- In an isometric drawing of Piping following points may be looked into.
- BOM ( Bill of Material) , Pipe routing with General Arrangement Drawing , Supporting
arrangement , Hydro test Pressure , Provision of drains and vents etc.
- All of the pipes will come in pieces and stubs are welded on it. The same is to be either
pre-assembled or erected and assembled at site. When fluid is gas , steam or air connection
will be from top and in case of water or fuel the connection will be at the bottom. This
type of arrangement is being followed in general.
- We provide high point vent to remove air from the pipeline and low point drain to remove
condensate or liquid after hydro test.
- When there is rise of steam pipeline against the flow of pipelines we provide drip leg to remove
condensate from the pipeline .This is to avoid water hammering in the pipe line .
- Steam lines with following lines come under the purview of Indian Boiler Regulation.
line for which design pressure is > 3.5 kg/cm2 .
line size above 10" with one 1.0 Kg/cm2 pressure.
- Normal upstream and down stream length required for an orifice flow meter is 15D
and 5D respectively.
- The thumb rule of two consecutive butt weld id 1D.
- Following hardness test are followed at site.
- Rockwell hardness test , Brinell Hardness test and Vickers hardness test.
- At site we carry out DE and NDE test. DE means destructive test such as bend test ,
Impact and hardness test. NDE means non-destructive test such as Radiography ,
Ultrasonic , Dye penetration test and Magnetic penetration test.
- In general Hydro test pressure is 1.5 times design pressure of the system.
For design temperature above the test temperature minimum test pressure can be
calculated as follows :-
P( test) = ( 1.5 * P* St)/ S
where P(test) = Minimum test Pressure ; P = internal design pressure.
St = Allowable stress at test temperature ; S = Allowable stress at design temperature.
- Stress Analysis now a days are carried out through a software . Stress analysis is done
at design stage to ensure that piping system stress is within limit and to solve dynamic
problem like mechanical vibration , pulsation , fluid hammer etc. Stress analysis is also
done to solve problems associated with temperature. This is designer domain and site
never does it therefore only a glimpse is given.
- Name of the few stresses are Axial stresses ( Tensile/ Comprehensive) , Shear Stresses ,
Radial Stresses and Hoopes Stresses.
- Stress formula due to thermal expansion is
stress developed - E * e/L ; E= Young' modulus ; e = Increase in length due to thermal
expansion ; L = original length of pipe.
- For calculating thermal expansion following formula is used.
E (expansion) = Co-efficient of expansion * L ( length of Pipe)* T ( temp differential).
- One of the major work of stress analysis is to locate hanger supports and anchor points.
For calculating that different loads are considered ( primary loads , secondary loads and
occasional loads ).
- Site has to locate the hanger accurately at the place marked in the drawing. Any displacement
form the designed location due to interference should promptly be reported to designer for his
acceptance . He can do analysis and confirm about displacement. Number of instances known
to me about failure in piping system due to above. All site engineer should be cautious in this
area.
-Pipe strain may distort the alignment of rotating equipment . Therefore it is customary
before welding the last joint with the machine freeness of pipes has been checked with
all supports are on line . This we did in case of Boiler Feed Pump and Turbines. Welding
will not start until and unless competent authority checks the freeness.
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