In recent years, the power industry had embraced alloy 2205 as a lightweight and cost-effective alternative over traditional stainless steel and carbon steel substrates in the construction of flue-gas desulfurization (FGD) absorbers and vessels. Early test reports indicated the substrate would hold up well in most conditions. However, many alloy 2205 vessels, located at more than 40 power plants across the United States, are showing evidence of severe pitting and corrosion under scale buildup including “worm holing” after just one year in service.
Much of the pretesting of alloy 2205 did not take into consideration the effects of a high concentration of chlorides/fluorides under the scale buildup, or that it creates the same corrosive effects of crevice corrosion. As a result, the increased demand for corrosion-related repairs has given rise to new corrosion solutions.
One option is to clad the FGD vessel’s interior with more resistant alloy metal. However, the sporadic availability and high price of the material and installation can cost $75 per square foot and up to $1 million per day in production downtime. Further, leaks can still seep under the cladding and attack the alloy underneath virtually unnoticed.
Vinyl ester linings can be very effective and are increasingly being utilized in alloy 2205 corrosion repairs. Nevertheless, multiple variables within a lining system’s chemistry — even environmental factors — can directly impact long-term effectiveness or failure on alloy 2205.
For a lining system to be properly specified, the plant owner and contractor must give the lining manufacturer a detailed list of the vessel’s operating conditions and planned goals for usage, since factors such as temperature can affect the permeation resistance of the material. Certain chemicals used inside the vessel may also require a specific polymer base such as an epoxy, epoxy novolac, polyester, chlorendic polyester, vinyl ester, novolac vinyl ester, hybrid novolac, etc.
In addition, an effective lining requires the optimization of other ingredients such as wetting agents, inhibitors, promoters, flexibilizers and resins, among others. Together, they can impact critical performance issues like chemical and abrasion resistance, adhesion characteristics, application properties, crack bridging capability, impact resistance and even regulatory compliance. A system’s application characteristics such as high-build, single-coat options and fast cure rates can also provide the quickest return to service. Above all, lining formulations must undergo extensive laboratory testing and demonstrate effectiveness during in-service evaluation.
At about half the cost of alloy metal cladding, an appropriate lining system like International Paint’s Ceilcote 6640AR Ceilcrete and 140 Flakeline can be installed in just several days. While other outside factors can delay the installation process, owners can expect a successful repair project to be completed in about two to six weeks — with up to 30 years of service and only minor maintenance.
For more information about International Paint’s full range of lining systems, please contact Bill Slama at bill.slama@akzonobel.com or call (440) 234-2900 Ext. 114.
