Blisters - Heavy plate defects

Blisters - Heavy plate defects - Rolling defects

Figure 1: Closed blister, plate thickness 30.9 mm, API 5L X70, +M.

Figure 2: Closed blister, plate thickness 30.9 mm, API 5L X70, +M

Defect name: Blisters
Record No.: 3435
Type of defect (Internal/Surface): Surface
Defect classification: Rolling defects
Steel name: Steel
Steel composition in weight %: No data.
Note: +M: Thermomechanically rolled.
Alternative terms: Closed blisters
Description: You may find an oval shape curvature on the plates surface, depending on the ratio of rolling in length and width direction of the plate. Closed blisters have not been opened during the rolling process. They occur in different sizes and they are randomly distributed on the plates surface or they occur in clusters.
Identification: Visual detection of the oval buckling on the plate surface.
Occurrence: Gas-filled cavities right beneath the slabs surface or an agglomeration of casting powder caused by the casting process. Due to the reduction in thickness during hot rolling they get near to the surface.
Possibility of mistaken identity: To be misdiagnosed with material elevations on the plates surface.
Remarks: None
Reference: Not shown in this demonstration version.