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Chapter 2. Installing the Pipe Nozzles
2.2.4 Installing the First Welding Boss - Diametrical
To install the first welding boss, complete the following steps:
1. Before welding the first boss, you must add another scribe line to the pipe, known as the oblique center line.
The oblique center line compensates for the slope or oblique angle of the boss. The oblique center line is offset
from the true vertical center scribe line marked earlier by a distance
diameter and the welding boss diameter as follows:
where, D = pipe outside diameter
d = welding boss outside diameter (1.660 in.)
Using the above equation, values of
NPS (inches)
2. Scribe the oblique center line on your pipe at the calculated distance from the true center line for your pipe
size. The oblique center line should be marked on the side of the true center line that is closer to the second
nozzle location, as shown in Figure 17 below.
12
D 2 ⁄
X
=
for some common pipe sizes were calculated and are listed in Table 1 below.
X
Table 1: X Values for Common Pipe Sizes
Pipe OD
DN (mm)
12
300
14
350
16
400
18
450
20
500
22
600
24
650
26
700
True Center Line
Figure 17: Scribing the Oblique Center Line
, which is dependent on the pipe outside
X
d 2 ⁄
---------------------------------------- -
–
-1
[
(
⁄
)
]
tan
sin
d D
X Dimension
inches
0.058
0.049
0.043
0.038
0.035
0.031
0.029
0.027
Oblique Center Line
Side View
mm
1.37
1.24
1.09
0.97
0.89
0.81
0.74
0.68
Model T17 Installation Guide
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