Corrosion Monitoring Strategy

One of the critical components of corrosion monitoring is analyzing the samples taken from the process stream and reporting accurate and relevant data to the system operators. 

A comprehensive review of the process plant materials, corrosion allowances, and operating conditions should be carried out to identify all areas that could be susceptible to significant corrosion within the projected lifespan of the plant. An assessment of the consequences of a corrosion failure occurring wiU be an integral part of the review. 

The identification of the specific corrosion processes likely to occur is essential to the selection of particular on-line corrosion monitoring devices to be used. The review should also identify those parameters that are instrumental in causing corrosion and that are likely to influence the corrosion rate. The results of the review should be used to develop a corrosion monitoring strategy encompassing the following  

For new projects, the corrosion monitoring requirements should be established during the early development of the design. 

The selection of the specific on-line corrosion monitoring devices will be determined by the known or perceived corrosion processes taking place. 

---

In a given situation, it may prove more economic to install a cheaper material with a high corrosion rate and replace it frequently rather than select a more resistant but more expensive material. This strategy would only be considered for relatively simple equipment with low fabrication costs, and where premature failure would not cause a serious hazard. For example, carbon steel could be specified for an aqueous effluent line in place of stainless steel, accepting the probable need for replacement. The pipe wall thickness would be monitored in situ frequently to determine when replacement was needed. 

One example of a single variable control strategy is applied to a stripper in a hydrocracking unit. The main purpose of the stripper is to remove H2S and noncondensable components from the bottom product. One of the key indicators identified is the water dew point at the top of the stripper column. As a matter of fact, the dew point is a function of column overhead vapor composition and the amount of water. There was no monitoring capability available for the dew point temperature. If the column top temperature is lower than the dew point, the hydrogen sulfide will dissolve in the condensed water and cause corrosion to the column overhead system. 

---