The key, reputable manufacturers of expansion joint technology in the European market have come together to establish this Division.
The Division will focus initially on non-metallic expansion joint technology, and will open out to cover metallic forms in due course.
Non-metallic expansion joints are flexible connectors designed to provide stress relief in ducting systems by absorbing movement caused by thermal changes. They also act as vibration isolators, shock absorbers and, in some instances, to compensate for minor misalignment of adjoining ducting or equipment. They are fabricated from a wide variety of materials, including synthetic elastomers, fabrics, insulation materials and fluoroplastics, dependent upon the process environment in which they must operate.
The objective of the Division is to serve as a focal point for all efforts to improve the manufacture, understanding and application of expansion joint technology. This will be achieved through:
- promotion of harmonised procedures in standards, specifications and terminology
- promotion of best practice in the design and manufacturing of expansion joints
- providing “user-friendly” guidelines for both manufacturers and customers
- encouraging engineering value in products and services
The Division aims to lead the entire industry towards a safer environment. For this reason, Members of the ESA Expansion Joints Division do not manufacture expansion joints using ceramic fibres which are classified by the IARC as Group 1, Group 2A or Group 2B.
Expansion Joint Guides
It is apparent that there is wide ambiguity with the terminology used in connection with expansion joint technology. Although there are a number of guides describing expansion joints and their application, these are either biased on a particular type of technology, or are more complicated than necessary. Consequently, the Division has focused initially on providing comprehensive guides to European expansion joint technology, which are easy to use and understand.
Correct design for the purpose
Materials and their use in fabric expansion joints are unlike the metal type not described in various standards. Also the frame design varies depending on supplier and user experience. As fabric expansion joints have been used in decades a number of basic designs have proven to be suitable for various conditions and are common used (as fx. described in our engineering guide). When it comes to more severe conditions and/or by special requirements even the best available materials will fail if they are not combined with a suitable design.
An example is expansion joints for gas turbine exhaust. These have normally special conditions such as rapid temperature increase and high gas velocity and strong turbulence. The rapid change in temperature of more than 500°C is a challenge by outside insulated frames as the temperature difference between inside and outside causes increased stress. Traditional frames perpendicular to the duct will suffer as the stress level will be severe. Round frames will spread the stress along its circumference though but distortion and buckling is common seen.
Square frames will concentrate the stress in their corners and cause fatigue cracks. To avoid distortion and high stress levels the frame must be made in such way that the maximum stress level is limited. This can be done by the shape and design of the frame and/or by lower the temperature difference. Various designs are used and the challenge is to design in such way it doesn’t cause other disadvantages. High gas velocity (locally sometimes more than 100m/s) and turbulence is also common by gas turbine exhaust. Vibrations and the forces on the steel parts as well as smooth flow must be taken into consideration by the design. Of the same reasons the soft parts needs to be very well protected. Otherwise the local vacuum and turbulence will cause their fibers to degrade quickly. This is an example of challenges which may not be ignored by the choice of design. Experience and knowledge is of most importance to achieve a good lifetime especially when it comes to more challenging conditions.