Electric resistance welding (ERW) is a process for creating spot or seam welds by using the electrical resistance of a material, combined with time and the force used to hold the materials together during welding. While ERW is a beneficial method for producing forged welds, the process is not perfect. Typical defects that can develop in the ERW process are:
* Entrapments (black penetrators)
* Pre-arcs (white penetrators)
* Lack of fusion (LOF)
* LOF at edges (puckers) or mid-wall
* Cast weld
* Porosity
* Stitching
* Hook cracks
* Paste welds (cold welds)
After welding, ID and OD trim (under or overcut) can result in downgraded or scrapped product. Before welding, skelp entering the line can contain surface or internal defects, or can be out of specification for thickness. For these reasons it is necessary to have the best ERW inspection system in place.
Traditional techniques for ERW inspection use piezoelectric transducers. While highly efficient, piezoelectric transducers need to be coupled to the part under inspection with high pressure or a liquid medium which can limit scanning ability or produce interference. Below are the top three advantages to using EMAT over traditional techniques for inspection of ERW welds.
EMAT does not require any type of couplant allowing the system to perform inspections on higher temperatures parts (200°C) while running at full production speeds. This advantage also makes it easier to integrate into automated production lines.
EMAT coils generate a wide vertical beam that fills up the volume of the material. Whereas some NDT processes need several sensors or a phased array, a single EMAT sensor allows detection of ID, OD, and mid-wall defects.
Welds can be inspected with EMAT immediately after the welding process, which minimizes waste by catching all weld discontinuities, API standard defects, and trimming defects. Trimming problems alone account for the majority of scrapped pipe because they are detected long after the problem develops.
These 3 advantages provide a superior return on investment (ROI) while still meeting all API standards and the most stringent oil company requirements.
To find out more about ERW inspection using EMAT, visit our In-Line ERW Tube Inspection webpage, watch our In-Line ERW video below or contact one of our integrated systems specialists.
