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Subchapter 2. Boiler and Fired Pressure Vessel Safety Orders
Article 7. Repairs

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§785. Permissible Welded Patches and Welded Repair of Cracked Plates in Material of Known Weldable Quality.

The following welded repairs are permissible:

(a) Cracks in unstayed shells, drums, or headers of boilers or fired pressure vessels may be repaired by welding provided:

(1) The cracks do not extend between rivet holes in a riveted longitudinal seam.

(2) The crack is not located within six inches (6") of the calking edge of any longitudinal riveted seam.

(3) The total length of any one crack shall not exceed sixteen (16) times the plate thickness or eight inches (8") unless the completed repair is radiographed and stress-relieved.

(b) Cracks or patches in stayed surfaces may be welded provided:

(1) The crack or patch seam is located between two (2) rows of staybolts.

(2) The crack or patch seam if located in a flange or knuckle runs in a direction transverse to the flange or knuckle.

(3) The patch is set flush with adjacent plate and the welds are located between two (2) rows of staybolts.

(c) Cracks between tube holes in water-tube boiler drums or heads may be welded, provided there are not more than two (2) such cracks in any one row in any direction, nor more than a total of four (4) such cracks in any one drum or header and providing the diameter of the drum is not more than one percent (1%) out of round.

(d) Fire cracks extending from rivet hole to rivet hole in girth seams may be welded, provided there are not more than three (3) consecutive cracked ligaments nor more than a total of six (6) cracked ligaments in any one girth seam.

(e) Cracks between tube holes in fire-tube boilers not exceeding three (3) consecutive cracked ligaments may be welded.

(f) Cracks not to exceed two inches (2") in length in wrought or cast steel (not cast iron) sectional headers of water-tube boilers may be welded except that not more than four (4) such cracks in any one header may be welded.

(g) Circumferential cracks in the knuckle or turn of a flange of a furnace or flue opening or adjacent to manhole opening of unstayed heads shall not be repaired by welding. When such cracks occur in an ogee flange, the affected material including the flange shall be removed and replaced by a flush patch of similar shape. The abutting edges shall be welded and the flange shall be riveted to the shell. Scotch marine and similar boilers shall have one (1) flange riveted to the shell or furnace and the other flange shall be attached by rivets or patch bolts.

(h) All welded patches installed in unstayed drums, shells or heads and exceeding the size of an unreinforced opening in paragraph PG-32 of the Code shall be flush-welded patches and shall be radiographed and post weld heat treated. The corner radius of such patches shall be rounded to a radius of at least twice the plate thickness. A joint efficiency of 90 percent (or more if allowed by the Code to which the boiler was built) shall be used in calculating the maximum allowable working pressure of such patches.

(i) Lap welded patches may be used to close openings in unstayed shells, drums, or heads providing:

(1) The maximum dimension of the opening does not exceed the size of an unreinforced opening in paragraph PG-32 of the Code.

(2) Two or more of such openings are not so located that they form a ligament in the longitudinal direction of the shell or drum.

(3) The patch plate is installed on the pressure side of the plate and has a lap of at least one inch (1").

(4) The patch plate is not exposed to the products of combustion.

(j) Any portion of the tube sheet of a horizontal tubular boiler may be repaired by a flush welded patch providing:

(1) No welded repair shall be permitted in the knuckle in a circumferential direction.

(2) The patch shall be held in place by stays, tubes, or both.

(3) Where the patch extends to the outer row of tubes, it shall include the flanged portion of the head and be secured to the shell in the same manner as the original construction.

(k) The top tube sheet of a vertical tubular boiler may be replaced by a flush welded patch, provided the welded seam is not located nearer than one inch (1") to the knuckle or curved part of the original head. The bottom tube sheet of a vertical tubular boiler shall not be so repaired.

(l) Pipe connections up to three-inch (3") pipe size may be installed by welding without stress-relieving, provided the coupling used has a flange on the pressure side of the sheet and the welding is for tightness only. This type of repair shall not be used for blowoff connections or openings exposed to the products of combustion.

(m) Post weld heat treatment of a repaired part by heating, when necessary, shall be done in accordance with paragraph PW-39 of the Code. Care should be exercised in applying heat in the vicinity of riveted joints to avoid loosening of rivets. Peening may be used in lieu of post weld heat treatment at the discretion of the Division.

(n) Radiography of welded repairs, when required, shall be done in accordance with paragraph PW-51 of the Code.

(o) The thickness of any patch shall be equal to but not more than one-eighth inch (1/8") thicker than the plate being patched.

(p) All flush welded patches in unstayed surfaces shall be butt-doubled-welded or equivalent. Patch material shall conform to the requirements of Order 794(g) and (h).

HISTORY

1. Amendment filed 11-2-66; effective thirtieth day thereafter (Register 66, No. 38). Approved by State Building Standards Commission.

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