Alloys of the reactive metal family typically exhibit superior corrosion resistance for many highly corrosive chemical processes. The common reactive metals – titanium, zirconium, and tantalum – are broadly used by the Chemical Process Industry when highly aggressive corrosion management is a concern. Alloys of these metals are typically selected to optimize availability, manufacture reliability, fabrication, performance, and cost. To further minimize cost, particularly when heavy wall sections are required, explosion clad is the dominant material of choice.
By John G. Banker, Clad Metal Consultants, Inc.
Reactive metal clad plates for pressure vessel manufacture are produced by several explosion-clad manufacturers globally. Due to market and technical challenges, over the past 60 years none of the clad manufacturers or pipe manufacturers globally have offered a clad option for the reactive metal piping components that accompany this equipment. Recently NobelCladTM introduced DetaPipeTM reactive metal clad pipe and related piping components, filling a highly onerous supply chain void.
Historical Background-Reactive Metal Clad
Typically, alloys of the reactive metal family exhibit superior corrosion resistance for many highly corrosive chemical process applications. The numerous technical advantages of these metals, including exceptional corrosion performance, were recognized early in the 20th century. In the following years, led by the emerging military, aerospace, and chemical companies, reactive metals became a well-respected material of choice for numerous high-performance applications. Superior corrosion resistance was a critical feature these industries often relied upon to overcome high-tech challenges. When considering the broad range of reactive metal elements, titanium, zirconium, and tantalum were chosen to optimize corrosion performance, availability, fabricability, and performance.
However, cost was a significant obstacle to developing many early chemical industry corrosion control applications. This was a particular concern for pressure vessels and accompanying piping where heavy wall structures were necessary. Applications requiring significant reactive metal thickness for strength reasons were rarely found to be commercially viable when constructed of solid reactive metal components.
During the 1950s, process equipment fabricators and engineers recognized that clad products, consisting of a thin corrosion-resistant alloy layer bonded to a much heavier steel base metal, would be necessary for the cost-effective construction of heavy equipment. These clad products included the full spectrum of metals, ranging from simple stainless steels to nickel alloys to reactive metals. The development of joining technology was relatively straightforward for metals like stainless steel and nickel alloys. Roll bonding and weld overlay quickly gained broad acceptance for clad plates. On the other hand, these joining technologies proved to be highly unsuitable for making composite metal clad plates from reactive metals. Brittle intermetallics formed at the interface, resulting in a deficient bond quality, unfit for forming, fabrication, and use. The 1959 discovery of explosion welding, a cold bonding technology, presented a reliable solution for manufacturing reactive metal clad plates and components.
By the end of the 1960s, explosion welding technology had been extensively codified, and the process was used broadly to manufacture clad plates with most industrial alloys, including reactive metals. Reliable design and fabrication methods for titanium, zirconium, and tantalum-clad vessels were developed, providing a proven platform for manufacturing reactive metal pressure vessels and similar equipment.
Nowadays, equipment constructed of reactive metal clad plate is used extensively worldwide. Global production of titanium, zirconium, and tantalum-clad plates for pressure vessels and similar applications typically exceeds 100,000 metric tons annually.
Both vessel size and pressures as well as piping size or requirements have grown significantly. Purified Terephthalic Acid (PTA) production and similar plants require a large tonnage of titanium clad for the chemical processing industry. A PTA oxidation reactor typically requires as much as 1,000 metric tons of titanium clad, wall thicknesses are often in the range of 3 to 4 inches (75 to 100 mm).
Pressure-leaching autoclaves for the hydrometallurgy industry similarly require around 1,000 metric tons of titanium clad each and operate at significantly higher pressures. Zirconium clad is used extensively in acetic acid plants and other polymer processes. As with the PTA process vessels, size and pressure have grown considerably. Piping for this equipment ranges up to 30 in (750 mm) NPS, with wall thicknesses often in the 1 to 2 inches (25 to 50 mm) range.
Reactive Metal Clad Pipe
The history of reactive metal clad pipe has been quite different from that of clad plate. The same explosion welding technology developed for a flat clad plate proved equally effective for producing clad concentric cylinders. For example, by the late 1960s, NobelClad began the promotion of reactive metal clad pipe and other cylindrical-clad components for the chemical process industry.
However, at this early stage in the growth of the reactive metal clad vessels, pressures were relatively low, and equipment and related piping were quite small by today’s standards. Solid alloy pipe was generally available in smaller sizes and schedules for the basic grades of titanium (Gr 2) and zirconium (Gr 702). These piping sizes and thicknesses were rarely large enough to benefit from the potential cost savings of clad. Like many novel new products of the era, concentric reactive metal clad components were a proven product seeking a need in what was then a nonexistent marketplace. Within a few years, efforts to promote reactive metal clad pipe were discontinued. Plans to install the unique equipment needed for handling pipes were scrapped.
By the early 2000s, the size and pressure of reactive metal clad equipment had advanced considerably. The significant need and cost savings of reactive metal clad pipe had become real, but there were no reactive metal clad pipe producers. For example, clad companies, such as NobelClad have amassed significant propriety technology for managing the complexities of reactive metal clad products. This unique technical knowledge has positioned them with the proprietary technology necessary to develop further and modernize clad pipe production capabilities for reactive metal clad pipe products.
For example, the DetaPipeTM offers a unique and proven piping product line that combines the superior corrosion resistance of reactive metal alloy cladding with the strength, durability, and low cost of steel. To simplify installation, straight pipe and related piping components are supplied as spools for mechanical assembly in the field. The bore and flange facing of the spools are integrally clad with the specified reactive metal cladding alloy. The steel pipe substrate can be almost any commercially available steel or stainless steel compliant with ASME/ANSI dimensional standards. The bonding technology provides unequaled high strength and exceptional fatigue performance while at high pressures and elevated temperatures. The bonding process does not alter the optimized corrosion properties of the reactive metal alloy or the mechanical properties of the steel base metal. Figure 1 shows a pipe spool typical of those for installation in new construction or replacement of aging components.
Considerable product testing, both analytical and physical, has been performed during the ANSI B31 qualification of the DetaPipeTM. FEA testing validated by third party independent witness confirms the suitability to withstand applicable mechanical loads during service for this product. Extensive fatigue cycle testing has been performed at elevated temperatures and pressures. This work has been predominantly performed on zirconium-steel piping, broadly considered the most challenging metal combination. Field testing is ongoing on several projects globally as well.
In general, piping installations require fitting components in addition to straight-run piping. The most common are elbows, tees, and reducers. These components are provided as specifically designed clad spools. Elbow spools are produced in 3D, 5D, and 10D sizing, Figure 2. Clad tees are produced with the single-leg diameter limited to 70% that of the straight-through legs. Valve components are typically provided using solid alloy valves welded into solid alloy spool end assemblies.
Filling the “Void” in Reactive Metal Piping Options
In general, pipe accompanying reactive metal pressure vessels and similar equipment should be of the same alloy and grade as the pressure vessel components to provide equivalent corrosion performance. For some reactive metal applications, pressures are low; vessel sizes are relatively small; piping is typically Schedule 10 to 40; and alloy requirements are commercial pure grades, commonly Titanium Grade 2. For these installations solid alloy piping is often available in the global marketplace with reasonable delivery times.
When the piping needs are outside these criteria, supply chain issues can become significant with minimal supply options for pipe diameters, schedules, alloy grades, and fittings. Frequently, the project team has few options other than mill production of the solid piping components. This typically includes excessive minimum order requirements and prolonged delivery. Down grading to an alternate alloy with inferior performance may be the only option. Alloys other than the basic chemically pure grades can add considerable complexity to the supply problems. Rarely is there more than a single supplier option for the solid alloy; price and delivery often reflect this situation. This has been the traditional commercial “void” in the reactive metal supply chain.
The cost benefits of reactive metal clad pipe versus solid alloy are similar to what the buyer faces for the adjacent reactive metal equipment. Clad can save considerable money for large, heavy piping spools and related fittings. As discussed earlier, the increase in the size of pressure vessel equipment over recent decades has been quite significant. The cost benefits of clad versus solid alloy pipe can be enormous.
Conclusion
A reactive metal clad pipe, such as the DetaPipeTM provides a proven, reliable alternative for the construction of highly corrosion-resistant chemical process equipment. Like explosion clad plate products, the novel pipe product line typically provides cost savings and shorter delivery times. Whether for new construction or repair and upgrades, the product fills a major void in reactive metal pipe supply options.
