Welding Variables- Essential variable, Non- Essential Variables & Supplementary Essential Variables

Essential variables in Welding are those variables that affects the mechanical & technological properties of a welding. They are classified for:

Essential variables for WPS Procedure Qualification
Essential variables for Welder Performance Qualification

This article covers Essential Variables, Non-Essential Variables & Supplementary essential Welding for WPS & Welder qualification both.

What are Welding Variables?

It is important to remember that the requirements of different welding codes and standards (E.g. ASME Section IX, AWS D1.1, or ISO 15614-1) have been adjusted to meet specific service requirements.

Each welding code and standard such as ASME Section IX or AWS D1.1 or ISO 15614-1 have given & considered:

Essential,
Nonessential, and
Supplementary essential variables differently.

Hence, to properly develop welding documents such as WPS, PQR, or WPQ, shall be reviewed by competent qualified Welding Engineer or Welding Inspector.

These qualified and responsible person shall review and decide the relevant & applicable welding variables such as essential, non-essential and supplementary essential variables for each qualification. A righteous review will ensure the documents comply to the code requirements to maintain the welding quality on job.

A qualified PQR & WPS specifying these variables within the qualified range is mandatory for a good welding quality and integrity. This is hence essential to perform this task with proper due diligence and utmost care.

A variable listed on a wps is required to be comply the qualification code. For example, ASME Section IX, requires all essential variables, non-essential & supplementary essential variable to be listed in WPS.

Watch this YouTube video for full classroom training on Welding variables, their types, and practical Importance.

Watch the online video and learn:

What is the welding variable?
Types of welding variables?
Procedure and Performance variables?

What are essential, supplementary, Non-essential, and special variables?
Importance of welding variables?

What is Essential Variable in Welding?

Essential welding variables are listed in the ASME Section IX, clause QG-105.1, QW-251.2, and QW-401.1.

For Essential Welding variables, a change in the essential variable is considered to affect the mechanical properties (E.g. tensile strength, yield strength & ductility) of the weldment and shall require the requalification of the WPS. Hence, the WPS must be requalified, if any of the essential variable is changed.

Examples of Essential Variables in Welding for WPS

The examples of some essential welding variables as per ASME Section IX are:

Base Metal P. Number
Base Metal Thickness qualified range
Decrease in preheat temperature more than 100 Degree Fahrenheit

Change in PWHT

What are Supplementary Essential Variables in Welding?

Supplementary Essential welding variables are listed in the ASME Section IX, clause- QG-105.3 & QW-251.2, QW-401.3

Welding Variables -group-number-in-ASME-

Supplementary essential variable affects the weld toughness properties (CVN). So, the supplementary essential variables shall be considered as essential variables for procedure qualification (WPS-PQR) when CVN toughness is applicable for the welding.

For example- a pressure vessel fabrication has toughness requirements for its weld, then supplementary essential variables must be considered too.

If there is no requirements for weld toughness, supplementary essential variables are non-essential variable only. For example- a weld operating at elevated temperature does not requires weld toughness as material is already having good ductility a high temperature.

Examples of Supplementary essential variables are for example- Group Number for base metal, thickness limit qualified in the PQR.

Examples of Supplementary Essential Variables in welding for WPS

The examples of some Supplementary-essential welding variables as per ASME Section IX are:

Groove design
Removal of backing

Change in welding rod diameter
Change in welding position
Change in welding progression

Change in polarity
Change in welding technique
Method of cleaning

What are Nonessential Variables in Welding?

Non-Essential welding variables are listed in the ASME Section IX, Clause- QG-105.3 & QW-251.3, QW-401.4

Nonessential welding variables refers to those conditions in which a change can be done without the need to requalify the existing WPS. The reason- changes in these variables does not affects the mechanical properties of the weld.

Although a change in the nonessential variable doesn’t require prequalification of the WPS but as per ASME, these variables shall be specified in the welding procedure specification (WPS).

Examples of non-essential welding variables for WPS qualification are:

Joint design,
filler wire/ electrode diameter

Root spacing
welding position
weaving or stringer bead

Peeing
Preheat maintenance
single pass/ multipass

Cleaning methods

Examples of non-essential welding variables for Welder Performance Qualification are:

Root spacing

Electrode Diameter
Welding current, voltage
Travel speed

Gas shielding
Base metal group Number
Base metal thickness

Examples of Supplementary Essential Variables in welding for WPS

The examples of non-essential welding variables as per ASME Section IX are:

Material Group Number
Weld metal Thickness qualified limit

Change in welding rod classification
Increase in interpass temperature
PWHT (Time & temperature change)

Welding Heat Input
Welding current & voltage

What are Special Process Variables?

Special welding variables are listed in the ASME Section IX, Clause- QG-105.4 & QW-251.4

Special process variables are conditions that apply only to special processes (Such as corrosion resistance overlay & hard-facing) that are described in the ASME Section IX.

Special processes are such as weld overlay applications. These processes are used for special purposes instead of joining applications.

WPS essential Variables

WPS Essential Variables are those conditions that influence deposit weld mechanical properties. Any change in these variables other than qualified will alter the mechanical properties of the welding. These properties can be:

Tensile Strength
Yield Strength
Toughness

Hardness
Ductility
Microstructural changes

Essential variables are listed in ASME Section IX QW-452 to QW-267 Table. Essential variables examples are:

Base Metal P-Number
Welding Electrode F-Number

Weld A-Number
Welding Preheat
PWHT

Qualified PQR Thickness (T)
Thickness (t) of weld deposit qualified

List of Essential and Nonessential variables in welding

Essential and Non-Essential Variables in Welding are covered in ASME Section IX for:

WPS Procedure Qualification
Welder Performance Qualification

WPS Qualification List of Essential and Nonessential variables in welding can be found in Table QW-452 to QW-267 for different welding processes. Below is the list of Essential and Nonessential Variables for WPS Qualification.

Welder Performance Qualification List of Essential and Nonessential variables in welding can be found in Table QW-352 to QW-357 for different welding processes. Below is the list of Essential Variables for Welder Performance Qualification.

Removal for backing
Change Base Metal P-Number

Change in Pipe diameter
Change in F-Number
Change in t-Weld qualified

Addition of a welding position
change from vertical uphill to downhill

SMAW-variables-for-WQT — List of Essential and Nonessential variables in Welding Performance Qualification

Essential Variables for Welder Qualification

Essential Variables for Welder Qualification are those variables that affect the welder ability to make a sound weld deposit. So basically, essential Variables for Welder Qualification influence the weld quality in term of soundness.

What must be done if an essential variable on a WPS is changed?

If an essential variable on a WPS is changed beyond the range qualified, it require re-qualification of the WPS by welding a new PQR. This condition is specified in ASME Section IX QG-105 clause.

An essential variable on a WPS is changed can be addressed in two ways:

Change in an essential variable within the range qualified
Change in an essential variable beyond the range qualified

For Change in an essential variable within the range qualified, can be made by revising the WPS as editorial revision.

For change in an essential variable beyond the range qualified, this required re-qualification of welding procedure by welding a new test coupon and testing it according to the welding qualification code, such as ASME Section IX or AWS D1.1.