Ultrasonic “smart pigging” inspection technology can be utilised to detect a multitude of defects within fired heater coils, aiding unit operators in identifying potential problems and preventing unplanned shutdowns. Utilising In-Line Inspection (ILI) technologies as a baseline allows for the earliest possible identification of true tube wall conditions, which is vital when planning future maintenance and tube life expectancy.
In March of 2017, Quest Integrity performed an inspection utilising its Furnace Tube Inspection System, FTIS™, on 4 platformer units in Germany. The inspections included data gathering on 100% of each pipe surface within the radiant section of the heater. At the time of inspection, the units were still at the manufacturer site and had not yet been shipped to the refinery. As such, the examination of the unit was considered a baseline inspection.
The pipes within these units were designed as 3-in. tubes with a nominal wall thickness of 4.0 mm (0.157 in.). However, the results of the inspection showed numerous localised areas with remaining wall thickness readings as low as 2.6 mm (0.102 in.), which was 35.0% thinner than the design wall. Many pipes within all coils (passes) of these heaters contained wall thickness readings between 0.2 mm (0.008 in.) and 1.4 mm (0.055 in.) thinner than the nominal design.
Figure 1. Baseline inspection reveals varying wall thicknesses within newly installed piping.
Wall thicknesses variations in new sections of piping is very significant for an operator. Without the initial baseline inspection, it would have been assumed that the thickness of the new piping was the same as the nominal design wall before the unit went into operation.
Had the initial in-line inspection occurred sometime after the new section had been placed in service, the operator may have concluded that wall loss of up to 1.4 mm (0.055 in.) had occurred due to corrosion or erosion. This would have resulted in a much lower remaining life for many of the pipes, based on the assumption that damage was occurring at a faster-than-normal rate. This is particularly important when determining the true lifespan of the unit.
Baseline inspections with ultrasonic in-line inspection technology should not be overlooked, as baseline inspections can identify problems before unit start up, and aid in future maintenance planning. The benefits of a baseline inspection allow for the complete understanding of operating assets at every life stage, providing confident decision-making, maximum operability and a greater return on investment.