How Do I Prevent Galvanic Corrosion In My Packing Gland?

Galvanic corrosion is an electrochemical process that occurs between two dissimilar metals, or between a metal and a conductive non-metallic material, when both are exposed to an electrically conductive media. In the case of a packing gland, it occurs between a metal component and the carbon or graphite packing. Under these conditions, the material that is closest to the anodic end of the galvanic scale will be corroded in preference to the one that is closest to the cathodic end of the scale. (See Table 1.) As the distance between materials on the galvanic scale increases, a corresponding rise occurs in the rate and the extent of the corrosion.

picture of galvanic series table 1

In a valve or a pump using packing made of either graphite or carbon, a galvanic reaction may be initiated as soon as any electrically conductive fluid, such as water, is introduced. Since graphite is more cathodic than the metals that make up valves and pumps, it is the metal that may be subject to corrosive attack.

Liquid Phase Needed

Even though a valve or pump may be packed with a graphite or carbon packing, many cases exist in which the metal parts will not be subjected to galvanic corrosion. For example, an electrically conductive fluid in a liquid state must be present for the galvanic reaction to take place. The temperature of a superheated steam valve prevents the accumulation of any significant amount of water, thereby nullifying the possibility of galvanic corrosion.

Stainless Steels

Another example of when galvanic corrosion protection may not be necessary is when the equipment is constructed of austenitic stainless steels (e.g., 300 series, 630, etc.). These stainless steels are much more resistant to galvanic attack.

On the other hand, the martensitic stainless steels (e.g., 400 series) are highly susceptible to galvanic attack. If a valve or pump is constructed of martensitic stainless steel and if it will be exposed to an electrically conductive fluid for any period of time, then consideration should be given to incorporating a galvanic corrosion inhibitor system into the carbon or graphite packing sets used to seal it.

When Are Corrosion Inhibitors Needed?

Continue reading How Do I Prevent Galvanic Corrosion In My Packing Gland?

The New Hygienic Forseal and Hygienic Pressure Seal From Freudenberg

Strict hygiene regulations in the food industry present major challenges for sealing technology. Freudenberg Sealing Technologies is enhancing its proven portfolio of hygienic sealing solutions with two products that are also designed for high-pressure applications. This was made possible thanks to special design solutions and the premium elastomer and PTFE materials developed in-house.

Food processing demands strict hygiene and cleanliness standards. It’s also important to ensure that no substances can migrate from the materials coming in contact with food, which could lead to contamination of the product. With its hygienic product line, Freudenberg Sealing Technologies has developed sealing solutions that fulfill food industry standards and are also resistant to CIP/SIP media. The Hygienic Forseal and Hygienic Pressure Seal are the newest members of this innovative product family.

Lena Eberspach, Rainer Kreiselmaier and Sina Etter (f.l.t.r.) from Freudenberg Sealing Technologies discuss the new products of the company’s hygienic sealing solutions portfolio. Copyright: Freudenberg Sealing Technologies

One of the basic requirements for sealing solutions in accordance with the hygienic design standards is a dead-space-free construction. It prevents the collection and settling of product residues and micro-organisms in undercuts, for example. The selection of applied materials and their resistance to hot water, steam, acids, alkalis and high pressures are also relevant. Observing the deformation at the relevant temperature plays a particularly important role in detecting distortions and the associated formation of dead spaces at an early stage in the product development. Continue reading The New Hygienic Forseal and Hygienic Pressure Seal From Freudenberg

Residual Torsional Stress: What Is It & Why It’s The Silent Killer

picture of cam forming

Why Stress over Residual Torsional Stress?

Residual torsional stress is a by-product of the helical forming process, evident by the hose’s visibly-twisted seam weld.

It’s no secret that torque is a killer for metal hose. If you’ve ever attended Hose Master University, you’ve probably heard our corporate trainer’s well-known adage- “Don’t twist the hose!” Torsional stresses are something that you want to avoid completely in all metal hose assemblies. When Hose Master inspects corrugated metal hoses and looks for torsional stress, it’s typically after installation while the hose is in service. However, we should also be concerned with torsion that can happen before installation during the manufacturing process. This is referred to as residual torsional stress.

Residual torsional stress (RTS) is problematic because it accelerates fatigue to the metal, thus reducing the ultimate service life of the hose. A key indication of RTS is when a hose has a visibly twisted seam weld. Despite the issues created by RTS, it is inherent in many hose forming processes used today The only way to prevent RTS in metal hose is through avoiding the use of manufacturing methods that cause it. Let’s explore some of the ways residual torsional stress can be created during manufacturing. Continue reading Residual Torsional Stress: What Is It & Why It’s The Silent Killer

Making Seals That Keep Dust Out Of Equipment

Dust is typically a minor annoyance that haunts the surfaces of our home. But in the world of engineering, machinery, and mechanical systems, it can be the difference between a reliable piece of equipment and disaster.

Dust can cause major damage to cylinder walls, rods, seals and other components inside of machinery. And if you’re not careful, dirt, mud, debris, and water can all cause damage as well.

These foreign contaminants are real problems for mechanical systems, especially as they build up in small quantities over time. A single particle of dust today may be no big deal. But a mote of dust a day will eventually become enough of a presence to cause serious issues, like friction, surface wear, and imperfect seal contact between surfaces.

These issues could compound until the mechanical system experiences a complete failure. It may seem like perfect is impossible, and that eventually some contaminants will get into your system no matter what you do.

But in some applications, like in automobiles and aircraft, failure is simply not an option.

Beyond those industries, many types of equipment need to stay clean on the inside, even when things get extremely messy on the outside. Examples include earth movers, hydraulic cylinders in steel mills, snow plows, and metal foundries, and in seals in logging equipment.

picture of wipers

How to Keep a Mechanical System 100% Dust-Free

Just as seals keep pressurized fluids and gases in piston and cylinder systems, there are components that are designed to do the exact opposite — keep contaminants out.

In the sealing industry, the three main types of components used to keep dust at bay are wipers, excluders, and scrapers. While each are a bit different, they all serve the same basic purpose, and are fitted on the exterior side of the main seals in a system.

The exact type of dust-prevention mechanism you need depends on what exactly you’re trying to protect against. Here are three different types below:  Continue reading Making Seals That Keep Dust Out Of Equipment

Sealing at Extreme Low Temperatures

Article re-posted with permission from Parker Hannifin Sealing & Shielding Team.

Original content can be found on Parker’s Website and was written by Nathan Wells, application engineer, Engineered Polymer Systems Division.


Heavy duty equipment moves industry forward in all climates, from the sunny Caribbean to icy Greenland. Effective, reliable sealing is what allows hydraulic systems in heavy duty equipment to do work, no matter the temperature. Reliable sealing solutions allow cylinders on dump trucks and excavators to move icy, frozen tundra, and allow actuators on subsea valves to operate 5,000 – 20,000 feet below the surface of the ocean. We depend on these seals for our safety and productivity, so a little chilly weather is no reason to call it quits.

What happens to seals at cold temperatures?

Most objects shrink as they get cold, with few exceptions, such as water. This applies to all matter in the universe. Materials shrink at different rates, and this is a measurable property called the Coefficient of Thermal Expansion (CoTE). Thermoset elastomers and thermoplastics shrink roughly 5 times more than metals for a given temperature change. This means at cold temperatures, seals shrink more than their housings, and thus have less “squeeze” to make a tight seal.

To make matters worse, elastomers also harden as the temperature drops. At some temperatures, known for each material as its Glass Transition Temperature (abbreviated ‘Tg’), seals become rock hard and brittle … like glass. We don’t make seals out of glass for a reason; they wouldn’t work. In order to keep seals springy and resilient, we need to specify materials with a Tg below the coldest temperature a system will see.

In very high pressure, low temperature applications, there is one additional concern. Applying pressure to seals effectively raises the Tg of the material by about +1°C per 750 PSI. This is called Pressure-Induced Glass Transition and is the reason high pressure seals fail slightly above their measured Tg. Continue reading Sealing at Extreme Low Temperatures

Tips for Gasket Storage and Maximizing Life

So you spend hundreds or even thousands of dollars every year on sealing solutions, like gaskets. But did you know that the way you store your gaskets could affect the effectiveness or life span of your gaskets? In this blog, we offer some tips for gasket storage and shelf life which, if followed, can help ensure that your gaskets are always ready for service.

Gasket Storage and Shelf Life: General Storage Principles

Rubber gaskets should always be stored in a cool location which is free from excessive humidity, direct sunlight, and the presence of chemical vapours or fumes. The storage location should ideally be indoors and free from exposure to the elements or inclement weather. If the storage guidelines given below are followed, rubber gaskets or gasketed components have the following expected shelf life:

storage life gaskets

Tips for Gasket Storage and Shelf Life

Tip #1: Limit exposure to light

Sunlight and strong artificial light can degrade some gasket materials. For this reason, rubber gaskets should be stored in cartons or opaque bags which prevent direct exposure to light.

Tip #2: Maintain relative humidity levels

Very moist or excessively dry conditions in a storage location should be avoided. Relative humidity levels below 75% are recommended for most rubber gaskets. Similarly, very low humidity levels which can cause some materials to dry out and become brittle should also be avoided. Continue reading Tips for Gasket Storage and Maximizing Life

The Braid Variations of Compression Packing

picture of compression packingSuccessful fluid sealing of valves and pumps cannot be accomplished without the appropriate sealing device. Whether using mechanical seals or compression packing, one must understand the specific needs of the application.

While mechanical seals in general are considered the superior sealing device, they are more expensive and less versatile than compression packing. Compression packing is more versatile due to the vast selection of materials used to make it and the various ways it is constructed. Materials such as vegetable fibers, man-made fibers, metals, graphite, and hybrids are all used to make packing. Construction types include braided, twisted, wrapped (rolled, folded), extruded, laminated, bulk, and die formed.

Construction types of compression packing each have variations within. This article will focus on braided packing. The most common braiding styles are square braid, round braid, twisted braid, braid-over-core, and lattice (interlock) braid.

Square Braid

The majority of braid types covered in this article are described by a geometric shape. One of the most common braids used to make compression packing is the square braid. Square braid is known to be soft and pliable, relatively loose, and can carry a large percentage of lubrication. Square braided compression packing can be formed from a variety of materials and can be woven as a homogeneous or composite product, where strands are passed over and under each other in the same direction and have a square or rectangular cross-section. Given its soft and loose characteristics, square braid will expand more radially than other braid types, which is especially effective when trying to seal worn, old equipment where voided space needs to be filled. Square braid packing is best used in applications of high speed rotary motion at relative low pressure. Continue reading The Braid Variations of Compression Packing

Spring-Energized Metal Seals Help Protect Equipment

Spring-energized metal seals provide numerous advantages in oil and gas applications, including but not limited to MWD and LWD tools, couplings, subsea compressors, enclosures/vessels, christmas trees, electronic submersible pumps and flowmeters. Extreme operating pressures and temperatures, together with more difficult resource recovery, zero tolerance for failure and environmental concerns, are placing unprecedented demands on this equipment.

Traditionally this industry has used solid machined seals that provide high compression loads but lack resilience. They also tend to have relatively high rates of leakage over time as flanges deteriorate. Recent advances in metal seal technology provide controlled compression, high resilience and reduced leakage.

Background

picture of spring-energized metal sealThe industry once used elastomeric seals extensively but discovered they work only within a certain temperature range, becoming brittle in cold and tending to flow at warmer temperatures. At elevated temperatures and pressures, seals can undergo a phenomenon called explosive decompression, extruding out of a flange and resulting in catastrophic failure of the seal. The porosity of elastomeric seals makes them subject to increased leakage over time.

In addition, they are limited in terms of chemical compatibility and have a tendency to degrade with age.

Metal seals, by contrast, offer greater chemical compatibility and longevity. They have no porosity problems and hold up better to aggressive media such as hydrogen sulfide. Metal seals have long been used by industry. Some companies even have their own sealing departments creating custom-machined metal and elastomeric seals to meet their specific requirements.

Among the machined metal seals these in-house departments produce are ring joint flange seals. These seals are inserted into trapezoidal-shaped grooves that allow them to tolerate bidirectional pressures. However, their lack of resiliency and plastic deformation results in extremely high seating loads.

Evolution of metal sealing

First used by the nuclear industry, metal O-rings were among the earliest types of resilient metal-to-metal seals. These were superseded by metal C-rings (Figure 1). Developed for the aerospace industry for weight reduction, these C-ring seals are more resilient than O-rings and require less load, allowing the use of smaller flanges and fewer bolts. Energized by higher pressures, C-rings are capable of achieving good sealing levels. Pressure-energized seals of this nature do not perform as well at lower pressures due to low seating loads and contact stress. In many cases, a silver coating can be used to improve sealing performance provided there is sufficient load to achieve plastic deformation.

Large-diameter spring-energized metal seals were originally developed for the French nuclear power industry. Unlike pressure-energized seals, they function by plastic deformation of a metallic jacket with greater ductility than the flange materials. This deformation occurs between the sealing face of a flange and an elastic core composed of a close-wound helical spring.

Spring-energized seals look similar to spring-energized C-rings but have a soft outer liner and open away from pressure (Figure 2). By contrast, spring-energized C-rings with plating have a hard outer layer and open toward the pressure.

The spring provides a specific resistance to compression, during which the pressure forces the jacket to yield, filling any machined finishes and imperfections on the face of a flange by making positive contact with it. Each coil of the helical spring acts independently, allowing the seal to conform to any surface irregularities on the flange.

Highly engineered with respect to pressure and leakage parameters, spring-energized seals are preferable not only to elastomeric seals but to plated metal C-rings as well. The soft liner/jacketing of these seals is typically three to five times thicker than such plating, providing more range to fill flange imperfections and rougher machined surfaces while eliminating the potential adhesion problems platings have at elevated temperatures.

Oil and gas applications

As noted, spring-energized metal seals are used extensively by the oil and gas industry. In North Sea operations they are used on the flanges of all equipment, where the seals provide longevity in the face of extreme temperatures and pressures. They also are used to protect subsea and downhole electronics that measure, log and transmit data while drilling. The seals can withstand typical operating temperatures from cryogenic to more than 538 C (1,000 F) and are subjected to pressures of up to 35,000 psi in a highly corrosive environment.

Another application for these seals is subsea valving systems, or christmas trees, where they prevent pressures of up to 15,000 psi from blowing out pipes and creating leaks. These also eliminate the potential for explosive decompression, which results in environmental issues and loss of production.

Valves are critical to subsea systems, yet some producers still use polytetrafluoroethylene and other elastomeric materials, which expand and contract drastically with changes in temperature and pose problems above 177 C (350 F). A better solution is to use spring-energized metal seals, which have the resilience to tolerate most operating temperature gradients.

Spring-energized seals are designed on a case-by-case basis. Like most metal seals, they have been used primarily in static applications, where movement due to thermal expansion, pressure cycling and flange deflection is not an issue. Due to the nature of recent oil and gas activity, traditional static applications are few and far between. It is not uncommon to see spring-energized seals in standard dynamic applications such as globe, ball and butterfly valves, where they serve as seat-sealing components. Designs of this type take time to develop.

Notwithstanding the difficulty of understanding flange dynamics and simulating actual operating conditions, semidynamic seals are continuously under development to accommodate greater flange movement. Helpful in this regard is a mnemonic acronym, STAMPS, that defines the basic criteria of seal design and selection, namely size, temperature, application, media, pressure and speed.

Spring-energized metal seals can be designed for a 30- year life while providing low leak rates with zero visible leakage over time. The seals can be manufactured using materials that meet the requirements of the U.S. National Association of Corrosion Engineers.

Another critical condition in oil and gas equipment is abrupt change in the axial direction of pressure, which can cause flanges, piping and seals to flex and shuttle. This can be an issue for some spring-energized seals, which must be specially designed to tolerate extreme bidirectional on/off pressures. It should be noted that bidirectional sealing capability is not a requirement for radial flange seal configurations.

Spring-energized metal seals are the sealing solution of choice for many oil and gas industry applications. The seals not only provide greater chemical compatibility and longevity than elastomeric seals but also the structural integrity that comes from metal-to-metal contact. In addition, they can offer more resilience and lower compressive loads than other types of metal seals.

picture of spring-energized metal sealCapable of handling extremes of temperature and pressure, the corrosion-resistant seals are particularly well suited for subsea applications, where they protect critical equipment and systems from harsh operating conditions. Their ability to absorb the flexing that accompanies temperature and pressure changes also protects piping systems in which the seals are installed.

Spring-energized metal seals meet both U.S. and other countries’ industry standards, helping assure compliance with applicable safety and environmental regulations. New versions are being developed for semidynamic and bidirectional applications, further expanding the capabilities of metal seals.


The original article was written by Jacob Young and Kevin Lamb at Technetics Group. Find the article on their website here.

For more information about spring-energized seals, contact Gallagher Fluid Seals today.

Vesconite Hilube for Pump Applications

Vesconite Hilube can last up to ten times the life of bronze

Vesconite - Hilube for Spindle PumpsVesconite Hilube is a thermopolymer, designed for particularly difficult operating environments. Hilube is specifically recommended for moist and underwater applications. These include the pump and marine industry, where regular maintenance is not practically feasible or cost-effective. Displaying superior wear life, especially in poorly lubricated and dirty conditions, Vesconite Hilube has been shown to offer up to ten times the life of bronze bushings.

Vesconite Hilube incorporates an internal lubricant that translates into an exceptionally low friction coefficient. With excellent dimensional stability, low wear rates, and a high load-bearing capacity, Hilube excels in difficult applications.


Vesconite Hilube has been used for decades in a wide range of specialized pump bearing applications.

The material thrives in water, keeping to machined sizes without swelling and with zero delamination.

Other advantages are that it does not corrode, and helps prevent the corrosion between metal components especially in salt water; is resistant to oils and fuels; and is easy to machine, fit and remove – and prolongs shaft life.

In addition, it allows dry startup for up to 1 minute.

Vesconite Hilube is recommended for most pump bearing applications, such as:  Continue reading Vesconite Hilube for Pump Applications

The Pros And Cons Of PEEK Back-Up Rings

peek back up ring picture

Back-up rings serve an important role in world of seals. While the design principle and construction are incredibly simple, they greatly extend the usefulness of the most common and prolific sealing device in the world: the O-ring.

Back-up rings are aptly named as they do just that: they back-up an O-ring.

Back-up rings are commonly nothing more than a ring of polymer meant to space the O-ring away from the extrusion gap in hardware. By blocking off the extrusion gap, the pressure-handling ability of an ordinary O-ring is greatly increased.

Solid or split back-up rings out of virgin PTFE can usually be found on the shelf, and are largely considered commodity items.

While the design and functionality of a back-up ring rarely changes, the material selected can greatly complicate this simple device. Some applications require specific material properties and/or special material certifications.

Back-up rings can be made for a variety of unique applications;: Military-spec back-up rings out of fully certified AMS 3678/1 virgin PTFE; Certified “MS” style back-up ring (MS27595 or MS28774); PTFE blends; Thermoplastic elastomers; Urethanes. But the most common custom material for back-up rings is usually PEEK (polyether ether ketone).

In certain applications, PEEK has some distinct advantages as a back-up ring material. But with these advantages comes some potential issues.

Read on if switching from a PTFE to a PEEK back-up ring sounds like an enticing proposition to see what you need to consider before making the change. Continue reading The Pros And Cons Of PEEK Back-Up Rings