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Socket Joint is wildly used in underground FRP pipe system. This method completely conform to ASTMD and ISO standards.
During actual installation process, each joint is allowed to have a deflection as following table.
THE ADHESIVE BONDED JOINT VS THE BUTT & STRAP METHOD
Enclosed on the following pages is one in a series of papers written by the Engineering Department of EDO Specialty Plastics on fiberglass reinforced plastic (FRP) piping systems. This paper, on the comparison of the Adhesive Bonded and Butt and Strap Joining Systems, is one in a line of papers written on the basic principles involved in the selection, specification, and design of the components involved in fiberglass piping systems.
EDO Specialty Plastics, as a designer, manufacturer, and installer of fiberglass pipe systems with two decades of experience in the advanced composites industry, provides this paper as a service to its customers involved in the design and selection of fiberglass reinforced plastics piping systems.
The intention of this report was to collect a wide range of data on the various joining methods in use today and to provide the interested reader with information necessary to compare and contrast two of the most common methods, the adhesive bonded joint and the butt & strap joint. The data used in this report is independent test data comparing both joining systems, thus allowing the user to make his own independent conclusions and to select his or her preferred joining system.
The guidelines drawn in the report are based on the results of the independent testing performed and on the history and experience of EDO Specialty Plastics in the fiberglass composite pipe industry. These guidelines, however, are intended to be just that - guidelines. Each application of an FRP pipe system is unique and must be treated as such. Furthermore, because of certain intangibles involved with FRP pipe systems, a "pre-engineered" system is not recommended. A detailed design of each pipe system is necessary to achieve the full potential of the FRP pipe system. By doing so, the customer is ensured of a "custom-designed," "custom-manufactured," and "custom-installed" system to his specifications and needs.
Introduction:
When investigating the use of fiberglass reinforced plastic (FRP) piping in the chemical, petrochemical, marine, and other industries, several decisions have to be made early on in the design of the piping system. These include the fabrication technique (filament winding vs hand-lay up, for example), the method of installation (flanged pipe vs plain end pipe, and field-fabricated vs shop-fabricated spools), and the joining system (adhesive-bonded vs butt and strap, for example), to name a few.
The joining method used in a piping system can often determine the success or detriment of the system over its years of use, thus making it one of the more important factors in the engineering design of the system. The two most common methods are the adhesive-bonded joint and the butt and strap, or butt- weld, joint. Each of these joining methods have advantages and disadvantages. This report will first give a description of each type of joint, provide an engineering comparison of the mechanical characteristics of each, tabulate the advantages and disadvantages, outline potential applications, and summarize with a set of selection process guidelines for choosing the joining method.
The purpose of this report is to provide the interested reader with independent information comparing the qualities of the adhesive bonded and butt & strap joints and provide a set of guidelines for the joining system decision making process. This is but one of the many aspects of FRP piping systems that must be investigated before a successful design can be completed. Fabrication materials, pipe flexibility, and pipe strength are but a few of the additional aspects that should be considered. By reading and understanding the information in this report, one step of many is taken toward the successful design of a fiberglass pipe system.
A Description of the Two Joining Methods:
The Butt and Strap
The butt and strap joining method (also known as the butt and wrap, the butt weld, and the reinforced overlay joint; and sometimes referred to as an adhesive) is the oldest and most reliable joining method in the industry today. The butt and strap is made as it is described - two pieces of pipe are butted together and layers of chopped strand mat and woven roving are wrapped around the pipe in a resin matrix. The weld is applied to the exterior of the pipe and, if accessible, the interior as well (usually on pipe larger than 18" nominal I.D.). Refer to Figure 1 for a typical butt weld joint. By using the same materials as the pipe, the butt weld joint can be designed with axial and bending strength properties equal to or superior than the pipe.
Sometimes the butt and strap joint is referred to as an adhesive, as it is a mechanical, not a chemical, bond. However, the butt and strap should not be confused with the adhesive bonded joints described next.
Figure 1. A typical butt weld or laminated joint.
The Adhesive Bond
A second type of joint was developed to act as a "joint of convenience" in the industry. This is the adhesive bonded joint. There are three common types of adhesive bonded joints: 1) taper by taper, 2) straight by taper, and 3) straight by straight. These three joints are shown and described in Figure 2.
The taper by taper joint uses a fitting with a tapered I.D. and a pipe with a tapered O.D., matched and joined by a thin glue line. This joint is slower to make than the other joints, but it is the strongest of the adhesive-bonded joints. A compromise to the taper by taper is the straight by taper joint which replaces the pipe's tapered O.D. with a plain end uniform O.D. Less installation time is involved, but a thin glue line is not always ensured, thus compromising strength. The straight by straight adhesive-bonded joint has no tapered surfaces. Medium strength is achieved with this joint while requiring fewer tools and less fit-up time.
When any of these joining methods is used, it is important to follow the procedures recommended by the manufacturer. Any joint, improperly made, will be a poor joint, and will lead to maintenance costs down the road.
Figure 2. Three different adhesive bonded joints: 1) the taper by taper, 2) straight by straight, and 3) straight by taper. Each joint uses a glue to bond the pipe to the fitting.
Edited by: Troy Chan
Hebei Xingtai FRP Co.,Ltd
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