| Chemicals are very much a part of our
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| | to be compatible to these chemicals. If
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| lifestyles. Every household detergent,
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| | the wrong material is selected, it can
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| solvent, and bleach that you use in your
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| | lead to dangerous and widespread
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| homes is a result of some production
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| | consequences of chemical spills,
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| efforts from manufacturing plants
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| | emergency evacuation, pollution,
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| somewhere in the world around you.
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| | environmental damage and other
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| Fertilizer, automobile radiator coolant,
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| | disruptions to the production facility.
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| shampoo, soap, insecticide, paint
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| | Engineers in such chemical processing
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| solvent, lubricants, fuel oil are just a
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| | plants need to know what materials are
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| few that I can name right now. I'm sure
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| | suitable to be used for their process. It
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| you can find more around you, but you get
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| | is much more complex than just selecting
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| the point. We use chemicals everywhere.
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| | materials for water pumps. Much detailed
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| Anyone who has visited a chemical
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| | and careful selection choices based on
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| processing plant is sure to notice the
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| | the chemicals, the temperatures (because
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| many pumps, agitators, tanks, piping, and
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| | some of the plastic materials can weaken
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| valves that are installed there. Liquid
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| | at temperatures that are considered
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| have to be transferred from one place to
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| | normal for metals), chemical reactions,
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| another. Pumps are therefore very
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| | safety, spills and many others have to be
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| important in a chemical processing plant.
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| | taken.
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| Without them the chemical processing
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| | The aim of any maintenance personnel is
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| plant will literarily come to a halt!
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| | to lengthen the lifespan of equipment
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| One of the main jobs for Plant Engineers
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| | under his care. Selection of chemical
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| is to maintain the numerous pumps
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| | resistant materials is not a
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| installed at their plant. These pumps can
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| | one-cure-fits-all solution. Some
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| count into the hundreds or even
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| | materials are not affected by certain
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| thousands, depending on the size of the
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| | chemicals but can be damaged by others.
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| plant. So you should realize that to do a
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| | Some have good mechanical strength while
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| proper preventive maintenance, it is no
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| | others cannot last long without
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| mean task. There must be regular
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| | reinforcement. Usually, materials that
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| schedules, proper tracking of jobs done,
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| | can withstand many types of chemicals are
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| available manpower and skills, suitable
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| | very expensive.
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| tools, replacement parts, materials and a
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| | Cost considerations need to be taken into
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| proper system of administration of all
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| | account when choosing a material for a
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| these.
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| | certain application. If there is a choice
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| Sometimes, even with all the maintenance
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| | of materials for a certain application,
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| activities being carried out, pumps do
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| | it makes better sense to choose cheaper
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| fail. And when they do, plant engineers
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| | materials if they can perform just as
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| will have to find out what causes them to
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| | well.
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| fail. Especially with new pumps where
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| | There are several components to check for
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| there is very little record trend of
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| | when selecting suitable materials:
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| breakdown, engineers will be hard pressed
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| | 1) Elastomers for flexible parts like
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| into finding solutions for this. This is
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| | seal rings and gaskets
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| when experience helps in pinpointing the
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| | 2) Metal parts like shafting, springs,
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| cause(s) of the failure.
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| | holders, bolts & nuts, and pressure
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| Pumps or other machinery will give
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| | gauges
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| tell-tale signs when they are not working
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| | 3) Plastic parts like housing, piping,
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| properly. An observant pump user will be
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| | impellers, and covers
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| able to avoid major breakdowns or damage
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| | Metals have good mechanical strength that
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| if the problem is corrected early.
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| | can last very long in operation. In fact
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| In order to solve any pump problem, we
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| | some parts need to be made of metal, e.g.
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| need to notice the symptoms carefully so
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| | bearing housing and shafts. Pump housing
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| as to determine the most likely causes.
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| | made of metal can be casted and machined
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| Instruments like pressure gauges are very
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| | easily. They are able to withstand
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| helpful and should be installed in the
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| | abrasive fluids and rough handling
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| pumping system.
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| | without any other reinforcement. One very
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| Very often we do have to rely on our 5
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| | important characteristic of metals is
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| senses to determine the exact symptom.
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| | heat conduction. If the chemical to be
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| Normally, pump problems can be classified
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| | pumped is hot, metal is always the
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| into:
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| | choice.
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| 1) Suction Related,
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| | Plastics have become the better choice
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| 2) System Related, or
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| | for many corrosive chemical applications
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| 3) Mechanical Related.
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| | because it is more resistant to chemical
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| It can also be a combination of these.
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| | action than metals. When using plastics
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| Most of the system related problems occur
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| | to replace metals, you have to compromise
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| because of design flaw. For example, the
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| | on the mechanical strength of the pump.
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| designer may have chosen the wrong pump
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| | If the pump does not encounter much rough
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| whose characteristic does not match the
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| | handling or abrasion, plastics can be
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| system requirement. Suction related
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| | used. Sometimes plastics are used to coat
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| problems are usually caused by air locks
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| | metal parts. These are fine as long as
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| that are due to a variety of reasons. I
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| | the plastic coating remains intact.
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| will not mention them here.
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| | Elastomers are the flexible materials
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| The effects of mechanical related
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| | that are needed for sealing the pump
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| problems could manifest themselves as
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| | parts. There should not be any compromise
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| suction related problems - air leaks in
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| | here. Laboratory tests on the suitability
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| the system, worn out impellers, and mouth
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| | of elastomers with certain chemicals
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| rings - but the most common symptom is
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| | should be followed. Unsuitable material
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| the presence of vibration and abnormal
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| | used can cause leaks that can lead to
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| noise in the equipment.
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| | other failures in other parts.
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| However, there is one area where we
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| | With so many chemicals in use today, how
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| seldom focus on - the effect of
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| | do we know what materials can be used for
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| chemicals. Was the material selected able
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| | what chemicals? Sometimes liquids to be
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| to withstand the chemicals? If you have
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| | pumped contain chemicals that are both
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| done all your designing right and you
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| | corrosive and abrasive. Should we choose
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| still find that leaks are occurring so
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| | a plastic or a metal housing? Sometimes
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| frequently, chances are that the
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| | chemicals may become hot either through
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| materials are failing due to chemical
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| | the process or through mis-operation of
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| reaction. Signs of corrosion at the seals
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| | the system - perhaps, somebody forgot to
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| are a strong indication of material
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| | open a valve. Plastic parts can weaken at
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| failure due to wrong usage.
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| | high temperatures.
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| Nowadays, waste treatment plants or even
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| | It's only through the result of test and
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| process plants are called upon to process
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| | actual operation that we are able to know
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| strong acids, alkalis, oxidizers,
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| | what materials to use. It is good to know
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| solvents, waste, slurry and other
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| | what to expect when we make a decision
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| corrosive and abrasive chemicals. And it
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| | for a choice of materials to use. A good
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| is not only pumps that are affected.
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| | choice may involve some compromise.
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| Agitators, storage tanks, and piping need
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