the metallurgy
and manufacturing processes of the specimen have a significant effect on its microstructure, mechanical
properties, and corrosion performance, the manufacturing process, microstructure, and mechanical
properties of the test material should be consistent with the engineering requirements of its potential
application.
Test specimens should be machined from the pipe products. Commercial coupons with the same or similar
specifications of pipelines of interest can also be an option.
8.2 Shape and size of specimens
The shape and size of the specimen should be determined according to the initial shape of the test material
and the test container. The specimen with large surface area per unit mass and small ratio of side to total
area should be used as much as possible. The surface area of each specimen should not be less than 10 cm .
It is recommended for plate specimens with an externa
...