Question

A gas pipeline with the thickness of 4mm is to be joint together by using welding process. You as an engineer need to choose the appropriate type of welding process to be used to weld the pipes. Elaborate your choice by evaluating and comparing the welding process you choose with the other welding processes to come to the decision

subject : manufacturing process

Answer 1

As we study the welding processes , there are variety of welding techniques available today for the fabrication work.These include solid state welding , arc welding , resistance welding , gas welding, brazing & soldering etc.But the selection of proper welding technique for the desired application needs the understanding of the material to be joined,quantum of work, envirnment & availability the equipment and cost of production.

For the gas pipeline we might need number of welds and quality of weld is of important consideration for selection.Since cost of rework is high due to off shop testing. Most of the time pipe material used for the gas carrying is steel or copper. Hence the suitable welding for the steel can be oxyful gas welding or resistance welding or arc welding. Now we have to choose the best amoung these. Here we will consider the merits and demerits of each process seperately and then arrive at final selection.

1.Gas Welding. :- This technique uses the oxygen & acetylene for the generation of heat to melt the metal rod into the pool of the joint. This welding can be used for the all types of welds and positions where overhead positions are bit difficult as compared to other techniques. As compared to the arc welding the filler material and heat source are different hence controlled seperately for the better quality of the weld. The equipement used can be used for gas cutting operation & brazing too. The main demerit of this technique is it's slower comparing the Arc and resistance welding processes. Safety is one of the concerns while using the acetylene and oxygen cylinders.

2.Resistance Welding :- Resistance welding process uses heat and pressure to make the joint. Heat is produced due to the electrical resistance of the joint.This process does not use any filler material or flux. The advantages of this process are the automation of the process & less skill of labour since these are based on machinery. This process have high production rate hence suitable for mass production. While its not suitable for field work & very thin joints.

3.Arc Welding :- Arc welding is one of the most versatile and widely used joining techniques in the fabrication industry today. Its because of its efficiency to generate heat by an electric arc, ease of operation & high productivity rate.There are varieties in arc welding as SMAW , GTAW & GMAW etc. These can be done in all welding positions. For thin welds(3mm-6mm) these are the best techniques to go with.The disadavantage of these processes is that it requires skilled personel with experience.

Considering the above three major welding techniques suitable process for gas pipeline with 4 mm thickness , Arc welding (SMAW/GTAW) is the best choise. The choice is based on below mentioned views.

1. Since pipeline welding is a field work which require all position welding , which can be easily done by SMAW , GTAW as per the material of the pipe, envirnment, availability of the consumables.Since at fields or sites, there are difficult welding conditions ,unavailaibility of fixures for set-ups.Hence SMAW or TIG are suitable due to less fit ups ,easily mobile after the job done.

2. For the thickness of 4 mm we can use SMAW ( Solid Metal Arc Welding) or TIG/GTAW( Gas Tungsten Arc Welding) very well as compared to other techniques with ease of weld preparation and quality weld.

3. For the pipe joining we need to make a butt joint & 'V' preparation (enough for 4 mm thickness) , which is one of the main consideration in selection of weld process, we can make a root pass of TIG weld over which reamaining passes of SMAW can be done when the pipe diameter is of bigger size compared to its thickness.

4. For pipeline welding , number of welds are requied which is easy to take with the SMAW because of its lesser welding equipment.Electrode availability and selection for the SMAW is quite easy due to its standardization.

5.High Quality welds can be obtained with the GTAW process. Hence a combination of GTAW and SMAW is highly productive and economical for the mentioned application.