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

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§797. Example of the Application and Explanation of Patch Tables and Charts.

(a) A patch is to be placed in the fire sheet of a horizontal return tubular boiler having a shell plate seven-sixteenths-inch (7/16,) thick, a longitudinal seam efficiency of seventy-four percent (74%), and a length of patch of thirty-six inches (36,). Find the width, W, of patch to be applied so that there will be no reduction in pressure, using a single-riveted seam of normal design.

Referring to Table 1, it is found that seven-sixteenths-inch (7/16") plate with fifteen-sixteenths-inch (15/16") diameter rivet holes, pitched two and one-fourth (2 1/4) gives a seam efficiency of fifty-six percent (56%).

Referring to Table 2, E= 0.74 and e= 0.56 gives a constant C= 1.75; then width W= Lx C = 36x 1.75= sixty-three inches (63").

(b) Pressure Allowed on an Existing Patch.

  A crescent-shaped patch has already been installed on a horizontal-tubular boiler. It is thirty inches (30") long and forty-eight inches (48") wide. The seam is single riveted with thirteen-sixteenths-inch (13/16") rivet holes pitched one and fifteen-sixteenths inches (1 15/16"). The boiler shell plate is three-eighths-inch (3/8") thick. The longitudinal seam is of the double-riveted butt-strap type having an efficiency of eighty-two percent (82%). The safety valve is set for one hundred twenty-five pounds (125#) pressure. What maximum pressure should be allowed on the boiler? Reference to Table 1, shows that the normal efficiency of the patch seam is fifty-seven percent (57%). (If the efficiency is not found in the Table, refer to any other available table or determine it in the manner described in paragraphs A-1, A-2 and A-3 of the Appendix of the A.S.M.E. Boiler Code.)  


  Divide the width of the patch, W = forty-eight inches (48") by the length, L= thirty inches (30") to find the constant, C= 48/30 = 1.60. Follow down column 0.57 of Table 2 until 1.60 is found. It will be noted that this is somewhere between 1.56 and 1.62 representing E somewhere between 0.72 and 0.73. As the difference between 1.56 and 1.62 is 6, and the difference between 1.56 and 1.60 is 4, Ewill be 0.72 plus 4/6 of 0.01 which is 0.7266.  


  The maximum allowable working pressure varies directly as the seam efficiency. Accordingly, P= (0.7266/0.82) x 125 = 110#. If this pressure allowance interferes with the operation of the plant, the patch shall be replaced by a new one with the proper dimensions giving a diagonal efficiency of eighty-two percent (82%).  


(c) Design of Patch for Water-tube Boiler.

Reference to Table 1 shows that a single-riveted lap seam with seven-sixteenths-inch (7/16") plate, fifteen-sixteenths-inch (15/16") diameter rivet holes, and two-and-one-half-inch (2 1/2") pitch has a normal efficiency of fifty-six percent (56%).

Reference to Table 3, shows E= 0.82 and e = 0.56, the constant C is 3.16.

Then width W = Cx 1P2.

W = 3.16 x 36P2 = 56.88 or practically fifty-seven inches (57").

Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6 

CONSTANT "C"                TRIANGLE OR CRESCENT SHAPE PATCHES   C = W / L    W = C X L       L = W / C
TABLE F-1 HEADS SUPPORTED   DIAMOND OR OVAL SHAPE PATCHES        C = 2W / L   W = C X L / 2   L = 2W /  C
"e" EFFICIENCY OF PATCH SEAMS

.50

.51

.52

.53

.54

.55

.56

.57

.58

.59

.60

.61

.62

.63

.64

.65
"E"

.65

1.68

1.60

1.51

1.43

1.36

1.28

1.20

1.13

-

-

-

-

-

-

-

-
 

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.66

1.75

1.67

1.58

1.50

1.42

1.35

1.27

1.19

-

-

-

-

-

-

-

-

.67

1.82

1.73

1.65

1.57

1.49

1.41

1.33

1.26

1.18

-

-

-

-

-

-

-

.68

1.88

1.79

1.70

1.63

1.55

1.47

1.40

1.32

1.24

1.16

-

-

-

-

-

-

.69

1.94

1.86

1.77

1.69

1.61

1.53

1.45

1.38

1.30

1.23

1.15

-

-

-

-

-

.70

2.01

1.91

1.83

1.75

1.67

1.59

1.52

1.44

1.36

1.30

1.22

1.15

-

-

-

-

.71

2.06

1.97

1.89

1.81

1.73

1.65

1.57

1.50

1.43

1.35

1.28

1.21

1.15

-

-

-

.72

2.12

2.03

1.95

1.86

1.79

1.71

1.63

1.56

1.48

1.41

1.34

1.27

1.20

1.14

-

-

.73

2.17

2.09

2.00

1.93

1.85

1.77

1.69

1.62

1.54

1.47

1.40

1.33

1.26

1.19

1.13

-

.74

2.22

2.14

2.06

1.98

1.91

1.83

1.75

1.67

1.60

1.52

1.45

1.39

1.32

1.25

1.8

-

.75

2.28

2.20

2.12

2.04

1.96

1.88

1.81

1.73

1.66

1.58

1.51

1.44

1.37

1.31

1.24

1.17

.76

2.34

2.25

2.17

2.09

2.02

1.93

1.86

1.79

1.71

1.64

1.57

1.50

1.43

1.36

1.30

1.23

.77

2.39

2.31

2.22

2.15

2.07

2.00

1.92

1.84

1.76

1.69

1.62

1.55

1.48

1.42

1.35

1.29

.78

2.44

2.36

2.28

2.20

2.13

2.05

1.97

1.89

1.82

1.75

1.67

1.61

1.54

1.47

1.41

1.35

.79

2.50

2.42

2.33

2.25

2.18

2.10

2.03

1.95

1.87

1.81

1.73

1.66

1.59

1.52

1.45

1.40

.80

2.55

2.46

2.39

2.30

2.23

2.15

2.06

2.00

1.93

1.86

1.79

1.72

1.64

1.58

1.48

1.45

.81

2.60

2.51

2.43

2.36

2.28

2.20

2.13

2.05

1.98

1.91

1.84

1.77

1.69

1.63

1.57

1.50

.82

2.65

2.56

2.48

2.40

2.33

2.25

2.18

2.11

2.03

1.97

1.89

1.82

1.75

1.68

1.62

1.55

.83

2.70

2.62

2.53

2.45

2.38

2.30

2.22

2.15

2.08

2.01

1.94

1.87

1.80

1.73

1.67

1.60

.84

2.75

2.66

2.59

2.51

2.43

2.35

2.27

2.20

2.13

2.05

1.99

1.92

1.85

1.78

1.72

1.65

.85

2.80

2.71

2.63

2.56

2.48

2.40

2.32

2.25

2.18

2.11

2.04

1.97

1.90

1.84

1.77

1.70

.86

2.85

2.77

2.68

2.60

2.52

2.45

2.37

2.30

2.23

2.16

2.09

2.02

1.95

1.89

1.82

1.75

.87

2.90

2.82

2.74

2.65

2.57

2.49

2.42

2.34

2.28

2.21

2.14

2.07

2.00

1.93

1.87

1.81

.88

2.96

2.87

2.78

2.71

2.62

2.54

2.47

2.40

2.32

2.25

2.19

2.12

2.05

1.98

1.92

1.85

.89

3.01

2.92

2.83

2.75

2.68

2.59

2.52

2.44

2.37

2.30

2.23

2.16

2.10

2.03

1.96

1.90

.90

-

2.97

2.89

2.80

2.71

2.65

2.57

2.50

2.42

2.34

2.27

2.21

2.14

2.08

2.01

1.95

.91

-

-

2.94

2.86

2.77

2.69

2.62

2.54

2.47

2.39

2.32

2.25

2.19

2.12

2.05

2.00

.92

-

-

2.99

2.90

2.82

2.74

2.66

2.59

2.51

2.44

2.36

2.30

2.23

2.17

2.10

2.04

.93

-

-

-

2.95

2.87

2.78

2.70

2.63

2.56

2.48

2.42

2.34

2.28

2.21

2.15

2.06

.94

-

-

-

-

2.91

2.83

2.75

2.67

2.60

2.53

2.45

2.39

2.32

2.25

2.19

2.13

.95

-

-

-

-

-

2.87

2.79

2.72

2.64

2.57

2.50

2.43

2.36

2.29

2.23

2.17

 
CONSTANT "C"                  TRIANGLE OR CRESCENT SHAPE PATCHES   C = W / L    W = C X L       L = W / C
TABLE F-2 HEADS UNSUPPORTED   DIAMOND OR OVAL SHAPE PATCHES        C = 2W / L   W = C X L / 2   L = 2W /  C
"e" EFFICIENCY OF PATCH SEAMS
.50 .51 .52 .53 .54 .55 .56 .57 .58 .59 .60 .61 .62 .63 .64 .65
"E" .65 2.20 2.06 1.93 1.80 1.69 1.56 1.45 1.35 1.24 1.14 - - - - - -
 

E
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 .66 2.30 2.16 2.03 1.90 1.78 1.65 1.55 1.45 1.34 1.22 1.12 - - - - -
.67 2.40 2.26 2.13 2.00 1.88 1.75 1.64 1.52 1.43 1.32 1.21 - - - - -
.68 2.50 2.36 2.23 2.10 1.98 1.85 1.73 1.63 1.52 1.42 1.31 1.19 - - - -
.69 2.62 2.46 2.33 2.20 2.07 1.95 1.84 1.71 1.61 1.50 1.40 1.30 1.17 - - -
.70 2.75 2.57 2.43 2.30 2.16 2.04 1.93 1.80 1.69 1.59 1.49 1.37 1.28 1.16 - -
.71 2.87 2.70 2.53 2.40 2.26 2.14 2.02 1.90 1.79 1.67 1.57 1.47 1.37 1.26 1.15 -
.72 3.00 2.81 2.65 2.48 2.36 2.23 2.11 1.99 1.88 1.66 1.56 1.45 1.36 1.26 1.14
.73 3.14 2.93 2.76 2.60 2.46 2.33 2.20 2.09 1.97 1.75 1.64 1.54 1.44 1.35 1.24
.74 3.28 3.07 2.87 2.71 2.55 2.42 2.30 2.19 2.06 1.83 1.73 1.62 1.52 1.43 1.34
.75 3.38 3.19 3.00 2.83 2.66 2.52 2.40 2.27 2.15 1.92 1.81 1.71 1.61 1.51 1.42
.76 3.52 3.32 3.14 2.96 2.78 2.62 2.49 2.35 2.24 2.01 1.90 1.79 1.69 1.60 1.50
.77 - 3.46 3.28 3.07 2.90 2.74 2.58 2.45 2.32 2.10 1.98 1.88 1.77 1.67 1.56
.78 - - 3.40 3.19 3.03 2.85 2.69 2.55 2.42 1.86 1.75 1.66
.79 - - - 3.32 3.16 2.97 2.80 2.65 2.51 2.94 1.84 1.74
.80 - - - 3.46 3.28 3.10 2.92 2.75 2.61 2.03 1.92 1.83
.81 - - - - 3.40 3.20 3.03 2.87 2.71 2.11 2.00 1.90
.82 - - - - - 3.34 3.16 2.97 2.82 2.19 2.09 1.98
.83 - - - - - 3.46 3.29 3.10 2.93 2.27 2.17 2.05
.84 - - - - - - 3.39 3.22 3.05 2.37 2.25 2.15
.85 - - - - - - - 3.32 3.17 2.44 2.34 2.23
.86 - - - - - - - 3.45 3.29 2.54 2.42 2.32
.87 - - - - - - - - 3.40 2.62 2.50 2.40
.88 - - - - - - - - - 2.71 2.59 2.47
.89 - - - - - - - - - 2.81 2.68 2.56
.90 - - - - - - - - - - 2.93 2.78 2.65
.91 - - - - - - - - - - 3.03 2.87 2.75
.92 - - - - - - - - - - 3.14 2.97 2.63
.93 - - - - - - - - - - 3.24 3.09 2.93
.94 - - - - - - - - - - 3.32 3.19 3.03
.95 - - - - - - - - - - 3.43 3.28

3.14

HISTORY

1. Repealer and new subsections (a) and (b) filed 8-12-76; effective thirtieth day thereafter (Register 76, No. 33).

2. Change without regulatory effect repealing and adopting new Figures 1-6 within subsection (b) filed 5-19-2008 pursuant to section 100, title 1,California Code of Regulations (Register 2008, No. 21).

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