Zhuojin Pipe Fitting Co., LtdManufacturing Process of Drawn Three-Way Combined Welded Header Pipe
Literature Overview
The paper by Bai Leijie, Liu Xu, and Bai Fuliang (2019), published in Steel Pipe (Vol. 48, No. 1, pp. 32-35), presents a manufacturing approach for header pipes (multi-way branch assemblies) using a combination of drawn tees, cylindrical shells, and pipe caps joined by welding. The work addresses the challenges of producing header pipes with multiple branch connections, which are commonly used in oil and gas gathering systems, chemical processing plants, and power generation facilities. The proposed approach combines the geometric precision of drawn (extruded) tees with the flexibility of welded assembly construction.
Structural Design and Manufacturing Approach
The combined welded header pipe concept utilizes pre-manufactured drawn tees as the primary branching elements, with cylindrical sections and caps providing the main body and end closures. This modular approach offers several advantages over monolithic forging or machining of the complete header assembly:
| Component | Manufacturing Method | Key Advantage |
|---|---|---|
| Drawn tee | Hydraulic extrusion/drawing | Standardizable, geometric precision |
| Cylindrical shell | Pipe cutting and preparation | Material flexibility, size scalability |
| Pipe cap | Forming or forging | End closure with minimal material waste |
| Assembly joints | Butt welding | Full-penetration integrity |
The drawn tees can be produced as standard components in various sizes and materials, enabling a modular design philosophy where different header configurations can be assembled from common building blocks.
Welding Process Considerations
The butt welding of drawn tees to cylindrical shells requires careful process control. The weld joint geometry, including the bevel angle, root gap, and reinforcement profile, must comply with applicable standards such as ASME B31.3, API 5L, or SY/T 0413. The material compatibility between the drawn tee and the shell pipe is critical, particularly when different grades are involved.
| Welding Parameter | Typical Specification |
|---|---|
| Welding process | SMAW/GTAW/FCAW/SAW |
| Preheat temperature | Material-dependent (typically 50-200°C for carbon steel) |
| Interpass temperature | ≤ 250°C for low-alloy steels |
| Post-weld heat treatment | Required for thick sections (> 25 mm) |
| NDT requirements | RT or UT for 100% inspection |
The combination approach may introduce weld joints at locations where stress concentrations already exist due to the tee geometry. This requires careful attention to weld quality and potentially supplementary stress-relief procedures.
Engineering Practice and Economic Analysis
The paper highlights several practical advantages of this manufacturing approach:
- Individual components (drawn tees, shells, caps) have relatively low manufacturing difficulty and can be produced by specialized suppliers.
- The approach is not constrained by specific material grades or diameter combinations, offering design flexibility.
- Manufacturing costs are lower compared to monolithic forging of large multi-way headers.
- Product performance is stable and reliable due to the use of well-characterized standard components.
From a quality assurance perspective, the modular approach allows for component-level quality verification before assembly, providing multiple quality gates in the manufacturing process. This aligns with the concept of build-up quality control described in API 5L and ASME B31.3 quality requirements.
Study Reflections
This manufacturing approach represents a pragmatic engineering solution to the challenge of producing complex multi-way header assemblies. The combination of drawn tees with welded assembly construction leverages the strengths of both forming and welding technologies while avoiding the limitations of each in isolation. The approach is particularly attractive for applications where large-diameter headers with multiple branch connections are required, as monolithic forging becomes increasingly expensive and technically challenging at larger sizes. The key engineering consideration is ensuring that the weld joints, which are the potential weak links in the assembly, are designed and executed to provide equivalent or superior performance compared to the base material at the tee branch intersection.