Zhuojin Pipe Fitting Co., LtdManufacturing Process of Drawn Tee Combined Welded Manifold Pipe
Literature Overview
This 2019 paper by Bai Leijie, Liu Xu, and Bai Fuliang from Julong Steel Pipe Co., Ltd., published in Steel Pipe (Vol. 48, No. 1), presents a manufacturing process for manifold pipes (collection pipes) constructed by combining drawn tees with welded assemblies. The study addresses the structural design, wall thickness optimization, and combination welding design of this manufacturing approach, demonstrating its advantages over conventional manifold pipe fabrication methods.
Core Technical Findings
The paper introduces a manufacturing concept where manifold pipes are assembled from individually manufactured drawn tee fittings, cylindrical body sections, and end caps, joined through welding. This modular approach contrasts with traditional methods that attempt to form the entire manifold geometry in a single operation.
Component Architecture
| Component | Manufacturing Method | Standardization Potential | Function |
|---|---|---|---|
| Drawn tee | Cold or hot drawing | Yes - standard catalog parts | Branch connection points |
| Cylindrical body | Seamless or welded pipe | Yes - standard pipe sizes | Main flow conduit |
| End cap | Forged or formed | Yes - standard caps | Pressure containment |
| Weld joints | Arc welding (SMAW/GTAW/SAW) | Process-controlled | Component joining |
The key innovation is treating each component of the manifold as a standardizable, independently manufactured part that can be assembled and welded to create the final product. This modular philosophy significantly simplifies manufacturing complexity while maintaining or improving structural integrity.
Interpretation of Technical Points
Manufacturing Process Flow
The manufacturing process follows a systematic sequence:
- Selection of appropriate drawn tee specifications based on manifold design requirements
- Procurement or fabrication of cylindrical body sections with specified wall thickness
- Preparation of end caps with proper geometry for pressure containment
- Welding assembly of components using qualified welding procedures
- Non-destructive testing of weld joints
- Hydrostatic pressure testing of the completed manifold
- Final dimensional inspection and surface treatment
Welding Design Considerations
The combination welding design requires careful attention to several critical aspects:
- Joint configuration: Butt welds between cylindrical sections and tees provide the strongest and most reliable joint type
- Welding procedure qualification: Must comply with applicable codes (ASME B31.3, ASME B31.4, or SY/T standards)
- Heat input control: Critical for maintaining mechanical properties in the heat-affected zone
- Weld geometry: Optimized for stress distribution and inspection accessibility
- Fit-up requirements: Proper alignment and gap control for full penetration welds
Material and Specification Selection
| Parameter | Typical Specification | Rationale |
|---|---|---|
| Base material | API 5L Gr. B/X42/X52 or equivalent | Pressure containment |
| Tee material | ASTM A234 WPB/WCC or equivalent | Compatibility with body material |
| Wall thickness | Calculated per ASME B31.3 or B31.4 | Pressure rating and corrosion allowance |
| Weld procedure | Qualified per ASME Section IX | Joint integrity |
| NDT method | RT or UT per applicable code | Weld quality verification |
| Hydrostatic test | 1.5 times design pressure | Leak and strength verification |
Standards and Code Compliance
The manufacturing approach must comply with relevant piping codes and standards:
- ASME B31.3: Process piping - covers design, materials, fabrication, and inspection
- ASME B31.4: Pipeline piping - for transportation of fluids in pipelines
- ASME B16.9: Butt-weld fittings - dimensional specifications for tees
- ASTM A234: Fittings, flanges, and flanged fittings for piping
- API 5L: Specification for line pipe
- SY/T 0413: Steel pipe fittings for oil and gas industry (Chinese standard)
The modular manufacturing approach offers advantages in code compliance because each component can be independently certified, and the weld joints can be individually inspected and tested. This traceability is particularly valuable for pressure-containing applications where regulatory oversight is stringent.
Engineering Practice Integration
Comparison with Conventional Methods
| Aspect | Drawn Tee Combined Welded | Single-Piece Forged | Single-Piece Rolled |
|---|---|---|---|
| Manufacturing complexity | Low (modular) | High | Very high |
| Material utilization | High | Moderate | Low |
| Size flexibility | Unlimited combinations | Limited by forging capacity | Limited by rolling equipment |
| Material grade flexibility | Wide selection | Limited by forging capability | Limited by rolling capability |
| Production lead time | Short | Long | Very long |
| Cost | Low to moderate | High | Very high |
| Quality consistency | High (standardized components) | Moderate | Variable |
| Repairability | Excellent (individual components) | Poor (integral structure) | Poor |
The advantages highlighted in the paper are particularly compelling for large-diameter manifold applications where conventional single-piece manufacturing becomes impractical or prohibitively expensive. The ability to use standard pipe sizes and standard tee fittings dramatically reduces manufacturing complexity and cost.
Quality Control Framework
A comprehensive quality control plan for this manufacturing approach should include:
- Incoming inspection: Material certification verification, dimensional inspection of purchased components
- Process control: Welding parameter monitoring, fit-up inspection, pre-heat verification
- In-process inspection: Visual examination of welds, dimensional checks during assembly
- Final inspection: NDT of all welds, hydrostatic testing, final dimensional verification
- Documentation: Complete traceability records from raw material to finished product
Study Insights and Implications
The modular manufacturing philosophy presented in this paper represents a practical engineering approach to solving complex manufacturing challenges. By decomposing a complex geometry into simple, standardizable components, the approach leverages existing manufacturing capabilities and supply chains while achieving superior product quality and cost efficiency.
The approach is particularly well-suited for applications where:
- Large diameters exceed single-piece manufacturing capabilities
- Multiple material grades are required in different sections
- Custom configurations are needed for specific field layouts
- Production volume is too low to justify dedicated tooling for single-piece manufacturing
- Repair and maintenance access requires modular construction
Engineers should consider this approach for manifold and header pipe applications in oil and gas processing, chemical plants, and power generation facilities. The combination of drawn tees with standard pipe sections provides a versatile platform that can be adapted to virtually any manifold configuration while maintaining code compliance and structural integrity.
The key success factor is proper welding design and execution. The weld joints represent the critical connections that must maintain integrity under all operating conditions. Investment in qualified welding procedures, skilled welders, and thorough NDT ensures that the modular approach delivers performance equivalent to or exceeding single-piece alternatives.