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A welding procedure is a statement of execution, a specific plan prepared by the welding contractor. The procedure details with listing of various variables associated with the proposed welding process giving an assurance that the resulting weld would guarantee that the required mechanical and metallurgical properties will be met. Any format of form may be used to develop a welding procedure giving essential details. Some international specifications especially addressing the welding requirements have developed a format for the purpose, AWS D1.1 has E-1 form for pre-qualified procedures, similarly ASME Section IX of Boiler and Pressure vessels code has a set of such forms for welding specifications, welding qualification records (PQRs) and welders’ qualification records, they are numbered as QW- 482, QW- 483 and QW 484 respectively. Other international standards for welding are EN ISO 15609-1, EN ISO 15609-2, EN ISO 15609-3, EN ISO 15609-4, EN ISO 15609-5, and EN ISO 15614. Till the last revision, the EN ISO 15614 had 12 parts dealing with specific topics on welding various materials like Steel, Aluminum, Cast Iron, Titanium, Copper etc.

The plan details all essential and non-essential variables that are important to achieve the quality of weld. These variables are welding process specific. Some of these variables are discussed in this book. In ASME section IX, these variables are listed specific to the particular welding process, they are subdivided into essential, supplementary essential, and nonessential variables. However, these variables are not specific to ASME but are in general agreement with welding technology.

Table 1.3 Shows the arc efficiency factors for various commonly used arc welding processes.

Welding process	Arc efficiency factor η
	Range	Mean
Submerged Arc Welding	0.91 - 0.99	0.95
Shielded Metal Arc Welding	0.66 - 0.85	0.80
Gas Metal Arc Welding (CO2 Steel)	0.75 - 0.93	0.85
Gas Metal Arc Welding (Ar Steel)	0.66 - 0.70	0.70
Gas Tungsten Arc Welding (Ar Steel)	0.25 - 0.75	0.40
Gas Tungsten Arc Welding (Ar Aluminum)	0.22 - 0.46	0.40
Gas Tungsten Arc Welding (He Aluminum)	0.55 - 0.80	0.60

Table 1.4 Indicates general limits of joining/welding processes that apply to the material listed in left column.

Material

Welding processes

Other joining processes

SMAW

SAW

GMAW

FCAW

GTAW

PAW

ESW

EGW

RW

OFW

DFW

FRW

EBW

LBW

B

S

Carbon Steel

x

x

x

x

x

x

x

x

x

x

x

x

x

x

Low alloy steel

x

x

x

x

x

x

x

x

x

x

x

x

x

Stainless steel

x

x

x

x

x

x

x

x

x

x

x

x

x

x

Cast Iron

x

x

x

x

x

x

x

Nickel and alloys

x

x

x

x

x

x

x

x

x

x

Aluminum and alloys

x

x

x

x

x

x

x

x

x

x

x

x

x

x

Titanium and alloys

x

x

x

x

x

x

x

x

x

Copper and alloys

x

x

x

x

x

x

x

Magnesium and alloys

x

x

x

x

x

x

x

Refractory alloys

x

x

x

x

x

x

Table 1.5 Arc efficiency factor.

Welding process	Arc efficiency factor η
	Range	Mean
Submerged Arc Welding	0.91 - 0.99	0.95
Shielded Metal Arc Welding	0.66 - 0.85	0.80
Gas Metal Arc Welding (CO2 Steel)	0.75 - 0.93	0.85
Gas Metal Arc Welding (Ar Steel)	0.66 - 0.70	0.70
Gas Tungsten Arc Welding (Ar Steel)	0.25 - 0.75	0.40
Gas Tungsten Arc Welding (Ar Aluminum)	0.22 - 0.46	0.40
Gas Tungsten Arc Welding (He Aluminum)	0.55 - 0.80	0.60

Essential variables are those in which a change, as described in the specific variables, is considered to affect the mechanical properties of the weldments, hence any change shall require requalification of the welding procedure. The Supplementary essential variables are required for metals for which other Sections specify notch-toughness tests and are in addition to the essential variables for each welding process.

The Nonessential variables on the other hand are those in which a change, as described in the specific variables, may be made in the WPS without requalification.

Some special process like corrosion-resistant and hard-surfacing weld metal overlays may have different additional essential variables. Only the variables specified for special processes shall apply. A change in the corrosion-resistant or hard-surfacing welding process requires requalification.

The correct electrode diameter is one on of the variables, when used with the proper amperage and travel speed, produces a weld of the required size in the least amount of time. Selection depends on the thickness of the material being welded, the position of welding in relation to the gravity of the earth, and the type of joint to be welded. The welder’s experience is also important since more skill is required to control the weld puddle in out of position welds, the different types of electrode coverings and fluxes, are important too. The inexperience may lead to poor quality welds that may have defects such as inclusions, porosities in the final welds.

Welding current can be either direct or alternating, depending on the process, type of electrode and available power supply and material being welded. DC provides a steadier arc and smoother transfer as well as good wetting action, and out of position control. Reverse and straight current polarities are used for specific applications. Reverse polarity produces deeper penetration and straight polarity produces higher electrode melting rates.

These topics are discussed in much detail in the subsequent chapters and in relation to specific welding process.

American Welding Society has developed the chart to describe all joining and allied process the chart above indicates those processes. Various welding process use different energy transfer modes, the table below groups those welding processes based on that.