All repairs must be acceptable to the applicable code jurisdiction (such as NBIC), therefore all repair methods must have the written approval of the chief inspector or authorized inspector. Guidance for flushing the patch can be obtained from RD-2060a Flush Patches of NBIC.

Perform a hardness test (DT) on the protruding area to determine the extent of the defect. Mark the limit line of the defective section to be cut based on the acceptable tensile strength obtained. Use the Vickers (HV) hardness test to test the metal strength of carbon steel. The repair method is called “flush patching”, which means the casing is trimmed around the fault in an elliptical or rectangular shape, and a new rolled piece of repeating plate is inserted to correct the curvature with the edge of the casing. original and butt-welded patch. For the rectangular shape, provide a precise radius as square corners will be avoided.

Consult the manufacturer’s drawing for casing material specifications and the patches must be made of material that is equal in quality and thickness to the original material. The edge will be aligned without overlap. Weld preparation to be double “vee” with an included angle of 60o to 70o. Gas Tungsten Arc Welding (GTAW) will be used for the initial step that joins the patch to the casing. The remainder of the weld shall be manual shielded metal arc welding using low hydrogen electrodes confirmed to ASME Code Section IX.

Weld the inside first, then re-gouge the outside. Grind away sound metal before continuing exterior welding. Grind to level accessible surface and after welding is complete visually check for weld undercuts and repair if necessary. Consult the manufacturer’s drawing on the NDT used during construction, and typically the weld on the flush patch to the shell is 100% X-rayed. Weld acceptance is in accordance with ASME code or BS 2970 code. Post weld heat treatment (PWHT) should be performed to relieve residual stress in the heat affected zone (HAZ). Perform hydrostatic test on the boiler. The test pressure will be 1.5 times the design pressure. The waiting time is 10 minutes.