Working with OFFSETS

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Working with OFFSETS
Working with OFFSETS
Multiple Angle Offsets Rolling Offsets
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Offsets (when pipe is shifted from one direction
to another) can be hard to understand or
calculate without some type of visual. By using
an isometric depiction of the pipe run, its
easier to see the turns and angles that the pipe
takes. BUT remember, its the accuracy of your
dimensions that make the calculations right. So
although you may take the artistic liberties in
turning or stretching your isometric to reveal
the lines and angles, its the dimensions that
make or break the finished fabricated product.
The best way to illustrate the steps for working
with and calculating offsets is to work through
an example from initial plan and elevation views
to the final sketches and calculations.
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Elbows arent the only piping components
installed in angular positions. Nozzles are
placed on vessels in location where interferences
are least likely to occur nozzles oriented at
angles of 10, 20, 45 etc arent uncommon. The
thing is that when offset or rolled elbows are
added, to the mix, complex math problems can
result. In those cases the multiple angle
configurations require additional calculations to
determine dimensions for the length of pipe.
The example well use for the multiple angle
offset is shown at right. Notice that the lines
appear as flat turns, no elliptical lines are
shown. Theres minimal information angles,
coordinates and information as to line size and
nozzle projection.
In this example, we need to find the dimension of
the horizontal angular pipe between the two
vertical runs. So, where do you start?
14-150 RFWN Nozzle Projection 4-9 1/8
Gaskets
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Now we know the dimension we need to solve for
we could just lay a scale on the line and get the
dimension that way DONT EVEN THINK ABOUT IT!!!!
With AutoCAD, you could just do an Aligned
Dimension command BUT, just how sure are you
that your lines are correct? Did you fudge a
little on one line???
OKAY, now that all the guess-ti-mates are out
of the way, lets solve this the right way.
First, drag out and dust off your calculator,
find your copy of the Pythagorean Theorem
formula, dig out the formulas for Right Angle
Triangles and the Conversion Table (Decimals of a
Foot).
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Look at the basic layout of the pipe. How many
RIGHT angles do you see? Cmontake a good look.
Okay, heres a hint There are 3
1
2
3
AND to solve for our dimension, we have to solve
for each of these. because I said so thats
why.
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MULTIPLE ANGLE OFFSETS
Okayso what do we already know about this
triangle? Check back on slide 3 if youve
forgotten
We were given the nozzle projection 4-9 and
the angle of 20 We know the gasket 1/8 We
know that the connection to the nozzle is FTF
14 90 elbow 21 14 150 RFWN 5
26 2-2 4-9 1/8 2-2 6-11 1/8
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For this 1st triangle, we have the angle of the
nozzle 20 AND the hypotenuse 6-11 1/8 Make
sure your calculators are set for degrees.
SA
SO

• Lets solve for SA (side adjacent) SA HYP
  (COS x)
• Convert 6-11 1/8 to decimals of an inch
  83.125
• Find the COS of 20
• In most cases, this is as easy as typing in 20
  and hitting the COS key on your calculator
• Now, plug those numbers into the formula

6 x 12 72 11 1/8
.125 83.125
SA HYP (COS x) 83.125 (.93969)
78.11173 SA 6-6 1/8
78.11173 78 6-6 .11173 x 16
1.78 2/16 1/8 6-6
1/8
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Now that weve got two sides of our triangle you
can pull out the old Pythagorean Theorem and find
the SO (side opposite).
HYP² SA² SO²
SO
Since were solving for SO², we want it on one
side of the equal sign of our equation, all by
itself. In this case, well subtract SA² from
both sides. HYP² - SA² SO² Plug
in the numbers you have so far (6-11
1/8)² - (6-6 1/8)² SO² (83.125)²
- (78.11173)² SO² 6909.7656
6101.4423 SO²
808.3233 SO² v 808.3233
SO 28.4310 SO 2- 4 7/16 SO
28.4310 28 2-4 .4310 x 16
6.896 7/16 2- 4 7/16
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Take a look at how the 1st triangle dimensions
fit into the plan view of the pipe run.
We still have some other dimensions to find So,
lets move on to triangle 2

• What do we already know about this 2 triangle?
• There are coordinates on at least two of the
  points.
• And we know that the BACK OF PIPE (BOP) is 5-0
  off the centerline of the tank.

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This one looks pretty easy. The hypotenuse
5-0 ½ (pipe OD) 5-0 ½ (14
pipe) 5-0 7 5-7
SA
The coordinates give the SO dimension W.
125-0 W. 122-6 2-6
Whip out the old Pythagorean Theorem and lets
get started
HYP² SA² SO² Remember youre looking for
SA² so fix the formula to reflect this
HYP² - SO² SA²
(67)² - (30)² SA²
4489 900 SA² 3589
SA² v 3589 SA 59.9082
SA 4- 11 15/16 SA
59.9082 59 12 4.9166 4
.9166 x 12 11 .9082 x 16 14.53
15/16 4 11 15/16
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Theres a 3rd triangle still to go, but lets
look at what information we have that will help
us in solving this one as well as solving for the
dimension we started out to find.
HYP ?
By adding and subtracting dimensions weve
already solved for, we already have two sides of
the 3 triangle. The dimension you were to find
is at the end of this next set of calculations!
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HYP² SA² SO²
HYP² (4-10 7/16)² (1-6 3/16)² HYP²
(58.4375)² (18.1875)² HYP² 3414.9414
330.7851 HYP² 3745.7265 HYP v3745.7265 HYP
61.2023 HYP 5 1 3/16
Congratulations!!! Youve just waded through the
steps for solving multiple angle offsets!!!
The next set of slides will lead you through
solving rolling offsets
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ROLLING OFFSETS

• compound offset formed typically by having two
  45 elbows instead of the 90 elbows you saw in
  the last few slides.
• this offset not only changes direction but also
  changes elevation at the same time
• an orthographic view cant fully describe the
  rolling offset so the use of an isometric
  provides the best way for representing and
  dimensioning the rolling offset
• for this topic well use a problem out of your
  text (pg. 242 prob. 8-8D)

TRAVEL
RISE
RUN
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To solve a rolling offset, you need 6
measurements4 length dimensions and 2 angular
dimensions.
Although you may have several of these
dimensions, you may have to solve for others by
doing simple calculations using elevations,
coordinates and existing dimensions.

• to solve our textbook problem, you dont even
  need the size of pipe, all the information you
  need to solve for the hypotenuse or travel is
  right in front of you

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So, how many triangles do you see?
2 These are the two that you have to
solve to get to the dimension you need. Remember,
everything you need is right in front of you.

• Solve for the triangle with the dimension first.
• Break out the Right Triangle Formulas
• Make a sketch of the triangle
• Put everything you know on the sketch

Where did 55 come from? The total number of
degrees in a triangle is 180 One corner is a
right angle 90 180 - 90 90
That means the other two angles of the triangle
add together to 90 Youve been given the 35
HOR. which is adjacent to one angle of the
triangle were solving. The sum of adjacent
angles 90 90 - 35 55
35
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The dimension thats needed from this first
triangle is the hypotenuse of this first triangle
BECAUSE it is the base of the 45 VERT. angle of
our second triangle.
x
SO SIN x
HYP
HYPOTENUSE
HYP
SA
89.25 .8191
SO
HYP
108.9610
HYP
108 12 9- 0 .9610 x 16 15.376
15/16 9- 0 15/16
HYP
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• What do you know about the 2nd triangle?
• Put everything you know on the sketch
• It has a 45 vertical angle
• One leg 9- 0 15/16 (Hint the length of the
  legs of a 45 are the same)
• Youre solving for the hypotenuse

TRAVEL
HYPOTENUSE
9- 0 15/16
9- 0 15/16
HYP² SA² SO²
HYP² (9-0 15/16)² (9-0 15/16)²
HYP² (108.9610)² (108.9610)²
HYP² 11872.4995 11872.4995
HYP v 23744.9990
154 12 12.8333 12 .8333 x 12
10 .0941 x 16 1.5056 2/16 1/8
HYP 154.0941
HYP 12-10 1/8
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12-10 1/8
Youve now got the basics for solving multiple
angle offsets and rolling offsets. Refer to this
tutorial when working assignments.
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Thanks for viewing this Tutorial. Any questions,
comments or complaints can be registered at the
next class meeting, via email or drop by my
office.
Email rstrube_at_mail.accd.edu
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REFERENCES
Parisher, Roy A. Robert A. Rhea. 2002. Pipe
Drafting and Design. 2nd Ed. Gulf Professional
Publishing_Butterworth-Heinermann.
Shumaker, Terence M. 2004. Process Pipe Drafting.
The Goodheart-Willcox Company, Inc. Tinley Park,
Illinois.
Weaver, Rip. 1986. Process Pipe Drafting, 3rd Ed.
Gulf Publishing Company. Houston, Texas.