EVENTS AND EXHIBITIONS
23
HEALTH AND SANITATION
23
SAPPMA quality
workshop
SAPPMA (Southern African Plastic Pipe Manufacturers’ Association) delivered a
well-attended presentation on 17 July at its premises in Midrand, on the subject
‘Understanding the elements of a pressure pipe system’.
Delivered by SAPPMA technical manager, Ian Venter, the actual subject matter will be provided
in the technical section of Plumbing Africa in November. The thorough presentation covered the
sub-topics: raw materials; pipe; fittings; systems; and conformance assessment; followed by
breakaway sessions to elicit the views on whether the EU standard BS EN 805:2000 would be a
suitable standard for South Africa.
“We’re sharing information on the bigger picture,” says Venter, “for you to use or not.”
Introducing the subject, Venter says, “Your design factor determines your design stress and not
design life. The creep rupture characteristics of these materials necessitated a new method for
selection of design stress, compared with other materials in use at the time, for instance. The
method adopted was that already in use in Europe – using the creep rupture (stress regression)
curve, select a time and establish the associated burst stress. Apply a design factor to the burst
stress to give the design stress. The time chosen was 50 years, already adopted in Europe, and is
still in use today in ISO, and CEN Standards. The use of this particular time interval has led to the
misunderstanding that it represents the pipe life.
“Selection of allowable stress is based on long term pressure testing in the laboratory and
regression analysis applied to the data obtained. The 50-year point is arbitrarily chosen for this
basis, as for all thermoplastic pipes. A factor is applied to the 50-year point in order to provide
the design stress. It shall not be taken that either: (a) the pipes weaken with time; or (b) the
predicted life is 50-years. System life is dependent on many factors. If the design stress were
used in relation to the regression curve, predicted pipe life would be indefinite, not 50-years,”
says Venter. PA
Ian Venter, technical director of SAPPMA.
October 2019 Volume 25 I Number 8
www.plumbingafrica.co.za