Failure analysis of carbon steel components in a water bath heater and the influence of ethylene glycol concentration

• The underdeposit corrosion was identified as the main cause of the failure inside the water bath heater.
• Water level below a critical depth cause condensation of water droplet on the roof that produces deposits after re-evaporation.
• Corrosion can be retarded by ethylene glycol above 10 vol.%.

Water bath heaters are designed to heat the gas prior to pressure reduction. In this paper, corrosion failure of coil tubes, fire tubes and inner surface of the shell from a large water bath heater is described and the effect of ethylene glycol concentration has been investigated. In order to study the main cause of failure, non-destructive and destructive tests, including evaluation of mechanical properties, X-ray diffraction, scanning electron microscopy, EDS (energy dispersive spectroscopy), microanalysis of corrosion products and chemical analysis of water used in the heater were carried out on specimens prepared from coil tubes. The results indicated that insufficient control of water level in the tank resulted in oxygen concentration corrosion. After evaporation of water content, a residue remained on the surface leading to under deposit corrosion and, through that, a blister-like damage took place on the shell roof. After detachment, corrosion products and scales, fell down and remained on the upper surface of the components, leading to scale corrosion of carbon steel coil and fire tubes. Results of laboratory corrosion tests revealed that water containing 10–40% ethylene glycol had the lowest corrosion rate, whereas with concentrations < 10%, the corrosion rate was high.