Accidents Involving Compressors, Hoses, and Pumps - …cntq.gob.ve/cdb/documentos/quimica/222/7.pdf · Accidents Involving Compressors, Hoses, and ... Compressor System Details The

CHAPTER 7

Accidents InvolvingCompressors, Hoses,and Pumps

Compressors, hoses, and pumps are very common, vital pieces of equipment in chemicalplants, petroleum refineries, and terminals. Each of these pieces of equipment regularlyconveys chemicals from one location to another in a safe manner. Each element serves theindustry very well, but each must be properly specified, correctly installed, and maintained.Some accidents involving these industrial components are detailed below.

Reciprocating Compressors

Reciprocating compressors are widely used in the chemical, oil, and gas industries for mov-ing compressible fluids reliably. Reciprocating compressors have the advantage over othertypes of compressors (e.g. centrifugal and rotary) when it comes to handling wide-capacityswings and generating a high-discharge pressure. [1]

When properly designed, installed, and operated, these compressors serve well.However, there are stories about problems with liquids from condensation of saturatedvapor streams entering the suction side of the compressor. The typical reciprocating com-pressor design is not very tolerant of an accumulation of liquids in the suction. There is thepossibility of blowing the compressor heads off if the compressors are subjected to incom-pressible fluids.

Just like any other piece of important operating equipment, the operator must under-stand the details of the equipment and its limitations. Trevor Kletz offers many excellentshort stories in his latest book, Still Going Wrong. He provides cameo descriptions ofprocess-plant errors with a message. [2]

Mr. Kletz provides a story about a packaged unit containing a reciprocating compressor.The compressor was started in error. The discharge valve was in the closed position, andthe pressure increased until the packing around the cylinder rod blew out. This compres-sor was equipped with a relief valve that was merely a sentinel to warn the operator to takeaction. The sentinel was incapable of relieving the full output of the equipment. It is notan acceptable design standard today, but this example supports the need for availableprocess-safety information on all equipment. [2]

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A Piece of Compressor Water Jacket is Launched

In the early hours of the morning in June 1997, a compressor head water jacket violentlyruptured and blew apart. A hand-sized fragment of metal was propelled about 50 yards.This chunk of metal flew across an in-plant road and an open area before striking a stor-age tank. The iron missile bent a hoop on a large acid tank’s ladder cage and caused somesuperficial damages to a large acid tank. [3]

The propellant was simply pent-up water and steam pressure. The destructive pressurebuildup occurred as the compressor operated for over five hours with no cooling waterflow. Cooling water was trapped in the water jacket on the compression head as the com-pressor piston continued operating. The team concluded that the fragmentation of thecompressor water jacket was a consequence of the operating condition, and a metal failureanalysis of the compressor head was not necessary. The damage was immediate and lim-ited, there was no release of gas, and the incident did not require the attention of the avail-able on-site emergency squad. Fortunately, there were no personnel injuries due to thisincident.

Compressor System Details

The reciprocating compressor was one of three identical units mounted side-by-side undera covered shed in an open-air chemical plant. These compressors were capable of com-pressing about 50 tons per day of acidic gases from 25 psig to 175 psig. The compressoroperated at 300 RPM and was driven by a 150-horsepower electrical motor. This 30-year-old compressor was initially designed with a well water cooling flow on the jacket.Initially a 3/4-inch valve supplied well water. The water flowed out of the compressorjacket and into a funnel, so the operator had a visual indication of flow and no provisionsto block the water. [3]

A plant-wide project to reduce the dependence on ground water was implemented adecade or more after the original installation. The cooling system was converted to re-circulating cooling tower water. At that time, the compressors were equipped with manu-ally operated 3/4-inch manual valves at the cooling water inlet, at the drain, and at thecooling water discharge fitting. If all three valves were in the closed position, cooling watercould be trapped in the confined space of the compressor water jacket. As the compressor pis-ton traveled back and forth, the confined cooling water within the jacket was heated and con-sequently pressurized. There were no temperature alarms for this blocked-in condition. [3]

Compressor Start-Up Details

One summer evening, the lead operator, accompanied by two operator trainees, started theNo. 1 and No. 3 compressors to supply a feedstock to a unit that had been shut down dur-ing most of the day shift. The second step of the start-up procedure was to “put water onthe compressor water jacket.” That step was inadvertently omitted in the start-up of theNo. 1 compressor, and the temperature must have risen slowly. (Typically the water valvesare not operated during brief shutdowns, so it may not have been checked.)

In retrospect, it was a simple mistake. The cooling water inlet, outlet, and drain valvewere left in the closed position. The heat energy developed by the operating compressor

148 Chemical Process Safety

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created an overpressure condition within the compressor water jacket. The frictionenergy generated heated the water and burst the outside compressor head water jacket. Theinvestigating team observed that the metallic lead washers on the compressor valve capsmelted, which, along with discoloration of the paint on the valves, confirmed the hightemperature. [3]

Root Causes of the Compressor Incident

The root cause of the incident was determined to be failure to unblock cooling water uponstarting the compressor. The equipment design was also a major contributor to the inci-dent’s occurrence. Engineering controls were not adequate for detecting or preventing theproblem from progressing once the step in the operating procedure was missed. The equip-ment design did not provide temperature indication or an alarm in the control room to

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FIGURE 7–1 Reciprocating compressor with ruptured water jacket.

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alert the operator of a high-temperature condition in the compressor. The compressorwater jacket was not equipped with a relief device to vent excess pressure. [3]

A series of hardware, instrument, and procedure changes were recommended andaccepted to eliminate any repeat performances. One of the ways similar incidents can bereduced without resorting to more hardware or software is the religious use of simplechecklists that require initials and the time each step in the start-up or shutdown processwas completed.

The Misuse of Hoses Can Quickly Create Problems

Hoses are essential within chemical plants. They are often necessary to purge vessels, towash vessels, to load and unload trucks, rail cars, barges, and ships. Hoses help to com-pensate for unavailable equipment, to prepare for maintenance, to safely vent systems, and


FIGURE 7–2 Close-up of ruptured water jacket on compressor.

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similar tasks. When hoses are misused, many unpleasant things can occur—including someof the world’s worst chemical plant accidents.

All plants have various utility fluids such as well water, compressed air, low-pressuresteam, and nitrogen, and anyone who has opened a valve on a utility service expects theutility fluid to flow from the utility header and out the hose. However, if a utility hose isconnected to a higher pressure system and there aren’t any check valves, undesirable chem-icals can back into the utility system and exit in unexpected places.

Some of the Many Unpublished Errors Created with Hoses

Many stories have been repeated in control rooms and at inter-plant meetings where in the1960s and 1970s flammables have backed into the nitrogen headers or where caustic soda,salt water, cooling tower water, or other undesirable fluids have backed up into the drink-ing water. One such 1960s incident involved a sandblaster using a hood receiving breath-ing air from a plant compressed air network. This painter suddenly received a slug ofammonia-tainted air in his hood while working early one morning. The night before thisincident, the compressed air was being used to pressurize a large condenser which wasabout 4 ft. (1.2 m) in diameter and 30-ft. (9 m) long.

According to the ambiguous instructions written in the log for the operator, he should havepressured up the ammonia condenser to compressed air system pressure. Next, he shouldblock off the air supply and discharge ammonia fumes to the atmosphere. The operator pres-surized the ammonia-laden condenser to full air system pressure, but unfortunately did notblock it off. Therefore at the beginning of the day when the arriving maintenance mechanics


FIGURE 7–3 Rebuilt reciprocating compressor.

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and operators put a high demand on the air system, the condenser acted as a surge tank. Asthe system pressure dropped, undesirable ammonia fumes traveled to the sandblaster’s hood.

Another undocumented story concerns a dangerous quantity of hydrazine (a very toxic vapor,corrosive to the skin and spontaneously igniting flammable liquid) backing into a power plant’sdrinking water supply from a utility well water hose connected to the boiler water treating sys-tem. This reportedly resulted in the hospitalization of a number of power plant workers.

In another tragic incident, a piping contractor was completing a major modificationwithin a chemical plant. The role of this piping contractor was the fabrication and instal-lation of long runs of 24-inch (61 cm) diameter fiberglass headers. The contractor hadnearly completed the job and crawled through the piping for an inspection.

During this inspection the contractor recognized that additional fiberglass work wasrequired. These repairs would require grinding to properly finish one of the field madejoints within this header. The contractor generally used a pneumatic grinder for these typeof repairs and this chemical plant was equipped with many compressed air utility stationswhich could be connected to nominal 3/4-inch (1.9 cm) hoses.

The unit was also engineered with several compressed nitrogen utility stations. Thenitrogen stations were equipped with different fittings (which were noninterchangeablewith compressed air) as a safeguard to prevent accidents. It seems that the contractor failedto understand why a utility station had different fittings and modified what he thought wasan “air” station to connect to a hose and a grinder.

Tragically, the repair job was many feet down the header, and the nitrogen-poweredgrinder exhausted into the confined space, asphyxiating the repairman. A well-intentioned,simple, one-minute modification to piping by a small contractor cost a life of a coworker.

Some of the most tragic and well-remembered accidents also had a start with a mini-modification made with a hose connection. The Bhopal Tragedy, the Three-Mile IslandIncident, and the Flixborough Disaster were initiated by the improper use of hoses.

The Water Hose at the Flixborough Disaster

As discussed in Chapter 5 the explosion in the Nypro factory in Flixborough, England, cre-ated a major impact on the entire chemical industry, and especially the European ChemicalIndustry. In short, this June 1, 1974 explosion was of warlike dimensions. The explosiveenergy was the equivalent to the force of 15 tons of TNT. Twenty-eight men perished atthe plant and 36 other individuals suffered injuries. Outside the plant, 1821 houses and167 shops and factories suffered some degree of damage. [4]

Almost every discussion on the hazards of plant modifications uses this accident as anexample of the need to control plant modifications. The authors, almost without fail, cen-ter their attention on the 20-inch (500 mm) diameter piping that was improperly installedto bypass the No. 5 Reactor which had developed a 6-ft.-long crack. But the reason for thecrack is usually just briefly mentioned.

Yes, a simple water hose or the temporary routing of cooling water to the stirrer gland ofNo. 5 Reactor was the precursory event of this tragedy. A hose routed a small stream of waterto the gland to cool and quench a small cyclohexane leak. The cooling water containednitrates. Unfortunately nitrates encouraged stress corrosion cracking, which created a crackon Reactor No. 5 so that it had to be repaired. [4] Pouring water over equipment was oncea common way of providing extra cooling, quenching, or absorbing leaking material.


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Hoses Used to Warm Equipment

Using a hose to pour water over certain equipment to warm the equipment or using a hose toroute steam has also been successfully employed in many chemical plants. In a plant thatrequired a small amount of chlorine gas from a ton cylinder, operators have poured warm waterover the vessel to slightly increase the chlorine vaporization rate. This has worked well for years.

However, there have been stories at inter-plant safety meetings that steam hoses createddangerous modifications. It seems that individuals who were unfamiliar with one-ton chlo-rine cylinder design placed steam hoses exhausting directly onto the portable cylinders toincrease chlorine vaporization.

A chlorine cylinder design includes three fuse plugs (which melt at 165˚ F or 74˚ C) ineach end. The heat from steam reportedly melted the plugs and the chlorine escapedthrough 3⁄8-inch (0.9 cm) diameter orifices. (See Chapter 3 for details.) (A tragedy alsooccurred when a steam hose was used on an ice cream refrigeration unit in Chapter 4.)

Three-Mile Island Incident Involved a Hose

At the Three-Mile Island Nuclear Power Plant in Pennsylvania on March 28, 1979, a hosecontributed to the front-page event. In short, a nuclear reactor overheated, a small amountof radioactivity escaped, and the public confidence in the safety of nuclear power was shat-tered. It is believed by the technical community that no one is likely to be harmed by thisrelease, but it led to a slowdown in the growth of nuclear power in the United States. [5]

Full details of this accident can be found in several major reports. This brief review isfocused on the utility hose and the “one-minute modification” aspects of the accident. It wasreported the trouble started when one of the parallel paths used to treat the secondary watersystem started plugging. When this resin polisher system, which is designed to remove traceimpurities, started to plug, an operator decided to clear the blockage with instrument air. [5]

Clearing any system with instrument air as a pressure source is a bad idea. Other pneu-matic sources such as utility air, plant air, or nitrogen should be used instead. However, theThree-Mile Island instrument air was at a lower pressure than the water stream on the resinpolisher system. Despite the presence of check valves, there was a reverse flow, water enteredthe instrument air system causing several instruments to fail, and the turbine tripped.Through a series of other errors, the water covering of the radioactive core was uncovered,allowing an escape of a small amount of radioactivity. Due to the widespread negative pub-lic reaction, the U.S. nuclear industry received a setback. If it were not for the improper hoseconnection or the erroneous “one-minute modification,” it is unlikely that anyone outsideof the Pennsylvania area would have heard of the Three-Mile Island power station. [5]

The Bhopal Tragedy Was Initiated by Use of a Hose

The front page and feature article of the Wall Street Journal in July 1988 explains theUnion Carbide belief that a disenchanted worker initiated a one-minute plant modifica-tion with a hose. The article begins with these three paragraphs:

On a chilly winter night, a disgruntled worker at Union Carbide India Ltd. sneaks intoa deserted area of its Bhopal pesticide plant where storage tanks hold thousands of gallonsof a toxic chemical. [6]


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He removes a pressure gauge on one tank, attaches a water hose to the opening and turns onthe faucet. Two hours after he steals away, a calamity he never foresaw begins unfolding. Thetank rumbles. Vapors pass into a vent tower. A large cloud of poison gas drifts out into the night.

Such a chain of events, Union Carbide Corp. believes, explains the gas leak that killed2,500 people and injured thousands more in Bhopal on Dec. 2 and 3, 1984. The com-pany insists that sabotage—not sloppy corporate practices in the Third World—causedwhat has been called the worst industrial disaster in history. [6]

Other news coverage or investigative reports do acknowledge the fact that the presenceof water in the system lead to runaway reactions. However, several other reports were notable to identify the precise route for the entry of water.

Improper Purge Hose Set Up for Maintenance CreatesMajor Problems

Two chemical process operators were preparing a piping header for scheduled maintenancebefore sunrise in a large outdoor facility. These well-respected, well-trained, conscientiousemployees were preparing to purge a pipeline when they inadvertently connected a utility airhose to the wrong pipeline. They hooked-up to the adjacent line, which was pressurized witha flashing acidic liquid. This action allowed the higher-pressured acidic liquid (being pumpedat about 250 to 290 psi) to backflow into the (90 to 100 psi) utility air system. This mistakeresulted in over $300,000 in repair costs and required a number of reports to environmentalagencies. It would be easy to conclude that this was a simple error, but it was more than that.

The piping arrangement under nighttime conditions was deceptive in geometry andcamouflaged by the rust-colored primer, versus the bright yellow-colored paint of the adja-cent fittings. There were three parallel 2-inch pipelines below the grating on the secondlevel; each line had purge connections that confused the team. (See Figure 7-4 for sketchof piping manifolds.) Each of the three parallel pipelines had individual 3/4-inch horizontalpurge piping connections equipped with 3/4-inch quick-connection fittings and valves forpurging. The purge connections were near the grating level. There were also three 4-inchdiameter vertical bottles that were properly labeled. However, the purge connection for thenorth bottle was directly in front of the middle bottle. The purge connection for the mid-dle bottle was directly in front of the south bottle, and the purge connection for the southbottle was not painted the same bright yellow color. Lighting was acceptable. [7]

To Make Matters Worse . . .

The task of purging pipelines for maintenance is almost second-nature to well-experiencedoperators in this unit. Typically, pipeline clearing is routine and is uneventful. This time,however, the utility dry air system was also being utilized as a source for instrument air inthe operating area. Hence, this corrosive material was able to backflow throughout theinstrument air system into monitoring and control systems. The backflow created expen-sive instrument damages.

Initially, fumes were found throughout the operating area. The magnitude of the prob-lem was hard to assess at night. It was difficult to identify the source of the leak. As a goodoperator response technique, the operators stopped the clearing procedure. Stopping theprocedure isolated the source, even though they were unaware of this at the time. Residual


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acidic gases in the header began to seep from air bleeds, purge points, and leaks and con-tinued for over four hours. Once the problem was identified as an erroneous hose hookup,a significant amount of the misplaced chemical was recovered to the sniff system. A formalinvestigative team was formed for the accidental release of an OSHA PSM-listed chemical.The team members included the Unit Supervisor, the Emergency Coordinator during theincident, an Engineering Services Supervisor, and others. [7]

Impact and Conclusions of Improper Purging

Damage to analyzers and instrumentation from the intrusion of acid gases into the instru-ment air system was extensive. Repair costs were about $300,000.

The investigating team concluded:

● The accident was a result of human error by talented, well-trained, dependable operators.The operators took several steps to change fittings to make the hose connection. The pip-ing arrangement was deceptive in both geometry and paint color. Under nighttime light-ing conditions, the piping connections are even more misleading.

● The use of the 100-psi dry air system for instrument air must be reviewed.● The release resulted from backflow of a corrosive into a utility air header because of

human error and from purges, bleeds, and leaks on the instrument air system that wasbeing supplied from the utility air system.


GAGE AND BLEED INDECEPTIVE POSITION

IDLED PIPELINE

TO BE CLEARED

INADVERTENTLY CONNECTED

TO PRESSURIZED PIPELINE

LIQUID SURGE BOTTLES

FIGURE 7–4 Sketch of piping manifolds. Courtesy of Manuel David.

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● Quick response by the operators in shutting down the clearing operation, even though it wasnot suspected to be the source, aided in minimizing the amount of corrosive gases enteringthe air system. The professional response by the emergency squad was very good. [7]

Recommendations for this Improper Purging Incident

The investigation report stated:

● Ensure that elements of this incident are discussed with a large group of operatorsthroughout the complex to remind them of the significant problems that can occur withhoses and of the value of double and triple checking.

● Improve the situation to reduce the deceptive appearance of this area and check for sim-ilar situations in that unit.


FIGURE 7–5 Expansion bottles protecting piping from overpressure.

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● Conduct a study of the 100-psi dry air system to determine proper use of the air system.The focus of this study is to discourage the habitual use of the dry air system as an instru-ment air source.

Although it was implied, the investigation report did not specifically state that there wasalso human error on the part of the piping designer/installer that contributed to the decep-tive appearance and by the people who reviewed the installation. These types of situationscannot be seen on P&IDs. Piping systems and situations that appear counterintuitive canyield mistakes more easily.

High-Pressure Hydrogen Inadvertently Backs Intothe Nitrogen System and an Explosion Occurs

Rande Grotefendt described a purging error similar to the one described above involving350-psi hydrogen backing into a 90-psi nitrogen system. This error ended-up creating anexplosion, but no one was injured. Mr. Grotefendt’s presentation, “Learning From WhatWent Wrong—Two Case Studies,” which he presented to the Mary Kay O’Connor ProcessSafety Center in October 2003 will be summarized below. [8]

During a polymer plant shutdown, the operator was supposed to remove the plug fromand connect a nitrogen purging hose to a fitting immediately downstream from an isolat-ing block valve connected to a depressurized system. Instead, the employee mistakenly con-nected to a pressurized fitting immediately upstream from the block valve, into a 350-psi


FIGURE 7–6 Close-up of piping arrangement that shows the hose connection for themiddle expansion bottle in front of the south bottle.

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hydrogen system. During the next two hours, combustible gas analyzers occasionallydetected the presence of flammables in unexpected places. Operators and supervisorsresponded to the alarms but did not detect any hydrocarbons. Two-and-a-half hours afterthe error, an explosion occurred in the final degasser. An automatic sprinkler systemtripped and extinguished the fire. [8]

This company’s approach was somewhat different than the approach described in theprevious incident. The polymer plant implemented a procedure to require force-loadedcheck valves for backflow prevention on any temporary connection to piping that con-tained flammables. The check valve had to be rated for the highest design process pressureof either fluid. [8]

A Nitric Acid Delivery to the Wrong Tank Makes Front-Page News

On a hot summer day in the late 1990s, one front-page headline of the Lake CharlesAmerican Press read, “Acid Mix-up Creates Toxic Vapor Cloud.” The accompanying photoshowed two emergency-response team members staring at the sulfuric acid tank that wasbeing cooled by water sprayed from three or more temporary firewater monitors. [9]

The plant manager is quoted as saying that the chemical company was expecting fouracid trucks on that Friday morning. Three of the trucks were carrying sulfuric acid and onewas delivering nitric acid. The nitric acid truck was misdirected and partially unloaded inthe sulfuric acid tank.

The plant manager related many details of the incident. About 2,600 gallons of the4,000-gallon load of nitric acid were off-loaded on top of the 16,500 gallons of sulfuricacid before the chemical reaction was observed by the driver and the plant employees.Commercial-grade nitric acid contains 35% water and the sulfuric acid has a strong affin-ity for the water. The heat of solution caused an exothermic reaction and the once ambi-ent-temperature acid shot up to about 160˚F. Nitrogen dioxide was liberated from the hotnitric acid creating a blue-white cloud drifting 25 feet in the air. An emergency shelterin place was called after the 11:45 a.m. accident to protect residents in the nearbycommunity. [9]

The emergency response team’s first concern was cooling the tank to reduce the possi-bility of rupture. Cooling water from fire monitors was sprayed on the shell of the vertical,cylindrical vessel and was sufficient to prevent a rupture. Later the acids were slowly mixedand scheduled to be neutralized with caustic.

How Do You Prevent Such an Incident?

With the huge number of truck deliveries of hazardous and sometimes incompatible chem-icals, how do does your company prevent such a potentially dangerous incident? If you can-not answer this by citing a well-worded and well-used standard operating procedure, maybeyou should put this book down and look into that situation. Over the years at various inter-plant safety gatherings, I have heard undocumented stories of large quantities of the wrongchemical unloaded into a storage tank at several different companies.

The newspaper piece said that the truck was properly manifested, and that four separateindividuals should have checked each chemical delivery prior to it being unloaded.


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Apparently, the procedure was either not followed, or there was a miscommunication.Maybe it had something to do with the fact that this occurred in a unit that was started upabout three months before with 38 new employees. [9]

Other Truck Delivery Incidents

In What Went Wrong? Case Histories of Process Plant Disasters, Trevor A. Kletz offers twopages listing incidents of emptying a truck into the wrong tank [10]. In one case, a tanktruck arrived at night. A unit was expecting a load of ethylene glycol, when a truckload ofisopropanol arrived. Without looking at the label or delivery note, they emptied the iso-propanol into the ethylene glycol. Fortunately, these two chemicals do not react.

In another case, Trevor Kletz discusses a chemical plant that received both caustic sodaand acid in tank cars. One day a tank truck of caustic soda arrived with the proper deliv-ery papers, correctly labeled, and with the special hose connections. The operators had themind-set that they were receiving acid and spent considerable time developing an adaptorto enable them to pump the caustic soda into an acid tank. [10]

Kletz also provided several cases in which tank trucks have been filled with the wrongmaterial. At the end of this section, he offered this sage-like advice, “Supplier’s papers tellus what they intend to deliver, not what is in the tank truck or car. We can find that outby analyzing the contents or by seeing what happens.” Hopefully, in this day of ISO-certified suppliers, this is no longer a necessity. [10]

An Operator Averts a Sulfuric Acid Unloading Tragedy

On a hot summer day just four days after the previous incident (and within a nearby chem-ical complex), a truck driver entered a unit with a load of 98% sulfuric acid. He parked hisrig in the correct location, hooked up the chemical delivery hose, and was given clearanceto off-load.

The receiving plant’s housekeeping was less than ideal. Somehow the driver hooked-up autility water hose instead of the compressed air hose to pressure his trailer to deliver the acid.An alert operator observed the potentially dangerous situation before the utility station valvewas opened. The housekeeping had been poor. The hoses had been left together on theground. The driver initially thought he had selected the air hose, but he was very wrong.

The technical employees understood that mixing water and the 98% sulfuric acid couldhave caused severe trouble, due to the heat of solution. The generation of heat could havecaused a pressure buildup that may not have been controllable by a relief device. Even ifthe vessel did not rupture, sulfuric acid spray could create severe burns to anyone in thevicinity of the unloading operation.

Investigating supervisors emphasized housekeeping improvements to the utility stationswith signs identifying the services. They also recommended that the air and water stationsbe separated to reduce the confusion.

Hoses Cannot Take Excessive Abuse

Chemical hoses must be designed for a specific service. Hoses are required to convey com-pressed gases, slurries, petroleum products, solvents, bulk chemicals, such as acids and


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caustics, and a full array of other chemicals that may exhibit flammable, toxic, corrosive,cryogenic, or other harsh properties. Chemical hoses are used for loading and unloadingtrucks, tank cars, barges, and ships. They may also operate to bypass equipment that hasbeen taken out of service.

Hoses built to United States standards have a four-to-one pressure design safety factor.This means that the maximum allowable working pressure (MAWP) must be one-fourththe hose’s minimum burst pressure. This rating is generally specified at 72˚F, and manyusers are unaware that, as the operating temperature increases, the hose assembly’s MAWPdecreases. [11]

In the article “Choosing Hose Assemblies for Safety’s Sake—Saving Money, ReducingAccidents,” Stephen Van Pelt stated, “Hose assemblies are generally the weakest link in apiping system because they are usually made from materials that promote flexibility. Itstands to reason that rigid systems are more durable than flexible lines. However, hoseassemblies must be flexible to accommodate piping misalignments, increase efficiency inprocesses having many connected parts, and act as vibration isolators and dampeners.” [11]

Hose Selection Guidelines

Hose specifications need to be based upon a number of requirements. Some hose criteriainclude size, delivery temperature, maximum pressure, chemical properties of the fluid,hose material, and end fittings. The major components of a chemical hose are the end fit-tings, an inner core, pressure/vacuum reinforcement, and the protective outer cover. Theexact selection of hoses is beyond the scope of this text. [11]

Maintaining Hose Integrity

Hoses should be casually inspected before each use. Obvious signs of damage, such asbulging, kinked, or broken covering must be addressed immediately. Naturally, the end fit-tings should be observed for leak-free tightness. If the material being delivered is extremelyflammable or highly toxic, the hose should be tested before each use. One chemical plantuses the hose-testing procedure outlined in the box on p.161.


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HOSE-TESTING PROCEDURE

Adopted by One Large Outdoor Chemical Complex

PURPOSE:

To assure that no injury, damage to equipment, or environmental incident occurs as a result ofusing a defective chemical hose.

HOSES COVERED BY THIS PROCEDURE:

Any hose used to transfer a liquid, including refrigerants, that has an agency-reportable quan-tity listed for a spill. It does not include normal utility hoses such as steam, water, nitrogen, andair. It does not include hoses that are supplied by a contract carrier. It does not includehydraulic hoses or other such hoses that are permanently mounted as a part of equipment thathas its own inspection schedule. Fire hoses are not included, but do have testing procedures forthat particular service. NOTE that good judgment should be exercised with the use of all hoses,and any obvious defects should be addressed.

PROCEDURE:

All hoses are to be tested and tagged when purchased and on a maximum one-year intervalafter purchase. Each hose is to be tagged with the following information: date tested, designpressure (tested at one and one-half of design pressure), design temperature range, and intendedchemical service (Do not introduce cross-contamination). Tags may be of different types, butthe hose must not be used if the tag is missing.

A visual inspection of the hose must be made before each use for loose or defective fittings,cracking, bulges, ruptures, and contamination in the hose that could result in a problem withthe material intended to be moved through the hose. Defects are to be repaired or the hosedisposed of to prevent inappropriate use later.

Braided hoses are to be tested every six months due to the lower reliability. Braiding should alsobe visually inspected before each use.

Each unit must have a written testing procedure for chemical hoses used in the area. If a proce-dure does not exist, a management of change must be written and approved before use of thehose in a chemical service. Each unit may determine the proper testing procedure for their serv-ice. Consideration should be given to safety of the testing procedure and clearing of the testingmedia to prevent contamination.


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This plant often sees a failure rate approaching about 50% after hoses are in use for ayear or more. Many of the failures can be attributed to mechanical damage. It appears thatmany are victims of motor vehicle traffic.

Centrifugal Pumps

Centrifugal pumps have a wide range of application for transferring fluids in industrialoperations. Centrifugal pumps are reliable and mechanically simple. Many chemical plantsand refineries have hundreds of centrifugal pumps of various sizes conveying sundry liq-uids and slurries. These vital workhorses are used for water, flammable liquids, acids, caus-tics, and most other fluids.

Centrifugal pumps serve the industries well, but can be involved in accidents even if theyare correctly sized and specified, made of the correct materials, and properly installed.Three pump incidents follow. This first case history involves an explosive incident thatoccurred during maintenance to remove a defective pump. Incidents two and threeoccurred during operations.

River Water Pump Piping Explodes

Imagine the surprise involved when what was viewed as a plain river water system producedan explosion. A chemical company had been safely operating three large, high-volume,low-head river water pumps and doing similar maintenance tasks for about 50 years with-out incidents. The explosion and injuries during the removal of the pump were totallyunexpected. It is a pumping system that has not had any significant changes in decades.[3]

A 30,000-gallon per minute vertical river water pump was performing poorly. The oper-ators suspected a damaged shaft, so they shut it down at about 6:30 A.M. on a Mondaymorning. It was a winter morning and the other pumps could handle the cooling require-ments. Work began on the pump on the next day about 10:30 A.M. [3]

Three seasoned mechanics were working to remove the pump on Tuesday. The bedplatebolts were removed and the 3/8-inch well water gland flush line was disconnected, althoughpump suction needed no disconnection, since it was suspended into the river. A welder usedan acetylene torch to cut the 30 bolts holding the discharge piping. As the welder made hisfinal cut on 42-inch diameter coupling on the pump discharge line, an explosion occurredwithin the water pump discharge piping. The force of the explosion knocked the welderback over eight feet. The welder sustained flash burns to the face and the chest, but returnedto work some weeks later without noticeable scars. Two nearby machinists were also struckwith explosion-propelled debris, but they were not seriously hurt. [3]

The mechanics and their supervisor were astonished because they did not know of anyflammables within this area. Furthermore, the previous hot work testing on the system didnot reveal any flammables.

River Water System Details

At this U.S. Gulf Coast location, the river water can be fresh water during rainy seasons,but it is often brackish. The river depth and quality depends upon rainfall, winds, tides,and the season. The water can be fairly salty during periods of low rainfall. During the fall,


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the operators sometimes catch shrimp and blue crabs on the inlet pump screens. The30,000-gpm river water pump is one of the original designs installed 50 years ago in apump house that shelters five pumps. [3]

As mentioned above, the defective pump was shut down early Monday morning beforesunrise, and the mechanics started work about 10:30 A.M. on Tuesday, after the equipmentwas locked out. The pump was idle for about 28 hours before the well water seal flush wasdisconnected and the mechanics started disconnecting the 400-hp electric motor.

On the afternoon of the second day, a crew of two machinists and a welder were assignedto disconnect the pump from the discharge piping. A hot work permit was issued, afterexplosion meter tests were conducted at a nearby coupling to ensure that the piping didnot contain any flammables.

The pump and piping are joined by a “Dresser” coupling. These “Dresser” couplings areheld together with 30 all-thread, 5⁄8-inch-diameter bolts. Once the bolts are cut with an acety-lene torch, the coupling is cut. The coupling is basically a 42-inch diameter short pipe (or col-lar) about nine inches wide, and is made of 1⁄2-inch-thick steel. The welder used his torch tocut about eight inches of the width of the coupling when sparks entered into the piping. Next,a machinist started massaging the coupling by pounding it with a 12-pound sledgehammer.This beating helps free up the piping, as steel in river water service is subject to corrosion.

The welder then relit his torch and cut the remaining part of the collar. As he made thefinal cut, sparks were shooting into the piping. The welder started to move away from thepipe and the explosion occurred, knocking him back 8 to 10 feet and covering him with ablack material. This black material was probably a mixture of soot, river water, slime, and


FIGURE 7–7 Photo of the adjacent river water pump system.

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metal grit. The force of the explosion thrust the heavy pump and base plate (about fivetons) backward and deflected a beam. The 180-pound cylinder-shaped coupling was pro-pelled away from the explosion and was expanded. [3]

What Was the Fuel?

How did a flammable gas enter the pump/piping system? Why did the explosion metertests prove negative? What was the fuel within the pump? Jobs similar to this were repeatedover the past 50 years. Why did it happen at this particular time?

A multi-disciplined team interviewed witnesses and performed tests, and the evidencewas followed to a sound conclusion. Investigators sent the explosion meters (flammable gasdetectors) to the instrument shop for examination. The welding torch was also inspected.Experts found both the torch and the meter behaved satisfactorily. There was speculationthat some aquatic life deteriorated and formed methane, but that was not the case. Theyconcluded that the fuel was dissolved methane from the well water system that was routedto the pump seal. Trace amounts of dissolved methane (about 0.02 percent by volume)accumulated in the well water stream flowing through the 3⁄8-inch-diameter stream on the


Air ReliefValve

400 HPMotor

Well Water To GlandSample PointFor Gas Test

Normal Water Level

42" DresserCoupling

30,000 GPM Pump

FIGURE 7–8 Sketch of the river water pump system at normal conditions. Courtesy ofManuel David.

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pump gland. This methane collected during the 28-hour period that the river water pumpwas shut down. Seal flush well water on a sister pump was monitored to determine thefacts. Many water wells in and along the U.S. Gulf Coast are in areas that have traceamounts of methane in the water. [3]

Why Was the Presence of Flammable Gas Not Detected?

The geometry of the piping layout trapped the lighter-than-air flammable gas. The cou-pling was 42 inches in diameter and there was a concentric reducer to 36 inches. This was


FIGURE 7–9 Photo of how the river water pump moved during the explosion.

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a unique situation. Evidence of methane and the piping layout led the investigators tounderstand the most probable situation. The accumulation of gas was sufficient to be pres-ent at the coupling, but not at the test point on the discharge piping. (See the sketch of thedetails of the river water pump system) The low-density methane was buoyant enough tohover as a separate layer in the upper portion of the pump and at the coupling. Methane’sdensity is about 0.6 in air. The methane floated on top of the air like fishing corks float onwater. When the first cut on the coupling was made, the area near the burning was believedto be fuel rich. After the initial cut and with an open high-point bleed, the air displacedthe methane to get sufficient mixing for a very energetic combustion. The energy releasedindicated the methane and air were well mixed, perhaps by a short-lived slow burn thatencouraged thermal mixing.

Investigators used an adjacent pump of the same detail and size to inspect for methaneaccumulation. A small flow of well water was routed to the gland on an idle sister pumpfor more than a day. The explosion meter tests performed after a day revealed that therewas sufficient accumulation of methane to be troublesome.

Why was this different from all the other times? The river water pump gland was origi-nally lubricated with grease. About 15 years earlier, in an effort to reduce potential envi-ronmental situations, such as an occasional sheen on the river water discharge, the greaselubrication was replaced with environmentally friendly well water. Furthermore, it isbelieved that when a river water pump was shut down for scheduled maintenance, themotor was shut off and the well water was turned off immediately. Despite the fact thatthis area handled only water, we must be concerned about the impurities that can be dis-solved in the water. [3]


FIGURE 7–10 Photo of how the pump pipe coupling yielded during the explosion.

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Corrective Actions

Corrective actions included:

● Replacing the well water used for lubrication with a river water stream.● Installing hot work test sample points closer to the cutting location and in the higher ele-

vations of the piping.● Sharing the incident details with hundreds of mechanics, chemical process operators, and

supervisors within the chemical complex. This training included stressing the properflammable gas detection strategy. [3]

Well water was routinely used within this chemical complex. This lesson was so uniquebecause it involved such fundamentals as gas density, flammable limits, and sample pointorientation. The company held a series of meetings and shared their recommendationswith over 800 maintenance and operations employees, engineers, and supervisors.


Air reliefvalve 11'-4"

Well waterto gland Sample point

for gas test

2'-6

"

6'4-

0"

42" Dressercoupling Normal water level

Methaneaccumulation

FIGURE 7–11 Sketch of how methane gas accumulated in the river water piping.

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A Severe Pump Explosion Surprises Employees

Some employees reported that it sounded like two railroad cars running into each other.Witnesses reported that windows rattled in a building located about 200 feet from thesmall pump that fractured into pieces. There were no injuries.

Part of the chemical manufacturing complex in Tennessee had been shut down, was idle,and there was no immediate intent to restart it. Some equipment had not yet been drainedand washed. The system included a 50% sodium hydroxide (caustic soda) tank and theassociated centrifugal pump. The pump was an ordinary 1750-rpm pump, driven by a10-hp electrical motor. Both the suction and discharge manual block valves on this causticpump were closed. However, the breaker box was still energized. [12]

Investigators learned that one afternoon, a contractor entered the area to start a localventilation fan in preparation for an unrelated nearby maintenance job. The electricalswitch used to start the pump was identical to the type of switch used to start the ventila-tion fan. Although the switch was labeled, the tag was hard to read. These switches wereover 50 feet from the outdoor caustic soda pump installation, well outside of the dikedarea. The pump continued to run, unnoticed by anyone. There was no instrument in anoccupied location indicating that the pump was running. [12]

Without warning, a loud boom rattled windows. In a spectacular manner, the pumpbowl and piping were knocked backwards. The impeller, shaft, and bearing housing were


FIGURE 7–12 Pump bowl is stripped of the pump and base plate. Courtesy ofEastman Chemical Company.

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FIGURE 7–13 Pump base plate and motor thrust into walkway. Courtesy of EastmanChemical Company.

FIGURE 7–14 Pump base plate and motor as well as the position of the bearing housing with impeller document the explosion. Courtesy of Eastman Chemical Company.

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propelled as a result of the forces generated by the explosion. The motor and base platewere completely upset.

The culprit was determined to be a remote start button that allowed the liquid-filledpump to start and run undetected and isolated for a significant length of time. The trappedliquid continued to heat, expand, and boil, creating pressures sufficient to allow a cata-strophic rupture of the pump.

A Large Condensate Pump Explodes

A 2,600-gpm centrifugal steam condensate pump catastrophically exploded, followinga major steam system upset. Before this incident there was a plant-wide power upset.As a precaution to prevent backflow through the de-energized pump, employees man-ually closed the suction and discharge valves. When the power was restored, the pumpran completely isolated. When the pump dramatically blew apart, the associated largepiping was grossly twisted and the rotor was forced out of the electric motor. A five-poundpiece of pump casing was found over 400 feet from the condensate pumping station.The accompanying photo displays the explosive force that blew the motor’s rotor outof the 75-hp electric motor casing. The investigating team established that this inci-dent was the result of a pump being operated with the suction and discharge valvesclosed. [12]


FIGURE 7–15 Heavily damaged condensate pump installation. Courtesy of EastmanChemical Company.

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References1. Yi, Gong and Neville Wright, “Avoiding Fatigue Failures in Reciprocating Compressors,”

Chemical Engineering, Dec. 2003, pp. 38–42.2. Kletz, Trevor, Still Going Wrong! Case Histories of Process Plant Disasters and How They Could Have

Been Avoided, Gulf Processional Publishing, 2003, p. 122.3. Sanders, Roy E., “Picture This! Incidents that Could Happen in Your Plant,” Process Safety

Progress, June 2002, p. 130,134.4. Warner, Sir Frederick, “The Flixborough Disaster,” Chemical Engineering Progress, Sept. 1975,

pp. 77–84.5. Kletz, Trevor A., Learning from Accidents in Industry, Guildford, U.K.: Butterworth Scientific,

1988, ch. 11.6. Hays, L. and Richard Koenig, “Dissecting Disaster,” The Wall Street Journal, July 7, 1988, p. 1.7. Sanders, R.E., “Designs that Lacked Inherent Safety: Case Histories,” Journal of Hazardous

Materials, Vol. 104, 2003, pp. 149–161.8. Grotefendt, Rande and J. Wayne Chastain, “Learning From What Went Wrong—Two Case

Studies,” 2003 Proceedings of the Mary Kay O’Connor Process Safety Center BeyondRegulatory Compliance: Making Safety Second Nature Symposium, pp. 39–44.

9. Lake Charles American Press, Lake Charles, LA, August 8, 1998, pp. 1, 4.10. Kletz, Trevor A., What Went Wrong? Case Histories of Process Plant Disasters, 4th ed. Houston: Gulf

Publishing, 1998, pp. 268–270.


FIGURE 7–16 Explosion forces rotor out of condensate pump motor. Courtesy ofEastman Chemical Company.

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11. Van Pelt, Stephen, Choosing Hose Assemblies for Safety’s Sake—Saving Money, Reducing Accidents,Chemical Processing, April 2002, pp. 29, 30.

12. Giles, Douglas S. and Peter N. Lodal, “Case Histories of Pump Explosions While RunningIsolated,” Process Safety Progress 20, no. 2, June 2001, pp. 152–156.


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