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Cart GUL Screening is normally used to rapidly and cost effectively locate and classify areas of damage on a pipeline. Since waves are sent along the pipe from the sensor location, 100 percent coverage (even of inaccessible areas) can be obtained.
Originally designed for detection of corrosion under insulation (CUI), the application of GUL Screening has expanded into many other areas. It is also widely used to inspect for corrosion at pipe supports, at air/soil interfaces, in buried sections, on overhead lines, and many more.
Please see the Screening Overview page or Screening Case Studies page for more information.
Wavemaker® is the product name of the guided wave system that GUL Screening utilises
The system comprises of 3 primary components: a sensor (the transducer ring), a Wavemaker® instrument, and a computer running the analysis and reporting software. Details of these can be found on the Wavemaker System page.
All three names refer to the same general inspection concept. However, we feel that GWT and GUL Screening most accurately describe the method and system being used. More information is available on the Terminology page.
GUL Screening has solutions for pipes with diameters from 0.75 inch (19.05 mm) and above. The applicable pipe wall thicknesses range from 3 mm to 40 mm (1/8 to 1.57 inch). We have a range of transducer ring types and sizes to meet your inspection requirements. Please see our PDF Product Catalog for standard products or contact us separately for custom sizes.
GUL Screening can be used on almost all metal pipes. However, it currently cannot be used on plastic pipes.
See the Applicable Materials page for more information.
Guided waves are those waves whose propagating characteristics are greatly influenced by the geometry of the structure in which they exist and not just the mechanical properties of the material. Since the structure ‘guides’ the waves, the waves are very sensitive to any change in the geometry of the structure (for example a loss of section caused by corrosion). Therefore, even at low frequencies, very small changes cause reflections that can be detected and analyzed. This allows for 100 percent coverage even far from the sensor. More in-depth information can be found on the What are guided waves? page.
GUL screening uses the T(0,1) torsional mode instead of the alternatives for several reasons including:
More detailed information is available on the Why Torsional page.
The torsional T(0,1) guided wave is generated within the pipe, via a ring of transducers. The guided wave will travel away in both direction from transducer ring at a speed of approximately 3,250 m/s (10,662 ft/s). The waves will be reflected from both pipe features (e.g. welds, supports, flanges) and defects (e.g. corrosion, erosion, mechanical damage), causing the signal to travel back towards the transducer ring. GUL Screening works by collecting and analysing the properties of these reflected waves (e.g. time of arrival, torsional and flexural contents).
The A-scan is a plot that shows the reflected guided wave signals against the pipe axial distance. The black and red signals are the torsional and flexural components of the reflected signal. The x-axis represents the relative distance of the signal from the transducer location. In other words x = 0 m is the transducer ring location and the positive and negative distances represents the forward and backwards direction from the transducer ring.
The DAC curves provide a quantitative link (or calibration curve) between the signal amplitude and cross-sectional area change (CSC) within the pipe. so that we can ultimately quantify the extent of the damages in terms of pipe CSC. An accurate DAC curve is required to call the severity of defects in pipes
The figure above shows an A-scan with the Weld and Call DACs labelled. In most inspections, the Weld DAC is established by using either weld size parameters or via the Absolute Calibration method. This results in a calibrated Call DAC, which can be used to estimate defect severity and determine end of inspection test range.
The Call DAC is the threshold level that is used to determine the defect severity if found. Typically, it is set between 1% and 6% CSC according to the sensitivity requirement of the inspection.
Absolute Calibration is GUL’s patented method of calibrating the DAC curves. Put simply, this method uses reverberation signals from pipe features, such as welds or flanges, to rapidly and accurately calibrate the DAC curves.
What is Unrolled Pipe Display in GUL Screening?
The Unrolled Pipe Display is a colour plot that shows the guided wave reflection amplitude as a function of axial distance and circumferential position. This plot is generated by using a proprietary algorithm that enables total focusing of the guided wave signals at all locations (within the valid inspection range), analogous to Total Focusing Method in phased array UT.
Using post processing to produce the unrolled display avoids the need to collect additional data making the inspection faster.
Identifying and eliminating pipe features is typically performed before an inspector sets out to detect defects in GUL Screening. This can be done by visual inspection on site, referring to engineering drawings and studying and characterising the reflection signal; e.g. weld signals are easily distinguishable by their high torsional component and uniform amplitude around the cross-section.
The Level 1 and 2 GUL Training (GULT) courses are designed to equip inspectors with the skills and knowledge to confidently and competently perform this task.
In general, the reliable detection sensitivity is 5% cross-sectional area change (CSC). Smaller defects, as small as 1% CSC, can be detected but is subject to the signal-to-noise ratio (SNR) level of the test. Essentially, the SNR level of the data determines the detection sensitivity.
The SNR level is mainly affected by the existing condition of the pipe. For example, a pipe in good condition will yield a higher SNR than a pipe that has severe general corrosion along its entire length.
The accuracy of defect location is ±100 mm (approx. 4 inches). By measuring the distance from the closest visible feature, defects can be located more precisely.
There are 2 types of noise considered in GUL Screening, namely coherent and incoherent noise. Coherent noise is not random and can be attributed to the pipe condition, corrosion, scales and other features that causes unwanted guided wave scattering. Incoherent noise is random (i.e. can be reduced by signal averaging) and is attributed to background and electrical noise.
After identifying a defect in the A-scan, the defects can be classified further as Minor, Intermediate and Severe. The classification is determined based on the cross-sectinonal area change (CSC), the circumferential extent of the signal and their relationships with the call DAC level.
The inspection range can either be determined by the intersection of the Call and Detection Threshold (DT) or by limited by certain pipe features such as flanges or elbows. The DT is typically defined as 6 dB above the noise level.
In ideal circumstances, the test range can be more than 200 meters (656 feet) in each direction. However, this may not always be the case as the inspection range can be limited by attenuation due to pipeline properties (coatings, surrounding environment and existing pipe metal condition) or features such as bends or flanges.
The figure below provides a guide to the typical and average inspection range for GUL Screening.
The dead zone is indicated by the green area in the A-scan. Data is not available in this area because the transducers are still transmitting the signal and not receiving any (pulse-echo configuration).
The near field zone is the gray area next to the dead zone in the A-scan. Data is available in this region, but should not be used for defect detection because the system is transitioning from a transmit to a receive mode, which affects the received amplitudes.
The size of the dead zone and near field zone are a affected by the frequency of the guided wave signal (higher frequencies = smaller zones). It can be estimated that the length of dead zone and near-field zone are 0.275 m (1 foot) and 0.9 m (3 feet) per sensor direction respectively.
GUL Screening can be used for detection of:
GUL Screening can be used to inspect:
| Pipe Feature | Can a 5% CSC defect be reliably detected on/at this feature? | Can we use data past this feature for GW inspection? | GW Inspection Comments |
|---|---|---|---|
| Girth Welds | Yes – observe for increased flexural content. | Yes | Important features for DAC calibration. |
| Spiral Welds | Yes, if welds are grounded and flush with pipe surface. | Yes | Pipe with this feature can be inspected but be wary of coherent noise level. |
| Simple Support | Yes – observe for increased flexural content. | Yes | Use unrolled pipe display to determine if reflection is at 6 o’clock. Reflection values will depend on pipe stress at the support location. |
| Drain/Vent | Yes – observe for increased flexural content. | Yes | Coherent noise caused by trailing echoes from the feature. Higher frequencies may reduce this effect. |
| Clamped Supports | Yes – for relatively loose clamps. | Yes – for relatively loose clamps. | It may be necessary to loosen clamps during GW inspection for best performance. |
| Welded Supports | Yes, if coherent noise reduced with higher inspection frequencies + good SNR. | Yes | Use higher inspection frequency to reduce coherent noise from this feature. |
| Concrete Anchor Supports | Yes | Yes | Use higher inspection frequency to reduce coherent noise from this feature. |
| Bushings | No | No | Guided waves do not propagate past this feature due to screw-type fitting. |
| Pipe Elbows | Yes | No – For short radius elbows and relatively small diameter pipes. | For short radius elbows (< 3D bends) and relatively small diameter pipes (< NPS 12), the Inspection data becomes less sensitive and reliable after the second bend weld. |
| Pipe Caps | No | No | Guided waves do not propagate past this feature due to 100% discontinuity. |
| Crosses | Depends on defect location and properties of the branch. Generally no – if same diameter. | Depends on defect location and properties of the branch. Generally no – if same diameter. | Reflection/noise would depend on ratio of opening diameters. Guided wave would typically propagate past this feature and continue inspection in the direction of the pipe where the transducer ring is attached. The branch distorts the 2nd weld, making it non-symmetric. |
| Flanges | No | No | Guided waves do not propagate past this feature due to rubber seal and 100% discontinuity. |
| Concentric Reducers | No | Yes – but not recommended. | Guided waves can propagate past this feature, but generally inspection past this should be treated with caution. Any indication should be followed up by additional guided wave test locations on the smaller diameter pipe after the reducer. |
| Nipples | No | No | Guided waves do not propagate past this feature. |
| Fitted Branch (Tee) | Depends on defect location and properties of the branch. Generally no – if same diameter. | Depends on defect location and properties of the branch. Generally no – if same diameter. | Reflection/noise would depend on ratio of opening diameters. Guided wave would typically propagate past this feature and continue inspection in the direction of the pipe where the transducer ring is attached. The branch distorts the 2nd weld, making it non-symmetric. |
| Unions | No | No | Guided waves do not propagate past this feature due to screw-type fitting. |
| Valves | No | No | Guided waves do not propagate past this feature. |
| Link Seal | Yes | Yes | Little-to-moderate reflection at the interfaces; potentially some attenuation within this feature. |
Transducer rings: From -40°C to +350°C (-40 to 662°F). The operating temperature varies across different transducer ring types.
| Transducer ring type
| Pipe operating temperature range
|
|---|---|
| Compact, EFC, HD Inflatable, HD Solid, Solid, | -40°C to +150°C |
| HT Inflatable, HT Solid, HT-HD Solid | -40°C to +350°C |
LEMO connectors: -40°C to +482°C (-67 to 662°F); according to equipment/component
LEMO cables: -40°C to 482°C (-76 to 662°F); according to equipment/compone
The GUL Screening is applicable to pipes with coatings or paint thicknesses of up to 1 mm (3/64 inch).
Yes. Please see links below:
GUL Case Studies
Using the default data collection procedures, data collection using the Wavemaker G4mini typically takes 2 minutes.
GUL Screening is currently not applicable to finned tubes or pipes due to the relatively large coherent noise generated from the reflections of the fins.
Reducers can often be inspected through as it depends on the relative size change. For example NPS14:NPS12 (DN350 to DN300) has little effect whereas NPS4:NPS2 (DN100 to DN50) would result in a much bigger signal loss.
Bends are similar – there is always some loss of signal, the tighter the bend the greater the loss. Analysis of the data allows the level of loss to be quantified so that the level of sensitivity obtained around the bend is known.
GUL Screening generates an Unrolled Pipe Display, which appears very similar to a conventional corrosion map. However, it shows cross-sectional area change (CSC) and does not directly map wall thickness. Nevertheless, it will locate areas of wall loss and we are able to estimate remaining wall for these areas.
Yes. To estimate the inspection range, we would need to know the thickness of the concrete lining and the pipe wall thickness, as well as the information on the condition of the concrete bond to the pipe, or if bonded at all.
GUL Screening is not designed for measuring stress in pipes.
GUL Screening require a specific transducer ring size for a specified nominal pipe size; a single ring size can tolerate small differences in the equipment’s intended nominal pipe diameter. For example, to inspect an NPS 8 pipe, you would need a NPS 8 Compact ring. The photo below shows a range of Compact ring with different sizes.
Two transducer rings can also be combined to form one larger ring. For example, a 30″-Compact and a 26″-Compact can be combined to inspect NPS 60 (DN 1500) pipes.
| Compact Ring Combine Size Chart | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| These combinations are not recommended. | Long arm required on at least one ring. | ||||||||||||||||||
| Ring Size | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 26 | 28 | 30 | 32 | 34 | 36 | 38 | 40 | 42 | |
| 8 | 20 | 22 | 24 | ||||||||||||||||
| 10 | 22 | 24 | 26 | 28 | |||||||||||||||
| 12 | 24 | 26 | 28 | 30 | 32 | ||||||||||||||
| 14 | 28 | 30 | 32 | 34 | 36 | ||||||||||||||
| 16 | 32 | 34 | 36 | 38 | 40 | ||||||||||||||
| 18 | 36 | 38 | 40 | 42 | 44 | ||||||||||||||
| 20 | 40 | 42 | 44 | 46 | 48 | ||||||||||||||
| 22 | 44 | 46 | 48 | 50 | 52 | ||||||||||||||
| 24 | 48 | 50 | 52 | 54 | 56 | ||||||||||||||
| 26 | 52 | 54 | 56 | 58 | 60 | ||||||||||||||
| 28 | 56 | 58 | 60 | 62 | 64 | ||||||||||||||
| 30 | 60 | 62 | 64 | 66 | 68 | ||||||||||||||
| 32 | 64 | 66 | 68 | 70 | 72 | ||||||||||||||
| 34 | 68 | 70 | 72 | 74 | 76 | ||||||||||||||
| 36 | 72 | 74 | 76 | 78 | 80 | ||||||||||||||
| 38 | 76 | 78 | 80 | 82 | 84 | ||||||||||||||
| 40 | 80 | 82 | 84 | 86 | |||||||||||||||
| 42 | 84 | 86 | 88 | ||||||||||||||||
| EFC, HT, HD Ring Combine Size Chart | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| These combinations are not recommended. | Long arm required on at least one ring. | ||||||||||||||||||
| Ring Size | 8 | 10 | 12 | 14 | 16 | 18 | 20 | 24 | 28 | 30 | 32 | 36 | 40 | 42 | |||||
| 8 | 21 | 23 | 25 | ||||||||||||||||
| 10 | 23 | 25 | 27 | 28 | |||||||||||||||
| 12 | 27 | 29 | 30 | 32 | |||||||||||||||
| 14 | 28 | 30 | 32 | 34 | 36 | ||||||||||||||
| 16 | 32 | 34 | 36 | 38 | 40 | ||||||||||||||
| 18 | 36 | 38 | 40 | 42 | |||||||||||||||
| 20 | 40 | 42 | 44 | 48 | |||||||||||||||
| 24 | 48 | 52 | 56 | 58 | |||||||||||||||
| 28 | 56 | 60 | 62 | 64 | |||||||||||||||
| 30 | 58 | 62 | 64 | 66 | 70 | ||||||||||||||
| 32 | 64 | 66 | 68 | 72 | |||||||||||||||
| 36 | 70 | 72 | 76 | 80 | 82 | ||||||||||||||
| 40 | 80 | 84 | 86 | ||||||||||||||||
| 42 | 82 | 86 | 88 | ||||||||||||||||
A long arm is an accessory for the inflatable transducer rings. It is required when combining rings to inspect larger diameter pipes in order to ensure the combined ring can successfully close and be secured on to the pipe. In some cases, the long arm can also be used to allow one ring to inspect pipe sizes slightly larger than the designed inspection size. For example, a 28″ EFC ring can be used to inspect an NPS 30 (DN 750) pipe.
For more info, you can refer to our spare parts for inflatable rings webpage.
| Transducer ring type | Radia Clearance |
|---|---|
| Compact
| 38 mm |
| Inflatable EFC, HD and HT
| 63 mm |
| Solid ring
| 76 mm |
| HT Solid, HD Solid and Claw
| 50 mm |
| Slinky
| 25 mm |
Calibration is recommended for the Wavemaker G4mini (or older generation system) and its calibration certificate is valid for 3 years. The transduction system must be shipped back to GUL annually for calibration.
Most of our equipment is supplied with a one year warranty. It is possible to purchase an extended warranty for some sorts of equipment (for example the electronics). Please note that the warranty only allows for normal wear and tear of the equipment; it does not cover misuse of the equipment such as large drops or immersion in water.
Typically, we offer cable lengths of up to 25 meters, however cable lengths can be as long as 100 meters.
In order to inspect large diameter pipes, two rings can be joined together using the 16 to 8 Channel Converter Box. However, the setup is only for testing a single pipe at a time (Connecting rings on multiple pipes at the same time is really only relevant for connecting multiple gPIMS to an autonomous data collector).
For technical enquiries, please contact us at support@guided-ultrasonics.com.
For more information, please see GUL Software Updates webpage.
The TRUNK is GUL’s cloud platform that provides data storage and analysis services for our customers.
No, remote upgrading is not possible. In order to upgrade the firmware of a G4mini Base to a Full, the equipment would need to be returned to GUL(UK).
The GUL Screening results can be exported out to a variety of formats including Microsoft Word, Excel or PDF; export into other formats can be done upon request and discussion.
For technical enquiries, please contact us at support@guided-ultrasonics.com.
Typically, a Level 2 GULT qualified and certified operator is required to perform GUL Screening; Level 1 operators can assist a Level 2 operator(s). For more information on training, please see GUL Training webpage.
Step (1) : Download the Repair Request Form.
Step (2) : Fill up the required details in the form.
Step (3) : Email it to repair@guided-ultrasonics.com.
Step (4) : A GUL member will contact you once they have received and processed your repair request form.
After investigation of the equipment, we will normally provide a quotation for the repair and ask for a PO (and in some cases payment) before proceeding with the repair. We seek to repair all items within two weeks of receiving them in our office.
However, this may be extended if we do not have all of the required parts on hand, there are a lot of items to be repaired, it is a holiday week in the UK, or there are delays in getting approval for the repair.
Yes, GUL offer consultancy services on reviewing GUL Screening data. For a price quotation, please email your enquiry to info@guided-ultrasonics.com.
For more information, please see GUL Repair and Servicing webpage.
Check out the GUL Screening webpage.
Please send us a message on our Contact Us page. We will be happy to help.
For the G4mini battery MSDS, please see Battery MSDS.
For the G4mini CE DoC, please see CE DoC.
