On-Site Repair and Re-Cladding Services for Clad Components

Overview and Technical Scope

On-site repair and re-cladding represent a critical value-added service that extends the operational life of clad components without requiring complete replacement. This capability is particularly relevant during scheduled maintenance shutdowns, where the availability of portable welding equipment and localized heat treatment systems allows restoration of worn or corroded cladding layers in situ. The technical challenge lies in maintaining metallurgical integrity of the existing base material while achieving adequate bond strength and corrosion resistance in the repair zone.

Portable Welding Equipment and Process Selection

Equipment Configuration

Equipment Type	Application	Key Specifications
Portable GTAW machine	Interface repair, thin cladding restoration	150–300 A, AC/DC, pulse capability
Portable SAW machine	Thick overlay restoration	400–800 A, flux feeder, wire feeder
Portable plasma arc (PTA)	Nickel alloy overlay, high dilution control	100–400 A, powder feeder
Portable FCAW machine	Rapid build-up, large area repair	200–500 A, self-shielded or gas-shielded
Portable hot-wire TIG	High deposition rate, low dilution	200–400 A, wire feed 1–3 m/min

Process Selection Criteria

The selection of overlay process for on-site repair depends on several factors:

Cladding material: Nickel-based alloys (Inconel 625, Hastelloy C276) typically require GTAW or PTA to minimize dilution and avoid carbide precipitation. Stainless steel overlays (304, 316) can be deposited by GTAW, SAW, or hot-wire TIG.
Repair area size: Small localized repairs favor GTAW; large area restoration may require SAW or hot-wire TIG for productivity.
Positional constraints: Vertical and overhead repairs are best accomplished with GTAW or hot-wire TIG due to better control of molten pool.
Base material condition: If the base metal has been weakened by corrosion or erosion, a backing plate or temporary support may be required.

Localized Heat Treatment

Post-weld heat treatment (PWHT) is often necessary to relieve residual stresses and restore the microstructure of the base metal. On-site PWHT presents unique challenges:

Induction heating is preferred for localized PWHT due to precise temperature control and minimal thermal distortion.
Resistance heating with heating bands is suitable for cylindrical components such as pipes and tubes.
Gas flame heating is limited to non-critical applications due to poor temperature uniformity.

The PWHT parameters must comply with applicable codes. For ASME VIII Division 1, the minimum PWHT temperature for carbon steel and low-alloy steel base plates is typically 595°C (1100°F) with a holding time proportional to the maximum thickness. For stainless steel cladding, the solution heat treatment temperature (1010–1120°C for 304/316) is generally impractical on site, so stress relief at 425–480°C is the typical approach.

Wear Parts Remanufacturing

Assessment and Decision Criteria

The decision to remanufacture versus replace a worn clad component follows a systematic evaluation:

Factor	Remanufacture Feasible	Replacement Required
Base metal remaining thickness	≥ 80% of original	< 80% of original
Base metal hardness	Within original specification ± 10%	Excessive hardening or softening
Corrosion depth	< 50% of base metal thickness	> 50% of base metal thickness
Geometric distortion	Within repair tolerance	Excessive warping
Number of previous repairs	≤ 2	> 2
Criticality of component	Non-safety-critical or adequately inspected	Safety-critical with limited margin

Remanufacturing Process Flow

Surface preparation: Mechanical removal of degraded cladding using grinding, machining, or thermal cutting. The removal depth must exceed the maximum observed corrosion or wear depth plus a safety margin of 1–2 mm.
Inspection of exposed base metal: Visual examination, magnetic particle testing (MT), and ultrasonic testing (UT) to detect subsurface defects such as HIC, laminations, or cracks.
Dimensional verification: Confirmation that remaining base metal thickness meets minimum code requirements.
Preheating: Temperature controlled per welding procedure qualification (WPQ) and code requirements.
Overlay welding: Multi-pass deposition following the qualified welding procedure specification (WPS).
Post-weld inspection: UT for bond strength verification, PT for surface crack detection, dimensional measurement of cladding thickness.
Heat treatment: Localized PWHT if required by code or specification.
Final inspection and documentation: Complete record including all test results, operator qualifications, and material traceability.

Quality Control and Code Compliance

On-site repairs must comply with the same quality requirements as original fabrication. Key considerations include:

Welder qualification: All operators must hold valid qualifications per ASME IX or NB/T 47014, with the qualification covering the specific repair process and material combination.
Welding procedure qualification: A valid WPQ must exist for the repair configuration, or a supplemental qualification must be performed.
Material traceability: All consumables used in the repair must have full chemical and mechanical certification.
Non-destructive testing: The extent of NDT must meet or exceed the original fabrication requirements. UT bond testing per ASTM E2340 or equivalent is essential for verifying interface integrity.

Study Insights and Practical Recommendations

On-site repair and re-cladding services offer significant economic and operational advantages, particularly for large components where removal and transport are impractical. However, the quality of repairs is directly dependent on the discipline maintained in following qualified procedures and the competence of the field personnel. I have observed that the most common cause of repair failure is inadequate surface preparation of the base metal prior to re-overlay. The tendency to minimize grinding time in the pressure of a maintenance shutdown schedule often results in incomplete removal of degraded material, leading to premature failure of the repair. A conservative approach—removing more material than strictly necessary—is always preferable to risking a substandard repair.