Compression Packing

Abrasive media comes in many forms—from mining slurries to wood pulp and even substances as seemingly mild as liquid chocolate. This diversity rules out a one-size-fits-all solution for abrasive pumping applications. However, today’s broad range of materials, from carbon fiber packing to graphite-filled polytetrafluoroethylene (PTFE) bushings, includes products capable of meeting an equally broad range of abrasive wear requirements.

Carbon Fiber Packing

Few materials offer the abrasive resistance and heat dissipation of carbon fiber yarns. Braided compression packing made from this material excels under extreme conditions, including exposure to a variety of chemicals, temperatures approaching 850 F (454 C) in oxygen-rich atmospheres (up to 1,200 F/649 C in steam) and shaft speeds in excess of 4,000 feet per minute (fpm).

The strength of carbon fiber yarns combined with their ability to draw heat from pump shafts make them the material of choice for resisting abrasive wear. Unfortunately, they do not seal as well as graphite foil packing. Upon closer examination, however, the speed and temperature capabilities of these two materials are similar.

Consider this hypothetical scenario: An abrasive pumping application is under control using carbon fiber, except for excessive leakage across the packing set. Depending on the nature of the leaking media, it may not be desirable to have it pooling on the plant floor. Even if it is just water, excessive leaking media is lost profit. If the leakage is clean, the carbon fiber packing is effectively excluding abrasives.

Carbon Fiber Rings and Foil Packing

When dealing with clean media, graphite foil packing becomes an option. At a subsequent repacking, it may be advisable to use just two carbon fiber rings in the bottom of the stuffing box and use graphite foil packing for the remaining rings.

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.

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?

Successful 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.

It’s highly likely that, at some point or another, you have seen braided packing in or out of its “natural environment.” Braided packing looks like rope and is cut into rings that wrap around a rod. While packing used to be available in fairly limited styles, the mechanical packing industry has expanded over time, resulting in braided packing that is available in everything from flexible graphite to fiberglass yarn. Let’s dive into this topic, and discuss the different materials from which braided packing is made in this day and age.

Fiberglass Rope

One of the reasons why fiberglass ropes are favored for braided is that it does not burn. It can be used in continuous temperatures, up to 1,000 degrees Fahrenheit. This makes it perfect for products that are going to exist in high pressure, high-temperature environments. Furthermore, E glass in particular consists of

Ensuring the correct materials are suitable for the application

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.”

In October 1990, the USS Iwo Jima was heading into port for routine maintenance in Manama, Bahrain. The ship was the first to be designed and built from the keel up as an amphibious assault ship in Puget Sound Naval Shipyard, Bremerton, Washington, on Sept. 17, 1960.

Small packing leak can turn catastrophic

Valve 2MS-7 was a globe valve in the boiler room, and it needed to be repacked for a small packing leak and reconditioned while in port. The valve was worked on by an outside contractor who had limited understanding of military specifications and procedures.

The mechanic—who had 10 years of experience—decided to replace the fasteners on the bonnet because they were worn. Apparently, the mechanic asked one of the boiler room personnel for new nuts and bolts and was given permission to look through the boiler room’s spare parts bins. He selected four bolts, eight studs and 20 3/4-inch nuts. The mechanic had not noticed that some of the nuts were brass. Because those fasteners were covered with a manufacturer-applied black coating, they were mistaken for the correct grade 4 steel nuts. Closer examination and use of a scratch or magnetic test would have revealed their metal content, but instead the black brass nuts were installed.

The next day the valve was reinsulated with lagging. The foreman had not inspected the work done on 2MS-7.

The valve should have been reassembled using only B-16 steel studs—anything else was a violation of good engineering practice based on the service condition.

When the brass nuts were used on the studs holding down the bonnet of the valve, no one realized this was a critical mistake since the valve was going to be in service above 800 F and the temperature limit for brass is 400 F.

On Oct. 30, 1990, in preparation to get underway and proceed to her operating area, fires were lighted in the boilers of the vessel.

Shortly after, one side of 2MS-7 was initially pressurized with steam generated from Boiler No. 1. Three hours later, valve 2MS-7 was opened to supply steam to the generator that supplied electrical power to the vessel.

As steam at 600 pounds per square inch (psi) and 850 F began flowing through the valve, the brass nuts were expanding at a greater rate than the steel studs. The bolts started losing the strength to secure the bonnet to the valve body. After less than 30 minutes of operation, the valve failed catastrophically.

Better and faster access to the seals you need to keep your production running.

King of Prussia, PA. October 29, 2019 /News and Updates/ -- Gallagher Fluid Seals (GFS) is excited to announce the launch of its e-commerce store, providing a brand new experience to shop for seals.

“It’s been a complete team effort,” says Chris Gallagher, CEO. “Our team has worked diligently over the past several months to prepare and deliver a state-of-the art e-commerce store for both new and returning customers.”

As the world’s economy has evolved to an online platform, GFS felt seal buying should be easier. Gone are the days of calling in and ordering a replacement seal - or sending an RFQ. This new online experience allows greater and faster access to the seals you need to keep your facility up-and-running.

“Maximizing the ease-of-purchase and visibility of fluid sealing products is imperative to the future of seal buying, and