Galvanizer Cuts Pickling Costs with Tailor-Made Inhibitor
Originally Published in Modern Metals October, 1997 A Trend Publication
Galvanizer Cuts Pickling Costs with Tailor-Made Inhibitor
Disposable dollars slashed by more than 50 percent; zinc consumption also reduced.
At American Galvanizing Co. (a division of A Reco Industries, Inc.), a job shop galvanizer in Folsom, New Jersey, steel is galvanized in a three-part process: surface preparation, hot zinc dip and finishing. In the preparation step, steel is initially caustic treated to remove oil and grease, and then pickled in an acid bath. The acid pickling cleans the steel to the point that no mill scale or rust subverts effective coating with the molten zinc. This is critical to the galvanizing process.
The natural result of pickling is spent acid, a hazardous waste. Considering the high charge for waste disposal, pickling costs are generally measured in terms of the haul-off cost of the spent acid/metal salt solution, as well as the cost of replenishing the acid.
In a two-year experiment, from 1994 through 1996. AGC cut haul-off costs by 53 percent by employing an acid inhibitor. Though inhibitors are frequently used with the more aggressive sulfuric acid pickling baths, AGC pickles in hydrochloric acid (HCI). As a point of reference, the galvanizing industry is equally split on its pickling medium: 50 percent sulfuric acid, and 50 percent hydrochloric acid.
American Galvanizing made its choice on the grounds that HCI less likely to over-pickle and eat into the base steel than sulfuric acid, and is more user-friendly to the employees. Traditionally, HCI pickling has seen less use of inhibitors because it is not as aggressive as sulfuric acid. This thinking, however, can potentially lead to such drawbacks as an increased quantity of spent acid created, and a higher ratio of acid used to metal processed.
Acid inhibitors allow the process to use a stronger bath, which works quicker without the fear of over-pickling. Additionally, the inhibitors reduce fuming by lessening hydrogen evolution. However, in the galvanizing industry many processors have chosen not to use inhibitors because their experience had not been positive.
AGC’s attempt to satisfy state government guidelines led to its successful experiment with Rodine acid inhibitors as developed and supplied by Henkel Surface technologies (HST), Madison Heights, Michigan. The inhibitor selected for the HCI pickling process is Rodine 1150.
AGC’s Full Process
New acid is brought in at about 30 percent concentration, placed in a pickling vat which is half full of water, creating a 15 percent HCI bath. After preliminary degreasing, steel is immersed in the pickling tank. Time in tank is calculated and set by AGC based on several factors, including strength of the HCI, and condition and physical dimensions of the steel. Once the steel is fully pickled, it travels through a flux tank containing zinc ammonium chloride. This removes oxides and prepares the steel for the proper chemical reaction to occur in the molten zinc at a temperature between 825 and 850F. After just a few minutes, the steel is removed and allowed to cool. It is then inspected and custom packaged as specified by the end-user.
“Indirectly, it was the state that got us thinking about inhibitors again,” said American Galvanizing’s president, John Gregor. “In 1993, New Jersey asked anyone in manufacturing who was listed as dealing with hazardous material to develop a five-year plan for reducing their waste systems. We advised the state we would kick off our plan by reconsidering the use of inhibitors to reduce the hazardous waste material, which we produce by the nature of our process.
“At the outset, we want to Henkel Surface Technologies and they provided us with the multi-use Rodine inhibitor,” he continued. “As we began using it we saw some improvement. However, we also spotted some white crystals forming on the tank and contracted HST. After taking several samples, it was determined that the (multi-use) product was better suited for sulfuric acid and not necessarily for HCI, particularly in the presence of high levels of iron and zinc. As a result, Henkel Surface Technologies introduced the Rodine 1150 inhibitor for a plant trial with our AGC bath. Since then we have had no problems.”
Halving Waste Removal Costs
With the use of Rodine 1150l, from 1995 through 1996, AGC has had a decrease of 25 percent in liquid waste removal, which netted a 27 percent drop in waste removal costs. Over the longer period of 1994 through 1996, using both initial and current Rodine formulation, AGC has experienced a cumulative 33 percent drop in liquid waste removal, which relates to a 52 percent decrease in actual costs.
Records for the experiment were kept for both acid use and acid waste. The first set of numbers reflected the amount of acid used relative to tons of steel produced in a year. The second set recorded the amount of spent acid that was hauled off relative to the tons of steel processed.
“These numbers were the only way of being certain that we were comparing apples to apples,” Gregor commented. “As a jobber, all that counts is usage in terms of tonnage processed. The good news is that in the last two years, we’ve done more tons of steel each year than we did in the previous year, and we’ve had fewer haul-offs each year. So our acid usage is less and we’re actually putting through more product. The only thing that has changed in the last two years is that we have employed the use of the inhibitor.”
Using Less Zinc
That was not the only positive result for AGC. The company noted that by not over-pickling, it was able to maintain a more consistent profile by opening fewer pores in the steel. This meant that AGC was actually using less zinc to achieve full, high quality galvanizing, since less zinc entered the pores in the steel. “If you’re putting through millions of pounds of steel, as we do, using less zinc– even in minute amounts—makes a notable difference,” Gregor stated.
AGC’s products serve many industries, including communications, transportations and petrochemical. In the communications industry parts are for towers, both large and small, as well as the auxiliary components that support the cellular, CAT, and HDTV industries. In the transportation field, AGC galvanizes parts for highway sign supports, sound barrier components, catenary structural, and a small amount of reinforcing bars for highway construction.
Does AGC see future growth? “Our infrastructure continues to be in dire need of refurbishing, and as long as wither federal highway appropriations or state appropriations continue, we will continue to grow,” said Gregor. “As for our use of the Rodine 1150 inhibitor being an experiment, it’s now SOP at American Galvanizing.
