Water, Sewage & Effluent March April 2019 | Page 14

which is an American standard. Every
welder is certified with a number. On
this project, we do a dye-pen (dye
penetrant) test on the joints, using a
penetrant and a developer to check if
there are any cracks in the welding.
There is a cement-mortar lining inside
the pipe, which we repair at every joint.
In addition, at each welder-joint, we
use a coating on the outside of the pipe
for corrosion prevention and sealing.
Quality plays a big role, and we have
our quality-control officer on site,” he
adds.
Steyn explains that every
pipe will have a block with the
chainage (linear pipe length),
the joint number, the welder
number, and the date the pipe was
welded, and every joint is recorded.
All this information is captured and
submitted to the client.
Barnard adds, “We have an in-house
fittings factory which manufactures the
elbows and joints — we’ll get the parts
and join them. It then gets sent to our
pipe supplier who 3-LPE coats it.”
Processes
Access under roads or railway lines is
made possible through pipe jacking.
Steyn explains the process: “A trench
is dug, and we start excavating under
the road or railway line, by hand usually,
using air breakers. Then, using huge
jacks, a concrete sleeve is pushed
through the excavation site until they
get to the other side. The resulting
‘tunnel’ is then secured with grout in
order to ensure that it doesn’t collapse,
and we slide our pipe through the
concrete sleeve.
“Another part of our pipe laying
process is the installation of air valves
and scour valves,” says Steyn. “The
air valves are always at the highest
point. When you pump water, air tends
to get trapped, and if you don’t get rid
of the air, the water won’t flow — it
forms an air pocket. Then, at the lowest
points, there are scours. If there is a
problem along the pipeline that needs
to be fixed, then the scours are used
pre-coated with a three-layer coating
process called 3-LPE. The first layer
is the corrosion protective layer
consisting of fusion-bonded epoxy,
which offers very good corrosion
protection and bonds well with the
blasted steel surface. The second layer
is the copolymer adhesive, which has
good chemical bonding to the fusion-
bonded epoxy, and layer three is
polyethylene, which also bonds well
and seals the layers.
“The pipeline is delivered in sections
of 18-metre lengths, so every
18 metres there is a weld to join
them on a spigot and socket
joint,” says Steyn. “Our welding
team are all API qualified,
The pipe sling attachment hoists and lowers the 18m-long pipes into the ground.
12
Water Sewage & Effluent March/April 2019
www.waterafrica.co.za