Technicians and operators of industrial equipment across all process industries share a common goal—corrosion control.
Controlling corrosion is a constant pursuit of nearly all industrial processes, especially in fuel processing units. Maintaining the integrity of industrial instrumentation and other process equipment is vital to avoiding losses caused by process shutdown and repair costs. Preventative measurements of pH and conductivity can be utilized to combat corrosion, particularly in crude oil and fuel treatment applications.
Crude Distillation
Crude distillation is how refineries separate crude oil into different hydrocarbon products such as kerosene, gasoline, and other fuels. However, each crude byproduct has unique reactive properties to temperature and steam cracking and is separated based on these properties. As the byproducts vaporize, the vapor will flow through an overhead condenser and into another distillation unit. Heavier hydrocarbons will settle on the bottom of the tower, while lighter molecules will rise to the top. The undesirable components within the crude, such as sulfur, ammonia, and certain salts, tend to concentrate in the upper portion of the distillation tower. As they change from a gaseous to an aqueous phase, these contaminants will focus in the condensed acidic water as it passes through the overhead. This can cause heavy corrosion to occur in the condenser.
The Role of In-line Analytics in Combating Corrosion
When combating corrosion in different areas of the distillation unit, operators will dose the process with chemical treatments. This is done as a means of controlling pH levels in addition to filtering out undesirable hydrocarbon byproducts. Although to be safer rather than sorry, an overdose of these chemicals is common and can negatively affect the process as well. Over time exposing process equipment to a mix of caustics, corrosive salts, and acids can lead to a buildup of dissolved solids. Despite constant monitoring, these dissolved solids can accumulate, potentially leading to costly equipment replacements. Preventative pH measurements are essential to avoiding excessive treatment and combating corrosion in various processes, such as:
- Desalters
- Overhead Condensers
- Furnaces
- Coker Units
- Heat Exchangers
- Feedstock Heaters
pH Monitoring
Preventative pH measurements are a crucial aspect of corrosion control. Low-pH acidic waters accelerate corrosion. Effluent water in the desalter is monitored for pH as a determinant of amines implemented into the process. Consequently, operators will boost pH if they notice levels dropping below a predetermined value. Additionally, by measuring the pH of wastewater flowing throughout the process, operators can better understand corrosive conditions within the process. A low pH reading in this water is a typical indicator of a corrosive environment within the unit. If this water continues to flow throughout the unit, the integrity of the piping in the condenser and, eventually, the distillation tower will be damaged due to corrosion.
Tools for Managing Corrosion in Crude Distillation
pH Sensors – Sour water monitoring is challenging for pH electrodes because the junction can be plugged by solids & sulfides. This can cause sensors to drift or fail. The SE 571 Memosens pH sensor is ideal for applications with oils and heavy buildup. The sensor’s PTFE annular junction design is resistant to plugging media. In addition, the KCL rings protect the Silamid® reference from poisoning, greatly extending sensor life.
A microprocessor in the head of the pH sensor enables offline calibration and sensor health analysis. When using a Portavo portable analyzer, technicians can calibrate and troubleshoot in the shop or lab instead of inside the process unit, providing more precise calibrations. After calibration, the technician carries it out to the installation, disconnects the Memosens inductive cable, and does a “hot-swap” with no additional calibration or configuration.
Field Transmitter – The Knick Stratos Pro is a two-wire loop-powered Class 1 Div 2 FM/CSA-rated transmitter. It provides a 4…20 mA output with HART process and diagnostic data. Plant operations can view the diagnostic data when using AMS software. Therefore, operators can now predict maintenance requirements, reducing the potential for unscheduled process interruptions.
Sensor Holder – Double block and bleed installations are a requirement in refineries. The CSR 3600 B is a simple ball-valve retractable holder. The user can easily insert or remove the sensor through the ball valve, isolating the sensor without interrupting the process flow. This allows the maintenance personnel to quickly exchange the pH electrode with minimum downtime.
Summary
In-line analytics is a crucial and cost-effective tool to use for corrosion control. By monitoring pH, operators obtain more insight into the condition of their equipment and the effectiveness of their corrosion control monitoring program. Precise pH measurements will significantly reduce chemical usage, maintenance costs, and equipment replacement. Review our application success stories for more information on which sensor, transmitter, or fitting can best suit your process.
