The unit was in a scheduled outage in October 2019, at which time the fireside of the tubes in the boiler were inspected by robotic UT. Wastage was discovered on both sidewalls above the existing field applied overlay, rear wall slope and burners, and front wall slope and burners. The type of damage is typical for opposed wall fired pulverized coal boilers operating in a reducing atmosphere with low NOₓ burners.
IGS was contracted to install 5450 EPRI Proven HVTS Alloy Cladding over the damage zones. IGS offered a rapid response and addressed the areas during the week of November 4, 2019. The IGS solution is a rather fast application – a total of 2,000 square foot of boiler tubing was protected with HVTS in 5 short days.
The project was executed in accordance with the IGS Safety Program. Safety is, and always will be Integrated Global Services’ first and highest priority. Our Management Team is dedicated to becoming the industry leader in Health and Safety while our excellent safety record bears witness to this fact. A continuous improvement process is utilized that enables all levels of personnel to take part in identifying and fixing hazards associated within the workplace. This is marked by our Safety Committee that involves members of all areas and levels of IGS.
IGS Thermal Spray projects are performed in accordance with the IGS quality control standards which have been developed in to meet customer requirements. All site work will be executed in accordance to the accepted Quality Control Plan (ITP/QCP) and accompanying method statement. The final project QC package will be issued along with this report.
WTE Boiler Fireside Corrosion of Alloy 625 Weld Overlay Cladding
The Hitachi Zosen Inova (HZI) furnace installed at Renergia is an inclined moving grate four-pass waste to energy boiler with an external economizer. The boiler’s thermal capacity is 47MW with the steam flow of 58 t/h and steam pressure of 41 Bar at 410°C.
Alloy 625 weld overlay was shop-applied on the fireside water wall panels to protect the WtE boiler tubes from fireside corrosion. After months of operation, an inspection revealed accelerated degradation of the Alloy 625 just above the grate.
Several solutions were considered to manage the boiler tube metal wastage and improve reliability and lifetime of the water walls, including replacement, field applied weld overlay and thermal spray.
Gee… not a Lucky Star
Inspection of a previously applied protection is a critical part of any project. During the inspection, IGS utilized both visual and magnetic lift-off (MLO) techniques to record any low readings.
Areas that were below the minimum specification were noted and recorded. A considerable amount of the existing coating was significantly eroded. In many cases, it had worn through to the substrate and in the worst cases had allowed significant tube gouging to occur. The amount of defects observed was significantly greater than expected, with 500 tube repairs performed.
Inspection in 2017
The inspection was carried out together with the 3rd party CFB Expert and Plant Manager. Cladding was observed to be in a flawless condition. This mini-outage verified the reliability of the IGS HVTS cladding. Extensive inspection was completed throughout the entirety of the cladding scope. With the top coat completely intact, the cladding system was confirmed to be in ‘as-sprayed’ condition.
Fouling was virtually eliminated in the cladded locations and any adhered fouling was no longer tenacious and was easily brushed away.