What is the

Supplementary Essential
Variable in Welding
Procedure Specification?
This article provides information about the supplementary
essential variable in welding procedure specification(WPS) based
on the requirements of ASME Code Section IX. The code defines it
as "Supplementary essential variables are conditions in which a
change will affect the toughness properties of the joint, heat-
affected zone, or base material".

The supplementary essential variable becomes an essential

variable when welding procedure qualification requires impact
testing. The question is that, why procedure qualification needs
impact testing? You can not find the answer in ASME Code
Section IX; the answer is in the construction code such as ASME
Section VIII. When construction code because of the material,
thickness and temperature combination mandates for impact
testing in the base material, then the related welding procedure
specification (WPS) must be qualified by impact testing
(additional to the tension and bend tests).

So, if you have pressure vessel, and it does not require impact
testing based on the requirement of ASME Code Section VIII, and
then your supplementary essential variable in ASME Code Section
IX must be considered nonessential variable. Contrary if your
pressure vessel dose needs impact testing, then supplementary
essential variable must be considered essential variable.

For instance, you a have pressure vessel with 2 inch thickness

and -50 degree Fahrenheit MDMT with SA 516 Gr 60 material.
Based on ASME Code Section VIII, the impact testing is
mandatory on the plate material at this MDMT, consecutively will
be mandatory in the WPS qualification.
You suggest you have this qualified WPS by shielded metal arc
welding (SMAW), and you want to use this WPS for another job
with the same condition but in different welding position. The
changing the position in the SMAW is supplementary essential
variable, so you need to revise your WPS and requalify it with
mechanical testing.

Consider above example with 10 degrees Fahrenheit MDMT, and

then impact test was not a code requirement, and the changing
of position would have been a nonessential variable.

Summary: Go back to construction code, if there is a requirement

for impact test, then all of your supplementary essential variable
in welding procedure specification will be essential variable and if
there is no requirement for impact testing all of the
supplementary essential variable will be nonessential variables.

Supplementary Essential Variable in

Welding Procedure Specification
Based on ASME Code Section IX
requirements
Normally, base metal group number, thickness out of specified
range, filler metal diameter, filler metal classification, position,
etc. are categorized on the supplementary essential variables.

The ASME Code Section IX provides a unique table for each

welding process and addressing all essential variable,
nonessential and supplementary essential variables.

Group number, Group number, T-Limit Impact, AWS

Classification, etc are the supplementary essential variables.

Related Articles:

F Number, A number, P Number, Welding Performance

Qualification, Pressure Vessel Inspections
 What is the Essential
Variable in Welding
Procedure Specification
(WPS)?
This article provides you with information about the essential
variable in welding procedure specification based on requirements
of ASME Code Section IX. The code defines this terminology as
"Essential variables are conditions in which a change, as
described in the specific variables, is considered to affect the
mechanical properties of the joint".

It means if you have a welding procedure and one of your

essential variable changes out of specified range then you need to
re-qualify that WPS because that change affects the mechanical
property of the weld.

For example, if you have a WPS with shielded metal arc welding
(SMAW) process with post weld heat treatment, and then you
need to use this WPS for another job without post weld heat
treatment, you need to re-qualify your WPS because post weld
heat treatment is an essential variable in SMAW process.

Essential Variable in Welding

Procedure Specification (WPS) in
ASME Code Section IX:
The ASME Code Section IX provides a table for each welding
process and identifies essential, nonessential and supplementary
essential variables. So if you have a WPS, and you need to use
this WPS in another job with the implication of some changes,
then you need to refer these tables to see if these changes fall
among of essential variables. If they fall, then you need to re-
qualify your WPS.
In most of welding process, The P number, F number, A
number PWHT, thickness (out of specified range) are essential
variable. Based on requirements of ASME Code Section IX all
essential variable, nonessential variable and supplementary
essential variable (such as Group Number) must be indicated in
the welding procedure specification.

When you have a change in the essential variable, you need to

write a new welding procedure specification and qualify that with
a new procedure qualification record (PQR). To have a PQR you
have to prepare a new test specimen that welded based on this
new WPS and make two tension test, two root bend test and two
face bend test.

This PQR number should be indicated in this new WPS. You need
to refer to ASME Code Section IX to find correct size and number
of test specimens, test specimen preparation, testing equipment
requirements and related acceptance criteria.

The essential variable not limited to the WPS, you have the same
variables with the different requirements in the welding
performance qualification.

What is the Welding

Procedure Qualification
Record (PQR)?
This article talks about procedure qualification record (PQR)
based on requirements of ASME Code Section IX.

The purpose of qualifying a WPS is that to indicate joining process

proposed for production welding has required mechanical
property.

The WPS is written by knowledgeable person but needs to be

tested to ensure the produced weld based on WPS has required
mechanical property. When the WPS provided, then a test sample
must be prepared and welded. All welding variable must be
recorded during the welding. Please note in WPS you have the
range but you will not have a range in the PQR, and you need to
record a single value for each specified variable.

For example, your WPS indicates preheat temperature as 100 to

160 degree Fahrenheit. You are starting the preheat process on
your test specimen and measuring base metal temperature with a
pyrometer and after few minutes you record the joint
temperature as 140 degree Fahrenheit, and then you stop
preheating and asking your welder to start welding. Your preheat
temperature in the PQR form will be 140 degree Fahrenheit. This
applies to all other variables such as joint design, filler wire
diameter, PWHT condition, material thickness, material grade and
type, voltage, amperage, inert gas flow rate and type, etc. You
should indicate a single value for each field, and the range will
not be acceptable.

Welding Procedure Qualification

Records in ASME Code Section IX
The test specimen size and dimension must be based on
identified values in ASME Code Section IX. After completion of
welding and heat treatment (if needed), you need to send the
test specimen to the metallurgical lab for mechanical testing. For
any PQR, normally two tension tests, two root face bend test and
two face bend test is required.

The acceptance criteria have been provided in the ASME Code

Section IX. The QW-451 table provides you the information about
number and type of tests. For example, if your test specimen is
greater than the ¾ inch you cannot perform root and face bend
test and instead you need to run 4 side bend tests.

The acceptance criteria for tension test have been provided in

QW-153.1. The test specimen should not be broken below the
minimum specified tensile strength of base metal, but if it breaks
in out of weld area or out of weld interface then would be
acceptable if it is not more than 5% below the minimum specified
tensile strength. For instance, if you material is SA 516 Gr 70,
and it breaks out of weld area on 67 ksi then the test would be
acceptable.
The acceptance criteria for bend test have been provided in QW-
163. Normally after bend test there should be any crack more
than 1/8 inch on the side that was placed on the stress.

The PQR documents what occurred during welding of the test

coupon and the result of the test coupon. The PQR gives
suitability of weld for required mechanical properties e.g. strength
and ductility. The tension test indicates the strength and the bend
tests indicate ductility.

Please note the procedure qualification record cannot be revised

otherwise the case for revising being typing error or misspelling.
The PQR must include all essential variable (such as P number, F
number, A number, PWHT) and supplementary essential
variables (such as Group Number). The nonessential variables are
not code requirements for PQR.

When construction code like ASME Code Section VIII Div

I requires impact testing, the impact testing must be included in
Welding Procedure Qualification Record technical testing.
Normally you need to conduct two set of impact testing, one set
in weld metal and one set in heat affected zone.

Related Articles

Welding Performance Qualification, Pressure Vessel Inspection

What is the Welding

Procedure Specification
(WPS)?
This article provides information about welding procedure
specification(WPS) based on the requirement of ASME Code
Section IX. The code defines it as "A WPS is a written qualified
welding procedure prepared to provide direction for making
production welds to Code requirements".
The WPS may be used to provide direction to the welder or
welding operator to meet the code requirement. The WPS should
include all essential, nonessential andsupplementary
essential variables i.e. joint design, base material, filler metal,
position, preheat and post weld heat treatment, gas composition,
electrical characteristic, etc.. These variables have been provided
in the article II QW-250 thru QW-280 of ASME Code Section IX.

Who Should Write the Welding

Procedure Specification?
A welding engineer or any knowledgeable and competent person
in the welding metallurgy with appropriate experience can write a
WPS.

How to write a WPS?

There is the standard form for the WPS in ASME Code Section IX
(Form QW-482). This form can be copied and used. The welding
engineer may use different sources such as welding handbook
etc. Each field in this form must be completed. This WPS is
written with the knowledgeable persons but still we need to proof
the written WPS produce a weld with desired mechanical
property.

The written welding procedure specification must be qualified by

mechanical testing that is called procedure qualification
record (PQR).

The WPS specifies ranges, and when you need to use related WPS
out of the specified ranges, you need to revise your WPS and re-
qualify it.

There are many grouping systems in ASME Code Section IX in

purpose to reduce the number of WPS's and PQR's. These
groupings are P numbers, A numbers, F numbers. These
numberings are grouping similar material or filler metal with
specific characteristics and cause to reduce the number of WPS's.
This grouping reduces the costs.

The ranges indicated in the article IV ASME Code Section IX. The
article IV should not be read directly; you should refer to
specified paragraph when referred in the QW-250 thru 280 for
the ranges. The article IV in ASME Code Section IX formed from
hundreds of paragraphs which are not related to each other and
each paragraph numbered and must be read when referred from
other places in the code.

For example, in SMAW (QW-253), for thickness range, it refers

you to the Article IV paragraph 403.8, you can find thickness
range in this paragraph. It will refer you to another table that you
can obtain thickness range based on your test coupon thickness.

Related Articles

What is the Nonessential

Variable in Welding
Procedure Specification?
This article provides information about the nonessential variable
in welding procedure specification based on requirements of the
ASME Code Section IX. The code defines it as " Nonessential
variables are conditions in which a change, as described in the
specific variables, is not considered to affect the mechanical
properties of the joint".

In other word, if you have a welding procedure

specification (WPS), and you want to utilize this procedure in
other job but you have to change some variable and these
variables are categorized in the nonessential variable, then you
do not need to re-qualify your WPS.

For example, you have WPS with shielded metal arc welding
process with V groove joint design, and you want to utilize this
WPS in another job with the same condition but with U groove
joint design, then you do not need to re-qualify your WPS. What
you need to do is to revise your WPS and put the number of
previous procedure qualification record(PQR) number on the
revised WPS.
It means you do not need to go to such ordeal with the
preparation of new test specimen and to conduct mechanical
property test. Because this change categorized as nonessential
variable and is not affecting the welding mechanical properties
because it is not essential variable.

Normally, joint design, filler metal diameter, the minor change in

the electrical characteristics, welding positions, welding technique
(some of them) are nonessential variable in welding procedure
specification..

Nonessential Variable in Welding

Procedure Specification on ASME
Code Section IX
The ASME Code Section IX on the article II provides a unique
table for each welding process and list the essential, nonessential
variables and supplementary essential variables. Based on the
code requirements the nonessential variables must be indicated
in the welding procedure specification.

The most common mistake is that the manufacturers do not

revise WPS's when there is a change in the nonessential variable.
They justify that it is the nonessential so they do not need to do
anything. This is not correct, actually they should produce a new
WPS but without performing a new PQR. The should add the
number of the previous PQR on the revised WPS.

It is the manufacturer quality control team and third party

inspector task, to check and make sure that welding procedure
specification is completely consistent with actual welding job that
is in the progress on the shop floor i.e. joint design, filler wire
type and diameter, inert gas type and flow rate, voltage, and
amperage, preheat and inter-pass temperature, etc.

Related Articles:

F Number, P Number, A Number, Group Number, Welding

Performance Qualification,Pressure Vessel Inspection
 What is the Group
Number in Welding?
This article provides information about Group number in welding
procedure specification based on the requirement of ASME Code
Section IX.

The Group number in welding assigned additionally to the P

number materials. These group numbers divide a P number to
several group numbers for the purpose of welding procedure
qualification when impact testing is a requirement by the
construction code. This subject might be a little bit complicated,
but I am going to give an example to comprehend better.

You assume, you have pressure vessel under the design process,
and your designer says to you that the impact testing is not a
code requirement based on ASME Code Section VIII, which is
your pressure vessel design code. The designer determines this
through the requirement of ASME Code Section VIII Div 1 – UCS
66 (thickness and minimum design metal temperature
combination identify the impact test requirement)

In this example, when you are preparing your welding procedure

specification and procedure qualification record, you should not
consider the group number. Consider, no group number exists.
The entire supplementary essential variable will be nonessential
variables in your WPS form.

Group Number in Welding is Essential

this Time
This time, consider that your designer says to you that the impact
testing is the code requirement for you vessel (probably you have
lower minimum design metal temperature and higher thickness
material), now the group number matters. In one P number you
might have several group numbers like:
P number 1 Group number 1

P number 1 Group number 2

P number 1 Group number 3

Now you need your welding procedure, be qualified by impact

testing as well. One set for weld metal and one set for heat affect
zone.

In this situation, if you have WPS that has been qualified for P
number 1 and Group number 1 cannot be used for another job
with P number 1 and group number 2.If you look at the tables
QW-252 thru QW-269, you will see many supplementary essential
variables which now are essential variables.

Your all supplementary essential variables are essential variables

now.

The ASME Code Section IX is not determining of application of

Group numbers; it is the construction code such as ASME Section
VIII Div 1, or B31.3, etc. that is determining it. Please note the
ASME Code Section IX is only a referencing code. The table QW-
422 provides material P number and Group numbers. Consider it
when impact test is a mandatory requirement by the construction
code.

Related Articles:

A Number, F Number, Welding Performance

Qualification, Pressure Vessel Inspection

What is the A number in

Welding Procedure
Specification?
This article provides information about A number in welding
procedure specification based on requirement of ASME Code
Section IX.
A number gives a similar chemical composition in a “as weld”
condition. The A number is essential variable in most of welding
process in ASME Code Section IX. The Table QW-442 in ASME
Code Section IX provides the list of A number. Please note the A
number inWPS does not refer to the filler wire or electrode
chemical composition; it refers to the deposited weld metal
chemical composition. The filler metal and deposited weld metal
have different chemical compositions.

How Do You Determine the A number

in Welding Procedure Specification?
It can be obtained from procedure qualification coupon. The small
piece of welding can be removed and chemical analysis test to be
performed. Then the obtained chemical composition must be
compared against the table QW-422 and A number to be
selected.

Alternatively if your welding process is one of SMAW, GTAW, LBW

and PAW processes you may use the filler metal specification or
test report of filler metal manufacturer.

Similarly you can do same assessment for GMAW and EGW

processes but the shielding gas should be as the same of welding
procedure specification.

Again, similarly you can do the same for SAW but the flux should
be as the same of welding procedure specification.

As mentioned in above, the A number like P number and F

number is an essential variable in most welding processes. It
means if you have a WPS and you need to use that in other job
with different A number (it means you are using different filler
metal) then you need to re-qualify your WPS because it is
essential variable. The A number 1 and 2 are exceptions. You can
consider it as nonessential variables.

Related Articles:

Group Number, Supplementary Essential Variable, Welding

Performance Qualification,Pressure Vessel Inspection
 What is the F number in
Welding Procedure
Specification?
This article provides information about F number in Welding
Procedure Specificationbased on the requirement of ASME Code
Section IX.

The F number grouping of filler metals refers to their similarity on

their usability characteristics. The usability determines the ability
of a welder to deposit a sound weld metal with a certain filler
metal.

The F number is essential variable in the most welding process

for welding procedure specification and also in welding
performance qualifications. Like the P number, the F number
designed to reduce the number of procedure
qualification and welding performance qualification.

I have seen some many people confusing about F number and

believing the F number is grouping for the similar chemical
composition. This is not true, and F number is only about of
usability characteristics such as welding position.

F number in Welding Procedure

Specification
Table QW-432 in ASME Code Section IX provides the list of F
numbers. Any change from one F number in welding to the other
F number is essential variable in the welding procedure
specification. The changing from one F number to other F number
is a little bit different in welding performance qualification. The
essential variable tables in welding performance qualification
(QW-352 thru 357) refer you to the QW-433 for the range of
qualification.
For example, a welder qualified with F number 4, he also will be
qualified on the F numbers 1, 2 and 3.

Some contractors use the essential variable tables (QW-352 thru

357) to minimize their costs. For instance, they might test the
welder for stainless steel material by using carbon steel material.
Consider the actual project material is stainless steel and you do
not want to waste stainless steel material for testing. You ask the
welder to weld in carbon steel material but with stainless steel
filler metal. Based on the essential variable table P number 1
(Carbon Steel) qualifies P 8 (Stainless Steel), and the F number is
the same. So you qualify your welder for stainless steel material
by using carbon steel material but stainless steel filler metal.

When you have a welder or welding operator with a certain

qualification, and you want to use him in some other job, you
need to see if all the variables in the essential variable table
confirm his qualification for the new job. Each of the item in the
table has veto right, if 6 out of 7 is Ok, but only 1 of them is not
meeting the requirements, and then you cannot use that welder
in the new job and you need to re-qualify him by the new test.

Related Links:

Nonessential Variables, Supplementary Essential Variables, A

number in WPS

What is the Welding

Procedure Qualification
Record (PQR)?
This article talks about procedure qualification record (PQR)
based on requirements of ASME Code Section IX.

The purpose of qualifying a WPS is that to indicate joining process

proposed for production welding has required mechanical
property.
The WPS is written by knowledgeable person but needs to be
tested to ensure the produced weld based on WPS has required
mechanical property. When the WPS provided, then a test sample
must be prepared and welded. All welding variable must be
recorded during the welding. Please note in WPS you have the
range but you will not have a range in the PQR, and you need to
record a single value for each specified variable.

For example, your WPS indicates preheat temperature as 100 to

160 degree Fahrenheit. You are starting the preheat process on
your test specimen and measuring base metal temperature with a
pyrometer and after few minutes you record the joint
temperature as 140 degree Fahrenheit, and then you stop
preheating and asking your welder to start welding. Your preheat
temperature in the PQR form will be 140 degree Fahrenheit. This
applies to all other variables such as joint design, filler wire
diameter, PWHT condition, material thickness, material grade and
type, voltage, amperage, inert gas flow rate and type, etc. You
should indicate a single value for each field, and the range will
not be acceptable.

Welding Procedure Qualification

Records in ASME Code Section IX
The test specimen size and dimension must be based on
identified values in ASME Code Section IX. After completion of
welding and heat treatment (if needed), you need to send the
test specimen to the metallurgical lab for mechanical testing. For
any PQR, normally two tension tests, two root face bend test and
two face bend test is required.

The acceptance criteria have been provided in the ASME Code

Section IX. The QW-451 table provides you the information about
number and type of tests. For example, if your test specimen is
greater than the ¾ inch you cannot perform root and face bend
test and instead you need to run 4 side bend tests.

The acceptance criteria for tension test have been provided in

QW-153.1. The test specimen should not be broken below the
minimum specified tensile strength of base metal, but if it breaks
in out of weld area or out of weld interface then would be
acceptable if it is not more than 5% below the minimum specified
tensile strength. For instance, if you material is SA 516 Gr 70,
and it breaks out of weld area on 67 ksi then the test would be
acceptable.

The acceptance criteria for bend test have been provided in QW-
163. Normally after bend test there should be any crack more
than 1/8 inch on the side that was placed on the stress.

The PQR documents what occurred during welding of the test

coupon and the result of the test coupon. The PQR gives
suitability of weld for required mechanical properties e.g. strength
and ductility. The tension test indicates the strength and the bend
tests indicate ductility.

Please note the procedure qualification record cannot be revised

otherwise the case for revising being typing error or misspelling.
The PQR must include all essential variable (such as P number, F
number, A number, PWHT) and supplementary essential
variables (such as Group Number). The nonessential variables are
not code requirements for PQR.

When construction code like ASME Code Section VIII Div

I requires impact testing, the impact testing must be included in
Welding Procedure Qualification Record technical testing.
Normally you need to conduct two set of impact testing, one set
in weld metal and one set in heat affected zone.

Related Articles

Welding Performance Qualification, Pressure Vessel Inspection

P number in Welding
This article provides information about P number in welding
procedure specification,welding performance qualification or any
other ASME Code section that this number is used.

The P number in welding assigned to the material by ASME Code

Section IX to reduces the number of welding procedure
qualification. Why we do want to reduce the numbers of PQR’?
because this part is expensive part, for each PQR you need to
produce a test sample and sent to metallurgical lab for
mechanical testing (two tension tests, two root bend tests and
two face bend tests).

P number assigned by ASME Code Section IX to the materials

based their similarity and characteristic such as chemical
compositions, weldability and mechanical property. That why you
do not see any material identification in the Welding Procedure
Specification. What you see is the assigned P number. So your
WPS can be used for group of material and not a single material.

This P number assignment reduces the number of PQR

remarkably. You need one PQR for a single P number which this P
number might include more than 20 or more specific materials
(when impact testing is not required by construction code such as
ASME Code Section VIII).

P number in Welding Application

The assigned P Numbers to the materials addressed in the table
QW-422. In addition, you can find minimum specified tensile
strength, group number, UNS number, ISO 15608 Group number,
nominal composition and product form.

P number is essential variable for most welding process. Similarly

it is an essential variable for welding performance qualification.

The welding is not the only application of this P number

assignment. This number also is used in construction code for
determining Post Weld Heat Treatment degree and duration
(UCS-56) also it is used to determine radiographic testing extent.
The ASME Code Section VIII provided a table which obtained from
combination of P number and material thickness which identifies
full radiography requirements. (UCS -57)

The simple categorization of P number is:

1 Carbon Steel

3 Up to 1/2% Cr and up to 1/2% Mo

4 1 to 2% Cr and up to 1/2% Mo
5A 2 to 3% Cr, 1% Mo Alloy Steel

5B 5 to 10% Cr, 1% Mo Alloy Steel

5C All 5A and 5B Materials heat treated to 85ksi+

6 Martensitic Stainless Steel

7 Ferritic Stainless Steel

8 Austenitic Stainless Steel

9 2 to 5% Ni Alloy Steel

10 Mn-V, Cr-V, 9%Ni, High Cr Alloy Steels

11 Low Alloy Steel, Quenched and Tempered to 95ksi+

21 1.2% Mg or Mn alloy Aluminum

22 1.2% Mn, 2,5% Mg, 0.25% Cu Aluminium

23 1.3% Mg, 0.7% Si, 0.25% Cr Aluminium

23 1.3% Mg, 0.7% Si, 0.25% Cr Aluminium

25 1.5% Mg, 0.8% Mn, 0.15% Cr Aluminium

31 Copper

32 Admiralty, Naval, Aluminium Brass, Muntz Metal

33 Cu-Si Alloys

34 Cu-Ni Alloys

41 Nickel

51 Titanium

61 Zirconium