California Code of Regulations › Title 8 - Industrial Relations › Division 1 - Department of Industrial Relations › Chapter 4 - Division of Industrial Safety › Subchapter 2 - Boiler and Fired Pressure Vessel Safety Orders › Article 7 - Repairs › Section 794 - Riveted Patches

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
(a)
					 Riveted patch seams exposed to the products of combustion may be double-riveted
					 or constructed similar to the original seams of the boiler.
(b) Patches exceeding twenty-four inches
					 (24") in length shall have the proper width as determined by these orders.
					 Patches exceeding fifteen inches (15") to and including twenty-four inches
					 (24") in length shall be triangular, crescent, diamond, or oval in shape and
					 width, W, in the circumferential direction, shall be at least twice the length,
					 L, in the longitudinal direction. Patches fifteen inches (15") or less in
					 longitudinal direction may be circular in shape.
(c) If it is found that a patch will extend
					 extremely high, and also to avoid calking in sharp corners, it may be shortened
					 in width to the extent that not more than four (4) rivets will be in a
					 longitudinal line, as shown in Figure 2.
(d) If it is found that a patch will have to
					 be sixty inches (60") or more in length, consideration should be given to the
					 use of a sheet having a width equivalent to five-eighths ( 5/8 ) of the
					 circumference of the boiler, and the longitudinal seam shall be of a design
					 similar to the design of the original seam of the boiler.
(e) In laying out new patches over
					 twenty-four inches (24") long, it is recommended that they be triangular or
					 diamond in shape as may be required for the particular job; with definite
					 straight-line sides but with corners properly rounded to permit adequate
					 caulking, as illustrated in Figures 1, 2, 3, and 4. The length designated as
					 "L" and the width designated as "W" are also shown in Figures 1, 2, 3, and
					 4.
(f) Rivets shall be used in
					 "riveted" patch seams unless their use is difficult or impossible, in which
					 case, patch bolts may be used. Rivet holes may be countersunk in patches on
					 shells that have the heads supported by tubes or braces, providing the angle of
					 the chamfer with the center line of the rivet hole does not exceed forty-five
					 degrees (45°), and the depth does not exceed half the thickness of the
					 plate.
(g) Patch material shall be
					 of fire box or flange steel depending upon the plate it replaces. Tank steel
					 shall not be used. The repair shop shall be required to produce a copy of the
					 manufacturer's mill test report for the material to be used.
(h) The patch plate material shall contain
					 the steelmaker's brand. If only a part of a plate is required and this part
					 does not contain the brand, the brand shall be transferred to the patch plate
					 in the presence of a qualified inspector or a representative of the plate
					 manufacturer before the plate is cut. Replacement rivets, patch bolts, and
					 staybolts shall be of material approved for new construction by the
					 code.
(i) All patch plates except
					 patch plates containing blowoff connections shall be placed inside of the
					 boiler shell or drum if exposed to the products of combustion and if installed
					 where there is a possibility that scale deposits may be pocketed. Patch plates
					 containing blowoff connections shall be placed on the outside of the boiler
					 shell.