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Corrosion problems in storage
Corrosion problems in transit
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Corrosion
Prevention in Storage & Transit -
Avoidable Problems
By
Dr A R Parkinson MSc, C.Chem, MRSC, Technical Director, Vapor-Tek Limited
Billions
of pounds worth of metal parts, assembled and part-assembled machinery
are stored and transported within, and exported from the UK annually.
It is a matter of general knowledge that unless the correct steps are
taken, corrosion will damage or effectively destroy a large proportion
of these goods.
Unless
reliance is placed on barrier films and desiccants (with their attendant
problems), corrosion of items during storage and transportation is usually
prevented by the use of 'temporary protectives' , so-called since they
are generally not intended to form a final finish, as in the case of
paints, but are often - though by no means always - removed by the ultimate
customer. It should be noted that 'temporary' is not meant to imply
a limited effective life, since goods often require continued protection
during years of storage.
Choosing
the right temporary protective
To
begin with, some assessment must be made as to the length of time goods
need to be protected and the severity of the conditions likely to be
encountered. It is well to err on the cautious side in making this assessment
on the grounds that ..."if anything can go wrong - it will".
Probably the most common error is to choose an inferior protective,
often on the basis of price (not cost - that can come later when
corrosion damage has to be put right).
This
is a truly false economy, since we are sometimes literally talking of
a few pennyworth of protective on items valued in many instances at
tens of thousands of pounds. Also, to put it in perspective, the cost
of application frequently exceeds that of the protective being applied,
especially if it is a thick, treacly product which can only be applied
by hand with a brush.
Space
here does not permit an exhaustive analysis of all the aspects of corrosion
prevention of metals in storage and transit. However, some of the more
important, and frequently overlooked, points are outlined below.
It
is a mistake to think that thick heavy coatings are necessary; the modern
corrosion inhibitor systems of Vapor-Tek's Steelgard
range permit the use of quite thin (10 microns or less) soft films which
are easier to apply and remove, (usually not required).
The
protective as received is fluid enough to enable it to flow into awkward
nooks and crannies and narrow crevices, since these are precisely the
areas where moisture and other corrosive contaminants may lodge and
cause trouble. A point worth noting here is that the protective should
leave a transparent film to enable the underlying surfaces to be inspected
at all stages, from assembly to final acceptance by the customer.
All
the Steelgards contain a water-displacing agent (to remove any condensation
which might be present) and a fingerprint suppressant. After evaporation
of the solvent, they will leave a 'self-healing' film effect on non-metals
which may be present, such as plastics, rubbers, paints, etc.
Effectiveness
as a corrosion preventive
A
corrosion 'preventive', capable of protecting goods from extreme adverse
conditions such as those encountered on long sea journeys to, or through,
tropical areas, will normally afford protection during long-term storage.
Accordingly, the properties needed for a high quality 'export' protective
will be considered here.
Steelgard
'Export' protects from humid atmospheres and salt water, since these
will be encountered on any sea journey. Less obvious perhaps is the
need to protect from acid fumes. Sulphur dioxide (which forms 'acid
rain') is ever-present in industrial atmospheres where it can form sulphuric
acid. Both sulphur dioxide and sulphuric acid are are extremely corrosive
and are known to cause corrosion damage to goods in storage or in transit.
In the case of packaged parts and machinery (usually in wooded cases
or in the presence of wood), it is vital to protect against acetic acid,
which is released by some woods and certain plastics, especially under
tropical conditions.
Other
acids can cause problems too: hydrochloric acid is released from PVC,
chlorinated rubber and certain adhesives; plywood and chipboard binding
resins and some rubbers and paints give off highly corrosive formic
acid, especially at high temperatures. All these acids promote corrosion
at very low concentrations. They can cause a great deal of damage since
they are not used up in the corrosion process, but are continuously
regenerated and, in fact, act as catalysts to corrosion.
Steelgard
'Export' gives excellent protection from moisture condensation, salt
water and the corrosive acids discussed above.
Surprisingly
high temperatures can be reached inside packing cases and containers
in tropical areas - up to 80°C has been recorded in direct sunlight.
It is therefore essential that any corrosion preventive used shall
not be adversely affected at these extremes. Some coatings will melt
and drain away at these temperatures, while others form resins and
gums which will cause problems of removal, or even render the goods
inoperative. How could you remove a coating the consistency of chewing
gum of shellac from, say, the fine needles of a carpet weaving machine?
The coating left by Steelgard Export does not form a gum or lacquer,
melt, drain away, or be otherwise affected by temperatures as high
as 100°C. At the risk of stating the obvious, care should be taken
to ensure that metal parts or machinery are corrosion-free at the
time of packing. A manufacturing or assembly operation extending over
a lengthy period affords an ideal opportunity for corrosion to start,
often in remote unobserved areas. To prevent this an 'assembly fluid'
having water-displacing, corrosion inhibiting and lubricating properties
can be used. The assembly fluid must, of course, be compatible with
the Steelgard 'Export' protective to be applied later.
Steelgard GP, available in 210 litre,
25 litre containers and also in aerosol form, serves as an assembly
fluid. For items to be stored, Steelgard GP will give up to two years
protection of metal parts under normal storage conditions.
The dangers discussed above are by no means the only ones: there are
many more traps for the unwary. Ideally, corrosion should be 'designed
out' of equipment as far as possible. Next best is careful preservation
with the correct materials and assiduous attention to quality control
at all stages of manufacture, assembly, storage, packing and transportation.
When it comes to corrosion, prevention (which is cheap) is almost
certainly better than cure, which is expensive even when it is possible.
Receiving corroded goods does not please a customer who knows full
well that corrosion is almost invariably due to carelessness and inattention
to detail. Corrosion is very bad for business.
For
details of other products in the Steelgard Range, see our Products
Range.
For
information on volatile (vapour-phase) corrosion preventives (oil,
paper and water solutions) click HERE.
For
further information, contact Dr A R Parkinson or Mr Colin Jones at Vapor-Tek
Limited. Tel: +44 (0)1204 521795.
Please
request a brochure/technical details by using our on-line enquiry
form
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