Plant Maintenance

The wrong combination of metals in electrical contact create a Galvanic Corrosion Trap that will cause many failures and costs in the future

Abstract:

The Galvanic Corrosion Trap. The wrong combination of metals can produce a corrosion cell of unequal voltage where one metal gives up its electrons and corrodes away. If the corrosion is not detected it will result in eventual failure of the equipment. Galvanic corrosion prevention is a design selection issue that one must always be aware of, as it can arise with the simplest of decisions. This article highlights a galvanic corrosion problem often seen in industry and sometimes missed by the person selecting equipment.

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When To Use Stainless And Alloy Steel In Place Of Plastic Or Carbon Steel. There are many times when it is false economy to use carbon steel and plastic items. It is often better to use stainless and alloy steels instead. They last longer and deliver a lower life cycle cost.

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There are only two ways to get high system reliability if you want a highly reliable system. Equipment in an operation can be configured in series or in parallel. In series, one item connects sequentially to the other. In parallel, each item is arranged as a companion, where one duplicates the other.

A series arrangement needs exceptionally reliable individual equipment to get a highly reliable system. A parallel arrangement can form a highly reliable system even if individual equipment has poor reliability.

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Often used to pump slurries, helical rotor pumps (also known as progressivity cavity pump, eccentric screw pump, mono pump) use a spiral rotor to move a chamber full of product through the pump. When moving slurries it is critical that the rotor wipes the rubber or elastomer stator firmly, else fine particles get between the rotor and stator and rip material out. This article discusses a major operating problem when the wrong size rotor was used in a stator.

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Road Tanker Compartment Design

Road Tanker Design For Fast Unloading And Onshore Pump Drain Tank. To completely empty a road tanker the compartments need to be designed to have a sump that permits total drain-out of the liquid from the lowest point. If a pump is mounted on the trailer, it is best mounted under the trailer. Where a pump is mounted on the tray or fenders it will cavitate at low tanker liquid levels. For an onshore unloading pump installation it is best to install a buffer tank between the tanker and onshore pump to let the road tanker completely drain-out before the pump starts cavitating. Tanker load-out pumps must have a very low net positive suction head requirement.

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Using Reliability Principles for a Cheap Way To High Pumping Circuit Availability. High plant availability is achieved by having redundant equipment that can be brought on-line as soon as the operating unit has failed. Redundancy is expensive as there are two items to buy, two to install and two to maintain at full operating capacity. There is an alternate option for maintaining high pumping circuit availability by designing quick methods to bring mobile equipment into the circuit when pumps are down. This article explains how to set-up piping for a mobile pump to maintain operation when the normal duty pump is out of use.

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Use an Isocorrosion Diagrams To Recognise High Corrosion Situations And Design Process Equipment Accordingly. A true story of how a high nickel alloy (Alloy 28) reactor was holed in 8 weeks by sulphuric (sulfuric) acid running down the inside wall. When the situation was reviewed in detail using an iso-corrosion diagram for the alloy in sulphuric acid it was obvious that such a problem would occur. The iso-corrosion curves clearly showed the huge corrosion rates that would happen at local contact points within the reactor. A clear and detailed understanding of how to use iso-corrosion curves would have highlighted the problem at the design stage.

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Mother Nature And Father Time have together built well. What they have left behind lasts a long time without failure. Humans can run for 100 years with very little maintenance. Trees can run for thousands of years without maintenance. There are lessons for us to take and apply. The life on our world shows us how to achieve truly outstanding reliability and availability. Do you want a thing to last 20 years trouble-free all its life, maybe 50 years without a problem? By looking at what the Mother Nature And Father Time left behind you will find the answers.

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Error Proof Quick Mating Part Location And Alignment. For speedy and easy maintenance it is best to design equipment with a means to insure accurate and exact location of contacting parts. This removes the opportunity for alignment errors during rebuilds and speeds-up maintenance overhauls. In this article is a sketch of two common methods used to provide positive and certain location and alignment between mating parts.

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Split And Clamped Mounting Hub For Shaft Attachments. For speedy and easy maintenance it is best to use a clamped hub to mount attachments to shafts when possible. This article presents a conceptual design of a split hub bolted and clamped to a shaft. The required attachment is then mounted to the removable hub.

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Pressure Flange Seal For Liquid Filter Pressure Vessel. When a leak occurs between pressure flanges and the arrangement cannot be successfully sealed, it is necessary to change the sealing design. This article explains a successful modification done to the lid and body flanges of a vertical pressure leaf filter used to remove particulate from a liquid stream. It incorporates a ‘tongue and groove’ sealing arrangement, with the ‘tongue’ in the lid flange and the recess in the filter body flange.

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Dust ingress into bearings is one of the great causes of premature bearing failure on bucket elevators. By selecting the right bearing housing and position, combined with this special dust seal arrangement, you can get quadruple the bearing life. The article provides the full details of the low pressure dust leak seal design along with a sketch of the successful set-up.

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There is always a degree of uncertainty in selecting instrumentation for difficult or corrosive environments. Material selection for chemical compatibility involves a strained decision between cost and equipment reliability and longevity. The other major uncertainty is whether the instrument is appropriate for the application – will it repeatedly give truly representative readings all it’s operating life? This article presents a list of instrumentation successfully used in a range of difficult and chemically demanding environments.

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The cyclo-drive gearbox is a variation of a planetary gearbox. They have the added advantage of not using gear teeth to drive the shafts; rather they use an internal offset cam arrangement to drive rolling pins that turn a cycloidal wheel inside the gearbox. The rollers are capable of taking 500% overload without breaking the gearbox. One other benefit of the cyclo-drive gearbox for users is that many models are grease filled and do not use oil.

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Acid Sparge And Acid Sparging. When you want to introduce acid directly into a liquid below its surface a sparge pipe is used. It is necessary to select materials that are compatible with the chemicals and the process. This article explains the issues to address when selecting the sparge pipe materials for injecting acid into a process reactor and what to consider when designing and installing the sparge pipe into such vessels or tanks.

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