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When a metallic bellows fails, the priority is restoring system integrity with minimal disruption to operations. In many facilities, the standard approach of removing and replacing the existing expansion joint is not always practical. Surrounding piping, structural steel, refractory systems, or insulation can make removal time-consuming, costly, and in some cases, simply not feasible within the available outage window.

A clamshell bellows addresses this directly. US Bellows fabricates two distinct configurations: oversized and the same size clamshells. Selecting the right one depends on the specific conditions of the repair.

This article explains how each type works, when to use one over the other, and what to consider before contacting an engineer.

What Is a Clamshell Bellows?

A clamshell bellows is a split metallic bellows assembly manufactured in two longitudinal halves. The halves are assembled around the damaged or leaking bellows and welded together,  either in the field or in the shop,  without requiring the full removal of adjacent piping, structural components, or surrounding equipment.

Clamshell bellows are fabricated in single-ply metallic bellows only. They are not suitable for fabric or rubber expansion joints, in these cases, contact us to discuss repair options. There are no inherent pressure or temperature class restrictions; each assembly is custom-designed to the material, geometry, and service conditions of the existing joint.

Note – Clamshell bellows are a temporary repair solution. They restore system containment and allow continued operation while a permanent replacement is planned.

The Two Configurations

Oversized Clamshell

An oversized clamshell uses rings to increase the enclosure diameter beyond that of the existing bellows. The assembly is built to enclose the failed joint from the outside, without making contact with it, cutting it, or removing it. The repair is performed entirely in the field.

This configuration is used when removing the existing bellows is not practical. Large-diameter joints surrounded by permanent piping, structural steel, refractory, or insulation are typical candidates. In these situations, the cost and time required to dismantle the surrounding system can far exceed the cost of the clamshell itself. The oversized design eliminates that work entirely.

Field installation requires slow, precise welding along the longitudinal seams. Access constraints, working at elevation, and tight clearances all add to the complexity of the weld. This is the primary tradeoff of the oversized configuration: it avoids disassembly, but the field weld must be executed carefully under site conditions.

Same-Size Clamshell

A same-size clamshell is manufactured to match the dimensions of the existing bellows. It is designed for situations where the existing joint, or the equipment it is part of, can be removed and either sent to the US Bellows facility for a shop repair or replaced in the field after the original bellows has been taken out.

This configuration is better suited for turnaround scenarios. When a failed bellows is discovered during a planned or unplanned outage, and there is sufficient time to remove the joint, a same-size clamshell can be fabricated and installed with tighter quality control, full weld access, and US Bellows can provide complete ASME documentation when required.

Comparison at a Glance

How to Determine Which Configuration Fits Your Situation

The decision comes down to two questions:

1. Can the existing bellows or equipment be removed?

If yes,  and there is time in the outage window to do it, the preferred option is for a new bellows replacement to be provided. However, in cases such as heat exchangers, where disassembly would be time-consuming, a same-size clamshell is generally the more controlled repair. It allows for shop fabrication, easier welding, and straightforward ASME documentation.

If removal would require cutting permanent piping, dismantling structural supports, removing refractory or insulation, or using crane support for a large-diameter joint, an oversized clamshell avoids that work entirely.

2. What are the access conditions at the joint location?

Oversized clamshells are designed specifically for constrained conditions. If the joint is surrounded by equipment, located at elevation, or embedded in a system where adjacent components cannot easily be disturbed, field installation of an oversized clamshell is the practical path.

What US Bellows Needs to Design A Clampshell

Regardless of which configuration applies, the following information is required to start the engineering review:

• Nominal pipe size and bellows outside diameter
• Material and ply count of the existing bellows
• Design pressure and temperature
• Type of movement accommodated (axial, lateral, angular)
• Accessibility constraints and site conditions
• Drawings or dimensional sketches of the existing assembly, when available

For urgent repairs, US Bellows’ engineering team is available around the clock. Both configurations can be designed and fabricated on emergency turnaround schedules when the situation requires it.

Have a bellows failure or an upcoming turnaround? Contact US Bellows or schedule a meeting with an engineer to discuss which clamshell configuration fits your situation.

The quality of an expansion joint is determined long before fabrication begins. It is determined by the accuracy and completeness of the information a customer provides at the specification stage. Incomplete data forces assumptions, and these assumptions often lead to joints that fail early, require rework, or arrive dimensionally incompatible with the system for which they were built.

US Bellows works across metal, rubber, and fabric expansion joints for refineries, power plants, chemical facilities, LNG plants, and data centers. The specification process is the same regardless of application, every successful design begins with the same core inputs.

What the System Carries Determines What the Joint Must Be

Pressure and temperature are the two parameters that determine the material selection of the expansion joint. The table below outlines the operational limits and typical applications for each joint type.

Equally important is the media, what is flowing through the pipe. Corrosive fluids, acids, and certain gases may be incompatible with rubber, fabric, and standard stainless steel alloys. Specifying the wrong material for the media leads to chemical degradation before the joint reaches its rated service life. For hazardous gas applications, hydrogen fluoride, carbon monoxide, or acid gas, additional design codes and testing requirements apply that cannot be accommodated after the fact. Customers must disclose the media at the point of inquiry.

The Dimensions and Connection Details 

Manufacturers need the pipe diameter, wall thickness, schedule, and end connection type. End connections come in many forms (i.e, threaded connections, couplings) but the  two main ones are:

• Welded pipe ends — the joint is welded directly into the pipe run and cannot be removed without cutting
• Flanged ends — bolted connections that allow the joint to be unbolted and removed for maintenance access

Overall length is equally critical. In replacement applications, the face-to-face dimension is fixed by the existing installation and must be measured from the line, not from a drawing. In new installations, the available space between anchors, turbines, elbows, and nozzles defines the physical envelope the joint must fit within.

How the Pipe Moves and the Force Required to Drive It

Metal Expansion joints absorb three types of movement, each of which affects joint selection:

• Axial — compression and extension along the pipe axis; handled by a single joint in any material
• Lateral — transverse displacement; fabric and rubber accommodate this within a single unit, metal requires a universal or double configuration.
• Angular — rotation about a fixed point; typically ±10° for metal, up to 30° for fabric and rubber
• Torsional – Metal Expansion joints are not recommended for Torsional Motion. Rubber and fabric can handle this motion. 

Customers must also state the expected number of thermal cycles. A joint designed for 1,000 cycles that is cycling daily will reach its fatigue limit within three years. For engineers running pipe stress analysis, the spring rate, the force required to compress the bellows by one inch, is an essential output that feeds directly into the piping model.

Another equally important detail for Pipe stress analysis and expansion joint is, whether the expansion joint will contain the pressure thrust of the line. This can be done via tie-rods, hinges, gimbal or a Pressure balanced EJ. If you are unfamiliar with this, contact us and we can discuss the options for your Piping design.

The Parameter Most Customers Under-Specify and What It Costs

Flow velocity is among the most frequently omitted parameters in expansion joint specifications, and consistently the most damaging when wrong.

US Bellows was engaged by an LNG plant experiencing repeated internal liner failures under bi-directional flow. Robotic inspection and X-ray analysis revealed widespread buckling throughout the metallic bellows installation. FEA and computational fluid dynamics identified the cause: liquid nitrogen running at 65 feet per second, far beyond the liner’s yield threshold. US Bellows recommended capping velocity at 10 feet per second and fabricated replacement bellows to that specification.

Less visible is turbulence caused by nearby equipment. A butterfly valve positioned immediately upstream of a bellows disrupts flow sufficiently to induce vibration even at low velocity. Customers should disclose all valves, fittings, and equipment in proximity to the intended bellows location.

The Code That Governs the Design Also Determines the Testing

The applicable piping design standard should be stated at the inquiry stage:

• ASME B31.1 — power piping; references EJMA as the governing document for bellows design
• ASME B31.3 — process piping for oil, gas, and chemical facilities; includes Category M  criteria for critical and hazardous service
• ASME Section 8 Division 1 — pressure vessel applications; uses a distinct set of design equations independent of EJMA

The applicable code determines whether X-ray, ultrasonic, or additional NDE testing is required. Customers who specify the applicable code from the outset avoid discovering mandatory testing requirements after fabrication has begun.

For critical installations where bellows failure would force a plant shutdown, US Bellows recommends two precautions: ordering a spare joint to minimise replacement downtime, and specifying two-ply testable bellows with a test port that detects inner ply failure before a complete breakdown occurs.

What Ships With Every Expansion Joint  

Every expansion joint undergoes a leak test before dispatch. Every expansion joint that we fabricate will have at minimum the following records: 

• Material Traceability Record (MTR) for pressure retaining parts
• Certificate of Conformance(COC)
• Non-destructive examination (NDE) reports
• Leak or pressure test report

Customers requiring review of quality documentation before shipment should state this at the order stage. All products carry a warranty of one year after installation or 18 months after shipment, whichever occurs first, provided the joint is installed and operated as intended.

Complete specifications at inquiry don’t just start the process right,  they keep it right, from first design to final performance 

Submit a specification inquiry or schedule a consultation with a US Bellows engineer.

Expansion joints are engineered solutions, not off-the-shelf components. When one fails, replacing it like-for-like without evaluating system conditions, operating history, and installation constraints is the fastest way to repeat the failure.

The following questions provide a practical framework for ensuring the correct selection.

Question 1: Do You Have the Original Design Specifications or Drawings?

The most reliable way to specify a replacement expansion joint is by referencing original design documentation, including drawings, datasheets, or nameplate data. While pressure and design temperature are the primary controlling factors, a complete specification requires the full STAMPED criteria: Size, Temperature, Application, Movement, Materials, Pressure, Ends, and Delivery. Missing any of these can lead to delays or incorrect selection.

Material selection follows directly from these numbers:

Question 2: How Long Did the Previous Joint Last, and What Was the Failure Mode?

Service life is one of the most diagnostic data points available when specifying a replacement. It tells you if the original product selection was correct, or whether there is a systemic issue that a new joint will not solve.

Joint lasted 15–20 years: The original specification was appropriate. Failure is the result of normal fatigue or corrosion. A like-for-like replacement is the correct approach.

Joint failed in under 12 months: There is an underlying cause that replacement alone will not fix.

Understanding the Failure Mode

• The most frequent cause of premature failure in metal bellows is piping misalignment. Expansion joints are designed to accommodate minor axial, lateral, and angular misalignment, but that tolerance is not a substitute for correct pipe alignment. 
• Physical handling damage is the second most common cause. Bellows are manufactured from thin-wall metal (typically 0.015″ to 0.065″ wall thickness). A dent or crease before the joint enters service creates a stress riser that accelerates failure.  

Question 3: Were There Any Upset Events During or Near the Joint’s Failure?

Design conditions represent normal operation, but failures often occur during transient or abnormal events, especially those occurring shortly before or at the time of failure.

Before placing your order, check whether any of the following occurred:

• Overpressurisation – A pressure spike above MAWP can cause the bellows convolutions to balloon permanently outward, a condition known as squirm. 
• Water hammer – Rapid valve closure or pump startup creates pressure transients that can shock-load the bellows.
• Flow-induced vibration – High-velocity flow or proximity to rotating equipment, pumps, compressors, turbines, cycles the bellows at frequencies that rapidly consume fatigue life. 

Flag any upset events when placing your order. The engineering team may recommend design modifications based on the actual service history.

Question 4: Are the Existing Dimensions Accurate to the Original Design?

Incorrect dimensional assumptions are a common cause of replacement failures. A key mistake is assuming that the installed joint dimensions reflect the original design intent. In many cases, they do not. 

Before ordering, verify the following:

• Face-to-face (F-F) dimension between mating flanges 
• Pipe outside diameter (OD)
• Flange bolt-circle diameter (BCD) and bolt-hole pattern
• Tie rod length and stop nut positions

Critical Check – Confirm whether the current dimensions match the original drawings, or if they reflect field modifications. Designing to incorrect field dimensions can introduce unintended stresses into the new joint.

Question 5: Is the Original Material Selection Still Appropriate for the Current Service?

Operating conditions change over a system’s life. A joint specified for moderate-temperature steam service may now be running a corrosive fluid at elevated pressure. 

Corrosive environments- Standard 304 or 316 stainless steel performs well in neutral applications. In high-chloride, acid, or caustic service, these alloys are susceptible to stress corrosion cracking. Specialty nickel alloys such as Inconel 625 or Hastelloy C-276 are frequently required. 

Vibration-sensitive applications- Rubber joints provide effective isolation in pump discharge and water service lines. Metal joints with internal flow liners are preferred for high-velocity gas applications.

Changed pressure or temperature ratings- If the line now operates beyond the original design envelope, a direct replacement is a code compliance issue. 

Address the Root Cause & Strengthen Your Piping System with US Bellows 

The most expensive maintenance pattern US Bellows engineers encounter is repeated bellows replacement without addressing the root cause of failure in the piping support system.

If original specifications or documentation are unavailable, the existing expansion joint can be sent for detailed examination. This enables accurate measurements and reverse engineering, allowing the engineering team to recommend the most appropriate solution.

In many cases, the root cause lies beyond the joint itself, in system alignment, supports, or operating conditions. US Bellows’ in-house field service team inspects complete piping systems to identify these issues and deliver long-term solutions. Schedule a consultation with a US Bellows engineer or request a quote with your specifications.