The choice of material and the pressure rating of the pipe components are important for both operating safety and for attaining the specified minimum operational life of the system.
The decisive factors are:
- operating pressure
- operating temperature
- medium transported
- duration of service.
Separate calculations are necessary if safety factors are different or the operational lifetime is modified.
In Australia we need to deal with joining both metric and inch piping systems; so we need to convert and understand how it measures up. For those unfamiliar with the difference between metric and inch sizes the following note may be helpful. In imperial systems, the sizes of pipes, fittings and other components such as valves are identified by reference to the nominal size of the bore of the pipe expressed in inches and fractions of an inch.
In metric systems, however, sizes are identified by references to the outside diameter of the pipe expressed in millimetres. For converting metric to imperial it should be understood that metric sizes are not simply inch sizes which have been converted into millimetres and called metric; their actual dimensions are slightly different and they are with the exception of 2½ ” (75 mm) and 5″ (140 mm) not interchangeable.
Water which has been produced using → Ion exchangers, reverse osmosis or distillation, but which still contains a residue of certain ions. Purified water (“aqua purificata”) prepared according to the → DAB (and used in many pharmaceutical products) belongs to this category. Its specific conductivity at 25°C lies between 1 µS/cm and 50 µS/cm. Water for injection (“aqua ad injectabilia”) used in hypodermic syringes is categorised in the → DBA as a “cleaner” pure water. It is used as a solvent and as a fluid for diluting those medicines which can be applied by injection or by infusion. Sterility is a prerequisite.
Water which is fully salt-free (deionized). It is produced by the use of ion exchangers or by distillation. The quality of the resulting product is codified by various standards (e. g. DIN, ISO 3696). No ionogenic contents (= anions and cations) may be present. The specific conductivity at 25 °C lies between 0.1 µS/cm and 1 µS/cm
Water of the very highest purity. It is made from distilled water using supplementary ion-exchange techniques, → Active carbon and other absorbing materials. It contains only the slightest traces of organic compounds, micro-organisms and electrolytes. The specific conductivity at 25 °C is less than 0.1 µS/cm.
Water can contain very many substances and has to be processed or purified according to its proposed use. The results are a variety of degrees of purity which can be characterised according to diverse criteria. [e. g. measurements of → Conductivity (electrical); determination of the amount of specific types of ion.]
Water with different qualitative features (its suitability as → Drinking water could be included) for business, industrial and agricultural purposes
Water with medium salt content, e. g. the mixture of fresh and salt water which is found at the mouths of rivers. The specific conductivity at 25 °C lies between 0.05 S/cm and 1 S/cm.
Water of a quality which conforms to the TVO (Trinkwasserverordnung = German Drinking Water Ordinance) regarding, for example, the maximum amount of pollutants. Drinking water has to be maintained at a temperature below 25°C. Its specific conductivity at 25 °C lies between 50 μS/cm and 5000 μS/cm.
GF Piping Systems would like to wish you a safe and enjoyable Christmas, and New Year. We look forward to a busy 2015 for all.
Please note that our blog will be not be monitored during the festive season from COB Tuesday 23 December 2014, until Wednesday January 7, 2014.
Please note our offices throughout Australia will be closed at midday Wednesday December 24, 2014, and will reopen on Monday January 5, 2014. If you have any urgent inquiries during this time, please contact Simon Naef on 0418 214 037.
Water hammer, or surge pressure, is a term used to describe dynamic surges caused by pressure changes in a piping system. They occur whenever there is a deviation from the steady state, i.e. when the velocity of the fluid is increased or decreased, and may be transient or oscillating. Waves of positive or negative pressure may be generated by any of the following:
• opening or closing of a valve
• pump start-up or shutdown
• change in pump or turbine speed
• wave action in a feed tank
• entrapped air
The pressure waves travel along at speeds limited by the speed of sound in the medium, causing the pipe to expand and contract. The energy carried by the wave is dissipated and the waves are progressively damped.
The pressure excess to water hammer must be considered in addition to the hydrostatic load, and this total pressure must be sustainable by the piping system. In the case of oscillatory surge pressures extreme caution is needed as surging at the harmonic frequency of the system could lead to catastrophic damage.
The maximum positive or negative addition of pressure due to surging is a function of fluid velocity, bulk modulus of elasticity of the fluid, pipe dimensions and the modulus of elasticity of the pipe material.
Pipe support for plastics pipes
Plastic pipe systems should be installed using supports designed for use with plastics and should then be installed taking care not to damage or over stress the pipe.
What is a loose pipe bracket?
A loose pipe bracket is a bracket which allows axial movement of the pipe, to allow stress free compensation of temperature changes and compensation of any other operating condition changes.
What is a fixed point?
A fixed pipe bracket is a bracket which prevents the pipe from moving in any direction. The aim of which is to control system stresses caused by temperature changes.
The outstanding chemical resistance of PVC-U extends to high concentrations; resistance against the influence of most mineral acids, bases and salt solutions and also sodium hypochlorite solutions is very good. Resistance to aliphatic hydrocarbons and elemental chlorine is also good.
PVC-U, in general, shows weakness against aromatic or chlorinated solvents, esters and ketones. Use with gases is also not recommended.
If the use of oils, varnish or fats is being considered, a prior investigation is advisable. These specifications are also valid – with exceptions – for adhesive joints, which normally are implemented by applying strongly dissolving gap-filling solvent cement to the PVC-U.
PVC-U is very resistant to weathering. Long-term influence of direct sunlight as well as the effect of wind and rain damage on the material is only superficial. Despite its very good weathering resistance regarding ultraviolet radiation, PVC-U loses some of its impact strength. In extreme applications it can be advantageous to protect the material from direct sunlight exposure.
Plastics constitute only a small percentage of the entire crude oil usage. But crude oil resources are limited. Already today we have to fall back upon raw materials which can be recycled and extend alternative energy sources. In this context we talk about re-usable raw materials.
All working processes need energy (heat, pressure, motor power). In comparison with metals, manufacturing plastics requires less energy. The production of 1 dm3 material requires an amount of energy which is given in kilograms oil equivalent per litre material in the chart below.