The PetrolPlaza audio version is presented to you by UNITI expo, the leading retail petroleum and car wash trade fair in Europe.

Swivel Joints Roll with the Flow

The innumerable design choices of swivel joints allow a rigid piping system to be moveable, flexible and reliable. The task of selecting the correct swivel joint for your application is complicated. John Hartmann provides a basic understanding of the make-up of swivel joints and offers some help in sorting through the jungle of choices.



Last update:
Author: Hartmann John P.
Piping and delivery system essentials
Thanks to Emco Wheaton’s Jim Canary, Oilco Liquid Handling Systems’ Richard Slawinski and OPW Engineered Systems’ Neil Clevenger for providing material for this article.

What would happen if piping and delivery systems at petroleum refineries, terminals and bulk plants were not equipped with swivel joints? At best, the systems would be down constantly for major repairs. At worst, some systems would have severe problems operating or would be so troublesome that they would have to be closed. From their critical use in large piping systems to their role in loading arms and hose reels, swivel joint technology enables piping and delivery systems to keep on rolling with the flow.

At terminal and bulk plant facilities, rigid pipe work will not accommodate connections to tank trucks or rail cars, which do not always park in the same location. There are essentially two options at such facilities: swivel joints or flexible hose. Hose is limited by its bend radius and will wear out prematurely if twisted or kinked. Swivel joints allow hard piping to be articulated to cover a wide area. They also allow these assemblies to be counter-balanced for ease of movement. In contrast, heavy product-filled hoses can cause excess strain on operators. Even when hose assemblies are used, swivels may be added to the ends of the hoses to keep them from twisting.

Swivel joints and flexible hoses are important components of this large system. Courtesy of Oilco Liquid Handling Systems

Swivel joint jungle
Swivel joints allow the affected parts of a piping system to move and flex with any force that causes turning, twisting and other movement. They are highly engineered products and come in innumerable designs. Manufacturers produce numerous different configurations of swivel joints, which may be made of five different metals: aluminum, bronze, ductile iron, carbon steel or stainless steel. Their design also may vary for different “planes of movement,” pressures, temperatures, corrosion resistance and other factors.

Given so many variables, designers have come up with thousands of combinations of materials, components and planes of movement from which to choose.

The following information should provide a basic understanding of the make-up of swivel joints and some help in sorting through the jungle of choices.


Swivel joints with chevron “v” ring seals: (1) sleeve, (2) lube fitting, (3) set screws, (4) spring adapter, (5) packing seals, (6) female adapter, (7) raceways, (8) sleeve raceway and (9) "O" ring.
Courtesy of Emco Wheaton.

Joint parts, functions and materials
Swivel joints typically consist of (1) bodies, (2) sleeves, (3) bearings, (4) bearing races, (5) seals and (6) threaded, flanged or beveled ends. All of these parts work together to absorb the twists, turns and other movement without leaking and without wearing out prematurely.

Body and sleeve
The body of a swivel joint is inside a sleeve. Usually, the body (or a flange bolted to it) is connected to the pipe on one end of the joint and the sleeve is connected to the pipe on the other end. One swivel joint unit can have more than one body, sleeve and other parts, depending on the planes of movement required.

Clockwise from top, Style 30F (white) 1 plane of rotation, elbow, flange x flange; Style 20 (red) 1 plane of rotation, straight, FNPT x FNPT; Style 60 (gray) 2 planes of rotation, elbow, FNPT x FNPT; Style 30 (brass) 1 plane of rotation, elbow, FNPT x FNPT; Style 40 (gray) 1 plane of rotation, elbow, FNPT x FNPT; Style 80 (red) 3 planes of rotation, 2 elbows, FNPT x FNPT; Style 50 (yellow) 2 planes of rotation, 2 elbows, FNPT x FNPT. Courtesy of OPW Engineered Products

When the pipe to which the joint is connected moves or twists, the body and sleeve move, relative to one another. The sleeve and body are held together by balls, which form the bearing mechanism. Raceways are machined into both the body and sleeve. The balls are inserted between the two halves of the bearing raceways at assembly.

Swivel joint bodies and sleeves can be constructed of carbon steel, stainless steel, aluminum, brass or ductile iron. The choice of material usually depends on the required strength of the joint. The strength of a component is expressed in terms of load-bearing capacity, which is determined not only by the body and sleeve material, but also by the size and material of the bearings and races. For example, carbon steel swivels that have flame-hardened ball-bearing races provide high load-bearing capacity and minimize wear.

Swivels can have either one or two raceways. Those with one raceway normally utilize larger ball bear ings to increase their capacity. Thus, swivels should not be selected based on the number of raceways, but on the load-bearing capacity of the unit.

Cutaway view of Low torque swivel joint. Courtesy of Oilco Liquid Handling Systems.

Carbon steel and stainless steel swivel joints are normally used near the base of loading arms, where the loads are the greatest.

Aluminum swivels are usually found where lighter weight is needed and the load requirement is smaller, such as the outboard areas of loading arms or on the end of a hose assembly.

Typically, carbon steel swivels have about twice the load capacity of stainless steel and 22 times the capacity of aluminum.

In addition to load capacity and weight, pressure affects the choice of material. High pressure applications, such as liquid propane gas, do not use aluminum because of its limited pressure capability.

Basic swivel joint styles turn “every which way but loose.” Courtesy of Oilco Liquid Handling Systems

 

Bearings and races
Swivel joint bearings and races are positioned between the body and sleeve, hold them together and enable the body to turn easily inside the sleeve. Bearings and bearing races may be made of carbon steel, stainless steel or aluminum, the choice being made on the basis of load requirements and weight. Also, the bearings and races may vary in size, depending on the size of the joint and the number of raceways.

The bearing races are machined into the sleeve and body. They require lubrication by built-in grease fittings. Recently, sealed and permanently lubricated deep groove ball bearings have been incorporated into swivel joint design. Permanent lubrication reduces service requirements and concerns about lubricants contaminating the product, such as jet fuel.

Seals
Seals prevent dirt from entering bearing races, lubricant from escaping from the raceways and product from escaping from the swivel joint. Swivel joint seals may be either O-rings, chevron packing (v-shaped) or spring-energized u-cups.

Seal materials are compounds of various products tailored to specific needs. Some base packing material is encapsulated in PTFE for protection from the product being handled. Typical seal materials and applications include fluorocarbons (Viton) and Nitrile for handling petroleum; EPT/EPDM for hot water; fluorosilicone for cold weather use and perfluoroelastomers (DuPont Kalez and Green Tweed Chemraz) for chemical applications.

Because swivel joints rely on the seals to prevent leaks, any potential adverse effects that the product has on seal material must be considered in selecting the material. These effects include swelling, compression set (loss of resiliency) and reduction in tensile strength. The temperature range of the application also affects the seal selection.

Operating pressure affects the ability of a seal to prevent leaks, but not in the way you might normally think. It is more difficult to seal liquid and gas at low pressures than it is at high pressures. This is because at the higher pressure, the contained liquid forces the seals against their seats and improves their effectiveness.

Threaded, flanged or beveled ends
The ends of a swivel joint body that connect to the piping may be either threaded (for simply threading onto the pipe), flanged (for attaching with bolts) and beveled (for welding). The end connections are usually determined by the standards used in the other pipe work where the installation is located. However, the design pressure of the system may require a particular standard, such as 300-pound flanges. Welded construction is sometimes used to reduce the number of potential leak points, but this can create maintenance problems if split-flanged swivels are not used.

 
 
Swivel joint with “O” ring seal. Courtesy of Emco Wheaton

Choosing the right joint
Correctly selecting the swivel joint that best suits your needs requires familiarity with, and consideration of, a number of variables. In addition to the basic make-up of swivel joints as discussed above, these variables include the following:

• The required planes of movement that the swivel joint must accommodate, and whether the joint needs to be the oscillating type (moving back and forth) or the rotating type (moving in one direction only)

• The piping system’s load-carrying demands, including the desired flow rate and the related friction losses of the various swivel joint configurations, the maximum anticipated operating pressure and the strength required to handle the physical stress from the weight of the contained product and its movement

• The viscosity and temperature of product handled in the system and the compatibility of components with the product (Swivel joints in petroleum handling systems are sometimes approved by a third-party laboratory, such as Underwriters Laboratories (UL), for the purpose for which they are used. For example, such usage may include handling compressed gas, which could be tested against UL 567, which is the standard for safety of pipe connectors for petroleum products and liquid propane gas; or Class 1A liquid and gas, which could be tested against NFPA 58, the standard for storage and handling liquefied petroleum gases.)

• The maximum speed of the movement that must be accommodated by the swivel joint (This is not normally an issue in loading arms and other pipe work assemblies. However, in other applications, such as hose reels, the speed of movement may become an issue.)

• Lubrication requirements.

Yes, the task of selecting the correct swivel joint for your application is complicated. Not all of the information one would need to make the right choice could be written into this article. But the information that is presented should acquaint you with the nature of the task and help prepare you to seek the proper advise from someone with expertise on the subject.

Discuss