Non-Contact Method For The Inspection Of Underground Pipelines

Summary
The Non Contact Magnetic Tomography pipeline survey technology enables the survey of pipelines of all configurations, underground and submerged, while they remain working at normal operating pressures and without the preparation procedures needed by in line intelligent pig techniques. The main features are summarised below:

Main features

Assessment of defects is based not on geometry but of the level of stress caused by them
Data is collected by a non-contact scanning magnetometer and is subsequently analysed by a patented software algorithm.
The pipeline remains in service throughout the survey thus eliminating cleaning, purging and downtime costs.
The survey report defines the location and extent of geometric and corrosion defects such as:


ß Dents, corrugations, scores, out of roundness and differences in wall
thickness
ß Loss of metal – including internal and external corrosion defects of
any nature
ß Delamination
ß Defects within welded joints eg cracks, pores, lack of weld penetration, displacement of edges and metal flakes
ß Crack-like defects in any orientation
ß Sections with deviations of a level of stress deformed conditions caused by, for example, sagging, landslips, washouts or transitions under roads.
ß Local corrosion under scaled insulating coating

The location of defects are defined within an accuracy of +/- 1.5m thus facilitating further investigation or repair
The final report defines the degree of danger of defects and recommends maximum safe working pressures and also the length of time it is safe to operate defective sections of pipe at those pressures.
The system can be used to survey trunk pipelines (across any terrain including water) and service pipelines within cities. Accuracy is not affected by either the close proximity of other pipelines or city traffic.

Data Collection Analysis

Fluctuations in magnetic field strength are used to automatically display, register and record in memory defects in the metal as the magnetometer is carried along the longitudinal axis of the pipeline by an operator. All data is then subsequently analysed to produce an integrated indicator of the hazard level of the defects detected. This is presented in chart form and references an identification of each defect and its location (obtained using GPS).

Flaws in the metal are located by relating the magnetic permeability of the pipeline to stress raisers and are defined by analysing the interconnection of stress concentration with a change in the polarity of the components of the earth’s magnetic field.

The effect of interfering fields is minimised by equipping the magnetometer with high sensitivity converters and dedicated software with filtration algorithms.

Identifiable Defects

The following internal and external defects, their parameters and their location can be accurately defined:

∑ Crack-like defects in any orientation (laps, scabs, scratches, stress corrosion, cracking and exfoliation)
∑ Weld defects (laps, pores, cracks, lack of fusion, lack of penetration, displacement, metal flakes, residual thermal stress within the heat affected zone)
∑ Compression marks, corrugations, scores, out of roundness and changes in wall thickness caused by corrosion pits and filiform corrosion
∑ Loss of metal – including internal and external corrosion defects of any nature
∑ Delamination
∑ Sections with deviations of a level of stress deformed conditions caused by, for example, sagging, landslips, washouts or transitions under roads.
∑ Local corrosion under scaled insulating coating
∑ Indents
∑ Buckles
∑ Deviation from the specified laying axis

Tolerance & Accuracy

Minimum length of detectable defects: >10mm
Opening of detectable defects: >300 microns
Depth of detectable defects: >5% of the pipe wall thickness
Measurement tolerance:
Crack length: +/-20%
Crack depth: +/- 30%
Wall thickness loss: <25%
Detection rate: 2m/sec max
Location and orientation of defects: No restriction

Process Limitations

Operating temperature: None defined. Has been used at -50 to + 63 deg C
Pipeline diameter: Min 56mm
Max 1420mm
(based on actual survey experience to date. Extensions to either stated limit may be possible)
Pipe wall thickness: Min 2.8mm
Max 22mm
(based on actual survey experience to date. Extensions to either stated limit may be possible)
Detection rate: 2m/sec max
Distance between magnetometer and pipeline: 15 x pipe dia max (refers only to measuring pipeline depth and axis deviation)
Cannot guarantee the detection of those defects which do not cause a change in the level of stress deformed condition – ie blow holes, pitting

Summary Procedure

1. Analysis of pipeline design, executive and operational documentation
2. Visual inspection of the pipeline route
3. Preparatory works
4. Pipeline inspection
5. Inspection data processing
6. Assess technical condition of pipeline section
7. (Mark out test pits if required)
8. (Additional NDT on exposed pipe if required)
9. Finalise results, conclusions and present report

Experience

Launched commercially in 2002 the technology has to date been used to successfully survey more than 20,000km of subterranean and submerged pipelines in the Russian Federation, Uzbekistan, Ukraine, Syria, Argentina, Brazil, Colombia, Mexico, Croatia, Saudi Arabia, Malaysia, Indonesia, China, UK and the USA. Monitoring throughout this period has demonstrated an efficiency rate and reliability level of not less than 87% .