Abstract
The Device Assembly Facility (DAF) is a collection of 30 individual steel-reinforced buildings connected by a rectangular racetrack corridor built in the Nevada desert in the mid-1980s. The DAF fire suppression system includes 29 carbon steel lead-in lines that run underground from the header loop line to a variety of risers inside the DAF. The lead-in lines are fabricated from 4-in. or 6-in. diameter carbon steel pipes lined and coated with coal tar enamel (CTE). Particles and flakes of the CTE lining have been appearing in water used to flush the fire suppression piping since the installation of the system. Discussions with DAF personnel indicate that the carbon steel lines were not flange-fitted together (as designed) during installation at the DAF; instead, the sticks of pipe used to form the lead-in lines were welded together. The welding caused substantial damage to the interior CTE lining. Screens have since been installed in the lead-in lines to prevent CTE particles and flakes from clogging sprinkler heads should their use be required in an emergency. An integrity assessment was recently performed to determine the nature and extent of corrosion damage and to determine the mechanism responsible for the delamination of the CTE lining. Borescopic video and Remote Field Tool (RFT) inspections confirmed that the CTE lining was substantially damaged by welding operations during construction of the lead-in line system. Several forms of corrosion are active or likely active in the system including general corrosion, MIC, pitting, crevice corrosion, and galvanic cell corrosion. No sessile samples were collected, but tubercle-like growths were observed and water testing confirmed that MIC-inducing bacteria are present in all the lead-in lines. If MIC is indeed active, MIC presents a significant threat to line integrity at the welded joints. Concentration cell and crevice corrosion were not directly observed, but are likely at the damaged joints given the geometry of the damaged area and the ongoing delamination of the CTE lining material. Away from the welded joints, blistering of the lining due to pitting corrosion presents the most significant threat to line integrity. Galvanic corrosion at the uninsulated joints between each steel line and the brass PIV is an additional significant threat to line integrity. Likewise, the galvanic cell created by electrical contact between the concrete-encased steel in the building walls and the DAF lead-in lines is accelerating the corrosion of the DAF lead in lines. Insulating kits should have been specified and installed to eliminate the galvanic cell between materials, but appear to be non-existent. Details of the findings and possible paths for remediating the damage are discussed herein.
