The key is major function, and that is to purify the weld pool and weld metal.

The shape of the output wave form from this type power source is referred to as square wave. These type power sources have enhanced performance on a.c. They can control the balance, amplitude, frequency etc… to allow better control of penetration and cleaning action.

The surrounding air around the weld pool, contains oxygen, nitrogen and hydrogen. These gases get into the molten weld pool and cause gas bubbles to form (porosity) and lead to embrittlement and weld cracking.

Weld backing is used on the back side of the joint to prevent melt through and to assure complete penetration of the weld joint.

The density of steel is 490 pounds per cubic foot and its specific gravity is 7.8 times that of water. Water weighs 1000 Kg/m³. Therefore, a cubic meter of steel would weigh approximately 7800 kg depending upon the exact grade of steel being checked. Porosity, slag inclusion or other types of discontinuities would reduce the weight but not the specific gravity. 

When welding, the melting point of steel (approx. 2780⁰ F) versus the solidification point of the fast freezing flux or slag (approx. 3200⁰ F)  is important to know. Also, it is important to know that the melting point varies with the carbon and alloy content of steel. Steel is magnetic until heated above the transformation temperature of approximately 1333 ⁰ F. How fast the metal conducts heat will have a large effect of preheat and inter-pass temperature control. How much the metal expands on heating and contracts when cooling needs to be understood to control buckling and distortion.

Undercut best describes this fashion. Some people want to call it “under fill” but it is not correct, since it is not in the weld being located next to the toe.

If the weld does not combine with another weld or the base metal it is referred to as Incomplete fusion.

WPQR determines if a welder is qualified to a Welding Procedure Specification.

This welding technique would appear in the welding instructions or in the welding procedure specification. This generally increases the heat input per weld pass, but will generally reduce the total number of weld passes required to fill the joint. 

A fisheye is caused by the presence of hydrogen in the weld. If this appeared on a break test of some type it may or may not be acceptable. Always verify the acceptance criteria per the code or specification.

This is also considered the operating factor and is thought of as the percentage of a shift that a welder/welding operator is actually welding. For robotic and mechanized welding, it can be as high as 90% while for manual and semiautomatic welding it can be as low as 10-20% operating factors.
 

Though the weld symbols are identical, the sequence of how the welds are made is different.  The back weld is made last and the backing weld is made first.

VT stands for Visual Examination. This is the most common NDE process and can be used before, during and after welding to assure product quality and productivity.

Capillary action is the ability of a liquid to flow in a narrow space or root opening. This is accomplished without the assistance of external forces and even in opposition of external forces like gravity.

A standard is established for use as a rule or basis of comparison in measuring or judging capacity, quantity, content, extent, value, quality, etc…

All industrial codes and standards reference the requirement for having qualified procedures. They need to be openly available and the welders need to be trained on their proper use. The welders need to be qualified on those procedures and their qualification must be current. The supervisor needs to do this by verifying the welder's continuity report.

Cotton and wool are generally recommended apparel around welding operations. Synthetics like polyester, rayon etc… are not recommended as they melt, creating more of burn hazard.