March 2017, Vol. 244, No. 3


Outlining a Structured Approach to Inline Inspection

By Scott Riccardella and Michael Fraser, Structural Integrity Associates, Inc., and Charlie Hall and Jay Keldsen, MESA

Recently proposed regulations in the Notice of Proposed Rulemaking (NPRM), titled “Safety of Gas Transmission and Gathering Pipelines,” combined with recent advancements in inline inspection (ILI) technology, are likely to cause an increase in the application of ILI as an integrity-assessment method of oil and gas pipelines. This in turn will expand the frequency and type of pipeline defects that will be encountered.

Lines previously considered “unpiggable” will be retrofitted and be capable of accommodating new ILI tools. Pipeline operators previously reliant on direct assessment as their primary assessment methodology will increasingly turn to ILI despite limited experience using these tools.

Operators who assessed lines for corrosion using ILI may turn to new ILI tools with linear indication detection and sizing capabilities to help identify threats such as stress corrosion cracking (SCC) and certain manufacturing defects.

The primary objective for performing an ILI is to determine the condition of the line, identify defects detrimental to the integrity of the pipeline for removal and ultimately ensure adequate safety margin exists. In addition to the technical aspects pertaining to physical line condition, specific regulatory expectations and deadlines must be managed.

As new tools and additional segments are assessed, it will be increasingly important to have a structured process and implementation plan for ILI. This article outlines a structured process to consider as part of an overall ILI project life cycle to ensure first-time run success.

Although the process is simple in nature: preparing for the inspection, running the tool, verifying indications and validating the ILI results, each step poses challenges and should be carefully considered. We will focus on the first step of the process.

Preparing for Inspection

The NPRM expands assessments to moderate-consequence areas (MCAs) that can accommodate ILI tools. In addition, the NPRM requires ILI tools that can evaluate an expanded list of threats, including corrosion, hard spots, deformation and mechanical damage, material cracking and crack-like defects, to which the segment is susceptible.

These regulatory changes will drive a significant increase in pipeline mileage assessed and the types of tools used. Thus, further emphasis will be required on the upfront planning, and the following should be taken into consideration to ensure a successful ILI assessment:

  1. Are all applicable threats to a particular pipeline segment properly identified? What are the applicable tools for detecting and what are the characteristics of these threats?

Select the appropriate tools to maximize the data collection process for the line segment. ASME B31.8S defines 21 known threats to pipeline integrity that should be managed.

ILI has proved to be a useful tool in identifying threats associated with anomalies in the form of mechanical damage/deformation, metal loss and crack-like indications.

Table 1: Tool Selection Purpose

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  1. Are line modifications required?

A thorough review of all available data sources is essential to understanding the pipeline system and ensuring all its components prohibitive to ILI are addressed. Interview operation technicians familiar with the line segment and review historical operating records to determine if historical issues will influence the ILI. These will include leak history, flow upsets and contract price (CP) data.

If no launchers or receivers are present, plans can be made for installation in accordance with applicable codes. If an existing launcher and receiver are intended for use, confirm it can accommodate the tool selected and will cover the segment of interest. An initial assessment of the type of tool provides an idea of the proper size of launcher and receiver required to facilitate the ILI tool required. Determine if there are any data deficiencies and prepare contingency plan to address.

Run a low-density poly-pig from launcher to receiver to validate line passage. Ultimately, a gauge plate will be required to validate to the ILI vendor that the pipeline is passable.

  1. Are flow conditions conducive to ILI?

Speeds may vary depending on pipeline, product type, and ILI tool being used. Typical speeds vary (2-8 mph), and the segment should be analyzed to ensure speeds are within specified tolerances of the ILI tool selected. Flow conditions may not be enough to call a line segment unpiggable. Vendors continue to develop tool solutions to lower the low-flow, low-pressure threshold.

Depending on the type of line modifications required, this process could take up to two years for planning, budgeting, engineering, contracts and installation. Once the line is confirmed as suitable for ILI or the necessary modifications have been implemented, tool and vendor selection may begin.

As part of the ILI-tendering process, a well-prepared statement of work (SOW) can help. Typically included in the SOW are inspection objectives, project location, line segmentation, expected operating conditions, line configuration and alignment sheets.

Once tenders are received from the designated ILI service providers, the contractual terms and performance specifications are then evaluated. From a technical performance perspective, the following should be considered:

  • Types of features to be detected
  • Wall thickness limitations
  • Detection thresholds and probabilities of detection (POD) for each anomaly
  • Probabilities of identification (POI)
  • Sizing capabilities
  • Limitations on the above due to anomaly shape and orientation, and wall thickness.
  • Location accuracy
  • Limitations related to tool speed
  • Inspection tool length and weight
  • Battery life and data storage limitiations
  • Geometric passage limitations for straight pipe, bends and fittings
  • Aboveground marker (AGM) placement specifications
  • Office locations where data analysis will be performed and a schedule of commitments for preliminary and final report delivery.

Once the tendering process is completed and the ILI service provider is under contract, a detailed planning process ensues. After confirming the line modifications are finished, scheduling the tool run can proceed. Careful thought should be given to when operations are conducive for running the tool, and when results that may require immediate follow up, such as a potential pressure reduction, can be received.

From an operations’ perspective, planning of product delivery volumes and pipeline availability needs to be taken into account and a management plan developed. To this end, coordination with the control room needs to be established. A tracking plan along with equipment setup and ILI run plan including safety considerations should be developed.

As part of the tracking, an ILI run should develop a plan for positioning aboveground AGMs. The plan should identify a maximum distance between locations for the AGM (preferably an optimal distance can be included). The spacing between AGM’s should not be greater than one mile, and additional AGMs may be spaced at closer intervals, if conditions such as multiple bends, road crossings and key locations warrant. The closer AGMs are spaced, the better the project quality control on data gathering will be.

To ensure efficient tracking, when establishing AGM locations, consider travel time, ingress/egress, local noise and other factors that could make it difficult to identify tool passage. Preparing a field “war map” for the pigging teams provides routes, directions, and AGM locations all identified by GPS points.

GPS access points on the pipeline, along with GPS points for each AGM, can greatly assist in the post-run analysis. In addition, establishing a communication plan with the tracking team and dispatch or gas control is necessary in conveying the precise tool location throughout the run.

Another key step in the planning process is defining the cleaning requirements which are a critical process needed prior to the ILI operation. Debris reduces the effectiveness of the operation and causes heavy wear to tool components.

On first-time line inspections, the cleaning tool sequence should include multiple pig runs beginning with a low-density poly-pig and working toward a steel body disk with brushes. A temporary separator/slug catcher should be considered so not to push any debris into the downstream segment. This will ensure downstream measurement components are not affected by line debris that can reduce data quality results.

If you don’t properly clean your line prior to inspection, the ILI tool will collect all line debris and limit chances for a successful run. The type of product affects the cleanliness of the pipeline.

There are various cleaning tools that remove excess debris from ILI tools. Running a gauging tool is also a standard procedure during cleaning to discover any restrictions. Historical data of deposits should be evaluated prior to inspection.

As evident from the steps identified here, ILI is an involved process that requires detailed planning for successful execution. SI and MESA have worked together to develop the supporting procedures and process, and have assisted a number of clients to ensure successful ILI assessments.


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