Cordemais, France
Summary
The EDF (Electricite de France) plant located in Cordemais is the largest thermal power facility in France. The coal-fired plant produces a significant amount of electricity from fossil fuel. The power station has been in service for more than 40 years. Over the decades, the flu gasses caused internal corrosion in the chimney stack, degrading the integrity of the flues. At 220 meters, the chimney is among the tallest structures in France. Several obstacles precluded the consideration of other repair alternatives. The cost of replacing flues would be prohibitive. A coating was considered to repair the element internally; however, the coating would not supply the structural reinforcement needed to restore the integrity of the flues. To restore structural integrity, CSNRI proposed an engineered composite repair that would extend the life of the carbon steel liners of the chimney stack. Based on performance features, CSNRI selected DiamondWrap MT as the best system for the repair.
Benefits of DiamondWrap MT
- Extends the life of aging and corroding assets
- No pipe cutting or welding
- Restores original strength in both hoop and axial directions
- Provides pressure-containing repair
- Minimal creep ensures a long service life
- Operates up to 313oF (156oC)
- No VOCs
- Prevents future external corrosion
- Complies with AB-539, ASME PCC-2, ISO 24817, ASME B31, US DOT, API and CSA Z6628
Challenge
To make the necessary flue repairs required that the chimney be shut down for a little more than two months. With repairs scheduled for the hottest months of the year, a plan was devised to force air through the chimney to maintain proper drying conditions for the DiamondWrap MT application. This helped to control the elevated temperatures and high humidity typically experienced within the chimney during summer months.
Working conditions posed several difficulties. The location of the damage required lowering a crew of three technicians into the chimney by basket to execute the repairs. Traveling two and from the repair locations took 23 minutes each time the team needed to enter or exit the work area. There were also considerations for the weight of the DiamondWrap MT materials, which were factored into a plan for a separate basket that could be lowered to the crew with prepared materials, ready to apply to the repairs. Rope access with a high-speed winch was located at the top of the chimney. This facilitates rapid delivery of materials through the 38-meter distance to reach the basket-based repair crew quickly. Technicians were able to request transfer of materials by radio.
The execution plan also required that all tools, marking or writing instruments be attached with a lanyard to manage the safety impacts of dropped objects.
Solution
The CSNRI engineering team put together a repair design in alignment with ISO 24817 standard with a design life of 10 years using DiamondWrap MT composite system. The design considered restoring the structural strength of the corroded sections, some of which were already holed as well as restoring the hoop strength and pressure retaining capacity of the steel flues.
DiamondWrap MT is an engineered, field-saturated repair system made of proprietary carbon fiber fabric applied with a two-part epoxy and a high-modulus filler material. It is used regularly in plants, refineries and terminals around the globe and is ideal for complicated geometry, such as tees, flanges, and varying diameter pipe. It is available in multiple kit sizes for any temperature and diameter.
Application
Corrosion damage was documented in three of four flues. With a Normandy-based general contractor, CSNRI provided full, turnkey service for the supply and installation of a fully engineered composite system to repair the flues. Four to six layers of DiamondWrap MT were specified to address column 4B, requiring a 24-meter repair length; column 5A, requiring a 32-meter repair length; and column 5B, requiring an eight-meter repair length.
Using DiamondWrap MT provided a cost-effective, chemically resistant solution for reinforcing the sections of the chimney that had lost significant steel thickness. The repair system, as engineered by CSNRI, was designed to add structural reinforcement as well as stop the flu gasses from corroding the exposed steel work.
The damaged areas were sandblasted to prepare for the DiamondWrap application. Because of the enclosed area, which can cause debris to ricochet, protective suits and masks were worn during the process. Remnants of the sandblasting that fell to the bottom of the chimney were removed before the plant resumed operation.
Two teams worked daily, with a combined crew of up to 20 people on site each day. Due to the chimney height, additional time was needed to maintain the 220-meter-high elevator. CSNRI carried out the composite installations over a two-month period, which included adjustments to the scope as additional damage and deterioration was discovered post-sandblasting. Weather challenges, such as multiple thunderstorms, also caused additional standby periods.
Results
CSNRI was able to engineer a cost-effective composite system to restore the wall thickness of the steel pipes at the EDF facility. The repair system provided a means to repair the flues with lower weight materials with no hot work required. The system, which combines carbon fiber and resins to bond to the damaged surface, produced a repair stronger than the original carbon steel.
The engineered solution recommended by CSNRI required:
- The reinforcement of 1,600 m² with the DiamondWrap MT composite system
- The repair of more than 200 holes in the structure
- Repairs to six hatches and three access doors
At completion, repairs were executed in all four flues of the chimney. Understanding the age of the chimney, EDF had anticipated the likelihood of additional damage and was pleased with CSNRI’s ability to manage the extended scope and make repairs in a very short time. With the successfully completed repair, EDF was able to extend to the life of the chimney, safely continuing much-needed power service in the region.
