Double-bellows Expansion Joint

A Double-bellows Expansion Joint, commonly referred to in the industry as a double-rod expansion joint, consists of two sections of bellows, an intermediate connecting pipe, and four (or more) pressure-bearing tie rods. Their primary function is to accommodate lateral (radial) displacement in pipelines, while also accommodating a small amount of angular displacement. The tie rods bear the internal pressure thrust of the pipeline, preventing it from being transmitted to equipment or fixed supports; these are the most commonly used expansion joints for elbows and U-shaped pipe sections.

Note: They cannot accommodate axial displacement; this is a key consideration during selection.

Product Structure

Stainless steel bellows (available in 304, 316L, or 321; material can be customized based on the medium)

Intermediate connecting pipe

Pressure-resistant tie rods, nuts, and limit assemblies

End connections (pipe stubs or flanges), available via welding or flanged joints

Product Advantages

1. Tie rods absorb the entire pressure-induced thrust, minimizing the load on pipe supports and reducing the cost of support structures.

2. Primarily designed to absorb large lateral displacements; ideal for piping elbows and lateral thermal expansion in pipe segments.

3. Features a stable structure with excellent fatigue resistance; simple to install and maintain.

4. Available in a wide range of specifications; suitable for use in thermal networks, chemical processing plants, power stations, and petrochemical pipelines.

Typical Applications

Used in 90° pipe elbows, U-shaped pipe segments, and at equipment inlets/outlets where lateral relative displacement occurs. ✅ Recommended for: Thermal distribution networks, process piping in chemical plants, and auxiliary piping in power stations. ❌ Not suitable for: Straight pipe sections that require the absorption of significant axial expansion or contraction.

Technical Parameter

Item	Parameter Specifications
Material	Customizable with special materials such as 304, 316L, 321, duplex stainless steel, Hastelloy, etc.
Nominal Diameter	DN25--DN6000mm(Custom dimensions can be designed)
Pressure Rating	PN0.25 – PN25 (higher pressure ratings available upon request)
Temperature Range	-196°C – 450°C
Connection Type	Welded pipe connection / Flanged connection
Compensation Capacity	Primarily designed to compensate for lateral displacement, with a limited capacity for angular displacement; not intended for absorbing axial displacement.

Selection & Installation Guidelines

1. The tie rods are load-bearing components; they must not be removed after installation. Only minor adjustments to the limit nuts are permitted.

2. This Double-bellows Expansion Joint cannot accommodate axial displacement; do not use this model for axial expansion or contraction in straight pipe sections.

3. Verify the pre-deformation amount before installation. Do not forcibly stretch or compress the bellows during assembly.

4. The piping system must be equipped with guide supports to prevent the pipeline from becoming unstable or shifting out of alignment.

FAQ:

Q1: Can project-specific fabrication drawings and calculation reports be provided during the tender/inquiry stage? 

A1: During the tender/budgeting stage, we can provide standard data sheets and general reference diagrams. Project-specific fabrication drawings and formal calculation reports will be issued after the order is confirmed. If the client requires a pre-award review of supplier drawings, this documentation service can be offered as an optional, value-added item with separate pricing.

Q2: Which international standards are followed for expansion joints and pipe supports/hangers? 

A2: Metal bellows expansion joints are designed in accordance with standards including EJMA, EN 14917, ASME B31.1/B31.3, ASME VIII Div. 1 Appendix 26, GOST 32935, GOST 27036, GB/T 12777, and GB/T 16749. Pipe supports and hangers comply with MSS SP-58, MSS SP-127, ASME B31.1/B31.3, EN 13480-3, GOST 22130-2018, and GB/T 17116.

Q3: What high-alloy materials are available for high-temperature corrosive environments, such as those found in FCC units? 

A3: We offer special alloys—including SS321, 316H, Inconel 625, and Hastelloy—suitable for catalyst piping and high-temperature erosion-corrosion conditions. A full Material Test Certificate (MTC) is provided for every heat/batch of material.

Q4: What export packaging options are available? How are oversized products packaged? 

A4: We provide standard export-grade plywood crates, as well as heavy-duty, moisture-proof, and anti-corrosion packaging designed for long-haul ocean freight. For oversized or overweight products that cannot fit into enclosed crates, we utilize heavy-duty steel cradles or frames, with special protective measures applied to the bellows and flange sealing surfaces; these are suitable for transport via break-bulk or flat-rack containers.

Q5: What technical documentation can be provided? 

A5: We have successfully secured formal projects and are capable of preparing a complete set of WPS (Welding Procedure Specification), PQR (Procedure Qualification Record), and ITP (Inspection and Test Plan) documentation. We also provide the full range of technical supporting data required for EAC/COC certification.

Q6: What is the product warranty period? 

A6: The warranty period is 24 months from the date the goods arrive at the port of destination, covering defects in manufacturing. This warranty does not cover damage resulting from improper transportation, incorrect installation, or operation under abnormal conditions.

Factory Scale and Production Capacity

Our cooperative production base spans 35,000 square meters and employs over 100 skilled technical and production personnel, backed by 14 years of experience in manufacturing piping components. The workshop is fully equipped for forming, welding, heat treatment, non-destructive testing (NDT), and hydrostatic testing. • Annual capacity: Up to 12,000 metal bellows expansion joints. Monthly capacity: Up to 1,000 units, covering nominal diameters (DN) from DN25 to DN6000. We are capable of producing large-diameter, multi-ply units, as well as products made from high-performance alloys such as Inconel 625 and Hastelloy. • Leveraging a mature local industrial cluster, we can scale production beyond our internal capacity; we establish the production standards and oversee manufacturing at partner facilities, ensuring that product quality and delivery schedules remain uncompromised. • We possess bellows-forming equipment capable of handling diameters up to 6,000 mm and material thicknesses up to 40 mm.

We offer both standard product series and customized solutions for projects in the petrochemical, refining, and power generation sectors. For large-scale project orders, we provide flexible production scheduling.