April 2017, Vol. 244, No. 4


Reducing Deepwater Pipeline Inspection Costs

By Andreas Haindl, Team Leader Account Management, and Herbert Willems, Global ILI Technology Support, NDT Global

Inspecting a pipeline is a complex operation. It is often fraught with complications due to the varying dimensions that the pipeline exhibits in order to operate in a deepwater environment. Designing the line with future inspections in mind is the exception, not the rule.

As a result, a deepwater line usually features at least one of the following characteristics that complicate inspection: thick pipe wall, internal corrosion-resistant alloy (CRA) cladding, high-pressure and temperature, non-constant internal diameter, small internal diameter, along with challenging launching and receiving conditions, such as short traps, subsea launching, restricted work space on deck and flexible pipe.

Each of these characteristics makes inspection difficult in different ways. Because each must be addressed individually, the process of inspection is often long and arduous. As pipeline maintenance managers come under increasing pressure to cut costs and speed up maintenance and repair programs, they struggle with these obstacles.

Apart from inline inspection (ILI), traditional methods of assessing the condition of a deepwater pipeline are limited and costly. Typically, ROV and support vessels are required to verify by external measurement. Despite the high cost of such operations, the quality of information gathered from scanning pipe surfaces is extremely limited. This is frustrating especially as the need to identify even the smallest anomalies in the pipe wall has increased in an effort to control corrosion, schedule inspection intervals and minimize risk.

Against this backdrop, pipeline maintenance managers want to execute inspections at a lower cost without compromising safety or incurring extended downtime. They are keen to embrace a field-proven, economical inspection solution that provides high-resolution inspection data.

NDT Global test yard.


In 2006, NDT Global produced its first high-pressure tool for small-diameter deepwater pipelines. Since then, it has extended its deepwater inspection options to include a line of ultrasonic technology (UT) inspection tools that have been used to inspect many deepwater pipelines worldwide.

These crack and metal loss UT tools provide extremely high-measurement resolution data. They detect flaws as small as 5-mm (0.2-inch) diameter and 0.8-mm (0.03-inch) depth, so that even the smallest anomaly, such as pinhole corrosion, is accurately identified.

With regard to the problem of thick pipe walls, when inspecting a line with a wall thickness of up to 50-mm (1.96-inch), magnetic flux leakage (MFL) tools are unsuitable because the magnets they employ are not strong enough to fully magnetize the pipe wall. UT provides quantitative, not qualitative – hence absolute – measurements and requires no calibration. It is versatile, which means that it is suitable not only for internally clad pipe, but also for flexible pipe. UT tools deliver accurate results that provide operators with a high level of certainty with regard to probability of detection (POD).


ndt 1
NDT Global inspection team is shown checking ILI tool.


UT technology is also useful for inspecting pipe that features internal CRA cladding which can pose inspection problems for other ILI methods. With CRA-cladded pipe made of metallurgical-bonded plates with a seam weld, the internal surface is typically quite smooth, so that it poses no limitations with regard to UT measurements. In addition, pipe constructed with an internal CRA surface produced by orbital or longitudinal welding can be inspected by UT tools with minimal impact on measurement accuracy.

As pipelines are built in ever deeper water, pressure increases. In many cases, temperatures also rise. Consequently, deepwater pipelines have special pressure requirements that must be kept in mind during inspections. Due to water depth and operating conditions, a deepwater pipeline must be able to withstand static pressure and pump pressure of up to 500 bar (7,250 psi). This means that inspection tools must be designed and rated accordingly to operate in this environment, for example, by using high-strength materials.

When designing ILI tools, non-constant internal pipe diameter is often the greatest challenge. There are several reasons for this lack of constancy. There might be different wall thicknesses for risers, flow lines, topsides piping and subsea structures. Or, manufacturing tolerances on seamless pipe can cause variations in thickness, as can dual-diameter design – for example, 6-inch risers and 8-inch flow lines. Tackling these problems posed by non-constant internal pipe diameter, operators employ multi-diameter inspection tools to navigate through these unpredictable environments to provide critical inspection data.

Experienced Team

Field-proven technology isn’t all that’s required to collect high-quality inspection data from a deepwater pipeline. It’s critical the inspection is planned and executed by experience gleaned from many such inspections.

The root cause of many deepwater inspection difficulties lies in the design of the pipeline itself. Involving ILI experts in the initial stages of designing the pipeline simplifies future inspections, delivering time and cost savings throughout its lifetime.

By collaborating with ILI experts in the pre-FEED phase of pipeline design or early stages of developing an asset, it is possible to change the design of the pipeline and subsea or topsides structures to reduce pigging-related risks, thereby avoiding associated complications and costs.

Case in Point

To illustrate, in the Gulf of Mexico, NDT Global is adapting a UT tool to requirements specific to a pipeline that is part of a project to extend an existing 12-inch deepwater oil production pipeline with a new 10-inch line to tie back a new field to the host platform. The maximum water depth is 6,000 feet. Previously, the company supplied a customized high-pressure metal loss UT tool for the 12-inch pipeline. The changes to the pipeline required that the design of the ILI tool be reviewed.

During the design phase of the pipeline extension, the operator sought advice on specific options, and information on how these would affect pigging and inspection of the new system. Following completion of the design work, a modification kit for the existing 12-inch UT tool was created. The new metal loss UT tool is now capable of measuring the entire 10-12-inch diameter range with the same accuracy as the previous 12-inch tool, making it possible to determine corrosion growth by comparing data from current inspection runs with previous ones.


Inspecting deepwater pipelines is complicated. They are thousands of feet below the surface and the nature of the deep sea environment means they are designed with certain characteristics that make inspection difficult. As most deepwater pipelines are not designed with ILI experts involved early in the design process, they are frequently not conducive to easy inspection.

As a result, inspections can be lengthy and costly. When investigating potential defects, pipeline maintenance managers struggle to collect the high-quality inspection data required to make accurate assessments. The common methods of inspection, which can be costly and time-consuming, often fail to generate the high-resolution data necessary for proper assessment of the pipeline.

When inspection experts are involved in the initial phases of the pipeline design process, their voices help ensure that the pipeline will be much easier to inspect in future. The time and money required to inspect and maintain the pipeline throughout its lifetime will be significantly reduced.

 Authors: Andreas Haindl is team leader of European Account Management at NDT Global. He attended the Karlsruhe University, Karlsruhe, Germany, where he received a master’s degree in engineering and economics.

Herbert Willems works in ILI technology support for NDT Global and was previously employed by Fraunhofer Institute for Non-Destructive Testing (IZfP) in the field of ultrasonic materials characterization. He holds a master’s degree in physics from the University of Saarbrücken, Germany.

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