An ILI report names the anomaly. It does not name the repair. Converting a dig list into a repair strategy requires three judgments the integrity engineer has to make for every dig: whether the anomaly is real and as-reported, what the appropriate code-compliant repair is for the wall loss and operating conditions, and how the repair fits into the operator's life cycle and budget.
This article walks through the decision framework operators use to convert an ILI anomaly into a defensible repair method, with the engineering criteria behind each option.
Step 1: Verify the Anomaly
Before any repair method is selected, the dig must confirm the ILI call. Field measurement procedures should follow API 1163 / API 1176 and the vendor's specification:
- Coating removal at the dig site to expose the anomaly, with care to preserve adjacent coating for re-evaluation.
- Pit gauge measurement of length, width, and depth of metal loss, against the actual pipe wall thickness from UT measurement at clean steel adjacent to the anomaly.
- Photographic documentation including a reference scale and station marker.
- Comparison of field-measured dimensions against the ILI call to validate vendor sizing accuracy for the run.
Discrepancies between ILI and field measurement should be tracked across all the digs in a campaign — they drive how aggressively the operator should treat the rest of the run.
Step 2: Determine the Required Repair Strength
The remaining strength of the anomaly is calculated using B31G, modified B31G, or RSTRENG, depending on operator preference and the anomaly geometry. The remaining strength factor and the maximum allowable operating pressure are the two inputs that drive the repair selection.
Most North American gas and liquids operators apply the criteria from ASME B31.4 (liquid) or B31.8 (gas), and from PHMSA 49 CFR Part 192 / 195, to determine whether the anomaly is:
- Immediate condition: Requires pressure reduction or repair within hours to days.
- One-year condition: Repair scheduled within twelve months.
- Monitored condition: Re-inspect on a defined re-assessment interval.
Repair Method 1: Recoat Only
When the anomaly is external corrosion that has not reduced wall thickness beyond allowable limits, and when the corrosion is no longer active, the appropriate repair is often coating restoration. The objective is to prevent further wall loss without unnecessary mechanical intervention.
- Surface preparation to SSPC-SP10 / NACE No. 2 at the corroded area and a defined margin into sound coating.
- Liquid epoxy or polyurethane coating applied per the manufacturer's specification, with DFT and holiday detection per liquid epoxy application controls.
- Backfill quality control to prevent damage to the new coating.
Recoat is the lowest-cost repair when it is the right repair. It is the wrong repair when wall loss exceeds allowable, when corrosion is active, or when the cause of the original failure has not been corrected.
Repair Method 2: Composite Repair (ASME PCC-2 Article 4.1)
Composite wrap repairs — fiber-reinforced polymer systems engineered per ASME PCC-2 or ISO 24817 — restore strength to a pipeline section without taking the line out of service. They are widely used on liquid and gas pipelines for external corrosion, mechanical damage (after dent removal), and selected manufacturing defects.
Composite repair is appropriate when:
- The anomaly is external and not leaking.
- The remaining wall thickness can support the design pressure without the composite, treated as a temporary loading case during installation.
- The pipe geometry allows the composite to be wrapped at the design tension and overlap.
- The operating conditions (temperature, pressure cycling, soil environment) are within the design envelope of the composite system selected.
Composite repair sizing — wrap thickness, axial extent, taper — is governed by the calculations in ASME PCC-2 Article 4.1 or ISO 24817. Our Composite Repair Sizing Calculator implements those calculations and produces a sized design that can be reviewed against the manufacturer's qualification data.
Repair Method 3: Type A Steel Sleeve
A Type A steel sleeve is a half-shell repair that provides reinforcement to a pipeline section without being welded directly to the pipe. The sleeve is fitted around the pipe over the anomaly, the longitudinal seams of the sleeve are welded together, and the sleeve does not seal pressure.
Type A sleeves are appropriate for non-leaking external corrosion when the geometry allows a tight-fitting sleeve and when there is sufficient remaining wall to carry the design pressure without the sleeve. The sleeve carries pressure-cycle stress and prevents the anomaly from propagating.
Repair Method 4: Type B Steel Sleeve (Pressure Containing)
A Type B sleeve is fillet-welded to the pipe at both ends. It carries pressure independently of the underlying pipe wall. Type B sleeves are appropriate for:
- Leaking anomalies, where the sleeve must contain pressure once the underlying pipe loses integrity.
- Anomalies that may grow over the planned service life.
- Repairs in services where composite materials are unsuitable (high temperature, severe pressure cycling outside composite qualification).
Type B sleeve fabrication requires welding qualified per the operator's procedures, post-weld inspection per the welding code, and an internal volumetric inspection of the underlying pipe before the sleeve is installed.
Repair Method 5: Hot Tap and Replace
For anomalies that are too severe for sleeves or composites, or where the underlying pipe is at the end of its life, the section can be removed and replaced. Replacement is performed live by hot tapping a bypass and routing flow around the cutout, or by taking the line out of service. The decision is driven by operational impact, regulatory constraints, and the engineering of the bypass.
Replacement is the highest-cost repair and is generally reserved for cases where less-invasive methods are not technically or economically justified.
Decision Matrix
| Anomaly Type | Wall Loss | Recommended Repair |
|---|---|---|
| External corrosion, not active | Below allowable | Recoat |
| External corrosion, non-leaking | Up to 80 percent | Composite (PCC-2) or Type A sleeve |
| External corrosion with through-wall leak | Any | Type B sleeve |
| Mechanical damage with dent | Per ASME B31.8 / PCC-2 | Composite after dent assessment, or Type B |
| Severe damage, end-of-life pipe | Any | Cutout and replace |
Coating Repair After Mechanical Repair
Every sleeve or composite installation removes the original coating in the work area. Restoring the coating to the same standard as the original is essential — the most common failure mode after a sleeve installation is corrosion in the annulus between the sleeve and the pipe, driven by inadequate coating restoration before the sleeve was installed.
Liquid epoxy applied per the controls described in our liquid epoxy failure modes article is the standard restoration system. CP system checks should confirm that the repaired section continues to receive adequate protection.
How Raphoon Helps
Raphoon supports integrity teams through dig plan review, composite repair sizing per ASME PCC-2 / ISO 24817, third-party inspection of repair installation, and post-repair coating QA. Our composite repair page describes our project-level support, and the Composite Repair Sizing Calculator can be used directly for in-house preliminary sizing. For project support, contact us.