Expansion Joints in Shell and Tube Heat Exchangers
Heat exchangers are critical equipment in many industrial processes. They allow the transfer of heat between two fluids without mixing them. Common examples include shell & tube heat exchangers used as condensers, vaporizers, and process coolers.
Selecting the right expansion joint design and materials is key for reliable, long-term operation. Let’s take a look at the expansion joint options for shell & tube heat exchangers and important factors to consider.
The Different Types of Expansion Joints
There are two main types of expansion joints used in shell & tube heat exchangers: bellows and flanged & flued .
Flanged & Flued expansion joints typically utilize two formed shapes that form a single large corrugation and are constructed of the same material and thickness as the shell cylinder. They are tough and reliable, but resolving a design that meets all conditions and requirements can be difficult.
Bellows type expansion joints have a flexible, accordion-like geometry that permits expansion differential between the tubes and shell. Benefits over Flanged & Flued is their flexibility in design to accommodate greater movement. Downsides is their thin-wall construction is less robust and at risk of physical damage.
Alternatives to Expansion Joints
Expansion joints should be avoided (if possible) to reduce cost and minimize complexity, so the following solutions may be considered first:
● Different TEMA type – U-tube or floating-head (S or T) type with even tube-side passes
● Hairpin type heat exchanger
● Change quantity of exchangers in series
● Match tube and shell metallurgies (avoid dissimilar metals)
● Change from counter-current to co-current flow
● Increase tube thickness
However, these options have limitations. An experienced designer should evaluate if they are feasible for a given application.
Why Expansion Joints Are Used
The main purpose of expansion joints is to absorb the growth and contraction of the heat exchanger tubes relative to the shell. Extreme stresses can occur in the tubes, shell, and tubesheet joints when the tubes and shell are expanding at different rates. This can occur when the mean-metal temperatures are different due to the process and design, and/or when the coefficient of thermal expansion is different (Dissimilar metallurgy of the tubes vs the shell).
Without expansion joints, thermal expansion may cause extreme stresses in the tubes. This can lead to deformation, tube buckling, tube joint leakage, and fatigue failures. Contraction without an expansion joint could pull tubes apart or out of the tubesheet joints.
Expansion joints minimize these forces and allow the exchanger to expand and contract freely within design limits. This avoids overstressing the tubes and tubesheet joints .
The Design Conditions
Proper selection and design of expansion joints rely on understanding the application conditions. This includes:
● Design cases for operating, start-up, shut-down, and upset.
● Mean-metal temperatures of tubes and shell for these cases
● Metallurgy of tubes and shell
● Calculated thermal movements for each design case.
● Expected thermal cycles during exchanger lifetime.
● Design pressures and temperatures
● Applicable codes and standards
The exchanger or expansion joint manufacturer will utilize this data to design an appropriate expansion joint style and materials of construction. Provisions for shipping, assembly, and hydrotest supports may also be needed. Anticipating the full range of operating conditions, including transients, is critical to ensure the expansion joints perform reliably.
Expansion Joint Failures and Common Problems
Despite best efforts, expansion joints can still fail prematurely if not designed, installed, and maintained properly.
Common failure modes include:
● Excessive movements
● Pressures exceeding design capabilities
● Material incompatibility with fluids resulting in corrosion
● Fatigue due to cyclic operation and vibration
● Wear and abrasion over time
● Mechanical damage during handling, installation, or operation
Which Factors Your Fabricator Should Consider
Reputable heat exchanger manufacturers will have the expertise to recommend appropriate expansion joint designs. Be sure your fabricator is able to consider the following:
● All process operating conditions (temperatures, pressures, etc.)
● Service life
● Ability to absorb movements in multiple planes (if needed)
● Internal and external protection for bellows type
● Inspection and maintenance needs
● Applicable codes and standards, including EJMA
This comprehensive approach will result in the optimum expansion joint selection and performance.
Contact Altex Industries for Shell & Tube Heat Exchanger Manufacturing and Design
Since 2001, Altex Industries has been a leader in the fabrication of shell & tube heat exchangers for oil refining, petrochemical, and other industrial processes. Our experienced team can recommend the right expansion joint solutions for your exchangers based on all design parameters and operational objectives.
For more information on heat exchanger manufacturing and design services, contact Altex Industries today.