ABC OF THERMAL POWER PLANT: FINAL PART OF CRITICAL PIPING -ABC OF THERMAL POWER PLANT

For critical Piping and Large LP piping are very important areas of thermal Power Station .

Erection of the piping starts around 16 -18 months from Zero date

( Project Zero date) and continues up to 32 to 35 months for a super thermal power project.

It has been observed that all critical materials and their accessories were imported from

developed countries because of their material composition. New material are introduced

to reduce the overall weight of the package in turn it will reduce the structure weight

(sizing) ,hanger sizes etc.

Because of that, restriction on welding are imposed . One has to follow Welding

Procedure Sheet given by OEM in totality . No compromise should be made.

Otherwise bigger problem will be crop up in coming days. Now for this welding you

require different consumables starting from filler wire, welding electrode

( 2.5 ,3.15,4 mm) , gases specially argon , and many other items required during

welding. Most of the items are available in India but electrode and filler wire may

not be available at the time of crisis. It is advisable to calculate the requirement

before hand and keep checking the stock available . This is

true for critical piping area only.

All the critical piping drawings to be taken and mark the joint number as per code followed

at site. Calculate the requirement of filler rod ( including wastage ) and welding electrode

different sizes. This will give fair amount of idea about the requirement.

Always check the straight and associated fitting specially internal Diameter. Piping

vendor may source it from different countries . There are developed countries

who may not be Following ASME or IBR code . Error happens may be very less but it

comes out at later date and there will be no time for fresh procurement . The project

will suffer for that.

Please also verify the availability of Test material ( welder test) at your disposal.

You need few materials to qualify your HP welder in P91 /P22 etc both pipe and tube.

A concept of orbital welding is now getting popular in India. This type of welding is being followed in developed countries at site but in India the same is limited to manufacturing unit only.

A short description of Orbital welding is given below .

Orbital welding uses the gas tungsten arc welding (GTAW) process as the source of the electric arc that melts the base material and forms the weld. In the GTAW process, an electric arc in established between a tungsten electrode and the part to be welded. To start the arc, a high-voltage signal is used to break down (ionize) the insulating properties of the shield gas and make it electrically conductive to pass through a tiny amount of current. A capacitor dumps current into this electrical path, which reduces the arc voltage to a level at which the power supply can then supply current for the arc. The power supply responds to the demand and provides weld current to keep the arc established. The metal to be welded is melted by the intense heat of the arc and fuses together.

Following sizes of pipes are generally used in a super thermal power station.

Sl No.	Base Metal	Dia.(mm)	Thickness(mm)
1.	SA182F22CL3	356	45
2.	SA335P12	356	45
3.	SA234WP12CL1	300	45
4.	SA182F12CL2	559	67.3
5.	SA106GC.C	559	67.3
6.	SA105	356	46.3
7.	SA 335P22	508	63.1
8.	SA182F12CL2	219	34
9.	SA335P12	219	34
10.	SA234WP12CL1	219	34
11.	SA234WP91	450	63.5
12.	SA335P91	457	63.5
13.	SA324WPC	500	63.1
14.	SA234P91	470	60
15.	SA234P91	89	15.5
16.	SA234P91	630	85

There are many reasons for using orbital welding equipment. The ability to make high quality, consistent welds repeatedly, at a speed close to the maximum weld speed, offer many benefits to the user:

1. Productivity. An orbital welding system will drastically outperform manual welders, many times paying for the cost of the orbital equipment in a single job.

2. Quality. The quality of a weld created by an orbital welding system (with the correct weld program) will be superior to that of manual welding. In applications such as semiconductor or pharmaceutical tube welding, orbital welding is the only means to reach the weld quality requirements.

3. Consistency. Once a weld program has been established, an orbital welding system can repeatedly perform the same weld hundreds of times, eliminating the normal variability, inconsistencies, errors, and defects of manual welding.

4. Skill level. Certified welders are increasingly hard to find. With orbital welding equipment, you don't need a certified welding operator. All it takes is a skilled mechanic with some weld training.

5. Versatility. Orbital welding may be used in applications where a tube or pipe to be welded cannot be rotated or where rotation of the part is not practical. In addition, orbital welding may be used in applications where access space restrictions limit the physical size of the welding device. Weld heads may be used in rows of boiler tubing, where it would be difficult for a manual welder to use a welding torch or view the weld joint.

Few pictures of weld held is given below for information.