GE T17, Руководство по установке

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Model T17 Installation Guide 29
Chapter 2. Installing the Pipe Nozzles
2.3.4 Installing the First Welding Boss - MR1 Mid-Radius
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
X
, which is dependent on the pipe outside
diameter as follows:
Note:
For convenience, refer to Table 5 on page 30 for tabulated values of the
X
dimension for some common pipe
sizes. For any values not listed in the table, calculate your
X
dimension with the equations above.
•
Example: To demonstrate the calculations, consider an
MR1
installation for a STD Schedule, 48” pipe .
a. From standard pipe tables: pipe
OD (D) = 48.000 in.
and pipe wall thickness
(W) = 0.375 in.
b. From GE documentation: welding boss OD (d) = 1.660 in.
c. From the 1st equation:
Y
0
= (48.000 - (2 x 0.375))/2) x 0.5 =
11.813 in.
d. From the 2nd equation:
Y
1
= 11.813 + 1.660/2 =
12.643 in.
e. From the 3rd equation:
X
= SQRT ((48.000/2)
2
- 11.813
2
) - SQRT ((48.000/2)
2
- 12.643
2
) =
0.492 in.
Note:
In the above example, the tabulated pipe OD of 48.000 in. was used in the calculations for clarity. Ideally, the
measured average pipe OD would be used instead.
Y
0
D 2W
–
2
-------------------
 
 
Chord Location
( ) ×
=
where, W = 0.375 inches and Chord Location = 0.5
Y
1
Y
0
d
2
---
+ =
where, d = welding boss OD = 1.66 inches
X
D
2
----
 
 
2
Y
0
( )
2
–
D
2
----
 
 
2
Y
1
( )
2
– – =
where, D pipe OD
=