SOME OF THE ERECTION TOLERANCE FOR STRUCTURAL WORK IN A POWER HOUSE                   (TYPICAL)

-Foundation for columns ( Top elevation)                                                  - 20 mm / + 10 mm.

-Dimension between two adjacent foundations for columns                 1mm/metre max. up to + 5 mm

-Adjacent pedestal diagonal difference                                                 1mm/metre max. up to + 15 mm

- Foundation Bolt pitch difference                                                          + 3 mm

- Foundation bolt diagonal difference                                                    + / - 5 mm

- Grouting Gap for secondary Grout                                                        + 25 to + 70 mm (max)

- Individual Column sweep and Camber                                    1mm/metre max. up to + 10 mm

-Total length after pre-assembly                                                    + / - 15 mm

- Sweep and camber for total length                                               max 15 mm.

- Out of vertical                                                                      1mm/metre max. up to 25 M

- Elevation Tolerance at reference level                                           + 5 mm

- Level difference of supporting joints                                              5 mm

- Deviation difference between purlins                                              5 mm

- Crane Girder centre to center spacing                                              5 mm

- Crane girder top level                                                                      5 mm

- platform level difference                                                                  5 mm

- HSFG bolt tightening                                           ( as per size of the bolt with torque wrench )

- when truss span <  25  metre                                                            + /- 7 mm

- truu span is > 25 metre                                                                     + / - 10 mm

- Beam span is < 25 metre                                                                    + / - 10 mm

-Beam span is > 25 metre                                                                      + /- 15 mm

SOME OF THE FABRICATION TOLERANCES

Name of Deviation                             column          Beams           Crane girder

Base plate and column                          0.1 mm

Frame Joints                                         2.0 mm

Web and flange                                    1.5 mm         1.5 mm               0.1 mm

Web & stiffeners                                   1.5 mm        1.5 mm               0.1 mm

Flange & stiffeners Intermediate

 stiffeners & Bearing stiffeners:              1.5 mm       1.5 mm               0.1 mm

Cap plate & column                               0.1 mm

Crane girder seat                                   0.1 mm

Beam brackets                                      2.0 mm     

          PORTABLE HOLDING OVENS FOR WELDER 'S USE  AT WORK SITE.

  
 
           A TYPICAL SKETCH OF COLUMN FOUNDATION SHOWING MEASUREMENT PTS.

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STRUCTURAL WORK CONTINUED WITH WELDING

- Suitable electrodes are to be used for the structural steel.

- Generally low Hydrogen electrodes are used for plates more than 20 mm thickness.

- All low hydrogen electrodes shall be baked and stored before use as per manufacturer recommendations.The electrodes shall be re baked at 250 C - 300 degree C for one hour and later on cooled in the same oven to 100 degree C. It shall be transferred to an holding oven maintained at 60 degree C -70 degree C. The electrodes shall be drawn from this oven for use.

-  Minimum pre-heating and inter pass temperature for welding is given below.

-  Thickness of thicker part at the point of welding     Welding with low hydrogen electrode or SAW 

    Up to and equal to 20 mm thickness                                            none 

    Over 20 mm and Up to and equal to 40 mm                                 20 degree C

    Over 40 mm and Up to and equal to 63 mm                                 66 degree C

    Over and Above 63 mm                                                               110 degree C

-  Pre -heating can be done by LPG heating , electric resistance heating or by electric induction heating.

- Temperature can be checked by thermal chalk or putting Thermocouple ( generally Nickel-cromium-Nickel ) . The relation between temperature and voltage is 4.12 mv /100 deg c rise (approximately).

- Sequence of welding to be followed as per WPS and drawings .However a few basics may be noted.

- The direction of welding should be away from restraint point and should be towards open end.

- Butt weld in flange plates and/or web plates shall be completed before the flanges and webs are welded together.

- Generally The beam and column stiffeners shall preferably be welded to the webs before the web and flanges are assembled.

- All welders including tack welders to be tested as per IS codes and identity card to be issued for verification time to time during actual job.

- Carry out Non Destructive examination  RT / UT /LPI  as per requirement.

 A general view of fabrication yard where plates are getting cut into pieces for further fabrication.

 A general view of electrode drying oven . The electrodes are dried here and transported to holding oven.

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STRUCTURAL WORK IN A THERMAL POWER STATION

Structural work comprises of Power House structure , Gallery , Miscellaneous building structures , pipe and cable rack structures etc. It has two parts one is Fabrication and other part is erection. In India   structural work ( civil) are executed at site unlike Boiler and other equipment . The approximate tonnage involved in structural work is given below .

- For a project 2x210 MW unit the structural steel required is                 13000 MT.

- For a project 2x500 MW unit the structural steel required is                 29000 MT.

- For a project 2x660 MW super critical unit structural steel required is  30000 MT.

Fabrication for the above tonnage is also done at site.

 

STRUCTURAL STEEL.

Some of the standard sections of structural steel are given below  for ready reference.

Angles : Designation                             Size ( lxbxt)                      weight in kg/M

              ISA 50x50x6                           50x50x6                                     4.9

              ISA 50x50x5                           50x50x5                                     4.1

              ISA 65x65x5                           65x65x5                                     4.9

              ISA 65x65x6                           65x65x6                                     5.8

              ISA 65x65x8                           65x65x8                                     7.7

              ISA 75x75x8                           75x75x8                                     8.9

              ISA 100x100x10                    100x100x10                               14.9

              ISA  130x130x10                   130x130x10                               19.7

              ISA  130x130x12                   130x130x12                               23.4    

 Beam    ISMB 100                               100 X50 ( HXB)                         8.9

              ISMB 125                               125 X 70                                    13.3

              ISMB 150                               150 X 75                                    15.0

              ISMB 175                               175 X 85                                    19.6

              ISMB 200                               200 X100                                   24.2

              ISMB 250                               250 X125                                   37.3

              ISMB 300                               300 X140                                   46.0

              ISMB 400                               400 X 140                                  61.5

              ISMB 500                               500 X 180                                  86.9

              ISMB 600                               600 X 210                                123.0  

Channel ISMC 75                                 75 X40                                       7.14

              ISMC 100                              100X50                                       9.56

              ISMC 125                              125X65                                      13.10

              ISMC 150                              150X75                                      16.80

              ISMC 200                              200X75                                      22.30

( these are few section mentioned above generally being used in thermal power structural fabrication.)

Besides standard machine cut plates are also used such as 6mm, 8mm , 10mm,12mm, 16mm ,20mm, 28mm ,32mm ,40mm, 50mm up to 63mm. ETC.

- Fabrication to be done as per fabrication drawing developed from the structural drawing. There are companies available in India who makes the fabrication drawings / detailed drawing. The fabrication drawing includes every detail requires for fabrication.

- Welding of structural items are done by electric arc process  as referred in the drawing. For resolving any disputes these documents may please be referred. 1. Drawing . 2. Welding Procedure defined (WPS) .3. Welding Manual . 4. NDE manual .5. Relevant IS codes like 817 , 7215, 12843 ,1852 , 2062 , 9595, 3502, 1239, 3589 etc 6. ASME sec IX  7.

- Submerged arc welding shall be used for welding longitudinal fillet welds.

- Longitudinal / transverse butt joints for fabrication of columns, framing beams and crane girders and

all other built-up members.

- Efforts should be made to position the job such a way so that down hand welding is possible.

-Only qualified welders are to be employed for welding procedures and positions.

- Fillet weld members should be close enough so  that gap is 0mm. In no case the gap should be more than 3mm. For example if the fillet gap is found to be 2 mm then fillet size of the joint should be increased by 2 mm.

        

PUG MACHINE

CIVIL WORK FINAL SUBMISSION FOR THERMAL POWER PLANT

Foundation of steam Generator under progress. This is last lift of the foundation where all the foundation bolts are placed temporarily. Engineers are checking the same with the help of Total Stations so that bolts can  be  locked with the template before pouring of concrete.

Series of foundations are shown here . This includes raft ,pile cap and final lift of foundations including placement of foundation bolts. Concrete blocks shown in the pictures are for pile load testing. Some of the unbroken piles are also seen here.

This is a picture of TG bay inside power house on early day of construction On the above all main power TG Deck supporting structures for Turbine and Generator auxiliaries will come to existence.

Completed foundation at TG Bay is shown. Preparation of removing shuttering is under progress. Pocket cleaning and final dressing under progress before offering to mechanical sub vendor for final checking and erection of equipment.

Fuel oil ( LDO or HFO) tank erection under progress. Please see the foundation retainer wall .

During last write up we have mentioned about different testing and sampling to be done  as per  Field Quality Plan. Frequency of sampling and testing of some of the major ingredients are given below.

Frequency of sampling and testing

Grain Size  Analysis                                              One in every 2000cu.m /type/source     IS 2720

Shrinkage Limit & Free Swell index                     One in every 5000cu.m /type/source     IS 2720

Organic matter, Calcium Carbonate, PH etc          One in every 5000cu.m /type/source     IS 2720

Standard Proctor test , Moisture content of fill     One in every 2000cu.m /type/source     IS 2720

Dry density and Permeability Test                         Random Test 

Coarse Aggregate 

Particle Size and Shape ,Moisture Content           One in every 100cu.m /type/source  IS2836

Specific gra­vity , density, voids, absorp­tion                     Once in 12 weeks /source                    IS2836

Flakiness and petrographic examinations              Once in 12 weeks /source                IS2836

others ,soundness ,Reaction with alkali etc                        Random.

                         ( Acceptance criteria will be governed by IS383.)

Fine Aggregate /Sand 

Particle Size and Shape                                      One in every 100cu.m /type/source     IS2836

Specific gra­vity , density, voids, absorp­tion ,
Soundness and petrographic Examination,
Mortar making Properties , Reaction with
Alkali,.                                                               Once in 12 weeks /source                IS2836

Bulkage , Moisture Content (Routine test)         Every day                                        IS 2836

Cement

Setting Time , Comprehensive strength , Fineness  One sample from each Batch      IS 4031

Water

Harmful substances, pH value, initial

setting time, compressive strength.                 Once in a month/source        IS 456

Concrete

Slump and compaction Factor     One Sample/2hr / mixing plant     IS 1199 & IS456

Crushing Strength                                      IS 456                                IS 516

Water Cement Ratio , Cement content       Random                              IS 1199 

Thus we have completed our discussion on civil job of thermal Power station. If posted all 

queries will be answered . However please refrain from advertising product on blog. From

next writing we will discuss about the structural work of the power station.

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TYPICAL FIELD QUALITY PLAN FOR CIVIL WORK AT THERMAL POWER STATIONS.

Now we will discuss the common  Field Quality Plan  for Civil work .

- Classification of checks like A,B,C and D  depends on the importance of the activity . Most important activity which need vendor signature , consultant signature and customer signature is termed as A. B is slightly less important therefore may be or may not be require the presence of customer. Like that it goes up to D or more. All this  classification of checks should be discussed and finalised  before the start of work.

- Type of checks can be classified  as R = record verification , V = Visual , M = measurement , P = Physical , T =Test

Following are few items  subjects to field quality checks . These are samples only. There are many more items will be under FQP's  purview. 

  i)             Bricks

ii)             Earth Work

iii)            Cement

iv)           Fine Aggregate (Sand)

v)             Course Aggregate

vi)           Reinforcing Steel

vii)          Water

viii)         Form Work (Shuttering)

  ix)         Concreting

There are number of items which comes under FQP in civil work.

Area of Work :  Civil works              Sub System of Civil works : Bricks ; Activities : Construction

s.no.                 Description         toc         instrument   class        Ref. doc   frequency   format

1.0     Ensure that the bricks are 

          free from cracks, war page

          and of uniform colour.          V                                    B            IS codes     1:10000       protocol

1.1      Check for the dimension, 

          Check for bond / closers 

          thickness of joints in masonry,

          Line, level and plumb,          M   Tape ,spirit level       B           IS codes     1: 10000      Protocol

1.2     Compressive strength & 

          water absorption                   M    laboratory                B           IS codes     1:10000       Protocol

Earth work ( excavation , filling ,compaction etc)      

2.0    Standard Proctor Test           M   Laboratory                A            IS codes      Note 1        Protocol

2.1     Relative Density Index          M   Laboratory                A            IS codes      Note 1        Protocol

2.2    Dry Density by Core Cutter

        Method / Sand Displacement

        Method                                  M   Laboratory                A            IS codes      Note 1        Protocol

2.3   Moisture Content of Fill

       before Compaction                  M   Laboratory                A            IS codes      Note 1        Protocol

2.4  Dry density by Proctor

       Needle Penetration                  M   Laboratory                A            IS codes      Note 1        Protocol

Cement

3.0  a)  Consistency of cement       M   Laboratory                A            IS codes      Note 2        Protocol  

Initial and final setting time    (vicat needle)

Compressive strength              (testing m/c)

  3days & 7 days

 4.0 Sand  ( Types of Test carried out on sand before acceptance )

a)      Silt & Clay content    M   Laboratory             A            IS codes      Note 3        Protocol  

b)     Sieve analysis (Particle size and shape)

c)      Bulking of sand

d)     Specific gravity, density, voids & absorption

e)      Moisture content

f)      Deleterious materials

g)      Petrographic examination

h)     Soundness

 i)  Reaction with Alkali :

 Mortar making properties 

5.0 Coarse Aggregate  (Types of test carried out on coarse aggregate  before acceptance.

a)      Sieve Analysis (Particle Size and Shape)

b)     Moisture content

c)      Specific gravity

d)     Crushing Strength

e)      Bulk density

f)      Absorption value, Abrasion value & Impact Value

g)      Voids

h)     Soundness

i)       Reaction with Alkali

j)       Petrographic examination

k)     Deleterious materials

l)       Temperature Cycle test

m)    Flakiness

   

The above tests are carried out site Laboratory as per IS codes mentioned in the FQP ,measured and protocol ed .

For actual work tests mentioned in the FQP to be followed strictly. FQP mentioned above  is only for example.

SOME OF THE LABORATORY EQUIPMENT SHOWN ABOVE.