Offsets in Plumbing

Basic trigonometry facts


geometria



sin    cos     tan



cos

sin

tan

cot


cos

tan

cot

sin

sin

cos

cos



Piping Offsets

( Center to Center )

This section demonstrates how to calculate distance for offsets.


45offset

Pipe Offsets


= fitting nominal angle


=


180 -


Travel = Offset / sin


Travel = Advance / cos


Advance = Offset / tan


Offset = Advance  x  tan


45o Offsets:


sin 45o = cos  45o = 1/1.4142 = 0.7071

tan 45o = 1


Advance = Offset

Travel = Offset x 1.4142

Travel = Advance x 1.4142

11.25_offset.gif

11 1/4o Offsets:


sin 11 1/4o = 0.1951 = 1 / 5.1258

cos 11 1/4o = 0.9808 = 1 / 1.0196

tan 11 1/4o = 0.1989 = 1 / 5.0277


Advance = Offset x 5.0277

Offset = Advance x 0.1989

Travel = Offset x 5.1258

Travel = Advance x 1.0196

22 1/2o Offsets:


sin 22 1/2o = 0.3827 = 1 / 2.6131

cos 22 1/2o = 0.9239 = 1 / 1.0824

tan 22 1/2o = 0.4142 = 1 / 2.4142


Advance = Offset x 2.4142

Offset = Advance x 0.4142

Travel = Offset x 2.6131

Travel = Advance x 1.0824

60_offset.gif

60o Offsets:


sin 60o = 0.866 = 1 / 1.1547

cos 60o = 0.5 = 1 / 2

tan 60o = 1.7321 = 1 / 0.5774


Advance = Offset x 0.5774

Offset = Advance x 1.7321

Travel = Offset x 1.1547

Travel = Advance x 2




Parallel Offsets

When running offsets parallel one another, it is important to shift the offsets in order to keep the distance between the pipelines equal throughout the offset. The distance between the pipelines is referred as Spread. The amount of offset is moved is known as the Spread Allowance.

Spread Allowance for any type of offsets is calculating using the formula:


formula



where


is the angle that is used to name the fitting, e.g. for  45o elbow use 45,

not 135,  the actual angle of a 45o elbow.


SA

is Spread Allowance


S

is Spread


45_parallel_offset.gif


formula


A = Advance

O = Offset

T = Travel

S = Spread

SA = Spread Allowance


=


/ 2


=


(180 -


) / 2


=


fitting nominal angle


45o Parallel Offset:

SA = S X sin ( 45o / 2) = S sin 22.5o

SA = S x 0.383


pipe 1b = pipe 1a - SA

pipe 2b = pipe 2a + SA

11.25_parallel_offset.gif





11 1/4o Parallel Offset:


= 11 1/4o

SA = S X sin ( 11 1/4o / 2) = S sin 5 5/8o

SA = S x 0.098

22.5_parralel_offset.gif



22 1/2o Parallel Offset:


= 22 1/2o

SA = S X sin ( 22 1/2o / 2) = S sin 11 1/4o

SA = S x 0.1951


60_parralel_offset.gif

60o Parallel Offset:


= 60o

SA = S X sin ( 60o / 2) = S sin 30o

SA = S x 0.5

Rolled Offsets

A rolled offset may be described as an offset that has a vertical rise and horizontal spread which determines the amount of roll.


rolled_offse3.gif

H = Offset

V = Vertical Rise

A = Advance

T = Travel

X = Value that must be found in order to calculate the length of a rolled offset


=


fitting nominal angle


=


90 -

           _______

X = √ V2 + H2


T = X / cos


= X / cos ( 90 -


)

           ______

A = √ T2 - X2 = T x sin



= T x sin ( 90 -



)

rolled_offse2.gif