In last few blogs we have discussed about the NDE procedure and process adopted
in a large thermal power station. Therefore it is time now to discuss about the work
to be carried out at field.
- We have to remember that for erection of critical piping only winches will help
no crane facility will be available. The whole erection procedure will be done by
winches , chain pulley block , max puller etc.
- For a boiler which is having side mill configuration the critical piping will come
between boiler front and De aerator BAY. The critical piping will start from SH
outlet to turbine and also going back from IP turbine to re heater header.
- Erection of MS valve comes under critical piping and it weighs around 8 to 10 T.
- The height will be around 85M to 90 M depends up on boiler. For large boiler
like 500 MW to 660 MW all these pipes will be of P91 material and tack welding
on P91 pipes are strictly forbidden only clamps are to used.
- It will be advisable to erect the permanent support en route rather than hang the
pipes on temporary supports. This activity is easy to tell but difficult to follow
in India. We have not succeeded in project hope in coming days this may be
achieved.
- Before start of erection one has to study the isometric drawings extensively and
find out the support structure is available or not and there is no fouling with structure
up to turbine . This is very important because any fouling will delay the process
of erection. This is known to every construction worker that path of critical piping
can not be changed without the permission of IBR authority and designer concern.
- Along with piping studies all the support structure with support should be made . It
may occur one or two supports need to be relocated at new place or one two supports
may entirely change . Please note with caution any change in support location from
its position mentioned in the drawing is not permitted without the consent of designer.
Designer locate those support after doing the stress and strain analysis of the pipe
through a software called "ceasure ". Therefore you may not know the impact of new
location on pipeline . It is highly recommended to consult designer regarding this take
technical approval from him. No deviation is generally accepted in this rule as failure
of support and pipeline occurs during steam blowing.
- During study of drawing identify the joints required to be welded at site and mark them
as per site procedure.
- Identify the straight length and pre-assembly joints to be carried out at ground level.
- For P91 induction heating machines are required for pre-heating , post -heating and
stress relieving cycle. In a 500MW or 66oMW critical piping around 20 joints to 30
joints can be done in pre-assembly with little bit of planning. Please note that a P91
joint in large power plant need at least 72 hours from start of pre-heating to end of
stress relieving cycle. Stoppage of cycle in between will attract non conformities therefore
not allowed. It is therefore recommended installation of DG set to carry out the welding
and other process during power cut. Sizing of DG set can be chosen judiciously after
seeing the site condition .
- A defect in the route for a main steam line will take 07 days from start to finish. As P91
material is very hard grinding will take enormous time. It is therefore recommended to
take every precaution to avoid any defect on welding. Any doubt on welding process to
be cleared before hand through discussion and in that loop welding supervisor , welders
are to be included.
in a large thermal power station. Therefore it is time now to discuss about the work
to be carried out at field.
- We have to remember that for erection of critical piping only winches will help
no crane facility will be available. The whole erection procedure will be done by
winches , chain pulley block , max puller etc.
- For a boiler which is having side mill configuration the critical piping will come
between boiler front and De aerator BAY. The critical piping will start from SH
outlet to turbine and also going back from IP turbine to re heater header.
- Erection of MS valve comes under critical piping and it weighs around 8 to 10 T.
- The height will be around 85M to 90 M depends up on boiler. For large boiler
like 500 MW to 660 MW all these pipes will be of P91 material and tack welding
on P91 pipes are strictly forbidden only clamps are to used.
- It will be advisable to erect the permanent support en route rather than hang the
pipes on temporary supports. This activity is easy to tell but difficult to follow
in India. We have not succeeded in project hope in coming days this may be
achieved.
- Before start of erection one has to study the isometric drawings extensively and
find out the support structure is available or not and there is no fouling with structure
up to turbine . This is very important because any fouling will delay the process
of erection. This is known to every construction worker that path of critical piping
can not be changed without the permission of IBR authority and designer concern.
- Along with piping studies all the support structure with support should be made . It
may occur one or two supports need to be relocated at new place or one two supports
may entirely change . Please note with caution any change in support location from
its position mentioned in the drawing is not permitted without the consent of designer.
Designer locate those support after doing the stress and strain analysis of the pipe
through a software called "ceasure ". Therefore you may not know the impact of new
location on pipeline . It is highly recommended to consult designer regarding this take
technical approval from him. No deviation is generally accepted in this rule as failure
of support and pipeline occurs during steam blowing.
- During study of drawing identify the joints required to be welded at site and mark them
as per site procedure.
- Identify the straight length and pre-assembly joints to be carried out at ground level.
- For P91 induction heating machines are required for pre-heating , post -heating and
stress relieving cycle. In a 500MW or 66oMW critical piping around 20 joints to 30
joints can be done in pre-assembly with little bit of planning. Please note that a P91
joint in large power plant need at least 72 hours from start of pre-heating to end of
stress relieving cycle. Stoppage of cycle in between will attract non conformities therefore
not allowed. It is therefore recommended installation of DG set to carry out the welding
and other process during power cut. Sizing of DG set can be chosen judiciously after
seeing the site condition .
- A defect in the route for a main steam line will take 07 days from start to finish. As P91
material is very hard grinding will take enormous time. It is therefore recommended to
take every precaution to avoid any defect on welding. Any doubt on welding process to
be cleared before hand through discussion and in that loop welding supervisor , welders
are to be included.
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