Hydraulic Shock

Hydraulic shock is the term used to describe the momentary pressure rise in a piping system which results when the liquid is started or stopped quickly. This pressure rise is caused by the momentum of the fluid; therefore, the pressure rise increases with the velocity of the liquid, the length of the system from the fluid source, or with an increase in the speed with which it is started or stopped.

Examples of situations where hydraulic shock can occur are valves, which are opened or closed quickly, or pumps, which start with an empty discharge line. Hydraulic shock can even occur if a high speed wall of liquid (as from a starting pump) hits a sudden change of direction in the piping, such as an elbow. The pressure rise created by the hydraulic shock effect is added to whatever fluid pressure exists in the piping system and, although only momentary, this shock load can be enough to burst pipe and break fittings or valves.

Christmas Post 2015

GF Piping Systems would like to wish you a safe and enjoyable Christmas, and New Year. We look forward to a busy 2016 for all.

Please note that our blog will be not be monitored during the festive season from COB Wednesday 23 December 2015, until Wednesday January 6, 2016.

Please note our offices throughout Australia will be closed on Thursday December 24, 2015, and will reopen on Monday January 4, 2016. Contact our customer service team to ensure we can meet your requirements before we close for the festive season.

Effective handling and transporting of pipes

Vehicles used to transport pipes must be capable of accommodating the full pipe length. The pipes must be supported to prevent them bending or deforming. The area where pipes rest (including side supports) should be lined with padded sheeting or corrugated cardboard to avoid damage by protruding rivets or nails. To prevent damage, pipes and fittings must not be slid over the transport vehicle’s loading area, nor should they be dragged along the ground to their place of storage.

Due care must be taken with loading and unloading. If lifting gear is used, this must be fitted with special pipe grips. Throwing pipes and parts down from the cargo surface is unacceptable.

Impacts must be avoided at all cost, especially at ambient temperatures below 0°C where many plastics (e.g. PVC) have significantly lower impact resistance.

Pipes and fittings must be transported and stored so that they cannot be soiled by earth, mud, dirty water, etc. It is recommended sealing pipes with protective end caps to prevent dirt entering the pipes.

 

Pressure loss with valves and fittings in pipelines

The pressure losses depend upon the type of fitting as well as on the flow in the fitting. The so-called ζ-value is used for calculations.

To calculate the total pressure loss in all fittings in a pipeline take the sum of the individual losses, i. e. the sum of all the ζ-values. The pressure loss can then be calculated.

The kv factor is a convenient means of calculating the hydraulic flow rates for valves. It allows for all internal resistances and for practical purposes is regarded as reliable.

The kv factor is defined as the flow rate of water in litres per minute with a pressure drop of 1 bar across the valve.

Pressure loss in straight pipes

When calculating the pressure loss in straight pipe lengths there is a distinction between laminar and turbulent flow. The important unit of measurement is the Reynold’s number (Re). The changeover from laminar to turbulent flow occurs at the critical value, Reynold’s number (Re) = 2320.

Laminar flow occurs, in practice, particularly in the transport of viscous media, i. e. lubricating oil. In the majority of applications, including media similar to water, a turbulent flow, having an essentially steady velocity in across-section of pipe, occurs.

Recommended material for compressed air pipelines

For compressed air pipelines PE (Polyethylene) or PB (Polybutylene) is recommended, typically jointed using fusion i electrofusion, socket fusion, or mechanical jointing ie compression, or other mechanical fittings.

Both PE and PB materials are lightweight, easy to install and corrosion-proof; they also have the advantage of high tensile strength and are good thermal insulators thus minimising variances in compressed air temperature. Hence, polyethylene up to a minimum temperature of -40 °C (e. g. outdoor applications), polybutylene up to a minimum temperature of 0°C (e. g. indoor installations) is recommended. Danger of explosion is excluded if you follow the operating instructions.

PE and PB are generally chemically resistant to compressor oils. Only for a few oils, which contain esters or aromates, chemical resistance cannot be guaranteed. Sealing materials, such as NBR or FPM, which are regularly used for compressed air networks, are also endangered in such cases.

In order to make it easier for the operator of a compressed air system to choose a compressor oil, GF Piping Systems have summarised many of the oils offered on the market and have divided them into sections according to their chemical structure. After consulting the oil supplier, it is also possible to choose an oil which is not on the list since we do not claim its entirety. The type of oil used must be included in one of the categories deemed by GF as suitable. Also recommend that the oil selected is approved by the compressor manufacturer as well.

For further information refer to PIPA POP002 Industry Guideline (POLYETHYLENE (PE) PIPES AND FITTINGS FOR COMPRESSED AIR).

The chemical resistance of PVC-U, PE and PP against disinfectants

GF Piping Systems have undertaken extensive tests to investigate the behaviour of a large number of commercially available disinfectants when transported in pipes and fittings made of PVC, PE and PP. Our tests on PVC have been supplemented by further tests carried out by the Henkel company, Düsseldorf.

Results of earlier preliminary tests served as the basis, providing the following criteria:

  1.  Disinfectant solutions have a strong capillary force. Pipe joints must therefore be treated with extreme care.
  2. The make or type of disinfectant is likely to be changed several times during the operating life of such a piping system.
  3.  Different disinfectants have different compositions and behave differently towards plastics.

The purpose of the experiments was to compile a planning guide taking into account the above criteria. For testing the resistance of the pipe material, the specimen was filled with disinfectant instead of water and long-term internal pressure tests were carried out as stipulated in the standards. The pipe joints suited to each pipe material were tested at the same time.

Disinfectants are usually aqueous or alcoholic solutions containing special active agents against microbes. They usually also contain detergents, whose capillary force enhances the antibiotic effect. Chlorine separators may also be used, depending on the application. The pH value may vary within certain limits, from slightly acidic to slightly alkaline, but this has practically no effect on the resistance of the plastics.

The tests encompassed pipes and fittings made of PVC, PE and PP as well as the appropriate joints.

PVC-U (Polyvinyl Chloride)

The different disinfectants investigated affected PVC in different ways. The long-term durability results for PVC with water were only partly equalled. With some of the disinfectant solutions tested, the specimen failed prematurely due to stress corrosion.

All the solvent cement joints tested remained leak proof up to the failure of the test specimen.

The required test duration could only be achieved by lowering the test pressure. The resulting load corresponded to that given in the standards for dangerous media against which PVC is resistant.

It was seen from these tests that stress cracking can only be expected at relatively high circumferential stresses, or after extensive periods of under load. The effective load placed on piping components in practice results from the internal pressure and possibly from transmitted stress occurring from the installation conditions.

PE (Polyethylene)

The nominal long-term duration of the pipes was equalled or exceeded with each of the disinfectants tested. The socket fusion joints remained leak-tight until testing was discontinued long after the nominal duration had been exceeded.

PP (Polypropylene)

PP proved not to be resistant to any of the disinfectants tested. The test specimens failed in every case even before reaching the minimum test duration.

What is an Environmental Product Declaration (EPD®)

An Environmental Product Declaration, EPD®, is a verified document that reports environmental data of products based on life cycle assessment (LCA), Product Category Rules, and in accordance with the international standard ISO 14025 (Type III Environmental Declarations), giving them wide-spread international acceptance.

The EPD® logo type and the acronym EPD® are registered trademarks within the European Union and use of them within the EU is therefore only allowed for certified EPDs within the International EPD® System.

The Australasian EPD® Programme was established by ALCAS (Australian Life Cycle Assessment Society) and LCANZ (Life Cycle Association of New Zealand), based on the framework set up by the International EPD® System.   All EPD®s in the Australasian EPD® Programme are published within the International EPD® System, for global alignment and market visibility.

What’s the Purpose and Benefits of an EPD ?

The overall goal of an EPD® is to provide relevant and verified information to meet various communication needs. An important aspect of EPD® is to provide the basis of a fair comparison of products and services by their environmental performance.  The methodology includes all relevant environmental impacts starting from the production of the raw material, to production, use of the product, through to the end of life (cradle-to-grave) eg raw material extraction, transportation to converters, converting process, transport to trench, construction, use and end of life.

EPDs are increasingly recognized in international markets and being demanded within procurement processes.  Green rating tools recognize EPDs, such as the Green Star tool of the Green Building Council Australia, which includes EPD Innovation Credits and LEED v4

An EPD ensures that you can effectively communicate your environmental credentials to your clients and avoids risks associated with unsubstantiated environmental claims (e.g. greenwash).

Further information:

www.epd-australasia.com

Georg Fischer has prepared five EPD’s for PE, PP, PVC, PVDF and PB plastic pipe systems in line with EN 15804 “Sustainability of construction works – environmental product declarations – Core rules for the product category of construction products”

http://www.gfps.com/content/gfps/country_AU/en_GB/about-GF-PipingSystems/sustainability/material.html

 

Which plastic piping material is best for the transportation of disinfectants?

Plastic pipes are widely used for the transportation of disinfectant solutions. Selecting the material requires great care since some types of disinfectant solutions can damage certain thermoplastics.

A series of tests were carried out in which PE proved to be suitable without reservation, whereas PP failed completely. PVC is also suitable, as long as certain rules are adhered to when making solvent cement joints and when establishing the operating conditions.

PVDF pipes are also suitable for these kinds of applications.

For several years now plastic pipes and fittings have been preferred for transporting disinfectant solutions in hospitals and clinics. Certain characteristics of disinfectants and the working conditions must be taken into account when planning the pipeline, e. g. in selecting the pipe material and the type of joints to be used.

This topic will be further examined in the next blog edition.

Cooling Calculation Tool

The COOL-FIT/iFIT calculation tool allows you to calculate all the pipe system parameters important for cooling, such as pressure loss, heat emission, contraction and temperature loss.

About the calculations
You can select a calculation type from the menu. It is possible to make different calculations such as Pressure loss, Condensation, Heat loss, Contraction and Temperature loss. Under the menu Supports, a table with recommended support distances are available. “Data” includes different kinds of documentation e.g. formulas and specifications of materials and fluids.Find the Cooling Calculation Tool at:

http://www.gfps.com/content/gfps/country_AU/en_GB/support_and_services/online_tools/cooling.html

If you have any questions regarding the tool or the data shown, please do not hesitate to contact us by replying to the blog or email australia.ps@georgfischer.com