Trig I think?

[pipeweldertoo]

I am a Pipefitter and would like to ask help for a formula. I have been working in a pharmacutical plant. Alot of the process systems require 1/8" slope per foot. The formula I am looking for would be, for example, if I know my cut length of pipe is 10' being level, what would it be at 1/8" per foot slope. I'm sure there is a formula for it, but I'm unaware of it. Thanks for your help!

 

[Deleted member 4993]

I am a Pipefitter and would like to ask help for a formula. I have been working in a pharmacutical plant. Alot of the process systems require 1/8" slope per foot. The formula I am looking for would be, for example, if I know my cut length of pipe is 10' being level, what would it be at 1/8" per foot slope. I'm sure there is a formula for it, but I'm unaware of it. Thanks for your help!

You have a rise of 1¼" - which could less than the diameter of your pipe!!

So your pipe is laying at a slope(1/8" per foot) and you want to know the horizontal distance covered (run)?

Let the horizontal run = H

let the vertical rise = V = H/(8*12) = H/96

Using Pythagorus

H² + V² = 10²

Then

H² + H²/(96)² = 10²

1.00019 * H² = 100

H = 9.999548'

\(\displaystyle H \ = \ ~9'11\frac{127}{128}"\)

The horizontal runs for the top of the pipe and the bottom of the pipe would be shifted.

 

[wjm11]

I am a Pipefitter and would like to ask help for a formula. I have been working in a pharmacutical plant. Alot of the process systems require 1/8" slope per foot. The formula I am looking for would be, for example, if I know my cut length of pipe is 10' being level, what would it be at 1/8" per foot slope.

The above response assumed the 10" length was on the slope. I interpreted your question to mean the 10' length was horizontal. You'll see that the practical results are the same:

Think about what “ 1/8” per foot slope” means. This can be represented by a right triangle with one leg (side) equal to 1/8” and the other leg equal to 12”. Since we know both legs of the right triangle, we can solve for the long side (hypotenuse) using the Pythagorean theorem: a^2 + b^2 = c^2 , where c is the side you are asking about. In this case, that means

(1/8)^2 + (12)^2 = c^2

1/64 + 144 = c^2

144.015625 = c^2

c = 12.00065”

In practical terms, this means that for a one foot length with a 1/8” drop, you couldn’t even see the required extra length because it’s so small.

Let’s consider your question for a 10’ length. The first triangle we just discussed had sides of 1/8”, 12”, and 12.00065”. We can multiple this triangle by any number we want to make a bigger triangle of the same shape, so multiplying by 10 we’d get a triangle with sides of 10/8”, 120”, and 120.0065” – so you still couldn’t see the difference in length (.0065”) between the sloped pipe and the horizontal pipe.

Let’s think about 100’ of horizontal run. The drop would only be 100 x 1/8”, right? That drop would be 100/8 = 12.5”. Imagine having one end of that pipe supported and fixed in one spot, and you are at the other end, moving it up and down one foot. You’d never see the difference in length required because it’s still only .065” (assuming a perfectly straight pipe).

However, if you have a 1,000’ run, the difference in length would now be .65” – about 2/3”.

I’m guessing you’re not going to run 1,000’ at a time, so in practical terms, you’re not going to have to worry about the extra length very often – just shoot with a laser level to control your drop accurately and have sufficient support points.

NOTE: The flex in the pipe will likely have a bigger effect than the extra length needed because of the drop, so you’ll need a sufficient number of support points to avoid problems from that source.

Hope that helps.