acid piping Technology celebrates 30 years of service

By: April Kabbash, Editor, Sulfuric Acid Today

When Ed Knoll started Acid Piping Technology (APT) in 1991, it was truly from the ground up—he even enlisted his sons, Alex and Fritz, to help pour concrete for the building during that summer. From those humble beginnings in Arnold, Missouri, Acid Piping Technology has grown to be a premier supplier of sulfuric acid piping, fittings, and tower internals around the globe. With excellent customer service and an unparalleled knowledge base, APT is known not only as a supplier of MONDI™ piping and equipment, but as a team of sought after experts in the field of acid piping. And what started as a family business has stayed that way – Alex is a member of APT’s sales team, while Fritz serves as Production Manager. As the company celebrates 30 years in the sulfuric acid industry, they took a moment to reflect on changes they’ve seen in the business, and what sets the company and its offerings apart.

Acid Piping Technology has focused on piping for the sulfuric acid industry for 30 years. What piping options are there for these facilities?

The choices of acid piping material in today’s sulfuric acid plants typically include MONDI™ high silicon ductile iron and high silicon stainless steel. There are other materials—such as Alloy 20, SS316, SS310, and Teflon®-lined piping—which can have specific uses within an acid facility and are not the best options for the contact areas of the plant. Those materials are better suited for smaller piping sizes, less than 3 inches (80 mm), such as sample lines and effluent drains. For hot, concentrated sulfuric acid in the drying and absorbing tower sections of the process, MONDI™ and high silicon stainless steel are the more appropriate choices.

What made Acid Piping Technology decide to focus on MONDI™ piping?

MONDI™ and alloy high silicon stainless steel products both work well when the plant is running within the recommended operating parameters. However, the true test of the real value of a sulfuric acid pip-

Two generations of the Knoll family work together to meet the needs of acid piping Technology’s customers. From left are ed, Fritz and alex Knoll. Fritz Knoll at age 15. Today, he serves as apT’s production Manager.

Fritz Knoll, left, and the late Jon Quarles, right, discuss the progress on apT’s headquarters in 1991 with one of the many craftsmen involved in the project.

ing system is how well it performs when the operating conditions go awry.

Over the expected service life of a typical sulfuric acid plant, it is not a matter of if, but when, a weak acid excursion will occur. MONDI™ is the only type of sulfuric acid piping system that can tolerate a weak acid excursion without suffering catastrophic damage.

First developed in 1983, MONDI™ is a proprietary material available from Acid Piping Technology and a registered trademark of Monsanto Enviro-Chem. The material evolved as the industry moved away from cast iron into ductile iron. While at the time the newer ductile iron was an improvement over brittle cast iron in some respects, the thinner-walled ductile iron piping corroded at a faster rate than cast iron. Though MONDI™ is in the ductile iron family, its metallurgy is an alloyed ductile iron with an increase in silicon and other alloying elements and thus an improvement over the previously used standard ductile iron materials. MONDI™ quickly became a preferred choice having over 800 plant systems worldwide. Today, at least 92 percent of the acid plants in North America use MONDI™ piping materials. Avoiding the problems of the thinner-walled materials available in the standard ductile iron industry, MONDI™ piping and fittings are produced with much heavier-walled sections providing a generous corrosion allowance. quires operating velocities no greater than 5 to 10 ft/sec depending on pipe size and conditions, MONDI™ has many advantages including: • Provides approximately four times the corrosion resistance of standard ductile iron. Of the choices available today, it is the only material able to handle the corrosive qualities of chloride and fluoride. • Suitable into the oleum ranges. • Has excellent ability to withstand weak acid excursions as compared to other choices. • Pipe walls are heavy, providing a generous corrosion allowance and long life. • Most fittings are designed with wall thicknesses heavier than 250 psi ductile iron patterns. • MONDI™ utilizes simple bolt together flanged connections. • Much less expensive than high silicon stainless steel by 1/3 to 1/4 the cost. • MONDI™ doesn’t require chaplets in fittings or pipe.

How reliable is MONDI™ piping in a strong acid environment?

It is in the best interest of sulfuric acid plant owners and operators to have the piping supplier provide the “available corrosion allowance” for the piping material that you choose. Generally speaking, the available corrosion allowance for MONDI™ piping is approximately one half of the original wall thickness.

As an example, a 24” MONDI™ Flanged Short Radius 90 Degree Elbow has an initial wall thickness of 1.16”, so one half of this thickness would be 0.58” of available corrosion allowance before the item should be considered for replacement.

The yearly corrosion rate of MONDI™ is approximately 5-8 mils (0.0050.008”)—so if you have 0.58” of available corrosion allowance, and you use less than 0.01” of wall thickness per year, you can see how long this MONDI™ elbow will last in sulfuric acid service.

By comparison, the available corrosion allowance for alloy high silicon stainless steel is approximately 1/32” (0.03125”). This miniscule available corrosion allowance leaves you very little margin for error.

The corrosion resistance of high silicon stainless steel varies depending on acid strength. Corrosion rates increase dramatically as the acid concentration decreases, and rates below 90% can result in catastrophic failure, since you only have 1/32” of available corrosion allowance to work with. Higher corrosion rates in the 60-90% concentration range are likely attributable to insufficient oxygen available to passivate the alloys.

Can you tell us a little bit about your service and customer satisfaction initiatives?

At APT, we do everything we can to make the purchase and installation process easy for our customers. MONDI™ arrives from several large U.S. inventories prefabricated as a flanged system ready to install with basic hand tools. Field fabrication or modification can be done by most machine shops. Custom-fabricated MONDI™ spools and the mating fittings can be shipped the same day if required.

Both the chemical composition and manufacturing techniques used to cast MONDI™ have evolved to the point where APT can now provide a virtual lifetime warranty on MONDI™ strong acid piping. The 30-year warranty applies to all MONDI™ fittings 6” and larger. It provides nocharge replacement for the first 15 years and pro rata for the balance; and it applies to new grass roots plant construction with temperatures and velocities in accordance with published guidelines.

As Acid Piping Technology heads into its fourth decade serving the sulfuric acid industry, the company will continue to bring the highest-caliber service and products to its growing list of satisfied customers.

For more information, please visit www.acidpiping.com. q

MONDI™ piping is a valuable option for sulfuric acid plants. apT can provide specialty items, like this large-diameter S02/SO3 damper valve, to fill any need.