Under Deposit corrosion (UDC) is one of the hardest types of corrosion to identify and a common mode of failure in boiler tubes. UDC is not only a high risk of eventual tube failure but it can also be deadly in black liquor recovery boilers. The biggest issue: it can't physically be seen. This localized corrosion was happening at a paper mill in eastern Georgia. Traditional inspection teams found a needle in a haystack when performing a maintenance inspection during a planned outage. They then brought in the Gecko Robotics Inspection Team (GRIT) to take millions of readings and identify areas to make these life saving repairs.
Gecko specializes in faster, safer, and data-heavy NDT inspections. With their fleet of robots, Gecko can perform inspections in ways that traditional hand-held inspections just can't deliver. Gecko was the first to deploy robotic inspection robots.
The paper mill in Georgia was experiencing problems with UDC on the waterside of the tubes in their black liquor recovery boiler. Plant inspectors found one spot of UDC pitting while performing a hand-held UT inspection. After confirming the UDC, it was clear that they would need a dense scan to find all the spots.
First, plant inspectors spent five days gathering nearly 10,000 readings, but when they realized that number of readings wasn't enough, they called Gecko for their ability to gather millions of data points, quickly. Gecko's team was onsite the next day to better understand scope, and began the inspection within 36 hours of initial contact.
GRIT was equipped with Gecko's TOKA 4, a robot with 32 transducers, 4 HD visual cameras, and moves at speeds of 60 ft/min (18 m/min), to perform a UT inspection on the boiler.
On day one, Gecko was able to expedite data from the left wall to hundreds of contractors waiting to make necessary repairs. Dozens of UDC locations were verified and confirmed with 100% accuracy by the plant using hand-held UT's.
GRIT continued performing the inspection on remaining walls while repairs were being made on previously inspected walls using Gecko Vision, Gecko's interactive thickness map. The map allowed hundreds of on-site contractors to have a clear and precise view of the necessary repair areas.
A look inside the tubes. Under Deposit corrosion discovered on the waterside of the tubes. Pitting is small and rare to find using hand-held methods.
UDC found on walls of tubes was sporadically spread throughout and found using Gecko's TOKA 4 robot.
Gecko Robotics completed the inspection in four days, gathering over 12 million readings. Through this, they achieved 99% coverage of the entire boiler at six different angles on each tube. Without this high-density coverage data, the boiler's eventual tube failure would have caused an explosion within the paper mill. Plant operators now have more insight into the state of their asset, allowing for better preventative maintenance and a longer asset lifecycle; thereby reducing forced outages, safety issues, and loss of revenue dollars.