Louisiana Administrative Code › Title 43 - NATURAL RESOURCES › Part XIII - Office of Conservation-Pipeline Safety › Subpart 3 - Transportation of Natural Gas or Other Gas by Pipeline: Minimum Safety Standards [49 CFR Part 192] › Chapter 51 - Appendices › Section XIII-5111 - Appendix F-Criteria for Conducting Integrity Assessments Using Guided Wave Ultrasonic Testin g (GWUT)

Current through Register Vol. 50, No. 6, June 20, 2024
This appendix defines criteria which must be properly
					 implemented for use of guided wave ultrasonic testing (GWUT) as an integrity
					 assessment method. Any application of GWUT that does not conform to these
					 criteria is considered "other technology" as described by §2910 .C.7 7,
					 and 3337.C.7, for which OPS must be notified 90 days prior to use in accordance
					 with §3321.A.7 GWUT in the
					 "Go-No Go" mode means that all indications (wall loss anomalies) above the
					 testing threshold (a maximum of 5% of cross sectional area (CSA) sensitivity)
					 be directly examined, in-line tool inspected, pressure tested, or replaced
					 prior to completing the integrity assessment on the carrier pipe.
I. Equipment and Software: Generation. The
				  equipment and the computer software used are critical to the success of the
				  inspection. Computer software for the inspection equipment must be reviewed and
				  updated, as required, on an annual basis, with intervals not to exceed 15
				  months, to support sensors, enhance functionality, and resolve any technical or
				  operational issues identified.
II.
				  Inspection Range. The inspection range and sensitivity are set by the signal to
				  noise (S/N) ratio but must still keep the maximum threshold sensitivity at 5%
				  cross sectional area (CSA). A signal that has an amplitude that is at least
				  twice the noise level can be reliably interpreted. The greater the S/ N ratio
				  the easier it is to identify and interpret signals from small changes. The
				  signal to noise ratio is dependent on several variables such as surface
				  roughness, coating, coating condition, associated pipe fittings (Ts, elbows,
				  flanges), soil compaction, and environment. Each of these affects the
				  propagation of sound waves and influences the range of the test. It may be
				  necessary to inspect from both ends of the pipeline segment to achieve a full
				  inspection. In general, the inspection range can approach 60 to 100 feet for a
				  5% CSA, depending on field conditions.
III. Complete Pipe Inspection. To ensure that
				  the entire pipeline segment is assessed there should be at least a 2 to 1
				  signal to noise ratio across the entire pipeline segment that is inspected.
				  This may require multiple GWUT shots. Double-ended inspections are expected.
				  These two inspections are to be overlaid to show the minimum 2 to 1 S/N ratio
				  is met in the middle. If possible, show the same near or midpoint feature from
				  both sides and show an approximate 5% distance overlap.
IV. Sensitivity. The detection sensitivity
				  threshold determines the ability to identify a cross sectional change. The
				  maximum threshold sensitivity cannot be greater than 5% of the cross sectional
				  area (CSA).
The locations and estimated CSA of all metal loss features
					 in excess of the detection threshold must be determined and documented.
All defect indications in the "Go-No Go" mode above the 5%
					 testing threshold must be directly examined, in-line inspected, pressure
					 tested, or replaced prior to completing the integrity assessment.
V. Wave Frequency. Because a
				  single wave frequency may not detect certain defects, a minimum of three
				  frequencies must be run for each inspection to determine the best frequency for
				  characterizing indications. The frequencies used for the inspections must be
				  documented and must be in the range specified by the manufacturer of the
				  equipment.
VI. Signal or Wave Type:
				  Torsional and Longitudinal. Both torsional and longitudinal waves must be used
				  and use must be documented.
VII.
				  Distance Amplitude Correction (DAC) Curve and Weld Calibration. The distance
				  amplitude correction curve accounts for coating, pipe diameter, pipe wall and
				  environmental conditions at the assessment location. The DAC curve must be set
				  for each inspection as part of establishing the effective range of a GWUT
				  inspection. DAC curves provide a means for evaluating the cross-sectional area
				  change of reflections at various distances in the test range by assessing
				  signal to noise ratio. A DAC curve is a means of taking apparent attenuation
				  into account along the time base of a test signal. It is a line of equal
				  sensitivity along the trace which allows the amplitudes of signals at different
				  axial distances from the collar to be compared.
VIII. Dead Zone. The dead zone is the area
				  adjacent to the collar in which the transmitted signal blinds the received
				  signal, making it impossible to obtain reliable results. Because the entire
				  line must be inspected, inspection procedures must account for the dead zone by
				  requiring the movement of the collar for additional inspections. An alternate
				  method of obtaining valid readings in the dead zone is to use B- scan
				  ultrasonic equipment and visual examination of the external surface. The length
				  of the dead zone and the near field for each inspection must be
				  documented.
IX. Near Field Effects.
				  The near field is the region beyond the dead zone where the receiving
				  amplifiers are increasing in power, before the wave is properly established.
				  Because the entire line must be inspected, inspection procedures must account
				  for the near field by requiring the movement of the collar for additional
				  inspections. An alternate method of obtaining valid readings in the near field
				  is to use B- scan ultrasonic equipment and visual examination of the external
				  surface. The length of the dead zone and the near field for each inspection
				  must be documented.
X. Coating
				  Type. Coatings can have the effect of attenuating the signal. Their thickness
				  and condition are the primary factors that affect the rate of signal
				  attenuation. Due to their variability, coatings make it difficult to predict
				  the effective inspection distance. Several coating types may affect the GWUT
				  results to the point that they may reduce the expected inspection distance. For
				  example, concrete coated pipe may be problematic when well bonded due to the
				  attenuation effects. If an inspection is done and the required sensitivity is
				  not achieved for the entire length of the pipe, then another type of assessment
				  method must be utilized.
XI. End
				  Seal. When assessing cased carrier pipe with GWUT, operators must remove the
				  end seal from the casing at each GWUT test location to facilitate visual
				  inspection. Operators must remove debris and water from the casing at the end
				  seals. Any corrosion material observed must be removed, collected and reviewed
				  by the operators corrosion technician. The end seal does not interfere with the
				  accuracy of the GWUT inspection but may have a dampening effect on the
				  range.
XII. Weld Calibration to set
				  DAC Curve. Accessible welds, along or outside the pipeline segment to be
				  inspected, must be used to set the DAC curve. A weld or welds in the access
				  hole (secondary area) may be used if welds along the pipeline segment are not
				  accessible. In order to use these welds in the secondary area, sufficient
				  distance must be allowed to account for the dead zone and near field. There
				  must not be a weld between the transducer collar and the calibration weld. A
				  conservative estimate of the predicted amplitude for the weld is 25% CSA (cross
				  sectional area) and can be used if welds are not accessible.
Calibrations (setting of the DAC curve) should be on pipe
					 with similar properties such as wall thickness and coating. If the actual weld
					 cap height is different from the assumed weld cap height, the estimated CSA may
					 be inaccurate and adjustments to the DAC curve may be required. Alternative
					 means of calibration can be used if justified by a documented engineering
					 analysis and evaluation.
XIII. Validation of Operator Training.
				  Pipeline operators must require all guided wave service providers to have
				  equipment-specific training and experience for all GWUT Equipment Operators
				  which includes training for:
A. Equipment
				  operation,
B. field data
				  collection, and
C. data
				  interpretation on cased and buried pipe.
Only individuals who have been qualified by the
					 manufacturer or an independently assessed evaluation procedure similar to ISO
					 9712 (Sections: 5 Responsibilities; 6 Levels of Qualification; 7 Eligibility;
					 and 10 Certification), as specified above, may operate the equipment. A
					 senior-level GWUT equipment operator with pipeline specific experience must
					 provide onsite oversight of the inspection and approve the final reports. A
					 senior-level GWUT equipment operator must have additional training and
					 experience, including training specific to cased and buried pipe, with a
					 quality control program which that conforms to Section 12 of ASME B31.8S (for
					 availability, see § 507).