Tag Archives: Fluid Sealing Association

Bolting Considerations for Bolted Flange Joints, Part 1

Often in the deployment of bolted flange joints, the end user is supplied with a targeted gasket stress with little appreciation for the compensations that are, or should be, included in deriving this stress. The informed end user realizes that there can be many such compensations. In all cases, it is important to understand the state of stress of the bolts and flanges.

The following is a two-part article that addresses the subject of bolt strength resulting from gasket stress compensations. Part 1 provides an explanation of the testing characteristics of both ductile and brittle bolting materials. Attention is drawn to the definition of yield and ultimate strength. Various types of bolting compensation are then discussed.

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Compression Packing Installation

In the world of safety, many accidents occur because people assume they fully understand how to respond or use equipment during an emergency. After reviewing some high-profile incidents, it becomes clear that their assumptions are often incorrect.

Recently, an end user reached out to the Fluid Sealing Association (FSA) regarding the calculation of flush pressure for a slurry pump. The pump manufacturer directed the engineer to set flush pressure 1 bar—14 pounds per square inch (psi)— above the discharge pressure on the pump. This kind of directive is often due to limited knowledge of the system. While it may seem like a safe assumption for a broad set of applications, this actually can lead to shorter packing life and more downtime for the plant. For this particular end user, there was the added issue of obtaining the required pressure in the plant.

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Assessing Alternative Pump Piping Solutions

Some industry professionals have voiced concerns relating to the use of rubber expansion joints in pump piping applications. One recent claim cited installation misalignment and the expansion joint’s stiffness or spring rate as the reason for increased vibration levels across the system and more force being applied on the pump.

While every pumping system is different, it is more likely that the pressure thrust force from an unrestrained expansion joint would impose far more force and adversely affect pump performance, as opposed to a few hundred pounds of spring rate load. It is important to understand that unless the rods of the control unit are tied snug tight, the expansion joint could still impose a potentially damaging pressure thrust force on the pump. This point is commonly missed and may explain why some hastily feel the solution is to eliminate expansion joints, increase the rigidity of the piping system and tighten installation tolerances.

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ASTM International Committee Releases Latest Room Temperature Tightness Test

The American Society for Testing and Materials (ASTM) International Committee F03 on Gaskets recently released the latest standard practice to derive gasket design constants for the proper design of bolted flanged joints (BFJs): ASTM F2836-18. End users of gaskets can then use these gasket constants for proper BFJ design using calculation methods that are currently being developed by a special working group of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Section VIII at the time of this publication. In this article, the current test procedure, the mathematical models of the test evaluation and the calculation of the characteristics are described and discussed.

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Updates to FSA’s KnowledgeBase

The online FSA KnowledgeBase was officially launched in May 2017 as part of the FSA’s mission to be “. . . the primary source of technical information” for the fluid sealing industry’s products and their applications. This marked the transition from a print-based handbook focus to an online focus for training and education resources. At launch, the KnowledgeBase contained approximately 35 pieces of content and videos across seven categories of mechanical seal subject matter. Since that time, the FSA has expanded and improved the site content, which now has more than 230 files on mechanical seals, expansion joints, and an archive of “Sealing Sense” articles spanning the full range of FSA topics. There are more than 750 registered users, and the site has tracked nearly 5,000 online sessions from that user base.

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How Not to Use a Rubber Expansion Joint

Rubber expansion joints are likely the least understood and most abused component in a piping system. They are flexible, stretchy and easily forced into lots of places despite what the installation instructions say. Most of the time, rubber joints are merely an afterthought in multi-million dollar piping systems – until things go awry.

The rubber joint is unmatched for vibration isolation. If properly installed, a rubber joint can greatly reduce equipment nozzle loads. Its resilience allows it to be installed in many different systems under a range of temperatures, pressure, and media. What could possibly go wrong?

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The Danger of Complacency in Equipment Selection & Installation

When working with valves, flanges and pumps, operators should never be complacent. The wrong gasket or packing in a deadly application could result in loss of life. Ensuring the correct materials are suitable for the application requires special attention because safety is critical. As Gordon DeLeys, compliance assistance specialist at the United States Occupational Safety and Health Administration (OSHA), said, “Safety should not be a company priority since priorities in an organization can and usually change. Safety and health need to be a core value of an organization. Safety is really a case of values versus priorities.”

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How to Prevent Galvanic Corrosion of Valve Stems

Valve packing is a necessity for plants trying to contain product and meet the latest emission requirements However, finding a sealing product that works and has longevity can be a challenge. Graphite-based packing can be a good choice for stem sealing when elevated temperature requirements are necessary. This is due to graphite’s ability to maintain its sealing properties at temperatures that cause polytetrafluoroethylene (PTFE) to break down and allow leaks to occur. However, graphite is not an electrical insulator like PTFE; graphite will act as a metal and undergo galvanic corrosion if the environment is right.

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The Bolt as a Machine & the Importance of Liberal Lubrication

The bolt as a screw is one of the six simple machines. A simple machine magnifies or changes the direction of an input force. By means of mechanical advantage, a bolt can dramatically increase its input force. Take for example an 8-bolt flange with 3/4-inch diameter bolts. By manual effort alone, a person can easily develop a total bolt load of over 110 tons. This article explains the mechanics by which the mechanical advantage is possible and then draws attention to how friction can deteriorate the end effect of a bolt’s mechanical advantage.

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What to Understand About Chemistry to Make the Best Materials Choices

In chemistry, a strong oxidizer is a substance (like chromic acid) that can cause other substances (like seals and gaskets) to lose electrons. So, an oxidizer is a chemical species that undergoes a reaction that removes one or more electrons from another atom. This causes a change in mass. Metals will turn into their respective heavier oxides, and the carbon in graphite will oxidize into carbon dioxide – which, although molecularly heavier, is a gas at room temperature. This happens in pumps, valves, pipelines or any other equipment that have seals and gaskets carrying a strong oxidizer. It will cause pitting or rust and, depending on your choice of seal material, may require shorter service intervals.

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