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At the Chem Show, recently held in New York, fabricator Roben Manufacturing Inc. presented the world's first-ever jacketed reactor made from HASTELLOY® C2000. This was certainly an eye catcher, drawing admiring glances from end users, engineering companies and competitors alike. Intrigued, Stainless Steel World traveled to the Roben's headquarters and manufacturing facility at Lakewood, New Jersey, USA, to talk to President Mr. Gary R. Huhn about the company's activities.
The World's first jacketed reactor made from HASTELLOY® C2000 was shown by Roben at the November 1997 Chem Show in New York. Jacketed reactors have in fact proved a lucrative business for Roben and are currently good for over half the company's annual turnover. The reasons for Roben's success in this area are outstanding design and fabrication procedures, believes Mr. Huhn: "For example, the traditional approach is to form the jacket coils from sheet material. This creates unnecessary butt welds which are prone to corrosion. By using strip as our starting material we can significantly reduce the number of butt welds, providing a qualitatively better product." Mr. Huhn further explained that at Roben each coil is pre-formed to shape and then slid in its entirety over the reactor vessel, whereby tolerances are often as low as 2mm! To achieve such a snug fit, Roben re-rolls each vessel after fabrication to ensure it is as round as possible. Once the coil is properly aligned and spaced, it is tack-welding to hold it in place. The subsequent welding procedure is yet another area where Roben applies only the best technologies. A root weld is performed using an automatic TIG process and the weld completed in a second pass (submerged-arc or MIG), which guarantees full penetration welding. Mr. Huhn: "Full-penetration welds are generally to be preferred, especially when the vessel will experience heating and cooling cycles. Under these conditions the standard fillet-type welds are prone to cracking." Dye-penetration, X-ray and boroscope analysis are used to confirm the integrity of the resultant welds, which burst tests have shown can withstand pressures exceeding 6000 psi(by comparison, fillet welds often crack at around 2500 to 3500 psi.) Roben can currently produce jacketed coils in 1 1/2", 3", 4" (180 degree half pipe) and even 6" (130 degrees) diameters. This later size was first realized to meet a customer's special request, who found that the standard 3", 180 degree coils on an existing vessel did not offer sufficient heat transfer capacity. Roben's 130 degree geometry with a 6" coil solved the heat transfer problem and also yielded extra benefits too. These included lower cost, as less material and less welding was required for the coil, and also a stronger vessel, as the coiled geometry provides wall reinforcement. Finishing off his discussion on Roben's jacketed reactors, Mr. Huhn said that the company has recently developed jackets with twin, parallel coils. Obviously, the pitch of a parallel coil is greater than that of a single coil, and the trick of the trade here, he said, is in understanding how to prevent the coils from twisting during manufacture. Vessels with parallel coils are used for applications where fine control of the heat transfer is imperative, and in fact Roben has had orders for four such vessels for a joint venture between Fluor Daniel and Witco. The specifications called for tanks in 316 stainless steel with with a 15-25 Ra internal finish, with 180 degree parallel coils with full penetration welding.
Material Selection
When asked where Roben procures its material requirements, Mr. Huhn mentioned that the company has good relations with leading stocking distributors and steel mills. In addition, a modest supply of popular grades is kept in stock. Coupled with comprehensive fabrication skills - including the ability to form vessel heads - Roben can therefore provide expedited delivery times, reduce fabrication costs and control entire projects in-house. In some instances Roben has fabricated stainless steel vessels within 24 hours! Other services which Roben can provide include metallurgical and corrosion advice, liaising with the steel mills if necessary to ensure the right material is selected for a specific application. As a prelude to an upcoming project, for instance, Roben is conducting corrosion tests with weld coupons of C2000, Alloy 686 and Alloy 59 placed in situ at a customer's premises. Once the optimum material has been determined, Roben hopes to re-fashion much of the plant using that material. In some circumstances, Roben's advice can also save the client money. For example, during Stainless Steel World's visit we saw a 3" thick stainless steel vessel in the make. Originally specified by the principal clad material, Roben calculated that the construction price for a solid vessel would be fairly competitive. The customer, based in the food and beverages industry, quickly opted for the more robust solid stainless steel, especially when shown the projected lifetime maintenance bill for a carbon steel shell. In another example Roben advised a client to select weld-overlaid components instead of using solid material. Mr. Huhn: "Obviously, all the wetted surfaces must offer the same corrosion resistance. However, for nozzles and stub ends it may be more cost-effective to use cheaper carbon steel components and weld overlay with a CRA. Moreover, as the mechanical strength of carbon steel outperforms that of HASTELLOY®, we can decrease the thickness of the overlaid component, which builds in extra economics for the vessel."
(This article originally appeared in Stainless Steel World, March 1998)
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