Corrosion monitoring in hydrogen bromide
For years, a major processor of hydrogen bromide has had a corrosion problem. The compressor that pushes hydrogen bromide gas through their plant required regular repairs and replacement, and each compressor was only able to provide five years of operation.
Hydrogen bromide is a highly corrosive gas, especially with water present. In this application compressors are used to push the gas throughout the plant for processing. The carbon steel lines are assumed to be dry, however thousands of dollars were being spent to repair/replace corroded parts on the compressor. When the compressor broke down, the ability to process also stopped, costing money in down time.
It was determined that water must be present in the line. How was the water getting in? When? What could be done to monitor this in the process? Moisture detection equipment was used for a time. This solution did not prove fruitful, and the devices often failed. Additionally, the equipment did not assist in any planned maintenance or repair. When they did work it only confirmed that water must be in the “dry gas line,” as corrosion would not be occurring otherwise. They were unable to link the information to other process control variables being monitored.
The solution to this problem was an online corrosion-monitoring device called CorrTran from Pepperl+Fuchs, Inc. The device detects and measures corrosion rates and provides that information in an industry standard 4-20mA signal to the DCS system. The device uses algorithms and data analysis techniques that measure corrosion rate and localized corrosion, or pitting. Harmonic distortion analysis is applied to improve the performance of the industry accepted linear polarization resistance technique used to measure corrosion rate.
The plant monitored the corrosion rate over a 60-day period. Carbon filters are used in the compressor lines to assist with removing/reducing moisture content in the line. Results showed that when corrosion rates started to rise and stay high, it was an indication that the carbon filters needed to be changed.
There is a direct correlation between the corrosion spikes and the fact that filters needed to be replaced. After replacing the filters, corrosion decreased. By making this part of planned maintenance, over time repair and parts replacement costs on the compressor will be significantly reduced, and the life of the compressor will be extended.