  About Central Boilers Board •Contents Chapter Wise • Contents Regulation WiseIndian Boilers Act 1923 Reg. 215
TUBE PLATES

Efficiency of Ligament

a) When a shell or drum is drilled for tubes in a line parallel to the axis of the shell or drum, the efficiency of the ligament between the tube holes shall be determined as follows : -

(a) When a pitch of the tube holes on every row is equal (as in Fig.10), the formula is :-

 p - d = efficiency of ligament Eqn.(54) p

where
p = pitch of tube holes, inches,

d = diameter of tube holes, inches,

The pitch of the tube holes shall be measured either on the flat plate before rolling or on the median line after rolling.

Example :- Pitch of the tube holes in the drums as shown in Fig.10 = 5-1/4 in. diameter of tube = 3-1/4". Diameter of tube holes = 3-9/32".
 p - d = 5.25 - 3.281 = 0.375, efficiency of ligament. p 5.25

(b) When the pitch of tube holes on an one row in unequal (as in Figs.11 & 12), the formula is :-
 p -nd = efficiency of ligament Eqn.(55) p

where
p = unit length of ligament, inches,

n = number of tube holes in length p,

d = diameter of tube holes, inches

Example - Spacing shown in Fig.11. Diameter of tube holes = 3-9/32".
 p - nd 12 = 12/ 2 x 3.281 = 0.453, efficiency of ligament. p 12

Example - Spacing shown in Fig.12 Diameter of tube hole = 3-9/32".
 p - nd = 29.25 - 5 x 3.281 = = 0.439, efficiency of ligament p 29.25

(c) The strength of those ligaments between the tube holes which are subjected to a longitudinal stress shall be at least one-half the required strength of those ligaments which come between the tube holes which are subjected to a circumferential stress.

(d) (i) When bending stresses due to weight are negligible and the tube holes are arranged along a diagonal line with respect to the longitudinal axis, the efficiency, (z) of corresponding ligaments is  given in Fig 14, with the ratio b/a on the abscissa and the ratio
 2a - d or d used as a parameter. 2a a

where
a and b are measured as shown in Figure 13 A & 13 B,

d = diameter of the tube holes.

NOTES :

1. The dimension b should be measured either on the flat plate before rolling or on the median line after rolling.

2. The data given on Fig. 14 are based on the following formulae :

 Z = 2 A + B + � (A - B)2 + 4C2

where,
 A = cos �2 + 1 2 ( 1 -d cos�  ) a

 B = 1 ( 1 - d cos � ) (sin2 � + 1 ) 2 a

C = sin � cos �
 2 ( 1 - D cos � ) a

cos � = 1
 � 1 + b2 a2

sin � = 1
 � 1 + a2 b2

( � = angle of centre line of cylinder to centre line of diagonal holes)

(ii) The same rule as in paragraph (i) should apply for the case of drilling holes to a regular saw-tooth shown in Fig. 13C

(iii) In the case of a regular staggered spacing of tube holes ( see Fig. 13A), the smallest value of the efficiency z of all the ligaments, longitudinal, circumferential, and diagonal, is given in Fig.15 by the ratio PC/PL on the abscissa, and the ratio

 PL - d or d used as a parameter PL a

where,

d = diameter of the tube holes;

PC = 2b = twice the distance between circumferential rows of holes;

PL = 2a = twice the distance between axial rows of holes.

NOTE : The dimension Pc should be measured on the flat plate before rolling or on the median line after rolling. The data on Figure 15 are based on the same formulae as shown in Figure 13 A.

(e) When holes spaced longitudinally along a drum are not in a straight line, the equivalent longitudinal pitch for each spacing may be used in the application of the above rules. The equivalent pitch is obtained by multiplying the actual longitudinal pitch by the equivalent efficiency obtained from Fig 14 for each spacing.     About Central Boiler Board Foreword • List of Amendments Ibr Forms • Home • Search • Help • Contact Us