Selecting the correct coating system is usually straightforward when the operating temperature is clearly defined. However, some piping systems do not operate under constant conditions, making coating selection much more challenging.

During a recent maintenance project, our team encountered an interesting situation while preparing a process line for abrasive blasting and recoating.

According to the project coating specification, the coating system to be applied depends on the operating temperature of the line. Before proceeding with blasting, a temperature survey was carried out on site. Surprisingly, the measured pipe surface temperature was below 55°C, which meant the line appeared to fall within the temperature range for the standard coating system specified by the project.

However, the operating team informed us that the line does not remain at the same temperature throughout its service. At certain times, the process temperature increases significantly, while during other operating conditions, condensation (sweating) can be observed on the external pipe surface.

To verify the actual condition, the site team decided to recheck the pipe temperature after blasting. If the measured temperature remained below 55°C, the work would proceed in accordance with the project specification.

This raised an important question among the inspection and engineering teams.

Should the coating system be selected based on the actual temperature measured during maintenance? Or should it be based on the maximum operating temperature specified in the process design, even if the pipe is currently operating below that value?

Another concern was the repeated occurrence of condensation. Although the measured temperature was below the project threshold, the presence of sweating indicated that the pipe was regularly exposed to moisture, which could increase the risk of corrosion if an unsuitable coating system was selected.

Situations like this are not uncommon in refineries, gas processing plants, and petrochemical facilities where process conditions can change depending on production demand, shutdowns, or seasonal operation. In such cases, selecting the correct coating system requires more than simply checking the pipe temperature on a single day.

It also highlights the importance of communication between the coating inspector, process engineer, operations team, and coating manufacturer before any repair work begins.

Discussion Questions

• If the pipe surface temperature measures below 55°C during maintenance, but the line occasionally operates at higher temperatures, which temperature should be used for coating selection?
• Should coating selection be based on the measured site temperature, the normal operating temperature, or the maximum design temperature?
• How would the presence of condensation (sweating) influence your choice of coating system?
• Have you experienced a similar situation where fluctuating operating temperatures created uncertainty in selecting the correct coating specification?

I'd be interested to hear how other inspectors, coating specialists, and engineers have handled similar cases in the field.