Selection of material of construction
This is determined by the
gas to be distributed, by its quality requirement
and the level of contamination that can be accepted
in the gas. The inner surface finish of components
is one of the critical parameters and relates
to the final purity of the gas at the point of
use. A better surface finish will make the pipe
system easier to clean and greatly reduce the
chance and risk of particles being released into
the gas stream.
Final pressure and free gas
volume in the canister will however be governed
by the vapour pressure limitations of gas components
in the canister. Specially designed Pressure Regulators
with very low flow rates for calibration purposes
will be required along with these canisters and
are also available.
Over the last few years, stainless steel
has become the number one choice of material for
pure gas applications. Stainless Steel can be
supplied with a very good surface finish and can
easily be cleaned.
- A storage area for the gas
cylinders, with adequate ventilation and lighting,
well isolated from the other work areas, but
nearest to the points of use is required.
- Connected gas cylinders are
placed in a separate area, preferably in adjacent
to the access area. Avoid transporting gas cylinders
- The gases are stored (separately)
according to fixed directives depending on their
- Ventilation is provided based
on safety requirements regarding the amount
and type of gas used.
cabinets and pipe systems
- Separate gas cabinets should
be used for corrosive gases and toxic gases.
- When using extremely dangerous
gases, it is recommended that flow control and
emergency cut-off and safe venting arrangements
- Routing and laying of gas
pipes shall be so that the risk of mechanical
damage is eliminated and that, as far as possible,
through areas where any leaking gas causes as
little damage as possible.
- To maintain the purity requirements and to
produce a tight gas system automatic computer
controlled pipe welding equipment is used. All
welding is carried out using internal and external
shield-gas purging, which results in a clean
and bright joints.
- The need of detection shall
be assessed. Regard should be taken to future
requirements concerning types of gas and suitable
flexibility to avoid unnecessary costs at a
- The possibility of an auto-stop
if a leak is indicated. This can be achieved
using detection equipment.
- The need of an alarm to an
operating centre and/or an evacuation alarm
within a certain area is to be assessed.
Pressure testing according to
applicable standards are carried out and a protocol
is established. A complete system is blown clean
and analyzed to determine the humidity and oxygen
content. Helium leak detection test is another
option to guarantee a leak tight system. A certificate
of tightness is drawn up.
Before a gas supply system can
be regarded as completed and is handed over for
start-up it is documented.
A complete set of documentation
- Layout document (shows the
entire supply systems design and positions in
- System specification including
- Technical information covering
- Spare part lists.
- Pressure testing protocol.
certificate where applicable.
- Tightness certificate where
- Operating and servicing instructions.