In the marine power system, the design requirement of marine flue gas expansion joint is the key technical basis to ensure the safe operation of smoke exhaust pipeline and the reliability of ship navigation. Different from land expansion joints, marine expansion joints not only have to bear the thermal expansion and mechanical vibration of high temperature flue gas, but also have to adapt to the unique dynamic loads such as hull deformation and wave impact. At the same time, the narrow engine room space and strict safety requirements of ships put forward higher requirements for the compactness, corrosion resistance and fatigue life of expansion joints. This paper will systematically analyze the core content of the design requirements of marine flue gas expansion joint from standard basis, design key points to material selection.
1. Design standard basis of marine flue gas expansion joint
1. Core standard system
The design requirements of marine flue gas expansion joints are mainly formulated according to the following national standards and industry norms:
According to GB/T 12522-2009, this standard is applicable to the expansion joints of internal combustion engine exhaust and other pipelines. It specifies the requirements of flange connection size and sealing surface, and adopts the MOD American Association of Expansion Joint Manufacturers (EJMA) standard。 The T/CANSI 79-2023 Group Standard, issued in October 2023, further standardizes the basic process and technical requirements for the layout of expansion joints and hangers for vessel smoke exhaust pipe systems, and was officially implemented on November 1, 2023。
2. Special working conditions requirements of marine expansion joints
Marine wave expansion joint must meet three core requirements：
- Displacement compensation: absorbs the displacement changes caused by thermal expansion and contraction, mechanical vibration, and the special displacement changes caused by the hull deformation caused by the influence of wind and waves
- Corrosion resistance: High temperature, seawater and chemical corrosion resistance
- High fatigue life: In order to ensure navigation safety, it is necessary to ensure that the expansion joint has a high fatigue life
2. Types and selection specifications of marine flue gas expansion joints
1. Metal bellows expansion joint
Metal bellows expansion joint is the main product of ship smoke exhaust pipeline. According to the product data of the 725th Research Institute, CQ series expansion joints for ships are suitable for exhaust pipeline systems of marine engines below 550℃. The types of expansion joints are mainly single axial type, with design pressure of 0.1MPa, maximum design temperature of bellows of 550℃, and design fatigue life of 5000 times。
The design requirements of marine flue gas expansion joint in material selection, corrugated pipe material can be austenitic stainless steel, corrosion-resistant alloy, white copper, industrial blunt titanium, etc. The size specification of circular expansion joint is DN50-4800mm。
2. Non-metallic expansion joint
Non-metallic expansion joints also have important application value in the marine field. Compared with metallic expansion joints, the compensation function of non-metallic expansion joints is much larger under the condition of the same external dimension, especially the compensation function of transverse displacement is almost one order of magnitude larger than that of metallic expansion joints。
Other advantages of non-metallic expansion joints include：
- Small compensation resistance: the pushing force on the peripheral equipment is small and the connected equipment will not be damaged
- Good acid and alkali resistance: The material has excellent high temperature resistance and corrosion resistance
- Thermal insulation and energy saving: The structure itself has thermal insulation properties, and there is no need to cover additional insulation layer
- Easy maintenance: No maintenance required during normal life cycle, much more convenient to replace than metal expansion joints
3. Key design parameters of marine flue gas expansion joint
1. Temperature and pressure design
According to GB/T 12522-2009 standard, the pressure of expansion joint of marine exhaust line shall not exceed 0.5MPa and the temperature shall not exceed 550℃。 The CQ series products of the 725th Research Institute can reach the design pressure of 0.1MPa, the maximum design temperature of 550℃, and the design fatigue life of 5000 times。
For high-temperature working conditions where the temperature exceeds 550℃, corrosion-resistant alloys or high-temperature alloys should be selected to make expansion joints, such as domestic materials FN-2, NS111 and B-315 or Incoloy800, 825, etc。
2. Displacement compensation calculation
In the design requirements of marine flue gas expansion joint, many factors need to be considered in the calculation of displacement compensation amount:
- Free Expansion and Contraction of Exhaust Line with Temperature
- Mechanical vibration of diesel engine during operation
- Ship hull deformation caused by wind and wave
Retractable expansion joint arrangement must be provided on the exhaust pipe near the diesel end。
3. Fatigue life requirements
Ship navigation safety puts forward strict requirements for the fatigue life of expansion joints. The design fatigue life of land expansion joints is usually 1000 times, while the requirement of marine expansion joints is higher-the design fatigue life of CQ series products is 5000 times。 High fatigue life is a key index to ensure navigation safety。
4. Arrangement requirements of expansion joints and hangers
1. Layout the basic process
According to T/CANSI 79-2023 "Requirements for Arrangement of Expansion Joints and Hangers of Ship Exhaust Pipe System", the arrangement of expansion joints and hangers shall follow standardized procedures to ensure that the pipeline system can operate normally under both hot and cold conditions。
2. Hanger and Support Configuration
The reasonable arrangement of elastic hanger, elastic support and fixed support is an important part of the design requirements of marine flue gas expansion joint：
- Exhaust pipes with expansion bellows shall be properly adjusted, straightened and clamped
- The exhaust pipe should be kept at a sufficient distance from other structures, especially glass fiber reinforced plastic (GRP) or aluminum structures
3. Overall requirements for exhaust lines
According to the Code for Design of Marine Exhaust Systems ：
- The exhaust pipe should generally be led upward, strive for short pipeline and few elbows
- Exhaust pipes and silencers shall be equipped with cooling water jackets or wrapped with heat insulation materials, and the surface temperature shall not exceed 60℃, so as to avoid burning management personnel
- Aluminum alloy materials should not be exposed to temperatures exceeding 150℃ for a long time to avoid degrading their mechanical properties
- The layout of the exhaust line should be straight and minimize elbows. If it is necessary to bend, the bend should not be less than 90°
V. Material selection and anticorrosion requirements
1. Bellows Material Selection
The design requirements of marine flue gas expansion joints are extremely strict on the selection of materials. The performance characteristics of marine corrugated expansion joints include high temperature resistance, seawater and chemical corrosion resistance, high flexibility, high fatigue life, compact structure and reliable sealing。
Principles of material selection：
- Carbon steel and low alloy corrugated expansion joints are only suitable for t ≤375℃
- Corrugated expansion joint made of austenitic stainless steel is suitable for t ≤500℃
- Corrugated expansion joints made of carbon steel or low alloy steel shall have a corrosion margin not exceeding 1mm, otherwise austenitic stainless steel should be used
2. Anti-corrosion and thermal insulation treatment
Surfaces such as exhaust pipes, bellows and connecting flanges should be insulated. If the exhaust pipe other than stainless steel is used, it shall be resistant to high temperature, seawater and exhaust gas corrosion。
Because of the precious space on ships, corrugated expansion joints with compact structure, good sealing and convenient installation should be adopted on exhaust pipelines。
6. Design Optimization and Thermal Stress Control
1. Design strategies for thermal stress reduction
The 2012 study of Ship and Sea Engineering shows that some equipment on the smoke exhaust pipeline of the engine room of the ship has a relatively high thermal stress limit on the pipeline. In order to reduce the thermal stress of pipeline equipment, the thermal stress of pipeline acting on the equipment can be reduced by optimizing the layout of smoke exhaust pipeline and optimizing the design of expansion joint, so as to achieve the purpose of protecting the equipment。
2. Flexible design concept
Because of the precious space on ships, the corrugated expansion joint with compact structure, good sealing and convenient installation is an inevitable choice。 The flexible design can provide adequate displacement compensation in a limited space while minimizing the reverse thrust on the equipment.
Key Points of Construction and Installation
1. Check before installation
- Verify that the model, specification and design of the expansion joint are consistent
- Check the bellows surface for mechanical damage and corrosion
- Verify that the direction of the liner cylinder (guide cylinder) is consistent with the flow direction of the medium
2. Installation precautions
- Exhaust pipes with expansion bellows shall be properly adjusted, straightened and clamped
- The exhaust pipe is kept at sufficient distance from other structures, especially if these structures are glass fiber reinforced plastic (GRP) or aluminum
- The exhaust pipe and silencer shall be equipped with cooling water jacket or wrapped with heat insulation layer, and the surface temperature shall not exceed 60℃
3. Acceptance criteria
- Check all joints, seals, gaskets to ensure that the seals are intact
- Conduct airtightness test to verify
sum up
The design requirements of marine flue gas expansion joints are the technical cornerstone to ensure the safe operation of marine smoke exhaust systems. Compared with land expansion joints, the marine design requirements have the following notable characteristics:
| Design elements | Marine design requirements | Difference from land use |
|---|---|---|
| Criterion basis | GB/T 12522-2009, GB 1153, T/CANSI 79-2023 | Marine Standard System, New Group Standards Released in 2023 |
| Type of displacement | Thermal displacement + vibration displacement + hull deformation displacement | New hull deformation displacement |
| Fatigue life | ≥5000 times | Higher than land use (usually 1000 times) |
| Corrosive environment | High temperature flue gas + seawater salt spray + chemical corrosion | More harsh seawater corrosion environments |
| Space constraints | Compact structure and reliable sealing | Cabin space is precious and more demanding |
| Surface temperature | ≤60℃ | Strict anti-scald requirements |
One-time standard design and selection can ensure the long-term reliable operation of marine flue gas expansion joint under harsh working conditions such as high temperature, corrosion and dynamic load. It is recommended to strictly follow GB/T 12522-2009 and T/CANSI 79-2023 standards in the design stage, and fully consider the special hull deformation and wave impact factors of ships to ensure navigation safety from the source.