R. W. KIEFER Research Department, Union Carbide Chemicals Co., Division of Union Carbide Corp., South Charleston, W. Va.
T w o PRINCIPAL FACTORS are involved in safety a t high pressures: mechanical and human. Safe practice regarding mechanical factors can be obtained by taking all precautions to prevent accidents, including anticipation of human errors, and then being prepared for an accident occurring from the unexpected. The human factor can be controlled only by training and practice. Major Equipment Design of major equipment is the joint responsibility of a reputable manufacturer and the purchaser. If told what is wanted and what is expected of the equipment, manufacturers can comply with requirements and submit designs for approval and correction. I t is important to insist on relief devices that have the proper capacity to protect equipment. H i g h Pressure Connections. The coned interference type of fitting, using a collar screwed on the tubing and a gland nut, is the most common joint used in high pressure work. A common error is threading the tubing to such a length that the gland nut has an engagement of only a few threads; this weakens the joint considerably. If thread length on the tubing is too short, the collar
Safety at High Pressure Losses from an accident can always be prevented but never cured keeps the coned faces from making contact and results in a leaking joint. Another common error is the “heavy hand,” or tightening the gland beyond the point needed for a leakproof joint. This results in either extruding the tubing into the fitting, sometimes closing the opening in the tubing, or cracked gland nuts. T o prevent this, open-end wrenches are used with the handles cut to a length of 31/2inches so that leverage applied to gland nuts is reduced to a minimum. Gages. Gages, whether used in operating or barricaded areas, should always be of a special type with a solid front and a blowout back. If two types are used, inevitably a regular gage will be used in the operating area and cause an accident. Glass fronts on gages should always be removed and replaced with either plastic or laminated safety glass. Bourdon tubes should be welded into sockets, rather than sweated or brazed, and of such composition to resist corrosion and consequent failure. Gages
should never be used a t more than two thirds and preferably at one half their rating. Used in this manner, they will remain in calibration longer and their life will be increased considerably. For replacement while the system is under pressure, all gages should have shut-off valves near the system under pressure. Also they should be protected by excess surge valves, needed in case of a gage failure to prevent loss of material in the system and, if the gage is in the operating area, to protect personnel. Low pressure gages, part of a high pressure system that can be exposed to pressures above their rating by error, must always be mounted in the barricaded area. Check Valves. Check valves should be used in a high pressure system for protecting auxiliary low pressure equipment such as feed cylinders and inert purge gas systems. They are the life preservers when the valves connecting this equipment are inadvertently left open. Low pressure systems should also
A vessel barricaded with a 5-inch concrete wall and protected with a rupture disk left: plug and cap were blown off by a detonation Center: the concrete wall was spalled on the operating side Right: plug and cap were blown through fence and landed on the opposite river bank 375 feet a w a y
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An explosion that was barricaded with a 16-inch concrete wall and blasting mat Left, Concrete on the cell side of the wall was broken, but not spalled on the operating side Center, Plug and cap were blown into a hillside. Transite i s in the foreg round Right, The blasting mat was intoct, even though Transite above the roof Yras shattered
be protected by low pressure rupture disks. When two materials, such as a catalyst and a reactant or otherwise incompatible liquids, are pumped into a system, the two lines should be protected by single and preferably by double check valves. Rupture Disks. Rupture disks, the best protection against slow to moderate pressure rises, should be installed on every piece of high pressure equipment. They will not, however, protect against detonations. Most systems should be protected by more than one disk so installed that all of the equipment is protected, regardless of plug-ups or closed valves. A valve should never be placed between a reactor and a rupture disk. Rupture disks should be installed on all feed pumps and compressors, between the instrument and the first valve in the system. Many pumps and compressors have been saved by this type of protection. Barricading
Barricading high pressure equipment is often minimized and sometimes overlooked. I t is protection for the accident that is not going to happen and many types have been described in the literature ( I ) . Heavy barricading is required only when there is a potential highenergy release. Hydraulic testing, for example, requires only minimum shielding. The high pressure building a t the Carbide research center in South Charleston, W. Va., is of conventional over-all design. I t consists of work areas, operating area, and high pressure cell area. The high pressure area is separated from the operating area by a 16inch specially reinforced concrete wall containing many 3/4-inch steel pipes for bringing all services to the cells. Those pipes not used are capped on both sides with steel caps. The cell partitions are of a welded sandwich construction composed of two 3/4-inch steel plates on 4l/2-inch centers with sand between them. Most of the cells are completely
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open and the few which are closed have blowout walls of Transite. A newer and better material for this purpose is sheets of laminated glass fiber-polyester plastic. I t is light in weight, does not shatter, and transmits light. The roof of the cell area is of Transite protected by blasting mats woven of 3/4-inch multistrand steel cable. The pressure side of the building faces a hill about 100 feet high. Recently, work has been started for a building on the property and the hill has been cut down some 40 feet. T o protect this new building, blasting-mat awnings have been installed to limit the trajectory from the high pressure cells to the remaining portion of the hill. An installation for another department of this company, on a flat site with operating areas directly behind the building, was handled in a different manner. Blasting mat was hung from a steel framework so a shock wave could be dissipated but there was no outlet for shrapnel in case of equipment rupture. Accidents That Have Occurred
One accident has occurred in a laboratory and three behind barricades. After the first laboratory accident in 1939, no piece ofhigh pressure equipment has been operated outside a barricade. Fortunately just before this accident, the personnel had just left the room. However, one person did receive bruises from something blown through the door, but this is the only injury incurred as a result of high pressure work. It was calculated that this vessel ruptured a t 30,000 to 35,000 pounds. Jn another accident, the plug and cap were blown from a rocking bomb by a detonation. The equipment was in a barricade of 5-inch reinforced concrete, and the explosion spalled the concrete on the operating side of the wall. Therefore, in the present building, the barricade wall is of 16inch concrete. A rupture disk of 5000 pounds per square inch protected the
INDUSTRIAL A N D ENGINEERING CHEMISTRY
equipment, but gave no protection from the explosion. When a detonation blew the plug and cap from a vessel in the present building, recoil of the vessel broke some concrete on the cell side of the 16-inch wall, but there was no spalling on the operating side. The threaded section of the bomb a t the base of the threads expanded 3 / ~ inch from its original diameter of 43/s inches. A three-liter rocking bomb was ruptured by a detonation. This bomb was protected by a 6000-pound-per-squareinch rupture disk. The rate of this detonation was so fast that the Bourdon tube in a 500-pound-per-square-inch gage connected to this bomb by a 20-foot coil having an inside diameter of 3 / 3 2 inch tubing was not damaged. Considerable shrapnel was thrown by this blast but no damage was done to the concrete wall or to the dividing walls. The outer layer of a ll,’d-inch, 5-ply bulletproof, sight glass was cracked, but none of the other four layers were damaged. The blasting mat roof protection was intact although the Transite roof was fractured. Conclusion
Respect, but do not fear high pressure equipment. Always fear the reaction that is taking place in the equipment. Because a reaction has been made several times before without mishap does not mean that there is no danger. Make every high pressure setup safe as possible-even expect the human element to fail, and then be prepared by barricading. Literature Cited (1) Lobo, P. A., Porter, R. L., Sliepcevich, C. M., IND.END.CHF.M.48, 841-5
(1956). RECEIVED for review April 8, 1957 ACCEPTEDSeptember 14,1957
Division of Industrial and Engineering Chemistry, High Pressure Symposium, 131st Meeting, ACS, Miami, Fla., April 1957.
