ENVIRONMENTALLY FRIENDLY VOLATILE
4119 White Bear Parkway
Saint Paul, Minnesota 55110
Volatile corrosion inhibitors (VCIs) were originally developed
to protect boilers and piping systems of ships to be mothballed.
Their effectiveness and ease of application attracted early users.
Over the years, the field of usage has increased to cover electronics,
packaging, process industries, reinforced concrete, coatings, and
Having clean parts is one of the main reasons of the ever-widening
acceptance of VCIs. For example, applicators and end-users do not
have to be concerned about removal and disposal as they would with
A new class of VCIs has been developed in harmony with the concern
for the environment. While these new chemicals offer excellent protection
to metal surfaces, they have a very low impact on the environment.
Corrosion protection and effect on the environment of several of
these new VCIs were studied. Performance in typical applications
was also investigated. These results are presented in this paper.
One morning in 1943, a scientist opened a desiccator that contained
some experimental nitrite-based compounds used for corrosion inhibition
of the interior of gasoline pipelines1-4. As he lifted
the lid of the desiccator he noticed white needle-like crystals
that had formed on the inside of the cover. It turned out that these
crystals were the pure amine nitrite compound placed at the bottom
of the container. The chemical compound had migrated to the lid
via sublimation. The scientist was quick to realize that combining
the corrosioninhibiting properties of the nitrite compound
with its volatility could lead to new ways of alleviating the oxidation
Like aqueous corrosion, atmospheric corrosion of metals has also
been the object of numerous efforts to mitigate it. The individual
and joint actions of humidity, oxygen and various corrosive gases
lead to severe damage if left unchecked. As there is no limit of
oxygen availability in the open atmosphere, atmospheric corrosion
of metals is mainly controlled by humidity. However, aggressive
gases such as hydrogen sulfide, sulfur dioxide, and ions such as
chlorides control the metal attack in industrial sites and marine
There are several ways of preventing atmospheric corrosion. While
methods such as the use of an inert atmosphere, dehumidification,
or coatings are fine in some applications, they may not be appropriate
in other situations due to cost or practicability.
Because of their volatility at ambient temperature, VCI compounds
can readily reach inaccessible crevices in metallic structures.
Protective vapors disseminate within an enclosed space until equilibrium
is reached. This equilibrium is determined by the partial vapor
pressure of the VCI compound.
The US Navy was one of the very first commercial users of VCI technology.
Following the end of the Second World War, several warships had
to be mothballed. The areas of concern were the boilers and piping
systems. The US Navy required a method that would be cost effective
and easy to carry out. Responding to these requirements, VCI technology
was selected and is still used by the US Navy to this day. Its range
of applications has widened to include on-board electronics and
other corrosion sensitive equipment12,13.
Besides its ease of use and cost effectiveness, VCI technology
offers several other advantages14. One of them is cleanliness.
Parts can readily be handled at any time during the protection stage
or thereafter. There is no superficial film to be removed or disposed
Another benefit is safety. Beyond the fact VCI use does not produce
unsafe work conditions, most VCI compounds have a low level of toxicity.
A new generation of VCI compounds was developed as concerns grew
over safety issues with the original VCIs such as dicyclohexylammonium
Over the years, the application field of VCI technology has increased
to cover electronics16,17, packaging18,19,
process industries20,21, coatings22, and metalworking
There are several methods to measure the effectiveness of vapor
phase corrosion inhibitors. One method that is used quite widely
is the Vapor Inhibiting Ability (VIA) test method24.
It was developed to rapidly assess the protection offered by VCI
compounds. The tested products can be powders, liquids or packaging
products such as papers or plastic films. Its ease of use made this
method attractive and it is still used by numerous laboratories
dealing with VCI technology. The test consists of placing a freshly
polished carbon steel specimen in a 1-liter glass jar. The jar contains
a measured amount of water blended with glycerin to control the
relative humidity. A control sample is made of a jar containing
only a steel specimen, while a test sample comprises of a jar with
a steel specimen along with the VCI source (powder, liquid or packaging
product). The VCI source never comes in contact with the metal specimen.
After a conditioning period during which the VCI vapors are allowed
to migrate from the source to the metallic specimens, the jars are
placed in an oven set at an elevated temperature for a few hours.
Once this time elapsed, the jars are placed at ambient temperature.
The metal specimen is rapidly cooled leading to condensation due
to the humid atmosphere. Effective VCI compounds provide protection
in this environment, while the control specimen heavily corrodes.
Due to stricter environmental regulations, cost effectiveness aspects
and other factors, car manufacturers are switching to VCI technology.
North American and European automotive concerns have established
guidelines to change the way of protecting parts in transit or storage.
Extended testing was carried out to validate the use of VCI technology.
In addition, the discharge of chemicals used as corrosion inhibitors
in a marine environment such as the North Sea oilfields has been
under an ever-increasing scrutiny due the potential impact on aquatic
life. Once the chemicals are disposed of in the sea, there are concerns
that some of them will persist and will have a detrimental effect
on the environment. These compounds may be toxic to marine life,
have a low level of biodegradability or may bioaccumulate in living
organisms. The Paris Commission (PARCOM) developed a protocol consisting
of three tests: bioaccumulation, biodegradation and toxicity.
Bioaccumulation. Bioaccumulation of substances within aquatic
organisms can lead to toxic effects over long periods of time even
when actual water concentrations are low. The potential for bioaccumulation
is determined by measuring the n-octanol/water partition coefficient
of a specific chemical compound. The partition coefficient is the
ratio of the equilibrium concentrations of a dissolved substance
in a two-phase system of two largely immiscible solvents. In this
case, it is defined as:
Pow concentration in n-octanol (1)
concentration in water
Since the partition coefficient is the ratio of two concentrations,
it is therefore dimensionless and is usually expressed in the form
of its logarithm to base ten, log Pow. Pow
is an important parameter in studies of the environmental fate of
chemical substances. A highly significant relationship between the
partition coefficient Pow of chemical compounds and their
bioaccumulation in fish has been shown.
The n-octanol/water partition coefficient may be determined using
high-performance liquid chromatography (HPLC)25-28.
According to the Organization for Economic Co-Operation and Development
(OECD) Guideline 11729, the log Pow must be
lower than 3.
Biodegradation. Biodegradation is a measure of the length
of time over which a substance will remain in the environment. The
OECD 306 test guideline30 is primarily used for biodegradation
in marine environments. Chemical compounds are subjected to a 28-day
Biochemical Oxygen Demand (BOD-28) test. The start of degradation
occurs when 10% of the substance has been degraded. In order to
be rapidly degradable, at least 60% degradation of the substance
must be attained within 10 days of the start of degradation.
The absence of rapid degradation in the environment can mean that
a chemical compound in the water has the potential to exert toxicity
over a wide temporal and spatial range.
Aquatic Toxicity. Toxicity testing is run on organisms related
to different levels of the food chain. This includes primary producers
such as algae (Skeletonema costatum), consumers such as fish
and crustaceans (Acartia tonsa), and sediment reworkers such
as seabed worms (Corophium volutator).
The toxicity is usually assessed by determining an algae species
72 or 96 hour EC50, a crustacea species 48 hour EC50
and a sediment reworker 240 hour LC50.
EC50 is the effective concentration of a chemical substance
necessary to negatively affect 50% of the aquatic organism population.
LC50 is the effective concentration of a chemical compound
required to kill 50% of the population.
A volatile corrosion inhibitor identified as VCI A was used in
the corrosion and toxicity tests. VCI A is made of amine carboxylates.
The lower end of its melting point range is 188ºC.
An assembly pictured in Figure 1 was used for corrosion testing.
Carbon steel UNS G1018() (Fed. Steel Spec QQ-S-698) plugs
(1.6 cm diameter, 1.3 cm long) were polished with a 240-grit silicon
carbide abrasive. The abraded surface was then polished with a No.
400 aluminum oxide paper at 90º to the previous abraded marks.
The plugs were cleaned with methanol, allowed to air-dry and then
placed in a desiccator.
Ten milliliters of a synthetic glycerin-water solution having
a specific gravity of 1.075 at 24ºC to create a 90% Relative
Humidity atmosphere was introduced into the bottom of the test assembly.
Five hundredths of a gram of VCI were placed in a dish. The
dish was then placed on the bottom of the jar. A lid was placed
on the jar, tightened and the junction of the glass and lid sealed
The whole assembly was then exposed to a temperature of 24ºC
for 20 hours. Then cold water at a temperature of 4ºC below
the ambient was added to the aluminum tubes until full. After 3
hours the water was removed from the tubes. The steel plugs were
evaluated for signs of corrosion.
In this test method, a visible change in the surface finish
such as pitting or etching is considered as corrosion. Stain alone
does not constitute corrosion.
Bioaccumulation. The partition coefficient Pow was
determined according to OECD-Guideline test number 117 (Partition
coefficient (n-octanol/water), High performance Liquid Chromatography
Biodegradability. The biodegradability of VCI A was determined
according to the OECD-Guideline test number 306.
Aquatic toxicity. The following species were used to determine
the aquatic toxicity of VCI A.
Algae test. For the toxicity of VCI A to algae,
the ISO/DIS 10253 (4th working draft water quality-Marine algae
growth test with Skeletonema costatum and Phaoedactylum
tricornutum) test method was used.
Crustacean test. ISO/DIS 14669-1997 (Water
quality-Determination of acute lethal toxicity to marine copepods)
was used to study the toxicity of VCI A to consumer species.
Sediment reworker. The effect of VCI A on
sediment reworkers was determined using the ASTM E1367-90 test method
(Standard Guide for conducting 240 hour static sediment toxicity
tests with marine and estuary sediments).
The results for the Vapor Inhibiting Ability test are shown
in Table 1.
The control plug had heavy corrosion, while plugs placed in
the presence of VCI A had no signs of corrosion. The test samples
were run in triplicate. The appearance of the plugs at the completion
of the test is displayed in Figure 2.
Bioaccumulation. The measured value of the logarithm of
the partition coefficient, log Pow, is reported in Table
Its value is below zero indicating the unlikeness of bioaccumulation.
Biodegradability. The 28-day Biochemical Oxygen Demand value
for VCI A is reported in Figure 3.
VCI A started to degrade quite rapidly. It was 10% decomposed in
less than two days. At Day 7, it was 76% degraded. It was fully
decomposed at Day 27. Ten days after the start of the degradation,
the level of biodegradation was above 60%, indicating that VCI A
could be classified as a rapidly degradable substance.
VCI A was compared to sodium benzoate, which is used as a corrosion
inhibitor. It is also a carboxylic salt. VCI A fully biodegraded
as its BOD-28 value reached 100%, while the BOD value for sodium
benzoate leveled off at 80%.
Aquatic toxicity. The aquatic toxicity test results are
reported in Tables 3, 4, and 5.
As the tests demonstrated, VCI A provides protection against corrosion
while being innocuous to the environment.
The VIA test is a method of determining the effectiveness of a
volatile corrosion inhibitor. Following the conditioning period,
VCI A was able to protect a steel specimen in a moisture condensing
environment. The VCI source never came in contact with the steel
plug, proving that VCI A reached the metal surface via sublimation.
As indicated by the value of the partition coefficient, Pow,
VCI A has a very low potential to bioaccumulate in aquatic organisms.
This means that VCI A would very unlikely have toxic effects on
aquatic life over long time spans. This is an important benefit
as there are applications where corrosion inhibitors are discharged
in marine environments.
Another factor that indicates the innocuity of VCI A to the environment
is its quick biodegradability. VCI A is fully decomposed in less
than 28 days. Substances that rapidly biodegrade can be quickly
removed from the environment. The impact of VCI A on the marine
environment is very limited.
OECD 306 refers to several levels of acute and chronic toxicities.
In the case of algae or other aquatic plants, the upper limit for
acute toxicity measured as 72 EC50 is 100 mg/l. According
to the test results, the 72 EC50 for VCIA is 240 mg/l.
This indicates that VCI A is not classified as an acute toxicant
per the criteria defined in the test guideline.
It was reported in the Bioaccumulation section, log Pow
for VCI A is less than 3. Furthermore, VCI A is a substance that
rapidly biodegrades as stated in the Biodegradability section. Therefore,
with a 72 EC50 above 100 mg/l, VCI A is not classified
as a chronic toxicant.
Similar statements may be made in regards to the crustacean and
sediment reworker test results.
In 1995 the Norwegian Pollution Control Authority (SFT) implemented
the OSPAR Harmonized Offshore Chemical Notification Format (HOCNF)
to document environmental properties of chemicals used in offshore
applications. The HOCNF format contains data on toxicity, biodegradation
and bioaccumulation of chemicals. The SFT issues discharge permits.
The permits are issued to oil companies operating in the North Sea.
They also require that the operator gradually and systematically
replace chemicals that have detrimental effects on the environment
with environmentally friendly products.
A large Norwegian oil and gas producing company operates several
offshore and onshore installations in the North Sea. In the past,
a gas line installation would be hydrotested and protected with
an oil-water emulsion. As the regulations about disposal came in
place, this oil company looked for other ways of protecting its
equipment. After several evaluations, it selected VCI technology
as it proved to be a cost effective and environmentally friendly
method. The use of an oil-water emulsion lead to disposal cost as
this product could not safely be disposed in the sea. In addition,
for gas pipelines, an absolutely clean surface is necessary for
proper use of the installation. The oil-water emulsion would leave
residues after hydrotesting. Subsequent cleaning of the surface
was required following the test operation.
VCI products have now been used for offshore and onshore applications
for several years. VCI A is used during hydrotesting and for preservation
of internal surfaces of pipes and vessels. This is carried out on
large pipe systems on offshore platforms or smaller systems on refineries
or on onshore oil and gas receiving stations.
It follows the same strict discharge requirements. After hydrotesting
the aqueous solution of VCI A powder is sent to a storage tank and
used again or simply discharged into the sea. The concentration
used for this application is based on the desired length of protection
and is usually between 1% and 3.5%.
VCI A was fogged inside the openings of recently
hydrotested metering stations (Figure 4) at a ratio of 500 g per
cubic meter. The final step involved capping the ends to
seal the installation. The units were thus protected for extended
periods of time until they were dispatched and installed at their
final destination. The VCI powder was either left in place with
no detrimental effect to the operations or simply flushed with water,
and subsequently disposed of in the sea.
Other applications where VCI technology is now used include onshore
pipeline (Figure 5) and pig launching (Figure 6) installations.
Solutions of VCI A were used to hydrotest and protect these pieces
of equipment. The solutions were sent to a storage tank for future
use or discharged in the sea.
First developed for a few specific applications, volatile corrosion
inhibitors are now used over a wide range of situations where atmospheric
corrosion damages exposed metals. These metals can belong to steel
structures, metal parts in transit or storage, or electronic devices.
VCI compounds provide effective corrosion protection while offering
several other benefits, such as cost effectiveness and cleanliness.
A new generation of VCI has been developed to address the toxicity
concern that some of the original VCIs have. Corrosion and toxicity
testing demonstrated that these new compounds not only provide excellent
corrosion protection, but also have a very low toxicity level when
placed in a marine environment. As a consequence, the oil and gas
producing industry in the North Sea now uses VCI technology with
The author acknowledges the assistance of Ole Lilland with Presserv
AS, Stavenger, Norway, in providing the field work information.
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Figure 2 Ü VIA Steel Plugs
Figure 3 Ü VCI A Aerobic Biodegradability
Figure 4 Ü Metering Station
Figure 5 Ü Onshore Pipeline Installation
Figure 6 Ü Pig Launching Installation
Table 1 VIA Test Results
OECD 117 log Pow
Table 2 Partition Coefficient
Exposure time, Hours
Effect Concentration (mg/l)
No observed effect concentration
Table 3 VCI A Toxicity to Primary Producers
Exposure time, Hours
Effect Concentration (mg/l)
No observed effect concentration
Table 4 VCI A Toxicity to Consumers
Exposure time, Hours
Effect Concentration (mg/kg)
No observed effect concentration
Table 5 VCI A Toxicity to Sediment Reworkers