In the design, manufacture and acceptance of flue gas pipeline expansion joint, the standard of flue pipeline expansion joint is the technical cornerstone to ensure product quality and safe operation of the system. Unclear specifications can lead to product selection errors and installation difficulties, or expansion joint failure, smoke leakage and even safety accidents. So, what are the standards for flue expansion joints? What are the core standards? What are the changes to the latest version? This paper will systematically interpret the standard system of flue expansion joint from national standards, international standards to industry norms.
I. Core national standard of flue expansion joint: GB/T 12777-2019
1. Standard Basic Information
The core of the standard system of flue expansion joints is GB/T 12777-2019 General Technical Specifications for Expansion Joints of Metal Bellows。 This standard was issued on May 10, 2019 and officially implemented on December 1, 2019, replacing the old GB/T 12777-2008。
This standard specifies the terms and definitions, classification and marking, materials, dimensions and deviations, design, manufacture, inspection and testing, inspection rules, marking, packaging, transportation and storage, type selection, installation and use requirements and safety recommendations for metal bellows expansion joints。 It is suitable for the design, manufacture, inspection, selection, installation and use of expansion joints installed in pipelines whose flexible components are metal bellows. Expansion joints in other occasions can be used by reference。
2. Version Evolution
| version | status | Key Changes |
|---|---|---|
| GB/T 12777-1999 | Be replaced | Earlier versions |
| GB/T 12777-2008 | Be replaced | Revisions to Version 99 |
| GB/T 12777-2019 | Current Effective | Current latest version, implemented in December 2019 |
The 2019 edition made important changes to the scope of application: the restrictions on the working conditions of expansion joints were removed, and it was clearly specified that expansion joints are used in pipelines, and their flexible elements are integrally formed unreinforced U-shaped, reinforced U-shaped and ω-shaped bellows。 At the same time, the previous version "This standard is not applicable to metal bellows expansion joints designed and manufactured according to GB150" is changed to "Expansion joints for pressure vessels can also be used by reference"。
Core amendments to GB/T 12777-2019
1. Bellows material requirements
The revision of corrugated pipe materials in the standard for flue expansion joints is one of the important changes: carbon steel and low-alloy steel have been removed and corrosion-resistant alloys have been added。 Carbon steel and low alloy steel are generally recommended for pressure vessel expansion joints, while corrosion-resistant alloys have been widely used to manufacture corrugated pipes with high requirements for corrosion resistance and high temperature performance。
At the same time, the standard also supplemented the requirements for the state and surface quality of corrugated pipe materials, and modified the upper limit of the allowable temperature range for some materials。
2. Improvement of design terms
The new version of the standard adopts the contents of EJMAS-93 equivalently, and adds design requirements for reinforcing U-shaped bellows and ω-shaped bellows。 Provisions for the design of corrugated shapes are also supplemented in Appendix A: for U-shaped bellows, specify that τ c = τ r ≥ (4+ n) δ; For ω-shaped bellows, specify L0≤ r/2, r0> 4N δ。
Revision of Fatigue Life Safety Factor: Design Fatigue Life Safety Factor nf is modified from ≥15 to ≥10。 This modification is based on the opinions of major domestic manufacturers and fatigue life test results. When nf =10 is used for design, the measured fatigue life values are all larger than the test fatigue life values required by the standard。
3. Reinforcement of Manufacturing and Inspection Requirements
The standard for flue expansion joints supplemented the manufacturing requirements by adding the manufacturing requirements for pressure joints (see 5.3.2) and adding the manufacturing requirements for connecting circumferential welds (see 5.3.3.1~5.3.3.4)。 The circumferential weld of bellows connection should be a butt weld with full penetration of bellows wall thickness, and the acceptance criteria for welding appearance inspection are specified。
In terms of non-destructive testing requirements, different quantities of inner and outer surface colored penetration testing or radiographic testing should be carried out for longitudinal welds of tube blanks according to different working conditions and conditions, and local radiographic testing should be carried out for longitudinal welds and circumferential welds of compressed tube sections generally。 For expansion joints with Pd ≤0.1MPa, the above three types of welds may not be inspected。
4. Pressure test requirements
With reference to the relevant provisions of ASME B31.3-97 and EJMAS-93, the revised version has made new provisions on the test pressure of the internal pressure expansion joint, which is based on the consideration that the bellows should not cause instability and yield under the test pressure。 The requirements for pressure test of expansion joints for vacuum conditions are additionally supplemented。
III. International standard: EJMA standard
In the standard system of flue expansion joint, the American Association of Expansion Joint Manufacturers (EJMA) standard is the most authoritative technical specification in the global expansion joint industry. EJMA standard specifies the design and calculation method of bellows expansion joint, including fatigue life calculation, stiffness calculation, stability check and other core contents。
The revision of GB/T 12777-2019 mainly refers to the latest version of EJMAS-93 in the United States, and also refers to international advanced standards such as ASME B31.3, ASME BPVC Ⅲ-1-NC and ASME BPVC Ⅷ-1。
4. Technical specification requirements of flue expansion joint
According to industry documents such as Technical Specification for Flue Expansion Joints, the standard for flue expansion joints also covers the following technical requirements：
1. Design performance requirements
- Displacement compensation: Expansion joints absorb axial and radial displacements of all connected equipment and flue in all operating and accident conditions
- Sealability: All expansion joints are designed to be leak-free and can withstand the maximum design positive/negative pressure of the system plus a margin of 1000Pa
- Anti-corrosion and heat insulation: the expansion joint on the low-temperature flue should be considered anti-corrosion, and the expansion joint of the flue should be insulated
2. Special design requirements
The expansion joint in contact with wet flue gas and located in the horizontal flue section shall be drained through the expansion joint frame, the drainage hole shall be at least DN150 and located on the center line of the horizontal flue section, and the drainage fitting shall be made of FRP or nickel-based alloy steel material。
The expansion joint on the flue is connected by welding, and the expansion joint connected with the absorption tower is connected by flange on the equipment side, and the arrangement can ensure that the expansion joint can be replaced。
V. Specification requirements for installation and replacement
Flue expansion joint standards also have clear provisions for installation and replacement:
- Selection requirements: Before replacing the expansion joint, the pipeline system shall be comprehensively inspected, and the appropriate expansion joint shall be selected for replacement according to the specific conditions of the pipeline system
- Installation standards: operate according to the installation standards, including the positioning of expansion joints, connection mode, tightening strength, etc.
- Testing standard: After replacing the expansion joint, comprehensive testing shall be carried out, including leakage, expansion and contraction, pipeline system pressure, etc
- Completion criteria: Record the date, model, specification and other information of the expansion joint, and carry out trial operation and acceptance
Special specification for fiberglass flue expansion joints
For FRP flue gas pipes, the installation of expansion joints should also follow the specification of SH/T 3522-2017: the distance from the fixed bracket should be ≤4 times the pipe diameter, the drainage slope should be ≥3‰ for horizontal pipe installation, and the guide bracket should be configured for vertical pipe installation。 Parallelism deviation of flange sealing surface ≤0.2mm/m。
VI. Standard Selection Guide
The selection of flue expansion joint criteria should be determined according to specific needs:
| Standard Type | Standard No. | Scope of application |
|---|---|---|
| Core standard for metal expansion joints | GB/T 12777-2019 | Design, Manufacture and Inspection of Expansion Joints for Metal Bellows |
| Design Calculation Reference | EJMA (American Standard) | Fatigue life, stiffness and stability calculation |
| Installation Specifications | SH/T 3522-2017 | Installation of Expansion Joints in Piping Systems |
| Flue Design of Power Plant | DL/T 5121-2020 | Design of Flue, Wind and Pulverized Coal Pipeline in Thermal Power |
| Non-metallic expansion joint | JB/T 12235-2015 | Design and Manufacture of Nonmetallic Compensator |
sum up
The standard system of flue expansion joint is based on GB/T 12777-2019 General Technical Specifications for Expansion Joints of Metal Bellows。 This standard was officially implemented on December 1, 2019, replacing the 2008 version, and is the latest national mandatory technical specification for the design, manufacture, inspection, selection, installation and use of expansion joints of metal bellows。
The core points are summarized as follows:
| gist | Core Content |
|---|---|
| Current national standard | GB/T 12777-2019 (implemented on 1 December 2019) |
| International standards | EJMA (American Association of Expansion Joint Manufacturers Standard) |
| KEY AMENDMENTS | Delete carbon steel/low alloy steel and supplement corrosion-resistant alloy; The fatigue safety factor nf is changed from ≥15 to ≥10; Add design requirements for reinforcing U-shaped and ω-shaped bellows |
| Manufacturing Requirements | Increase the manufacturing requirements of pressure cylinder sections and circumferential welds, and supplement the specific requirements of non-destructive testing |
| Test Requirements | Modify the pressure test regulations and quantify the requirements for the number of displacement cycles of fatigue test |
The selection and acceptance of expansion joints strictly following GB/T 12777-2019 standard can ensure the product quality from the source and avoid early failure problems caused by unclear standards. It is recommended to use this standard as the technical basis in the design, procurement and acceptance links to ensure the safe and reliable operation of flue gas system.