As we all know, an asset’s condition and circumstance can vary – and that can sometimes lead to pipelines being characterized as “unpiggable.” In these cases, the operating conditions or accessibility do not allow for conventional in-line inspection tools. However, this does not negate the need for an inspection solution. ROSEN develops tailored solutions for these unique cases, as was needed for the integrity of a 30” and a 42” gas pipeline inspected for a Mexican operator.

There are a number of alternatives for accessing a pipeline that has been deemed “unpiggable,” but each one comes with additional challenges of its own. One of these options, direct assessment, is one strategy used when in-line inspection techniques are not feasible. However, it is one of the most complex integrity management techniques to be implemented in the oil and gas industry. The inability to retrieve data from smart pig inspections represents a significant challenge in the process of ensuring the integrity of the asset.

Conduction feasibility study

Figure 1: When pipelines are deemed unpiggable (i.e., only accessible externally) a few options are available for integrity management.


After careful consideration and evaluation of the necessary inspection specifications, the ROSEN integrity engineering team determined that an external direct assessment was the best solution. This service would provide the information needed to comply with regulations and maintain the operational availability of the assets. The operator needed an inspection solution for 2 pipelines lines, a 30” and a 42” gas line, that would provide very detailed and reliable data in order to appropriately maintain the integrity of the given assets.

First, a data and gap analysis was completed. Next, an ICDA (Internal Corrosion Direct Assessment) and ECDA (External Corrosion Direct Assessment) were completed, along with geohazards identification, welding procedures and material review, and identification of areas susceptible to containing geometric anomalies. Lastly, a fitness-for-service assessment was performed to conclude the assessment process.


As a result of the findings, ROSEN provided a recommended course of action to ensure the operational capacity and integrity of the assets moving forward. It included creating a corrosion management strategy to minimize risks in case gas presents abnormal operating conditions and to reduce the possibility of internal corrosion. Recommendations to optimally manage external corrosion threats were considered in the analysis, as was the establishment of preventive and corrective maintenance programs, which included:

  • Frequent CIPS (Close Interval Potential Survey) inspections
  • DCVG (Direct Current Voltage Gradient) inspections every 3 to 5 years
  • Potentials and rectifiers readings biannually
  • Follow recommendations due to AC thread on SPUR according with the survey and carry out an AC survey on TGN II

The advantages of adequate information management by the operator was that an evaluation of the threats was possible during the construction process. The evaluated documentation helped to establish only preventive inspection programs with nondestructive techniques to maintain the integrity and reliability of the transportation system.