Tag Archives: Fluid Sealing Association

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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Custom Rubber Expansion Joints

Keeping aging facilities and equipment maintained is an everchanging task that can jeopardize the goal of maximizing uptime. Years of thermal cycling, vibration or foundation settling can disorient piping or pumps. Piping engineers will use rubber expansion joints to account for these types of challenges in a rigid piping system. Permanent misalignment can set
in after years of operation. The original size expansion joint could no longer be the best fit when it comes time to replace.

Replacing a permanently misaligned expansion joint connection with the original part could lead to reduced service life and/or missed expectations of the new expansion joint. Determining the best way to accommodate this when it comes time to replace the existing expansion joint can have long-term effects on reliability.

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Sealing High-Speed Shafts in Turbomachinery

Rotating liquid pump shafts that are originally sealed with soft packings mostly use contacting face seals, also known as mechanical seals. Typical rotational speeds are roughly between 1,000 and 3,600 revolutions per minute (rpm). In turbomachinery — such as compressors and expanders—the rotational speeds are higher and mechanical seals would not
immediately appear to be an option, due to greater rubbing speeds along with a lack of liquid cooling and lubrication.
Nevertheless, from the late 1970s when they were first marketed, noncontacting mechanical seals, known as dry gas seals in cartridge form, have been used in most gas turbomachinery.

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API 622: Valve Packing for Fugitive Emissions

The American Petroleum Institute (API) has developed two commonly used standards designed specifically for the petroleum industry. They include API 622 “Type Testing of Process Valve Packing for Fugitive Emissions,” and API 624 “Type Testing
of Rising Stem Valves Equipped with Graphite Packing for Fugitive Emissions.” API 622 and API 624 may be specified by an end-user. Valve OEMs must use API 622-approved packing for any valve on test for API 624.

Since the introduction of the U.S. Clean Air Act in 1963, the U.S. Environmental Protection Agency (EPA), as well as individual states, have set increasingly stringent restrictions regulating fugitive emissions from industrial facilities.

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Across the broad spectrum of process industry applications today, fluid handling sealing systems perform a vital role in plant safety, maintaining pump efficiency, reliability, energy consumption, water usage and control of emissions to the environment. Often well hidden within the visible pumping equipment structure, mechanical seals operate 24/7 performing the critical function of static and dynamic sealing between the fixed pump housing and rotational drive shaft. From aqueous solutions to very abrasive slurries to highly volatile and hazardous fluids, mechanical seal technology continues to advance meeting the increasingly demanding application conditions and emission control standards required of users today.

Mechanical Seal Design
The most basic mechanical seal is comprised of a primary wear ring element fixed to the rotating shaft and a stationary opposing wear ring element that is fixed within the pump housing. Having precisely machined surfaces, these two wear components or seal faces are axially spring loaded together creating a seal interface. Dynamically, the wear faces operate on an extremely thin, highly engineered fluid film creating a stable, controlled operating environment between rubbing surfaces of the seal faces.

Maximum Sealing Safety and Reliability
Seal education and operator safety awareness training is of the highest priorities that the Fluid Sealing Association member companies promote. The FSA KnowledgeBase (fsaknowledgebase.org) shares design tools, best operating practices, and guidelines to meet government regulations using best available control technology, which emphasizes the importance of applying the right seal design for each given set of operating conditions. Seal selection based on all working conditions, fluid properties, equipment operating procedures and proven performance to industry standards like API-682 all must be considered and applied to achieve maximizing mean time between planned maintenance.

Environmental Responsibility
Recent advances in mechanical seal technology are playing a significant role in our collective responsibility to promote and achieve fluid control systems that meet the highest levels of environmental responsibility. The development of engineered seal face materials is lowering the coefficient of friction on seal faces thereby reducing power consumption, heat generation, and the associated the volume of cooling water required. Gas lubricated dry running dual seals that further minimize power consumption and fully isolate the process fluid from atmosphere are achieving near zero emissions to the atmosphere and the utilization of fluid dynamics modeling tools providing highly predictive behavior of seal interface conditions is optimizing performance on highly critical applications.

Fluid Sealing Association Releases Latest “Compression Packing Technical Manual”

The Fluid Sealing Association (FSA) has released the fourth edition of the “Compression Packing Technical Manual.” This update represents a four-year intensive joint effort of FSA and the European Sealing Association’s (ESA) compression packing technical committee’s new technical learnings. These learnings can help inform end users on industry best practices and performance characteristics of compression packings.

New sections to the manual have been added including:
- environmental controls
- compression packing vs. mechanical seals – leakage rates
- pump packing power consumption
- determining stuffing box dimensions

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Unusual Mechanical Seal Applications

There are applications where the use of a mechanical seal would either not be considered or present major technical challenges. Here are some unusual examples of how mechanical seals can be applied to solve problematic sealing tasks.

LATEX
Liquid synthetic latex is an emulsion of polymer particles suspended in an aqueous solution. It is used in making coatings, glues and gloves and more.

Sealing latex has historically been a problem for mechanical seals because it solidifies when exposed to either heat or friction (shear). When latex is exposed to heat, water separates from the polymer particles leading to solidification or coagulation. A more challenging issue with sealing liquid latex is that when it enters the gap between the mechanical seal faces, it gets sheared which also leads to local coagulation.

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A User’s Guide to Expansion Joint Control Units

It is no secret that one of the greatest demands for an expansion joint is the expectation to serve a long, leak-free life with little to no maintenance. Once installed, these flexible rubber connectors should require little attention. The preservation of this investment (and one’s sanity) can be maximized with an in-depth overview of how control units can prevent a new expansion joint from being overstressed.

The purpose of a control unit is to act as a safety device against excessive movement resulting from pressure thrust. A typical control unit assembly is comprised of threaded rods, steel gusset plates, nuts and washers.

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