FAQs

Advice – As per most of the International Standards and Codes, Ultrasonic testing shall be performed on a ground bare metal surface for effective transmission of ultrasound in to the material under the test and to obtain accurate repeatable test results. For a general purpose, Ultrasonic testing may be possible if the coating completely adheres to the metal surface.
If lead paint is a concern, then alternative thickness measurement such as Pulsed Eddy Current testing (PEC) can be performed without removing lead paint or any other coating. PEC does not require any surface preparation or coating removal.

Advice – This is not 100% true. PECT cannot detect an isolated pit. But it can detect cluster of pitting. In UT, asset owners nominate to perform random or 100mm grid spacing UTT. Most of the time the probe is twin crystal, 10/2 diameter probe. Hence in a 100x100mm grid, ONLY 0.78% of the surface area is tested. (79mm2 out of 10,000mm2). This means there is 99.2% probability that UTT will not detect an isolated pit or even cluster of pitting in a 100mm grid pattern. Also, UTT depends on the flatness of the back wall. Several published papers indicate that on most occasions, UTT measures incorrect corroded minimum remaining wall thickness because the reflecting surface is either not perpendicular to the compression waves or the sound simply dissipates due to rough surface.
Whereas in PEC, the smallest footprint is 35mm diameter, and because of its speed, 100% of the surface area is scanned without coating removal. Hence, if there is a considerable loss of wall as a result of an isolated pit or a cluster of pits which can affect the fitness for purpose pressure vessel calculations then PEC will 100% indicate volumetric thinning.

Advice – PEC can measure wall thickness of ferrous steel having surface temperature up to maximum 5500C and adequately insulated so that the surface temperature on the cladding surface is limited to 700C maximum. It should be noted that alternative test method such as conventional ultrasonic testing cannot be performed at such a high temperature.
If the cladding (weather jacket) surface temperature is exceeding 700C then a ceramic shoe can be added at the bottom of the probe and perform PEC. It should be noted that it is not a safer practice to work at such a high temperature.

Advice – UTT & RT are too much operator dependent and hence the probability of the traceability of results is uncertain. Whereas in PEC, operator’s involvement is only to place a probe on the cladding after the Level 3 has entered all essential parameters. The instrument provides assessment results storing of results, reporting of data, colour pelleting, etc.

Advice –PEC is an average wall loss measuring technique and is ideal for screening and measuring general corrosion through insulation, cladding or other non-conductive coverings. For detection of localised damage such as pitting or cracking, DANHOLSEN’ NDT experts and inspectors can advise on the most appropriate techniques, which may include eddy current array (ECA) testing for detection of linear discontinuities, phased array ultrasonic testing (PAUT) for the detection of small pits and wall thickness, or one of the many other available NDT methods

Advice –Ultrasonic requires sufficient ground flat surface for the transducer coupling for sound transmission. PEC works on Electromagnetic principle which does not require direct contact. Hence PEC can measure wall thickness on a live pipeline without the need of surface grinding and without the need of coating removal.

Advice –DANHOLSEN can find weld location on your insulated pipe or vessel using PEC - Pulsed Eddy Current test method. As compared to Radiography, exclusion zone required and multiple exposures required, PEC is a single person operation and it can be completed within few minutes on site.
Expertise:
Compared to conventional ultrasonic testing, Pulsed Eddy Current testing (PECT) instrument and sensors are complex and expensive. This test method requires highly trained, skilled and experienced technicians. DANHOLSEN engages certified and experienced engineers to provide Pulsed Eddy Current - PEC testing.

Advice – If the coating system is of good quality and adequately adhered to the pipe surface then no additional need for surface preparation. But in most cases, the coating condition is of unacceptable quality or coating flaking off. Hence it is recommended to sand blast or remove surface coating of 500mm width around the pipe circumference. This location should be preferentially chosen away from a butt weld or a flange end.

Advice – Yes, DANHOLSEN can perform LRUT on your cast iron pipeline, conditional to that the pipes are metallurgically bonded (e.g welded) and not joined by flanges or screw joints. If later is the case, then each pipe will need to be scanned individually using LRUT single point of contact system.
Graphitization is the common mode of corrosion in cast iron pipes. LRUT should be able to detect considerable graphitization (non-conductive layer) when the sound conductive loss of cross section has occurred. The sensitivity may not be as effective as it will be on carbon steel pipes.
Note – Most of the cast iron pipes are either bell type joint (with rubber inserts) making them conductivity wise non-continuous pipeline. Hence each of the pipes will require LRUT assessment. LRUT has a near zone effect of 1m. This means a typical 2.4m pipe will need scanning from both ends of the pipe.
Alternative for this is to use Magnetostrictive collars which produces slightly higher frequencies and has shorter near filed zone. This test method is like Short range guided wave ultrasonic. If LRUT or SRUT is not a possibility for your pipe then MFL is recommended.
LRUT does not require couplant as is the case in conventional ultrasonic. But in-service cast iron pipe may have textured surface which may not permit LRUT dry coupling.

Advice – Carbon steel, alloy steel, stainless steel, Cast iron, etc

Advice – Although, LRUT cannot assess 100% of the weld quality, the test system can detect lack of penetration, excessive penetration, weld root erosion or severe corrosion in the HAZ.

Advice – Yes, DANHOLSEN can perform assessment near a fillet weld using a LRUT by placing the transducer assembly away from the fillet weld. DANHOLSEN will need to evaluate the other side of the fillet weld (or Tee branch) by placing the LRUT collar again on the other side of the fillet on the pipeline.
Similarly, the first or second bend can be examined from one side of the pipeline and then assessing from the other side of the bend.

Advice – DANHOLSEN experienced engineers will be able to interpret data for up to 2 bends or 2 branches, depending on the attenuation of ultrasound due to your pipeline condition and signal to noise ratio. It may be required to collect data at additional locations to cover 100% of the bend zone.

Advice – DANHOLSEN LRUT collar is only 30mm thick. If temporary space can be created between pipes at the collar mounting location (for the period of maximum 30 minutes), then DANHOLSEN experienced engineers will be able to attach transducers collar and perform testing for tens of meters of pipe length.

Advice – When the LRUT collar is placed near the flange end, a lot of energy is reflected towards the transducers, making it difficult for the trained personnel to differentiate signals. The flange end of the pipe can be examined by attaching the transducer assembly further away from the flange end and transmit ultrasound towards the flange end. There is no need to place the LRUT collar at the flange end to assess this area. In unavoidable circumstances, wherein there is very limited access, and for the best signal quality, DANHOLSEN experienced engineers will position the collar in such a manner that the first ring of transducers is approximately 60mm from the start of the flange.

Advice – LRUT is a test method to find abnormality (discontinuities) in a deemed to be normal pipeline. If the pipeline is already severely corroded then LRUT is not a suitable solution. But if the asset owner assumes that the pipeline under test is normal then LRUT can diagnose that the pipeline is severely corroded by interpreting the LRUT signals