FORMULAS 1. WEIGHT PER FOOT CALCULATION
To determine the weight per foot of a copper tube:

Subtract the wall thickness from the O.D. then multiply by the wall thickness.

Multiply the figure from above by 5.526.
*All values in inches.

2. COST SAVING BY WALL REDUCTION

Calculate the weight of both the proposed tube with a lighter wall and the present tube.

Subtract the smaller weight from the larger.

Divide this figure by the weight of the present tube.

Multiply this percentage times the total cost per kilogram (including metal) to determine the savings in Rs./Kgs.

3. BURST PRESSURE CALCULATION

Burst pressure for copper tubing is calculated using the following formula:

P = burst pressure (PSI)

P = 2TS/D where: T = wall thickness (inches)

D = tube diameter (inches)

S = ultimate strength (PSI)

(30,000 PSI for annealed tube and 36,000 PSI for hard tube).

Safe Working Pressure:
To calculate the safe working pressure for copper tubing; divide the desired factor of safety eg. 5, 6, 7, 10 etc.

4. FLARE DIAMETER

It should not exceed 1.3 times the tube O.D.

5. FLANGE DIAMETER

It should not exceed 1.5 times the tube O.D.

6. BEAD DIAMETER

It should not exceed 1.5 times the tube O.D.

7. SEAMLESS PLUG DRAWN TUBING

Will have a smooth cold worked I.D. surface.

Will have a temper through the cross-section of wall thickness.

8. BENDS

Safe bend radius is 2.5 times the O.D. of the tube.

For tighter bends specific mandrels are required.

Compound bends are possible.

9. CALCULATING LENGTHS
In determining the required lengths of a tube before bending, the lengths of the straight sections are added to the lengths of the curved sections in order to make the proper allowance for bends. The following rules may be used for finding the lengths of the curved sections. (For these calculations, the radius is measured to the center of the tube):

Rule 1:
To find the length of 90-degree bend, multiply the radius of the bend by 1.57.

Rule 2:
To find the length of a 180-degree bend or U bend, multiply the radius of the bend by 3.14

EXAMPLE
A 90-degree bend is to have a radius of 10 inches and straight sections on each side of the bend of 5 and 15 inches respectively. Find the total length of the tube before bending. Length of curved part: 1.57 x 10 = 15.7 inches. Therefore, total length = 15.7 + 5 + 15 = 35.7 inches.

Rule 3:
A general rule for finding the lengths of sections having degrees of curvature other than 90 and 180 is as follows: multiply the radius of the bend by the included angle, in degrees, then multiply the product by constant 0.0175. The result is the length of the curved section.

To prevent flattening at the ends there should be a straight section adjoining the bend equal at least to the tube diameter.