Weld Toe Grinding, Toe reconditioning method to enhance the fatigue life of weld structures.

This Video is to explain #reconditioning methods that may be used for enhancing the #fatigue life of weld structures, particularly when the applied stress is normal to the axis of the weldment. Mainly this video is all about the correction of #Weldtoes and associate factors related to #fatigué Life
Research at #TheWeldingInstitute CambridgeEngland identified an acute line of #microscopic #Slag intrusions along with the toes of the welds made by all arc processes except #GTAW
All processes however were found to create some degree of undercut at the toe notwithstanding ideal #weld #weld profiles apropos of #fatigue Life.
Microscopic intrusions at weld toe act as pre-existing #discontinuities
The practical implication is that all welds have a pre-existing discontinuity in the form of either microscopic #undercut or #slag intrusions, or both.
Normal #inspection methods cannot detect these discontinuities, which in any case are inevitable and unavoidable when using existing #welding technologies
In plain material, fatigue life is spent in #crack initiation and propagation.
In weldments, however, it is assumed that cracklike discontinuities already exist.
Therefore, the fatigue life of welds is spent solely on crack propagation along with #residual #tensile #stresses at or near the yield point, is the essential reason why #weldments can tolerate fewer cycles to fatigue #failure than a similarly loaded plain material.
So Fatigue life enhancement can be obtained by reconditioning the weld toes.
The small pre-existing discontinuities are either removed or the sharp openings dulled, rounded, or blended.
The following techniques enhance fatigue life only from the point of view of failure from the weld toe.
However The possibility of fatigue crack initiation from other features of the weld, especially the root area should not be overlooked
#Hammer_peening is performed using steel hammer bits having approximately Sami-spherical tips with diameters between 6 mm and 12 mm. In peening process resulting indentation should be centred on the weld toe so the metal on both side (weld metal and parent metal) is indented and resulting in a smooth surface free from obvious individual blows.
Toe Remelting by GTAW Welding Process
The subject GTAW dressing is an #autogenous welding methodology that consists of remelting of weldment at the toe area to approximately 2 mm fusion penetration depth without using filler metal. The weldment subject to autogenous dressing should be free of rust, slag, and scale. The tip of the tungsten electrode should be kept sharp and clean. The tip of the electrode should be positioned horizontally 0.5 mm to 1.5 mm from the weld toe at the susceptible heat-affected zone. Optionally after autogenous dressing, the tempering pass can be applied.
 A high-speed grinder with a #tungsten carbide #rotatory #burr of 12mm diameter is recommended to use. Which comply with the requirements of #AWS D1.1, #dnvgl -ST-0126, and #NORSOK M-101.
 The diameter of the burr shall be as large as geometrically possible to ensure the complete removal of the toes as well as a smooth transition at the start stop grinding.
 The axis of the burr should be at approximately 45 degrees to the main plate.
 The angle of the burr axis should be 45 degrees of the direction of travel to ensure that the grinding marks are nearly perpendicular to the weld toe line (parallel to the direction of stress).
 Grinding should extend below the plate surface.
 The edges between the grinded profile and the brace or chord shall be rounded, no sharp edges are allowed.
 If the weld toe grinding is not to be performed on the complete circumference of the joint, then a #smooth transition between the #grinded profile and the non-grinded weld shall be ensured.
The depth of grinding shall be 0.5 mm below any visible undercut. However, the grinding depth is normally not to exceed 2 mm or 5% of wall thickness whichever is less
The edges between the ground weld profile and the unground weld profile shall be rounded, no sharp edges are allowed.
Final grid marks should be kept small and always be normal to the weld toe if the main loading is normal to the weld toe.
• #visual #inspection and #NDT inspection #MT or #PT shall be carried out to prove that the ground surface is free of any, undercuts or other discontinuities.
• The final surface should show a smooth finish with no visible score marks.

[@sankarvijayan]

Great video bro