EPS vs. Acid Pickling: Line Operations

EPS ‘green’ pickling offers more than environmental and economic advantages. It provides important advantages in flexibility and simplicity of operation over push-pull acid pickling. Some of the most notable are explained below:

ACID PICKLING

EPS PICKLING

Descaling Consistency

For low carbon material, the acid immersion time and line speed are routine enough that descaling is generally reliable. But for high carbon, AHSS, silicon steel, etc., there is a lot of variability – overpickling and underpickling is common. For these grades acid picklers often rely on human visual inspection, and that’s not always good enough.

EPS descaling is always consistent. The inline surface inspection system correlates surface brightness with level of descaling. It automatically adjusts line speed to achieve and maintain the desired level, so there’s no guesswork and no human judgement involved. Most important, there’s no over/under pickling.

Line Stop

A line stop while acid pickling a coil is a real problem. Pickling stains, like that shown above, will occur over a long section of strip. In some cases, overpickling and an etching of the steel substrate can occur and the coil will probably have to become secondary material.

A line stop during EPS pickling, no matter what the duration, has little impact on strip appearance (see above). The affected area is small – just what’s under the slurry stream at time of stopping. And restart from a brief line stop takes less than 1 minute.

Tension Leveling

Acid pickling is not a tight line process – the strip must droop in the acid tanks. The tension needed for control of uncoiling and recoiling is often provided by large, high-horsepower bridle rolls (see above). They do tension level the strip, but add significant cost and length to an acid pickling line.

EPS is a tight line process. It uses forward tension generated by the recoiler with back tension generated by the uncoiler, scale breaker and leveler to reliably tension level the strip. This simple arrangement is a standard feature of the line, so there’s no added cost, space or complexity.

Standby

The economics of acid pickling are tough. You don’t often shut down a line because restart is difficult and expensive. But keeping the line in standby (say, over a weekend) requires lots of energy to keep the acid tanks heated, so it’s expensive as well.

Starting up and shutting down an EPS pickling line is ‘push-button’ easy. When the EPS line is put in standby mode, the only cost is inexpensive electric warming of the filtration water. And restarting the EPS line from standby mode takes  about 8 minutes.

EPS Operations and Maintenance Instructions

All technical documentation for operation and maintenance of an EPS Cell is available online. That assures the user is always working with the latest information, plus the documents are searchable and they can be viewed right on the operator display.

EPS technical documentation includes detailed maintenance schedules, information on specifications, quantities and sources for supplies and consumables, plus links to videos that demonstrate maintenance procedures. During EPS line commissioning, the TMW service technician trains customer operation personnel directly from the online documentation, so they understand both the use of the manuals and the instructions they contain.