CLADDING TECHNOLOGY SHANXI CO., LTDDouble-Sided Overlay Tube Sheet Deep Hole Hydraulic Sealing Expansion Jointing Technology
Literature Overview
This 2017 publication from Shanghai Petrochemical Machinery Manufacturing Co., Ltd., authored by Gu Shanqiu and published in China Chemical Equipment, addresses a highly specialized fabrication challenge in heat exchanger manufacturing: the integration of double-sided weld overlay on tube sheets with deep-hole hydraulic sealing expansion jointing. The work reflects the practical demands of petrochemical and refinery service where aggressive process media require corrosion-resistant surfaces on both the process side and the cooling water side of heat exchanger tube sheets, while simultaneously achieving reliable tube-to-tube-sheet joints through expansion.
Core Technical Challenge
The fundamental difficulty lies in reconciling two traditionally competing fabrication requirements: overlay welding creates a hard, dense corrosion-resistant surface layer that resists mechanical deformation, while hydraulic expansion jointing requires the tube sheet material around each tube hole to be plastically deformed to achieve a metal-to-metal seal. When the overlay layer is present on both sides of the tube sheet, the expansion process must work through or around this hardened layer without causing cracking, delamination, or loss of bond integrity.
Technical Approach and Process Sequence
The fabrication sequence typically involves the following critical steps:
- Base tube sheet machining and hole drilling
- First-side overlay welding (process side)
- Overlay layer grinding and surface preparation
- Second-side overlay welding (cooling water side)
- Second-side grinding and hole preparation
- Hydraulic expansion of tubes through the overlay layer
- Final inspection and qualification
Critical Process Parameters
| Parameter | Typical Range | Rationale |
|---|---|---|
| Overlay alloy | 304L/316L or 321/347 | Match process and coolant side corrosion resistance |
| Overlay thickness | 1.5–3.0 mm per side | Sufficient corrosion allowance without excessive expansion resistance |
| Welding process | SAW or GMAW multi-pass | Control dilution and ensure uniform microstructure |
| Interpass temperature | ≤150°C | Prevent grain coarsening and reduce residual stress |
| Expansion pressure | 20–35 MPa | Sufficient to deform overlay layer without cracking |
| Expansion ratio | 1.5–2.5% | Achieve full metal contact without exceeding material limits |
Deep Hole Expansion Through Overlay Layer
The deep-hole geometry (typically 1.5D to 3D hole depth relative to tube sheet thickness) presents unique challenges. The hydraulic expansion tool must traverse the full hole depth while applying uniform radial pressure through the overlay layer on both sides. Key considerations include:
- Overlay layer ductility: The dilution zone between overlay and base material must retain sufficient elongation to accommodate plastic deformation without cracking.
- Bond integrity preservation: The metallurgical bond at the overlay-base interface must not be disrupted by the expansion-induced stresses.
- Tool design: Specialized expansion tools with hardened tips and controlled pressure profiles are essential to distribute deformation energy evenly.
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Overlay cracking during expansion | Excessive hardness, insufficient ductility | Optimize dilution ratio; reduce single-pass thickness |
| Bond delamination | Poor interface fusion; residual stress | Apply post-weld stress relief; control heat input |
| Incomplete expansion | Insufficient pressure; tool wear | Monitor expansion force curve; replace worn tools |
| Overlay spalling | Excessive impact force | Use gradual pressure ramp; reduce expansion speed |
Engineering Practice Insights
From a manufacturing standpoint, this technology represents a significant advancement over conventional approaches where overlay is applied only on the process side. Double-sided overlay eliminates the need for separate corrosion-resistant tube sheet rings or inserts, reducing assembly complexity and improving long-term reliability. However, the technology demands careful process qualification under NB/T 47014 or equivalent welding procedure qualification standards, with specific attention to expansion joint acceptance criteria per TEMA or GB/T 151 requirements.
The hydraulic expansion process itself must be qualified through a combination of macroscopic bond tests, microscopic examination of the expanded zone, and functional leak testing. The expanded overlay layer should show uniform plastic deformation without microcracking, and the tube-to-tube-sheet joint should demonstrate full circumferential contact.
Study Reflections
This work exemplifies the trend toward integrated fabrication solutions that consolidate multiple functional requirements into a single component. The ability to achieve both corrosion protection and mechanical sealing through a unified tube sheet design reduces the number of potential failure interfaces and simplifies quality assurance. Engineers working on similar projects should pay particular attention to the interaction between overlay microstructure and expansion-induced strain, as this interaction governs the long-term joint integrity under cyclic thermal and pressure loading conditions.