21. Where the use of electrode E7018 is recommended?
The use of electrode E7018 is recommended for welding the following:-
A. For high strength steel.
B. For high thickness carbon steel plates.
C. Higher carbon equivalent material.
22. Why the electrode E7018 is called low hydrogen electrode?
The low hydrogen electrodes have in their coating ingredient, which produces carbon di-oxide during melting. This CO2 gives a gaseous shielding for the metal and prevents atmospheric hydrogen from entering in arc atmosphere. By this way the weld metal has low level of hydrogen.
23. What should be the content of chlorine in water while conducting hydrotest for CS & SS pipes?
For CS – 250 PPM.
For SS – 30 PPM.
24. What is the affect if the quantity of hydrogen induced in weld metal is more?
When hydrogen is more in weld metal, it tends to make the material brittle & subsequently leads to cracking. These cracks are called hydrogen induced cracking or delayed crack. To avoid this the electrode before using is backed at 250C to 300C for one hour in mother oven & then cooled down to 100C in the same oven & finally transferred to portable oven for use where temperature is maintained at 60 to 70.
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