CONSTRUCTION TIPS ON PRESSURE PARTS ERECTION FOR A THERMAL POWER PLANT.

Colour Coding of filler wire

Specification                                   Brand Name            Colour Code

RT ½ Mo (ER 80s-D2)                      TGSM                        Green

RT 1 Cr ½ Mo (ER 80s –B2)           TGS 1CM             Silver grey/white

RT2 ¼ Cr 1 Mo (ER90s –B3)          TGS 2CM             Brown /Red

RT 9 Cr 1 Mo ¼ V                            TGS9Cb                     -

RT 347 (ER 347)                               TGS -347             Blue

Low and extra low Hydrogen Electrodes    

As per IIW (Indian Institute of welding) classification of Hydrogen

Content classify electrodes is given below.

High   : greater than 15 ml /100gm

Medium: 10-15 ml /100gm

Low: 5-10 ml /100 gm

Extra low: less than 5 ml /100 gm

Baking, Storage and Handling

The electrodes have tendency to pick up moisture when exposed

to atmosphere and the amount depends on the time, relative humidity

and also the type of coating on the electrode. The recommendation

of baking electrodes are given below.

AWS Classification              Baking temperature & Time   Holding temp

E-7018                                 250-300 & 2 hrs                        100 deg C

E-7018 -1                            250-300 & 2 hrs                        100 deg C          

E-7018- A1                         250-300 & 2 hrs                        100 deg C

E -8018 –B2                       250-300 & 2 hrs                        100 deg C

E-9018- B3                         250-300 & 2 hrs                        100 deg C

E-8018- B2L                      250-300 & 2 hrs                         100 deg C

E-9018 –B3L                      250-300 & 2 hrs                        100 deg C

E309 & E347                      250-300 & 1 hr                          100 deg C     

** - After issue the electrode from site store to welder the temperature

Portable oven should be around 65 to 70 deg C during actual use by welder.

This is not applicable to E309, E347 and E 6013.

Selection of electrodes for non –pressure parts work

Material P1 + P1

A. For butt welds, up to 6mm inclusive:  E6013

                                      

                                       > 6mm            :  E7018

B. For fillet welds up to 8mm inclusive    :  E6013

                                      

                                    > 8mm                   :  E7018

Carbon Steel + P1                                     : E6013 or E7018

Carbon steel + Carbon Steel                     : E8018 –B2

Note: E6013 can be used for all non load carrying welds of all thickness

of IS2062 plates 20mm thickness and 8mm fillets. For structural material

like Ceiling Girders thickness of material is > 63 mm needs preheating (120

Degree C) and stress relieving (600-700 degree C) depends on material.

Common Knowledge required by construction supervisors engaged in boiler work

Weight Calculation for tubes:-

W = (D-1.1425t) x 1.1425t x 0.024466 Kg/M

           

            W= Weight of the tube in kg/M

            D = Specified outside diameter in mm

            t = Specific thickness

Weight Calculation For pipes:-

W = (D-t) t x 0.02466 kg/M

         

           W- Weight of pipes in Kg/M

            D- Specified outside diameter

            t - Specified thickness

Weight Calculation for ID controlled pipes/tubes

  

W = (Dot) t x 0.02466 kg/M

           

            W- Weight of pipes in Kg/M

            D- Specified outside diameter

            t - Specified thickness

 Temperature Measurement

For measuring the stress relieving temperature we generally use

Thermocouples. The thermoelectric voltage in a thermocouple depends

 on the temperature difference between two junctions and is used and

is used for the purpose of temperature measurement when one of the

temperature is known. At project site we use Chromel – Alumel thermocouple

popularly known as “ K “type.

Colour Code of thermocouple is yellow (+) and Red (-) over all Brown.

(Polarity +/- should be known otherwise it will give erroneous reading)

Thermocouple extension wire Yellow (+) and Red (-) overall yellow.

(Thermocouple can only be connected by thermocouple extension wire not

by any other wire)

There are other types of thermocouple but in India “K” type is only used at

the project site. The temperature – milivolt curve is linear. The increase is

4.13 mv per 100 degree C. (approximately)

Radiography Source

In India for industrial radiography we use two type of source i.e Cobalt -60

and Iridium -192. Out of that use of Cobalt -60 is extremely unpopular

because it requires stringent safety precautions to be followed and it

affects the progress of work. Instead of cobalt -60 now a day’s all are

using ultrasonic machine to detect the fault. Ultrasonic machine requires

Test block (made of same material to be tested) to be made as per the

Specification of IIW.

Iridium -192 is having half life of 74.4 days. All our pipes and tubes are

Radio graphed by this source except pipe /structural thickness of > 60 mm.

In those cases only UT is performed. The Iridium source should be more

than 30 Curie strength. It will require less exposure time and time can be

saved. Exposure time is inversely proportional to the strength. In 500MW

/660 MW boiler around 10,000 to 12000 shots are taken.

For surface defects of welds two very simple tests are carried out (i) Magnetic

particle test (ii) Dye Penetration test. 

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