CORROSION MONITORING
What Is Corrosion Monitoring?
Corrosion monitoring can be described as "The regular measurement of
corrosion or corrosivity as it effects an asset". It is most often used to
make comparisons between actual and predicted corrosion rates, or for the
evaluation of measures taken in prevention or mitigation. Some but not all
corrosion monitors are sensitive to erosion that may occur in process plants due
to high flow rates and entrained solids.
The asset may equally be a pipeline, a concrete bridge, a large HVAC system in a building, an offshore oil & gas facility or a printed circuit in a computer. When that part of the asset that is of interest is inaccessible, simple methods such as visual inspection or manual measurement cannot be used and special techniques must be introduced. This is especially true of continuous processes where internal corrosion may advance at a rapid rate and lead to catastrophic failure long before traditional "inspection" can detect it. Corrosion Monitoring has therefore, come to be associated mainly with internal corrosion of process equipment, although there are a wide range of other applications where the techniques can do valuable work.
Why monitor?
Corrosion is not an isolated phenomenon; it is a natural process that attacks
any material, particularly metals, under the right conditions. It is therefore
prudent to expect corrosion; to look for it and to be prepared to prevent it
once a tendency to corrode is discovered.
However carefully a process plant is designed and the materials of construction selected the risk of corrosion is only reduced. Experience tells us, often with horrific consequences, that it is never eliminated. Failures due to corrosion can be costly to repair, costly in terms of lost or contaminated product, costly in terms of pollution and environmental damage (which in turn may result in fines or closure of the installation), and ultimately it may be costly in terms of human safety.
Fear of corrosion can result in over-design or selection of materials which are not otherwise ideal. By adding to capital cost this may make projects commercially unattractive or unfeasible, so that ultra-safe design alone is not a correct response. Many projects are designed with corrosion allowances in the calculations and monitoring in place to evaluate actual corrosion rates against those predicted, allowing action in good time if a variance is observed. In addition to this valuable service, corrosion monitoring can be used as a pro-active tool to assist with operating the plant in a more effective way, thereby prolonging life and gaining optimum throughput. For example, in the oil & gas industry the produced hydrocarbon liquids or gas and associated water are to some degree variable in composition, temperature, pressure and flow rate. This causes complex corrosion and erosion problems in the production process equipment that are often episodic in nature.
Most operators seek to solve these problems by using some form of chemical treatment in conjunction with careful materials selection. In each case a fine balance must be found between the cost of treatment, the rate of plant deterioration and the rate of production if the business objective is to be met. Corrosion Monitoring is a key tool for this, advising when to treat and what the corrosion rate will be in any given mode of operation. This is information that can drive a continuous improvement process.
Corrosion monitoring methods
In order to incorporate corrosion monitoring into a strategy it is necessary to
understand the basics of CORROSION MONITORING METHODS and the tools
available. The range of available monitoring methods is wide, but they fall into
three main groups: -
Metal Loss types: which measure the physical loss of material due to corrosion or erosion by either physical or electrical means.
Electrochemical types: which measure the corrosivity of an environment independent of actual material loss.
Supporting Analyses: Iron counts, biofilm testing, pH monitoring etc., a range of sampling based laboratory techniques which add to the overall understanding of the system performance. These are not directly relevant to this document, but should be considered part of the tool-kit available to the technical team.
Range of Products:
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For more detail:
CORROM PTE LTD
Blk 5030 Ang Mo Kio Industrial Park 2
#01-197 Singapore 569533
Tel: 65 64837301 Fax: 65 64837261
Email: corrom@singnet.com.sg
