How to ...
How to ...
select and install pipe flanges
Pipe systems in the irrigation sector use a number of different jointing systems dependent on the pipe material , the operating pressure of the system and the need to be able to dismantle the system for maintenance or operational reasons . Flanged connections satisfy all of the above criteria and are an essential jointing system in the piping Industry . - by Mike de Villiers
INTRODUCTION
Standard pipe jointing systems vary from solvent cement and integral rubber ring joints in PVC , to compression and butt-welded joints in HDPE , insert joints in LDPE and quick couple joints in removable surface irrigation systems . However , when it comes to the interconnection of differing pipe and fitting materials , the jointing systems have to be compatible with each other . For example , HDPE pipes will utilise a compression male adapter to connect the pipe to say a female brass valve . The most commonly used jointing systems for interconnections in the smaller diameters are BSP threaded fittings , whereas flanged connections are used in the larger diameters . High pressure valves and pumps are usually manufactured from ductile iron , a specialised form of cast iron . The need to remove these items from the line for maintenance or replacement makes the use of flanged connections an essential feature . Flanged connections also enable the direct connection of different pipe materials to these items over a wide range of diameters .
FLANGE SPECIFICATIONS
A flange is a round piece of steel or plastic , with holes drilled around its circumference . Two flanges are used to complete a joint . They are bolted together with a rubber gasket between the faces , in order to achieve a water-tight joint . However , flanges are not that simple . Apart from the pipe diameter , one needs to consider the pressure rating as well as the flange specification , also known as the “ flange drilling ”.
South Africa has its technology rooted in Imperial dimensioning ( inches ). With the formalisation of the use of metric systems in the RSA in 1962 , flange options became far more complex and we live with this history to this day . BS 10 table D flanges ( Imperial dimensions ) are historically very popular in the Irrigation sector , however metric flanges to SANS 1123 is the industry standard for valves and pumps in the RSA . Note that Table D flanges are pressure rated at 600 kPa ( 6 bar ) and that SANS 1123 has tables that cover the entire pressure range up to 4000 kPa ( 40 bar ).
Needless to say , one cannot directly connect a Table D flange to a SANS 1123 flange because of the different dimensions . Flange suppliers , however , hold stocks of blank flanges and drill these according to demand , which mitigates some of the historical preferences for imperial flanges .
The pressure rating of a flange is dependent on the thickness of the disc as well as the size and number of holes drilled in the flange . The holes are drilled to accommodate the securing bolts that , when tightened , hold the two flange faces together . The size of the bolts is a very important aspect of the flanged joint , as the bolts have to withstand the massive pressure differentials that are at play , especially in valves during opening and closing functions .
The holes are drilled around the flange in a circle and each flange size , corresponding to the pipe size , has a different diameter measured between the bolt centres . This is known as the Pitch Circle Diameter , or PCD of the flange . Some of the smaller flanges , called universal or multi-drilled flanges , are compatible with both Table D ( Imperial ) and Table 1600 / 3 ( metric ) flange drillings , however multi-drilled flanges have a maximum pressure rating of 10 bar . Other drilling tables are available , such as BS 4504 ( Imperial ) and ASME 16.5 ( American ) but these are not common in the irrigation sector , they may be used on some specialised equipment . The “ tables ” mentioned above refer to the dimensional tables contained in the flange specifications , which are shown below . The tables below show the popular flange sizes . Refer to the full tables for the complete range of flange sizes .
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SABI | APRIL / MAY 2017