Case Study 7: High Purity Sulfuric Acid

Problem: Impurities caused by permeation of metallic ions

A manufacturer of high-purity sulfuric acid used as a cleaning solution by several large producers of semiconductor devices required a lined tank container for international shipments and long haul shipments within the U.S.  The lining material would have to be resistant to 98% sulfuric acid and most importantly maintain the stringent purity requirements needed by the semiconductor industry.

A  68” I.D. x 198” straight side “tank container” had been previously coated internally with another manufacturers spray applied system which had failed to prevent metallic ion contamination of the load. The chosen lining system would not only have to acid resistant but also not impose capacity restrictions because of it’s weight, and be extremely resistant to both the thermal and mechanical shock associated with the container transportation.

Solution: PFA bonded sheet lining system

Electro Chemical forces stripped the internal areas of the container, neutralized the carbon steel substrate and grit blasted the surface to white metal.  All internal areas of the container were then lined with a 90 mil thick PFA knit glass backed sheet lining.  The lining was carried through all nozzles and out over all flange faces.  All seams were welded using a hot gas process which incorporates a 1/8” diameter PFA weld rod and PFA cap strip.  All internal areas were inspected and tested using a dielectric spark tester and helium leak tested to guarantee that the lining was pinhole free.

Benefit: Increased purity by reducing permeation of metallic ions

The PFA lining system has been successfully preserving the purity of the sulfuric acid product- with no fillers or plasticizers to leach out and contaminate the sulfuric acid. PFA has proved to be an excellent choice for handling of high purity corrosive chemicals.