Wear-Resistant Weld Overlay Pipes, Spiral Augers, and Grinding Roll/Disc Repair Overlay Technology

1. Definition and Fundamental Principles

Wear-resistant weld overlay technology involves the deposition of hardfacing alloys onto the inner or outer surfaces of pipes, spiral augers (helical conveyors), grinding rolls, and grinding discs to create a protective layer that significantly resists abrasive, erosive, and impact wear. The fundamental principle relies on metallurgical bonding between the base material and the overlay deposit, achieved through controlled thermal input during arc welding processes. The overlay layer typically contains carbide-forming elements such as chromium, tungsten, molybdenum, cobalt, and carbon, which form hard ceramic-like phases (Cr₇C₃, Cr₂₃C₆, WC, Co₃W₃C) that dramatically increase surface hardness to 55–70 HRC while maintaining ductile-to-brittle transition characteristics compatible with the base substrate.

For inner-wall pipe overlay, the challenge is achieving uniform coverage on cylindrical internal geometries, often requiring robotic orbital welding or manual TIG/MIG techniques with precise torch positioning. Spiral auger overlay requires conformal deposition along helical flight surfaces, demanding careful heat management to prevent distortion of the auger geometry. Grinding roll and disc repair overlay involves resurfacing worn cylindrical or flat working surfaces, restoring dimensional accuracy while simultaneously upgrading the surface to a wear-resistant alloy.

2. Category and Business Positioning

This technology falls squarely within the wear-resistant product category of Cladding Technology Shanxi Co., Ltd.'s capability portfolio. It represents a high-value-added service that bridges the gap between base material manufacturing and surface engineering, positioning the company as a critical partner in asset integrity management for power generation and cement production industries.

• Product Classification: Wear-resistant overlay components (pipes, spiral augers, grinding rolls, grinding discs)
• Service Model: OEM overlay manufacturing, field repair and refurbishment, and condition-based maintenance support
• Revenue Positioning: Recurring revenue stream driven by planned maintenance cycles and unplanned emergency repairs in continuous-process industries
• Competitive Differentiation: Combination of metallurgical expertise, robotic automation capability, and on-site service flexibility

3. Technical Purpose and Value Proposition

3.1 Life Extension of Conveying Systems

The primary technical purpose is the extension of service life for material conveying systems in power plants and cement kilns. Conventional carbon steel or low-alloy steel conveying components subjected to abrasive coal, limestone, fly ash, or clinker material experience progressive wall thinning, flight erosion, and roll surface degradation. Without intervention, replacement cycles of 6–18 months are typical. With properly engineered wear-resistant overlay, service life extensions of 3–8 times the original design life are routinely achievable, translating directly into reduced unplanned downtime, lower spare parts inventory requirements, and improved overall equipment effectiveness (OEE).

3.2 Economic Value

• Direct Cost Savings: Elimination of premature component replacement (pipe sections, augers, grinding assemblies)
• Indirect Savings: Reduction in shutdown duration, labor for disassembly/reassembly, and logistics for spare parts
• Performance Improvement: Maintained conveying capacity through preserved geometric accuracy of augers and rolls
• Safety Enhancement: Prevention of catastrophic failures such as pipe perforation, auger breakage, or roll seizure

4. Key Process and Implementation Points

4.1 Overlay Alloy Selection Matrix

Application	Wear Mechanism	Recommended Overlay Alloy	Typical Hardness (HRC)	Key Alloying Elements
Coal conveying pipe (inner wall)	Abrasive + erosive	Cr-C-Ni-Mo hardfacing (e.g., Stellite 6 equivalent, D211, D256)	58–65	Cr 25–30%, C 2.5–4%, Mo 5–8%, Ni 12–15%
Coal conveying pipe (inner wall) – severe	High-energy abrasive	Co-based hardfacing (Stellite 6, 21)	55–62	Co base, Cr 21–28%, C 0.5–1.2%, Mo 5–7%
Spiral auger flights (coal/ore)	Abrasive + impact	Fe-Cr-C high-carbon martensite (e.g., D256, A235)	60–67	Cr 10–13%, C 3.5–4.5%, Mo 3–5%
Spiral auger flights (cement/clinker)	Abrasive (hard particles)	Fe-Cr-C-Ni-B hardfacing	58–65	Cr 12–18%, C 3–5%, Ni 5–8%, B 0.5–1.0%
Grinding roll surface	Rolling contact + abrasive	Fe-Cr-C (D256/D257) or Co-based	58–68	Cr 10–18%, C 3–5%
Grinding disc (cement mill)	High-pressure abrasive	Fe-Cr-C high-carbon (D256 equivalent)	60–67	Cr 12–14%, C 4–5%, Mo 3–5%

4.2 Process Parameters for TIG Weld Overlay

Parameter	Inner Pipe Overlay	Auger/Spiral Overlay	Roll/Disc Repair Overlay
Welding Process	TIG (GTAW) – manual or orbital	TIG (GTAW) – manual with rotation	TIG (GTAW) or MIG (GMAW)
Shielding Gas	Ar 99.99% (or Ar/He mix for thick sections)	Ar 99.99%	Ar 99.99% (TIG) or Ar/CO₂ 80/20 (MIG)
Current (A)	80–150 (depending on rod diameter)	100–180	120–220 (TIG) / 150–280 (MIG)
Deposition Rate	0.3–0.8 kg/h	0.4–1.0 kg/h	0.5–1.5 kg/h (TIG) / 1.5–4.0 kg/h (MIG)
Layer Thickness (per pass)	2.0–4.0 mm	2.5–5.0 mm	2.0–4.0 mm (TIG) / 3.0–6.0 mm (MIG)
Interpass Temperature	≤200°C (≤300°C for Fe-Cr-C alloys)	≤200°C	≤250°C
Preheat Temperature	150–250°C (for thick sections or high-C alloys)	100–200°C	150–300°C
Post-Weld Heat Treatment	450–550°C × 2h (stress relief)	450–550°C × 2h	500–580°C × 2h (stress relief + temper)

4.3 Implementation Sequence for Inner Pipe Overlay

1. Surface Preparation: Remove rust, scale, oil, and contamination using grinding (Grit blast to Sa 2.5 per ISO 8501-1). Ensure base surface roughness Ra ≤ 12.5 μm for optimal metallurgical bonding.
2. Fit-up and Positioning: Establish weld position indicators. For orbital TIG, verify internal access for robotic torch head. For manual internal welding, ensure adequate clearance for torch manipulation (minimum 150 mm working space).
3. Transition Layer Deposition: Apply a 1–2 mm transition layer of matching or compatible alloy (e.g., 309L or Fe-8Ni) to ensure ductility at the base/overlay interface and prevent cracking in subsequent hard layers.
4. Build-up Passes: Deposit 2–4 passes of hardfacing alloy, maintaining interpass temperature below specified limit. Use weave pattern or orbital rotation for uniform coverage. Overlap adjacent beads by 30–50%.
5. Final Pass and Finishing: Apply final pass with optimal composition for surface hardness. Grind flush if dimensional tolerance requires (note: grinding reduces hardness by 3–5 HRC in the ground zone).
6. Post-Weld Heat Treatment: Perform stress relief per alloy manufacturer recommendations. For Fe-Cr-C alloys, temper at 500–580°C to reduce residual stress without significant hardness loss.
7. Quality Inspection: Perform hardness verification, thickness measurement, and NDT per acceptance criteria.

4.4 Spiral Auger Overlay – Special Considerations

Spiral auger overlay presents unique geometric challenges due to the helical flight profile. Key implementation points include:

• Rotation Strategy: Rotate the auger shaft at controlled speed (5–15 RPM) during welding to achieve uniform circumferential coverage. Manual welders must synchronize torch movement with rotation.
• Heat Input Management: The thin flight section (typically 8–15 mm thick) is susceptible to distortion. Limit heat input to 1.5–2.5 kJ/mm and monitor angular distortion. Use back-up plates or clamping fixtures to restrain movement.
• Layer Build Strategy: Apply overlay in 2–3 passes, building thickness from 0 to 6–10 mm total. First pass establishes wetting; subsequent passes build volume. Final pass provides surface hardness.
• Geometric Verification: Post-overlay, verify auger runout (≤0.5 mm TIR) and flight thickness uniformity (±0.5 mm) to ensure balanced operation in the conveying system.

4.5 Grinding Roll and Disc Repair Overlay

Repair overlay of grinding rolls and discs in cement mills and grinding stations involves restoring worn surfaces to original dimensional specifications while simultaneously upgrading surface properties:

1. Wear Assessment: Measure remaining material thickness using ultrasonic thickness gauging. Determine minimum remaining thickness for structural integrity (typically ≥ 2× original wall thickness for rolls, ≥ 15 mm for discs).
2. Surface Preparation: Grind worn surface to remove decarburized layer and expose sound material. Achieve surface roughness Ra 6.3–12.5 μm.
3. Overlay Application: Apply 2–4 passes of hardfacing alloy to build up to specified thickness. For rolls, ensure uniform coverage around the full circumference. For discs, cover the full working face with overlap beyond the original contact zone.
4. Dimensional Restoration: Grind or machine the overlay surface to restore original diameter (for rolls) or thickness (for discs) to specified tolerance (typically ±0.1 mm for rolls, ±0.2 mm for discs).
5. Hardness Verification: Confirm post-grinding hardness meets specification (typically 55–65 HRC). If grinding reduces hardness below minimum, apply an additional thin overlay pass.

5. Applicable Standards and Acceptance Criteria

5.1 Governing Standards

Standard	Scope of Application	Key Requirements
GB/T 13814-2008	Welding consumables – Hardfacing electrodes	Classification, composition, hardness requirements for Fe-Cr-C, Co-based, Ni-based hardfacing alloys
GB/T 21433-2008	Welding consumables – Hardfacing wire for GMAW	Composition and performance specifications for MIG hardfacing wire
GB/T 5314-2012	Welding consumables – Hardfacing rods for TIG	TIG hardfacing rod specifications, including chemical composition and mechanical properties
ASTM A388/A388M	Welding consumables – Hardfacing electrodes	Classification system for hardfacing electrodes (A-class, B-class, C-class, D-class)
ASTM A538/A538M	Welding consumables – Hardfacing wire for GMAW	Specifications for hardfacing wire for gas metal arc welding
ASME Section IX	Welding qualification – PQR and WPS	Qualification requirements for welding procedures and welder performance
ASME Section II, Part D	Welding consumables – Filler metal	Filler metal specifications including hardfacing alloys
ISO 8501-1:2007	Surface preparation – Visual assessment of cleanliness	Surface cleanliness grades (Sa 2, Sa 2.5, Sa 3) for pre-overlay preparation
ISO 14555:2019	Welding – Qualification of welding procedures for hardfacing	Procedure qualification requirements specific to hardfacing applications
GB/T 11345-2013	Ultrasonic testing of welds	UT inspection acceptance criteria for overlay welds
NACE MR0175/ISO 15156	Sulfide stress cracking resistance (if applicable)	Material and welding requirements for H₂S-containing environments

5.2 Acceptance Criteria

• Hardness: Overlay surface hardness must meet minimum specification (typically ≥55 HRC for Fe-Cr-C, ≥50 HRC for Co-based). Measured per ASTM E18 (Rockwell C scale) at intervals of 5–10 mm across the overlay surface.
• Thickness: Minimum overlay thickness verified by ultrasonic measurement (per ASTM E797) or magnetic induction gauge. Typical minimum: 3.0 mm for pipes, 5.0 mm for auger flights, 2.0 mm for roll/disc surfaces.
• Metallurgical Bond: No delamination at base/overlay interface. Verified by macrographic examination of cross-section per ASTM E3. Transition zone microstructure examined for cracking or excessive dilution.
• Crack-Free: No cracks in overlay or at the base/overlay interface. Verified by penetrant testing (PT) per ASTM E165 or magnetic particle testing (MT) per ASTM E709. Acceptance: no linear indications ≥1.5 mm length.
• Ultrasonic Inspection: No indications of lack of fusion, delamination, or subsurface cracks. Performed per GB/T 11345 or ISO 17640. Acceptance: no indications exceeding specified amplitude threshold.
• Dimensional Tolerance: Post-overlay and post-grinding dimensions within specified tolerance (typically ±0.2 mm for pipes, ±0.5 mm for augers, ±0.1 mm for rolls).

6. Common Risks and Control Measures

6.1 Metallurgical Risks

Risk	Cause	Control Measure
Hot cracking in overlay	Excessive sulfur/phosphorus in base metal; high heat input; unsuitable alloy selection	Preheat to reduce cooling rate; select alloy with low hot cracking susceptibility; limit heat input; use pre-cleaning to remove S/P-rich zones
Cold cracking (hydrogen-induced)	High carbon equivalent of base metal; rapid cooling; hydrogen from moisture	Preheat per CEV calculation; use low-hydrogen consumables; post-weld bake at 200°C for 2h to diffuse hydrogen
Excessive dilution	High heat input; inadequate layer build strategy; large groove preparation	Limit heat input per pass; use multiple thin passes; ensure adequate overlap; consider transition layer
Reduced hardness after grinding	Grinding removes hardened surface layer; heat from grinding causes tempering	Apply additional overlay pass after grinding; control grinding parameters (speed, pressure, coolant); verify post-grinding hardness
Delamination/spalling	Inadequate base surface preparation; poor wetting; thermal cycling in service	Achieve Sa 2.5 surface preparation; ensure proper wetting with first pass; use compatible alloy with good thermal expansion match

6.2 Geometric and Process Risks

• Distortion of spiral auger: Control by limiting heat input, using clamping fixtures, and welding in a balanced sequence (opposite sides of the same rotation).
• Uneven coverage on internal pipe surface: Control by using orbital welding equipment or trained manual welders with positional indicators. Verify coverage by UT thickness mapping.
• Roll runout after overlay: Control by uniform deposition around full circumference and post-overlay machining to restore geometric accuracy.
• Porosity in overlay: Control by ensuring proper shielding gas flow, clean consumables, and adequate base surface preparation (no oil, moisture, or oxide).

6.3 Service Performance Risks

• Premature overlay failure in abrasive service: Mitigate by selecting alloy with appropriate carbide morphology for the specific wear mechanism (sliding, rolling, impact). Perform tribological testing or reference existing service data.
• Spalling under thermal cycling: In hot service (e.g., hot cement clinker), select alloy with good thermal fatigue resistance. Consider Co-based alloys for high-temperature applications above 500°C.
• Impact brittleness: High-carbon martensitic overlays may be susceptible to impact spalling. Mitigate by tempering to reduce brittleness while maintaining adequate hardness (55–60 HRC range).

7. Application Across Three Technology Routes

7.1 TIG/MIG Weld Overlay (Primary Route)

TIG (GTAW) and MIG (GMAW) weld overlay constitute the primary and most versatile technology route for this application. This route is applicable to all components described:

• Inner pipe overlay: TIG welding with consumable rod (ER type) provides precise heat control and excellent penetration characteristics. Orbital TIG systems enable automated, repeatable coverage for large-diameter pipes. Manual TIG is preferred for small-diameter pipes or field repairs.
• Spiral auger overlay: TIG welding with manual rotation control provides optimal heat management for thin-flight augers. MIG welding can be used for thicker flights where deposition rate is prioritized over heat control.
• Grinding roll/disc repair: Both TIG and MIG are applicable. TIG is preferred for precision repair where minimal heat input is critical. MIG offers higher productivity for large-area resurfacing.

WPS Qualification: For each application, qualified Welding Procedure Specifications (WPS) must be developed and documented per ASME Section IX or ISO 14555. Qualification variables include base material, filler metal classification, heat input range, preheat/post-heat treatment, and deposition thickness. Performance Qualification Records (PQR) demonstrate successful execution with hardness, metallurgical, and NDT verification.

7.2 Hydraulic Explosive Bonding (Complementary Route)

While hydraulic explosive bonding is primarily associated with clad plate and pipe manufacture, it contributes to wear-resistant pipe applications in the following manner:

• Pre-clad pipe substrate: Hydraulic explosive bonding can produce pipe with a wear-resistant inner cladding layer (e.g., 3Cr13, 14Cr28Ni, or high-carbon steel) that serves as a durable substrate for subsequent TIG overlay. This combination provides a two-stage protection system: the bonded cladding layer provides base wear resistance, while the TIG overlay provides enhanced surface hardness and wear performance.
• Corrosion-wear dual protection: For applications where both corrosion and abrasion are concerns (e.g., wet coal slurry conveying), hydraulic explosive bonding produces a pipe with a corrosion-resistant inner layer, onto which a wear-resistant overlay is applied. This leverages the strength of both technologies.
• Thick cladding without dilution: For applications requiring thick wear-resistant layers (≥5 mm) where weld overlay dilution would degrade hardness, hydraulic explosive bonding provides a thick, fully bonded cladding layer with zero dilution, followed by a thin TIG overlay pass for surface finish and hardness optimization.

7.3 Explosion Welding (Specialized Route)

Explosion welding (explosive cladding) is applicable to wear-resistant component manufacturing in the following scenarios:

• Large grinding roll manufacture: For new grinding rolls requiring thick wear-resistant surfaces, explosion welding can bond a wear-resistant layer (e.g., high-carbon steel, Stellite alloy) to a ductile base roll core. This produces a component with the toughness of the base material and the wear resistance of the overlay, without the dilution and residual stress associated with thick weld overlay.
• Auger shaft-cladding assemblies: For heavy-duty augers subject to extreme abrasion, explosion welding can produce a shaft with a wear-resistant outer layer, which is subsequently machined to final auger geometry. This provides superior wear life compared to weld overlay alone.
• Large-diameter pipe manufacture: For large-diameter conveying pipes (≥300 mm) requiring thick wear-resistant linings, explosion welding produces a clad pipe that is subsequently formed, welded into length, and installed. This is more economical than TIG overlay for very thick layers on large-diameter pipes.

Integration Strategy: The optimal approach often combines multiple routes: explosion welding or hydraulic bonding produces a pre-clad substrate, which is then finished with TIG/MIG overlay for surface optimization. This hybrid approach leverages the strengths of each technology while mitigating their individual limitations.

8. Contribution to Qualification Building, Product Delivery, and Customer Value

8.1 Qualification Building

• WPS/PQR Portfolio: Each overlay application generates qualified WPS/PQR pairs that expand the company's procedural qualification portfolio. These qualifications are portable across customers and projects, reducing time-to-production for new orders.
• Welder Certification: Welder performance qualifications (WPQ) for hardfacing overlay establish a trained workforce capable of executing complex overlay procedures. These certifications (per ASME Section IX or ISO 9606) are recognized across industries and enhance the company's service credibility.
• Material Qualification: Qualification of specific alloy combinations for specific service conditions (coal, cement, clinker, fly ash) builds a technical database that supports rapid specification for new applications.
• System Qualification: For power and cement industry customers, overlay service qualifications contribute to vendor approval processes (e.g., supplier qualification for major utilities or cement groups).

8.2 Product Delivery Capability

• Standardized Products: Overlay specifications for common applications (coal pipe, cement auger, grinding roll) can be standardized into product catalog items with defined performance guarantees, enabling rapid quotation and delivery.
• Custom Engineering: The technical depth of overlay capability supports custom engineering for non-standard applications, providing value-added service beyond commodity products.
• Field Service Capability: Portable TIG/MIG equipment enables on-site repair and overlay, reducing customer downtime by eliminating component removal and shipping. This field service capability is a key competitive differentiator.
• Production Scalability: Orbital TIG systems and automated MIG overlay equipment enable scalable production for large orders (e.g., full conveying system overlay for a new cement line), while manual TIG supports small-batch and repair work.

8.3 Customer Value Delivery

• Quantified Life Extension: Customers receive documented life extension data (e.g., "overlay extends pipe life from 8 months to 36 months based on wear rate testing"), enabling reliable maintenance planning and budget forecasting.
• Reduced Total Cost of Ownership: Despite higher initial investment, overlay reduces total cost of ownership by 40–70% compared to periodic replacement, considering labor, downtime, and spare parts costs.
• Performance Guarantee: Hardness and thickness verification at delivery, combined with service life guarantees, provides customer confidence and reduces procurement risk.
• Technical Partnership: Deep metallurgical understanding and application experience position the company as a technical partner rather than a commodity supplier, enabling collaborative optimization of conveying system design.
• Environmental Benefits: Life extension through overlay reduces material consumption, manufacturing energy, and waste generation, supporting customer sustainability objectives.

9. Quality Management and Documentation Requirements

9.1 Process Documentation

• WPS (Welding Procedure Specification): Documented per ASME Section IX or ISO 14555, specifying all essential and non-essential variables, process parameters, and acceptance criteria.
• PQR (Procedure Qualification Record): Records of qualification welds with hardness, microstructural, and NDT results demonstrating compliance with acceptance criteria.
• WPQ (Welder Performance Qualification): Individual welder certifications for each overlay process, with defined expiry periods (typically 6–12 months).
• Inspection and Test Plan (ITP): Defines inspection stages, acceptance criteria, and responsible parties for each production batch.

9.2 Inspection and Testing Protocol

1. Incoming Inspection: Verify base material grade, consumable certification (mill test reports for rods/wire), and surface condition.
2. In-Process Inspection: Monitor preheat temperature, interpass temperature, deposition rate, and visual weld appearance during production.
3. Post-Weld Inspection:
   • Visual examination (VT) – 100% of overlay surface
   • Hardness testing – minimum 5 points per component, or per customer specification
   • Ultrasonic thickness measurement – grid pattern covering 100% of overlay area
   • Penetrant testing (PT) or Magnetic Particle Testing (MT) – per acceptance criteria
   • Ultrasonic testing (UT) for bond quality – per ISO 17640 or GB/T 11345
4. Final Inspection: Dimensional verification, surface finish confirmation, and compilation of quality documentation package.

9.3 Traceability

Each overlay component must carry traceable documentation linking base material heat number, consumable lot number, WPS number, welder ID, inspection results, and delivery date. This traceability supports quality assurance audits, warranty claims, and continuous improvement initiatives.

10. Conclusion

Wear-resistant weld overlay for pipes, spiral augers, and grinding rolls/discs represents a high-value technical capability that directly addresses the life-extension requirements of power and cement industry conveying systems. Through rigorous metallurgical selection, controlled process execution, and comprehensive quality verification, this technology delivers quantifiable performance improvements and significant economic value to customers. The integration of TIG/MIG overlay as the primary route, complemented by hydraulic explosive bonding and explosion welding for specialized applications, provides a comprehensive solution portfolio capable of addressing the full spectrum of wear protection requirements. Systematic qualification building, standardized product development, and field service capability together establish a sustainable competitive position in the industrial surface engineering market.