In-situ relining saves shutdown at Dow Corning

A storage tank lining solution from Dow Corning.

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By Steve Beach

PlantServices.com

Dow Corning has manufactured silicone products at its Carrollton, Ky., facility for more than 35 years. In April of 2004, the lining of a spent sulfuric acid storage tank required repairs.

As a mechanical engineer in the Reliability Engineering group, I was faced with three options: 1) install a spray-on epoxy liner; 2) remove the tank and have it recoated with a spray-on fluoropolymer; or 3) have the failed lining stripped and a new sheet lining installed in the field.

My research indicated an epoxy lining would not withstand the process chemistry. The time and money required to ship the tank to be coated or lined at a contractor’s facility were deemed unacceptable, ruling out the second option as well. In addition, few ovens are available to cure the spray coating on a tank that size.

We believed that field installation of a fluoropolymer lining was our best bet. We already had two other vessels in the same application performing very well with KYNAR sheet linings, so we were sure we would get the desired life out of a KYNAR lining.

We contacted Electro Chemical Engineering & Manufacturing Co. (www.electrochemical.net) in late April, 2004 to consider the project requirements. I was aware of their quick response time, and their reputation in the industry as excellent sheet lining applicators and one of the few contractors offering field installation.

Stripped, repaired, blasted and inspected
“Within just a few days of the initial phone call, we were onsite with eight trained field technicians and the necessary equipment and materials to complete the job,” says Mike Bunner, Electro Chemical president. “The vessel was stripped, repaired and grit-blasted to a white metal finish in preparation for the lining installation. Our crews then began working around-the-clock until the KYNAR FLEX sheet was installed inside the vessel.”

Due to its location on the Ohio River in Kentucky, jobsite humidity had to be closely monitored during and after surface preparation and applying adhesive. To control the humidity and provide the required airflow for ventilation, Electro Chemical brought a large skid-mounted dehumidification unit that operated continuously until the job was done.

Lining goes up tight
Upon completion of the interior blast, the tank’s inner surface was primed and coated with an adhesive before installing the polyvinylidene fluoride (PVDF) sheet lining. The 90 mil-thick fabric-backed sheet lining system was bonded in place using Electro Chemical’s proprietary elastomeric adhesive system, which provides a flexible, tenacious bond capable of withstanding stresses from the differences in thermal expansion between the fluoropolymer lining and the carbon steel shell.

The lining was applied continuously to all wetted surfaces, including through the nozzles and out over the flange faces, to provide a pinhole-free corrosion barrier. The bond between the fluoropolymer and the substrate surface was tested in accordance with ASTM D-903.

“We provided Dow Corning with documented installation procedures, plastic welders well-trained on American Welding Society (AWS) standards, and plastic welds tested in accordance with ASTM C-1147 to ensure a quality installation,” says Dale Heffner, Electro Chemical vice president.

Once the lining was installed, internal areas were visually inspected and tested for pinhole leaks using a dielectric spark test. “This attention to detail and quality ensures a PVDF lining system of the highest quality,” says Heffner.

Trained technicians worked 24/7 on the project and completed it in two weeks. After final inspections, we brought the tank back online without issue. We expect to get 25 years of service from this lining.

Steve Beach, reliability engineer, Dow Corning, Carrolton, Ky., may be reached at steve.beach@dowcorning.com.