Special Applications

Electropolishing of Large Vessels

Electropolishing the interior surfaces of tanks, mixers, and other large pieces of equipment requires the use of special equipment and techniques depending upon the product to be polished and the finish specifications. Sometimes the tank can be filled with solution and used as its own vessel for polishing; in other cases, the tank is partially filled with solution and is rotated around a stationary cathode to achieve the desired finish. Internal tank finishes in the range of 0.5 RMS units are reportedly produced in this manner.

The photo above shows a steam-jacketed vessel of 10,000 gallon capacity being electropolished to pharmaceutical specifications on the interior surfaces.

An investment of $25,000-$100,000 is typically required to establish the capability to electropolish tanks; the cost varies with the size of the tanks and the production volume.

Electropolishing of Pipe & Tubing

Manual or automatic machines are available for electropolishing the inside surface of stainless steel pipe. Lengths of pipe or tubing up to 30′ are handled in production volumes using such machines.

The principle involves pumping electropolishing solution through the pipe and using either stationary or moveable interior cathodes which distribute the current along the length of the pipe during the electropolishing cycle. The equipment can be designed to polish up to 20 lengths of pipe or tubing simultaneously. Machines have been built to process tube diameters ranging from ¼” to 6″. Finishes in the range of 3-5 microinches are achieved by these methods.

The typical investment for a semi-automated machine to electropolish tubing in the range of ¼” to 2″ in diameter varies from $80,000 to $200,000 depending on the number of different diameters to be electropolished and the production volume.

The electropolishing machine above is designed for simultaneous ID electropolishing of ten tubes, 20 feet in length. The capability of the machine includes selected tube diameters from ¼” to 1”. Typical production rates are about 2000 feet of tubing per shift. Finishes in the range of 3-5 Ra are routinely achieved. Machines have also been designed for larger size pipes up to about 6” in diameter.