TIPS ON CRITICAL PIPING ERECTION- ABC THERMAL POWER STATION

A few information on critical piping is written below for knowledge:-

Life cycle designed for critical piping is 30 years approximately.

All the piping  design ,erection and testing will be done according to ASME code 31.1 and Indian Boiler Regulation.

Inside diameters of piping shall first be calculated for the flow requirement of various systems. For that velocity of fluid flow to be known ( e.g for 660MW Main Steam Piping is 76M/sec , BFD (4.0-6.0 M/sec).

Piping system shall be of carbon steel for design temperature up to 400 deg. C and alloy steel for design temperature above 400 deg. C.

To account losses /drops 1.00/0.75 mm thickness are added on calculation based on ASME B31.1.

All high points in piping system shall be provided with vents. All low points shall be provided with drains. Provisions of drains on steam piping shall be as per ASME code TDP-1.

All piping shall be sloped towards the system low point such that slope is maintained in both hot and cold condition.

All drain and vent lines in piping system with design pressure 40 Kg/cm2 (g) and above or with vacuum service shall be double valved.

A clear head room of not less than 2.5 metres above the walkways/working area is available .

Cold pulling is not permitted.

All hangers and supports shall be erected such that they are vertical when the piping is in hot condition (rated parameters).- Important

Maximum cladding temperature after insulation should be approximately 60 degree C.

All stubs welded to the pipe including welded thermowells and instrument source tappings shall be installed on the pipe prior to stress relieving.

For all globe and check valves, the direction of flow to be clearly stamped on the body of the valve.

Where control valves, flow nozzles, orifices and other piping items are to be installed, they shall be installed only after steam blowing and chemical cleaning operation. After the completion of the steam blowing/chemical cleaning spool pieces will be removed and original components installed.

Field run piping shall be erected only after completion of erection of all other piping system, structures and equipment.

The hydrostatic testing of the piping system shall be done after proper installation of all permanent hangers/supports. Spring hangers shall be locked during hydrostatic test. Prior to steam blowing all hangers which had been locked for the hydrostatic testing shall be unlocked.

 All piping systems shall be hydro tested at 1.5 times the design pressure subject to regulation of 374 IBR. However, for such systems where it is practically not possible to do hydro tests, the tests as called for in ANSI B31.1& IBR in lieu of hydro test shall also be acceptable.

Two or three major problem arises during erection of critical piping of super thermal power. One is mismatching of Internal diameter of pipe and fittings differences ranges between 10 -15 mm . The other problem belongs oversize pipe which was cut to size and fouling ,shifting of hanger support.

A few pictures are attached to elaborate piping.

Area is Boiler furnace roof top and i.e starting point of critical Piping.

For 500 MW /600 MW or lesser sub critical unit boiler down comers are erected

first . Here the unit is 660 MW super critical therefore with downcomer seperator piping is also can be seen.

heating and stress releiving equipment for Pressure Parts and critical Piping.

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