We recently introduced a new Expansion Joint Frequently Asked Questions section on our website. This new database of questions provides the answers to a lot of common questions regarding metallic expansion joints, fabric expansion joints, expansion joint testing, and more! The list of questions is continually expanding, so check back often for more valuable expansion joint information.
U.S. Bellows offers many accessories to protect the bellows and extend the life of your expansion joint. This article briefly describes a few of them including protective covers, internal liners, limit rods, hinges and purge connections.
|*||External covers protect the bellows element from mechanical damage, during shipping, maintenance activities, and plant construction|
|*||Cover may be used for the application of insulation when the ductwork is insulated|
|*||Protective covers are provided in removable and non-removable configurations|
|*||The picture shows the installation of a protective cover on a 30″ diameter spent catalyst standpipe metallic expansion joint with pantographic linkage|
|*||Internal liners, also known as “Internal Sleeves” and “Telescoping Sleeves,” extend the life of a metallic expansion joint|
|*||Protects the convolutions from direct flow impingement, which can cause flow-induced vibration|
|*||Standard liners are fabricated from 300 series stainless steel (optional materials include Inconel 625 and Inconel 600)|
|Limit rods are used to limit axial expansion or compression to prevent the bellows from over-compression. Limit rods are designed to absorb the pressure thrust of the expansion joint in case of anchor failure.|
|Hinges permit angular rotation in one plane only by the use of a pair of pins through hinge plates attached to expansion joint ends. Hinges and hinge pins are designed to restrain the thrust of the expansion joint due to internal pressure. Hinges can also be designed to carry piping loads.|
|*||Angular rotation in one plane|
|*||Eliminates pressure thrust forces|
|*||Transmits external loads|
|*||Prevents torsion on bellows|
|*||No main anchors required|
|*||Minimum guiding required|
|*||Low forces on piping system|
|*||Used in systems where sediments can collect between the outside of the internal liner and the inside of the bellows element|
|*||Purge connectors can be added to the upstream end of the liner|
|*||Inert gas or air can be injected to periodically blow collected material out or can be continuously supplied during system operation|
The U.S. Bellows exhibit featured a cut-away view of an expansion joint with insulating and abrasion resistant refractory lining and miniature models of various types of metallic expansion joints. Discussions at the booth included how to solve regenerated catalyst and spent catalyst standpipe expansion joint reliability problems. Talk to the engineers at U.S. Bellows about your flue gas expansion joint problems. We can help with your fabric expansion joint problems in low pressure flue gas systems.
These rectangular fabric expansion joints measure 136″ x 54″ with a weight of 135 lbs each. They were fabricated out of fiberglass fabric with stainless steel frames and are designed for ± 5 PSIG and 400°F. The expansion joints were manufactured according to specific customer specifications.
PT&P has acquired the metal expansion joint business of RM Engineered Products, Inc. This acquisition included the design software, drawings, business records and all the equipment used to manufacture metal bellows. The equipment was moved from their plant in Ladson, South Carolina and installed in our new building here in Houston. The move and installation efforts were managed by Rick Thompson who joined PT&P in 1995. Rick will be in charge of manufacturing and fabrication of these products.
How to Make a Simple Bellows
Photo 2 shows a roll of stainless steel next to a shear which is used to cut the starting piece for the bellows. The particular metal required depends on the temperature, pressure and other design parameters for the expansion joint. Table 1 shows the standard metals used and the corresponding ASTM specification.
|Material Type||ASTM Material Specification|
Rectangular pieces are rolled to form a cylinder with an open seam. The automatic TIG flat bed welding machines shown in Photo 3 require only a few minutes to produce a homogenous weld. Proper set-up of the machine is critical to the quality of the weld. One of the capabilities we have added is an x-ray machine to verify the quality of the welds.
The next step is to shape the required convolutions. Convolutions provide the flexibility required and the total movement capacity of the bellows is proportional to the number of convolutions. The convolutions are formed in two steps. The first step produces a v-shaped circular expansion at the center line of each convolution. The second step extends the triangular shape and provides a flat ring shape for the convolution. This entire process is called roll-forming. Photo 4 shows a roll-forming machine. Different size convolutions require varying set-ups. The arms of a machine for much larger units can be seen in the background.
Bellows are the primary “building blocks” for a variety of expansion joints. The spring rate is determined by the size of the convolutions and the metal used. The compression, extension, lateral offset, rotation etc. required for a particular application determines the design required for the entire expansion joint. Photo 5 shows a “wedding cake” machine used to size bellows when fitting them to other components of the expansion joint.