8.3 Temporary and Permanent Repair Methods (ASME PCC-2 & API 570)

8.3 Temporary and Permanent Repair Methods (ASME PCC-2 & API 570)

Repairs, alterations, and rerating of in-service piping systems must comply with the requirements of API 570, Section 8, and the piping design code (such as ASME B31.3). For detailed repair procedures and calculations, API 570 refers to ASME PCC-2, 'Repair of Pressure Equipment and Piping.'

Welded Split-Sleeves (Full-Encirclement Sleeves)

Welded split-sleeves consist of two halves of a pipe or curved plate placed around a damaged piping section and welded together along their longitudinal seams. They are used to repair localized thinning, cracks, or leaks.

Type A Split Sleeves (Non-Pressure Containing)

Type A split-sleeves are welded along their longitudinal seams, but their ends are NOT welded to the pipe wall.

• Function: They provide structural reinforcement but cannot contain process pressure.
• Limitations: Type A sleeves are not permitted for repairing leaking piping or cracking. They are only suitable for reinforcing areas of localized thinning or external damage. They are considered temporary or permanent depending on the engineering assessment and corrosion allowance.

Type B Split Sleeves (Pressure-Containing)

Type B split-sleeves are welded along their longitudinal seams, and their circumferential ends are welded to the pipe wall.

• Function: They are designed to contain full system pressure and load.
• Application: They can be used to repair leaking areas, localized thinning, and cracking.
• API 570 Rules: A Type B sleeve is considered a permanent repair under API 570 if it is designed by a piping engineer, fabricated from matching or compatible materials, and fully inspected.
• In-Service Welding Caution: Welding a Type B sleeve onto an active, pressurized pipeline poses a risk of burn-through if the pipe wall is too thin. The inspector must verify the remaining wall thickness of the pipe under the weld area and calculate the minimum safe wall thickness for in-service welding.

Fillet-Welded Patches (Lap Patches)

Fillet-welded patches (lap patches) are plates that are bent to conform to the pipe radius and fillet-welded over the degraded piping surface.

API 570 Rules for Lap Patches

• Temporary Repairs Only: Under API 570, fillet-welded patches are generally restricted to temporary repairs on low-pressure or non-hazardous systems.
• Engineering Design: The patch must be designed by a piping engineer to withstand full system pressure. It must have rounded corners (minimum 1-inch radius) and must cover the entire degraded zone plus a margin.
• Inspector Approval: The inspector must authorize the installation.
• Removal Requirement: Temporary fillet-welded patches must be removed and replaced with a permanent repair (such as an insert plate or spool piece) at the next available turnaround.
• Permanent Patch Exception: In rare circumstances, a fillet-welded patch can be approved as a permanent repair if evaluated and approved by both the piping engineer and the inspector, taking into account the fatigue life and service environment.

Engineered Box Enclosures

Engineered box enclosures (leak clamps or enclosures) are custom-designed metal boxes that are bolted or welded around a leak or localized thin spot. The box is then filled with a high-temperature sealant.

• Design Requirements: Every box enclosure must be designed by a piping engineer. The design must account for the system pressure, temperature, piping loads, and the potential for the leak to spread within the enclosure.
• Authorization: The installation must be authorized by the inspector.
• Service Life: Enclosures can remain in service as permanent repairs if designed for the life of the plant, but they must be logged and periodically monitored for leaks or degradation.

Insert Plates (Flush Patches)

Insert plates involve cutting out the degraded section of the pipe wall and welding a new plate flush with the existing pipe.

• Welding Requirements: The insert plate must be welded using full-penetration butt welds. Fillet welds are not permitted.
• Material & Thickness: The insert plate material, thickness, and welding electrodes must match the original piping specification.
• API 570 Status: Insert plates are considered permanent repairs.
• NDE & Inspection: The welds must meet the requirements of the construction code (such as ASME B31.3). Radiographic testing (RT) or ultrasonic testing (UT) must be performed on the butt welds.

Composite / Non-Welded Repairs

Composite repairs involve wrapping the pipe with high-strength glass or carbon fibers impregnated with a polymer resin (polyurethane or epoxy).

• ASME PCC-2 Standard: Composite repairs must be designed in accordance with ASME PCC-2 Article 4.1 (for non-metallic wraps).
• Application: They are highly effective for repairing external corrosion, local thin spots, and minor leaks.
• Class Restrictions: Under API 570, composite wraps are typically restricted to temporary repairs in hazardous hydrocarbon services. They can be considered permanent for non-hazardous utility services (such as cooling water, air, or steam condensate) under specific engineering approval.
• Design Lifetime: The wrap must be designed for a specific lifetime, which is documented and monitored.

Mechanical Clamp Repairs (ASME PCC-2 Article 306)

Mechanical clamps (also called leak clamps or bolted clamps) are non-welded pressure-retaining enclosures bolted around a leaking or thinned pipe section. ASME PCC-2 Article 306 covers design, materials, installation, and inspection of these clamps. On the February 2026 API 570 BOK, Article 306 is explicitly testable.

When Clamps Are Used

• Temporary leak containment until a permanent welded repair or replacement can be scheduled
• Locations where hot work is prohibited (hydrocarbon atmosphere, live units)
• Emergency response when a pinhole or packing leak must be stopped without depressuring the entire unit

Inspector Checks for Clamp Repairs

1. Design package – clamp rated for design pressure/temperature of the circuit; gasket/seal compatible with process fluid
2. Pipe condition under the clamp – remaining wall must support clamp bearing loads; severe local thinning may require engineered load paths
3. Bolt torque and follow-up – uneven torque can unload seals; re-check after thermal cycles
4. Temporary status – API 570 expects temporary repairs to be tracked and removed or made permanent at the next opportunity; leaving a clamp for years without engineering revalidation is an audit finding
5. NDE after installation – leak check (often bubble test per Section V Article 10 Appendix I) at operating or reduced pressure per the repair plan

Clamp vs Fillet Patch vs Type B Sleeve

ASME PCC-2 Articles on the February 2026 BOK

The API 570 Body of Knowledge lists these PCC-2 articles (and appendices) as testable. Use this map when a question names an article number:

Authorizations and Approvals

A critical focus area of the API 570 exam is the division of responsibilities between the Piping Engineer and the Piping Inspector.

Piping Engineer Responsibilities

The piping engineer must approve all repair designs. This includes:

• Design calculations for split-sleeves, box enclosures, and patches.
• Material selection and compatibility checks.
• Review of fitness-for-service evaluations.
• Approval of permanent fillet-welded patches or composite wraps.

Piping Inspector Responsibilities

The piping inspector is responsible for the authorization and quality control of the repair work. This includes:

• Pre-Authorization: The inspector must authorize the repair method prior to the start of any work.
• Welder Verification: Ensuring the welders are qualified in accordance with ASME Section IX.
• WPS Verification: Verifying the Welding Procedure Specification (WPS) is appropriate for the material and service.
• Visual & NDE Checks: Performing visual inspections and verifying that all required NDE (such as RT, UT, PT, or MT) is executed and meets acceptance standards.

Repair Selection Matrix

Exam Tips & Scenarios

Worked Scenario: Fillet-Welded Patch Sizing Check

An engineer is designing a temporary fillet-welded patch (lap patch) to repair a localized thin area on a 10-inch nominal (NPS 10) carbon steel piping system (Class 2 service). The host pipe outer diameter ($D_o$) is 10.75 inches, giving an outer radius ($R$) of 5.375 inches. The host pipe nominal wall thickness ($t_{host}$) is 0.365 inches. Inspection data shows a localized circular thinning defect with a diameter of $d_{defect} = 2.5$ inches.

To satisfy ASME PCC-2 Article 2.12, the patch must extend beyond the boundary of the degraded area into sound metal by a minimum distance of $\sqrt{R \cdot t_{host}}$.

1. Calculate the Minimum Extension ($W_{min}$): $W_{min} = \sqrt{R \cdot t_{host}}$ $W_{min} = \sqrt{5.375\text{ inches} \times 0.365\text{ inches}} = \sqrt{1.9619} \approx 1.40\text{ inches}$
2. Calculate the Minimum Patch Diameter ($D_{patch}$): The patch must cover the defect diameter plus the minimum extension on all sides: $D_{patch} = d_{defect} + 2 \cdot W_{min}$ $D_{patch} = 2.5\text{ inches} + 2 \times 1.40\text{ inches} = 5.30\text{ inches}$
3. Final Patch Sizing: The engineer rounds the design up to a standard circular patch diameter of 5.5 inches (or a 5.5-inch square patch with 1.0-inch radius rounded corners). The size of the fillet weld leg must be specified by the engineer (typically matching the patch plate thickness, which must be at least equal to $t_{host} = 0.365$ inches). The inspector verifies these dimensions before authorizing the repair.