Document Ne8LBoDb5Yj97bzv1rmzL5MvE

^ , |a , i , valve. This 8" Inconel disc, with Monel retaining rings spot welded at the disc periphery to eliminate torquing prob lems, was positioned below a remov able stainless steel knife blade unit. As the disc buckled upon overpressure it was pierced by the knife blades to allow pressure relief. The disc held in place by nickel-piated flanges and the knife blade assembly were designed as a unit. Set pressure of the disc was 63 psig at 350F, that is, the system pressure was 84% of the disc rating. Another interesting application arose in a heat exchanger where light gaso line hydrocarbon at 1000 psig on the tube side is thermaily contacted with steam at 200 psig on the shell side. Obviously, a tube failure could admit the 1000 psig pressure into the conden sate system with possibly damaging results. The shell is protected by two reverse buckling discs in series, the pair discharging directly into the' flare sys tem and capable of being isolated by two shut-off valves. The first disc was exposed directly to the steam pressure. If this disc should fail by fatigue or other than emergency reasons, the pressure would be contained by the second disc with no unnecessary loss or distur bance. Both discs were designed for approximately 200 psig. An emergency failure immediately would blow both discs, thus protecting the low pressure system. The cavity between the discs was put to use, and was monitored by a max imum reading, two pointer, pressure gauge which showed existing pressure at any time as well as most recent high reading since manual reset. A positive gauge reading would indicate leakage, requiring replacement of the disc. Measures similar to the above exam ples have been extended throughout this large plant and the program is continuing. Results The discs, where used with safety valves, have provided a 100% seal against the corrosive effects of the process gases and vapors. The relief valves now remain clean and free from residue, Repair costs are substantially reduced. From the environmental standpoint, the escape of hydrocar bons to the air or flare system has been stopped. A considerable labor savings has been effected in valve maintenance costs. On the primary crude column de scribed, after nine months of continu ous service, the disc still is intact. The 100% protection of the relief valve led to the decision to install similar reverse acting knife blade types under the other valves. In the case of the heat exchanger, all relief valves with attendant mainte nance, and repair costs have been avoided. The in-series method of disc installation protects the equipment from incursion of high pressure and the maximum reading gauge provides a more constant self-checking security measure. Shell feels that this ongoing program of the planned use of rupture discs used both alone and in conjunction with relief valves is substantially reducing maintenance costs. Shell intends to continue in this direction. Stocks are maintained and the plant engineering force has developed its own criteria for application. The ZAP reverse buckling knife blade type disc described in this story is a product of The Continental Disc Corpo ration, 4103 Riverside N.W., Kansas City, MO 64150. Circle 125 opposite last page. The S-90 reverse buckling disc also used at Shell is a product of BS&B Safety Systems Inc., 7465 46th St., Tulsa, OK 74145. Circle 126 opposite last page. WE'RE ON THE LEVEL! NOW YOU CAN HAVE A COMPLETE, EXTERNALLY MOUNTED. LEVEL/ WEIGHT MEASUREMENT SYSTEM FOR YOUR BIN, TANK, SILO, OR HOPPER FOR LESS THAN $500. The new Kistler-Morse WEIGHLITETM uses the unique Kistler-Morse Microcell strain sensors that have been proving themselves for years under tough industrial applications. With the externally mounted sensor, the WEIGHLITE System can't be damaged or corroded by material in the vessel. WEIGHLITE can be installed with out interrupting normal operations. mu Sf ` Sub|l^ve^r^i:a^fpecisions ' lppLLARS<; &rfw8<wHrL^a?h^a4lh^dri\5^</.f9moyL^L^lrT'p.th;er<^greiional:aart;-- HP^i.TtcSUbstacicC0ot>o'rA9t(TS<^y,^~tn1?>iersmadi3;hjtljst---.nojrrous!avy i<J GET THE FACTS. Contact KistlerMorse Corporation, 13227 NorthrupWay, Bellevue, WA 98005. Phone 206/641-4200 Kistler-Morse Circle 127 opposite last page. $0 ITRj Circle 128 opposite last page. AUGUST 1981 PLANT SERVICES 29 PCB-ARCH-EXT0376435