CLADDING TECHNOLOGY SHANXI CO., LTDStrip Cladding Process for Lock Hopper Cone Components in Oilfield Engineering
Literature Overview
This study note examines the technical literature by Guo Xiaochun from Daqing Oilfield Engineering Construction Co., Ltd. Building Materials Company, published in 2012 in the journal Welding Technology. The paper addresses the strip cladding process for lock hopper cone components, which are critical equipment in oilfield separation and processing systems where the combination of abrasive slurry, corrosive fluids, and cyclic pressure loading demands exceptional surface durability.
Component Description and Service Requirements
Lock hopper cones (also known as cyclone cones or separation cone components) are integral parts of oil-water separation systems in oilfield processing facilities. These components operate under continuous exposure to:
- Abrasive slurry: Oil-water emulsions containing sand, scale, and solid particles at high flow velocities (5–15 m/s)
- Corrosive media: Hydrogen sulfide (H₂S), carbon dioxide (CO₂), chlorides, and acidic water
- Cyclic thermal loading: Temperature variations between ambient and process temperatures (up to 120 °C)
- Pressure cycling: Repeated pressurization and depressurization during separation operations
| Service Parameter | Typical Value | Design Implication |
|---|---|---|
| Flow velocity | 5–15 m/s | High erosive wear |
| Solid content | 1–5% by weight | Abrasive wear |
| H₂S concentration | 0.1–5% by volume | Sulfide stress cracking risk |
| Chloride concentration | 500–5000 ppm | Pitting and SCC risk |
| Temperature | 40–120 °C | Thermal expansion mismatch |
| Pressure | 1.5–10 MPa | Mechanical integrity requirement |
| Service life requirement | 3–5 years | Economic replacement interval |
Strip Cladding Process Design
The strip cladding process selected for lock hopper cone components is strip cladding (also known as strip welding or strip overlay), which offers high deposition rates, low dilution, and good surface quality. This process is particularly well-suited for the conical geometry of hopper components, as the strip electrode can be fed along the cone surface with consistent contact.
Cladding Material Selection
| Overlay Material | Application Zone | Rationale |
|---|---|---|
| 316L stainless steel | General corrosion resistance | Excellent chloride resistance, good toughness |
| 321 stainless steel | High-temperature zones | Stabilized against sensitization, good thermal stability |
| Inconel 625 | High-H₂S zones | Superior resistance to sulfide stress cracking |
| 316L + Inconel 625 (gradient) | Critical transition zones | Combined corrosion and mechanical performance |
Recommended Strip Cladding Parameters
| Parameter | Value | Notes |
|---|---|---|
| Strip material | 316L or Inconel 625 | 3–5 mm thick, 40–80 mm wide |
| Base material | Q235 / 20# / 16Mn | Low-carbon steel cone |
| Current | 2000–3500 A | DC, strip as positive |
| Voltage | 25–32 V | Including slag voltage |
| Travel speed | 100–250 mm/min | Adjust for cone curvature |
| Preheat | 80–150 °C | Prevent cold cracking in base |
| Interpass temperature | < 200 °C | Critical for overlay microstructure |
| Post-weld treatment | Stress relief 580–620 °C / 2 h | Reduce residual stress |
| Target overlay thickness | 4–8 mm | Minimum 3 mm for erosion resistance |
| Surface finish | Ra 25–50 μm (as-welded) | Machining to Ra 6.3 μm if required |
Process Challenges on Conical Geometry
The conical geometry of hopper cone components presents unique challenges for strip cladding that differ from flat-plate applications:
Geometric Challenges
| Challenge | Impact | Solution |
|---|---|---|
| Varying curvature | Uneven contact of strip with base | Use flexible strip guide; adjust travel speed |
| Circumferential vs. axial welding | Different gravity effects on slag | Weld horizontally or with slight uphill angle |
| Small radius at cone apex | High stress concentration | Reduce current; increase passes |
| Transition from cone to cylinder | Geometric discontinuity | Use transition strip or supplementary GTAW |
| Access to internal surfaces | Limited electrode access | Use external welding with deep penetration |
Thermal Management on Cones
The varying wall thickness and geometry of cone components create non-uniform heat distribution during cladding. Thicker sections at the cone base absorb more heat, while thinner sections at the apex cool more rapidly. This thermal asymmetry can lead to:
- Differential cooling rates causing residual stress concentration.
- Variations in dilution across the cone surface.
- Distortion of the cone geometry, particularly for thin-walled components.
The recommended approach is to implement a multi-pass cladding strategy with the first pass at the cone base (where heat absorption is highest) and subsequent passes progressing toward the apex, allowing for progressive thermal equilibrium.
Quality Control and Inspection Protocol
The quality control program for lock hopper cone cladding must address both the overlay integrity and the corrosion performance of the finished component. The inspection protocol should be structured according to the criticality of the application.
| Inspection Stage | Method | Acceptance Criteria | Frequency |
|---|---|---|---|
| Pre-weld | Visual + UT of base | No cracks, no laminations | 100% |
| In-process |