In order to find the causes that promoted a rupture in a 26-Inch gas pipeline, the information available was gathered to perform the analysis.  

Input data:

• ILI result information

• Cathodic protection data

• Historical pressure cycling

• Any information regarding coating condition and gas quality details

• Soil type, resistivity and pH.

• Historic failure data and Repair history

Regarding to the historic failure data, the following was detected: 

✔️ Five ruptures in the pipeline for combination between external corrosion processes, coating damages and pre-existing crack-like defects in the pipe, according to previous Fitness for Service level 3 assessment.

✔️ During the assessment, some sections of metal were taken of the pipe for lab analysis. In addition, input data was aligned and analyzed, in order to find the root cause failure and evaluate the pipeline integrity conditions.

Data and Findings:

1. Pre-existing crack-like defects that remain in the pipeline.

2. External corrosion located in the heat affected zone (HAZ<3t).

3. Coating damages.

4. Only 7% CP readings meet the NACE -850 mVcse polarized potential criterion.

5. -There was a relationship between the external corrosion metal loss features and the coating damages. In addition, the failure matched with a low elevation profile of the pipe and low soil resistivity.

6. -On the other hand, there was evidence of pressure cycling which had promoted the propagation and growth of crack-like defects.