A major oil transportation company in Canada planned to inspect a 6-in. sour gas pipeline with conventional in-line inspection (ILI) methods. However, it was determined that traditional ILI methods were not a viable inspection option due to heavy tool damage on gauge pig runs. Some of the pipeline conditions were unknown to the operator due to acquisition of the line from another company. The Projects Engineer believed there was a high probability of a significant dent in the pipeline, and that it would be necessary to excavate and make modifications to the line in order to complete an in-line inspection.
The operator contacted Quest Integrity to inspect the line using a unique ultrasonic ILI tool for difficult-to-inspect and unpiggable pipelines. Because of the tool’s large collapse factor, it successfully navigated this sour gas line despite heavy bore restrictions (see Figure 1). The inspection tool captured 100% of the interior and exterior pipeline data, providing the client with a complete data set for the line including wall thickness changes, bend locations and inner radius profile within 30 days.
The UT ILI tool identified 5 wall thickness changes in one 20-ft section of the pipeline. These changes ranged from 0.864 in. (21.95 mm) to 0.265 in. (7.1 mm). In addition, the tool successfully navigated and inspected the two joints present in this section. It was noted these joints accounted for the tool damage that occurred on previous gauge tool runs instead of a significant dent.
Figure 1. Inner radius and axial view of heavy wall pipe
A full API 579-1 / ASME FFS- 1 2007 Fitness-for-Service assessment was conducted utilising the high-quality inspection data provided by the ultrasonic tool. The data was analysed for wall thinning and anomalies such as corrosion, denting and ovality using specialised pipeline assessment software. The Remaining Strength Factor (RSF) and Reduced Maximum Allowable Operating Pressure (MAOPr) were also determined for the line. The ultrasonic in-line inspection found:
- 130 external metal loss anomalies individually identified
- Wall loss at 58.0% identified in one section of the pipeline
Figure 2. External metal loss found on the pipeline
Figure 3. 2D and 3D views of pipeline wall loss
The operator did not have to excavate or make any line modifications in order to complete the inspection, effectively saving both time and money. The inspection and assessment pinpointed specific areas of degradation, allowing the client to make the necessary repairs and return the line to service quickly. In addition, the inspection data confirmed the cause of the gauge tool damage. The inspection and assessment were executed safely and efficiently, allowing the operator to make confident, timely decisions in managing the pipeline’s long-term integrity.
THE BENEFITS OF ULTRASONIC IN-LINE INSPECTION
Modern UT ILI is now able to overcome challenges associated with traditionally difficult-to-inspect and unpiggable pipelines.
Improved Safety and Flexibility
- Lightweight, self-contained, compact tools are handled easily; no lifting machinery required
- Superb minimum passage and bend capabilities; negotiates damaged or restricted pipe
- Lower pressure differential requirements and bi-directional capability minimise line disruptions
Reduced Operational Risk
- Unique design reduces wear, impact and debris collection associated with conventional in-line inspection technology
- Direct high-density UT measurement delivers accurate, repeatable results
- Solutions oriented: analysis of all line data vs. individual flaw locations
- Single pass combined geometry and metal-loss data provides 100% overlapping coverage
- Linear UT sizing minimise verification digs and improves excavation and repair confidence
- Permanent line modifications not required
- Efficient inspections minimise offline status
- Onsite turnaround and rapid data analysis allows real-time operating decisions
- UT inspections do not permanently magnetise pipe, thereby eliminating demagnetisation repairs
Author: Quest Integrity
Read the article online at: https://www.worldpipelines.com/project-news/30102018/overcoming-heavy-bore-restrictions-a-quest-integrity-case-study/
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