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seams were machine welded, the horizontal ones were formed by hot gas extrusion welding. From
DVS 2205, Part 1 we get the following values for the above factors for the copolymer:

K = 9.3 N mm-2 (from Fig. 7 for 2.2 x lo5 h at 20"; see Appendix 3)
fs = 0.6 (for hot gas extrusion welding)
At = 1 .O (i.e. no chemical interaction)
A4 = 1.1 for polypropylene copolymer
S = 2.0 (caustic soda is hazardous).

Then

9.3 x 0.6
QZUI = 1.0 x 1.1 x2.0 Nmm-2

= 2,54N1nrn-~.

Appendix 2

Equation for wall thickness

The standard expression for the hydrostatic head pressure, p at a depth h in a liquid of density
p is

P = hP9 ('43)

where g is the acceleration due to gravity.
The hoop stress, 00, in a circular vessel of diameter d and wall thickness s due to an internal
pressure p is

Pd
Q --.
- 2s

so that the wall thickness is

s=- Pd
208.

Combining eqns (A3) and (A5) gives the equation for the wall thickness, s