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