Measuring corrosion in large tank especially in petroleum industries are crucial. Increasing flexibility in the variety of crude qualities that can be processed in a refinery may increase the risk of increased corrosion to plant integrity. This results in unplanned shutdowns.
If unnoticed and unmitigated, this excessive corrosion could lead to hydrocarbon leakage and, in the worst case, to an explosion or fire that could lead to human disaster, prolonged disruption of operation, loss of tradition, cost of comprehensive equipment reconstruction etc.,
Different Corrosion monitoring methods:
There are several types of equipment commonly used in oil refineries to track corrosion. Corrosion tests and manual ultrasound are two of the most common.
Corrosion probes:
This is an indirect method:
The method of corrosion measurement is carried out with a sacrificial tip that is dipped in the process liquid and is (normally) constructed from the same material grade as the surrounding equipment. As the sacrificial tip corrodes, its electrical resistivity increases, which is reported externally (usually on a local data logger), but these are also increasingly available wirelessly.
The sacrificial tip corrosion is used to measure the level of corrosion that the surrounding equipment is experiencing.
Ultrasound method:
This is also a widely used method:
The technique involves the generation of ultrasound directly on the metal surface from a transducer. The ultrasound is conveyed through the steel until the inside back wall reflects it. The reflected ultrasonic signal (or A-scan) is registered and the time difference (the’ time-of-flight’) between the signals sent and reflected provides the wall this calculation.
The problem with this method is very time-consuming.
Continuous corrosion monitoring technology:
This method helps to overcome the disadvantages from the above two methods. There are two methods:
- Permanently installed, local/point measurement
- Permanently installed, area measurement
Area measurement methods provide a valuable way to determine the frequency of corrosion activity within a given system and the estimated extent of the total loss of material.
An increase in the measuring area, however, results in a related decrease in the resolution or sensitivity of these measurements
If these instruments show a 1% loss of metal volume throughout the entire measurement area, it requires highly skilled and highly trained experts to decide whether this is a standardized loss of metal throughout the area or the loss of metal from a single pit;