Some key aspects of writing welding procedure specifications. A good learning point for people who have no experience in the field, and a good reference for seasoned engineers

1.
How to write a welding procedure
specification
ISO 15614­1

2. One of the most important documents in regards to welding is the WPS (Welding Procedure
Specification) and many people working with WPS look at them like they are just an issue, or
something that only the engineers and quality control technicians have to worry about, but is
it a hard thing to create and/or look at? Let’s break it down into parts
I am providing a WPS form that is compliant with ISO 15609 and ASME IX which you can
download ​here​.
This article will be related to ​ISO 15614­1​ and ​ISO 15609­1​. I shall cover ASME IX
on a future article. Let’s get started with a summary of the essential variables:
1. 1 Essential Variables
● Base Material Groups (§8.3.1)
● Base Material Thickness (Table 5 for Butt Welds, Table 6 for Fillet Welds ­ §8.3.2.2)
○ Throat thickness is also essential for fillet welds
● Diameter, for pipes (§8.3.2.3)
● Branch Angle (for branch connection welds ­ §8.3.3)
● Welding Process (§8.4.1)
● Process Mechanization (§8.4.1)
● Welding Positions (§8.4.2)
● Weld Type (§8.4.3)
● Product Type (§8.4.3)
● Filler Material Classification (§8.4.4)
● Type of Current and Polarity (§8.4.7)
● Heat Input (§8.4.8) ­ if there are hardness and/or impact requirements
● Preheat Temperature (§8.4.9)
● Interpass Temperature (§8.4.10)
● Postheat Temperature (§8.4.11)
● Post Weld Heat treatment (§8.4.12)
Note: Take a look at §8.4.5 for process specific essential variables
2. 2 Header
Some of these informations are not related directly to ISO 15609­1, but your clients will want
you to specify which project this WPS is related to and, as such, you should also include
your client’s company in there.
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3. The biggest and most relevant piece of information here is the ​WPS Number​ (in this case
I’ve named it “Sample WPS (ISO)”, but you should use your own designations.
There should also be spaces where logos should go. In this specific example I have two logo
spots, in which the left one should be your company’s logo, leaving the right space for your
ISO 9001 certification body, or your client’s logo.
3. 3 Basic Information
Most WPS will be backed on a PQR (Procedure Qualification Record) and this information
should always be stated in the WPS. All you need to do is reference the PQR number which
will allow any reader of your WPS to trace back to the original qualifying document.
The standard is also related to the PQR, in this case it is ISO 15614­1, but ISO 15609­1’s
WPS format is relevant to other standards, such as ISO 15614­2/3/4/5 or even ISO 15613.
As you already know, the PQR always have approval ranges based on what was welded for
the approval of that specific test. One of the main points in how to elaborate a WPS is that
you may use these approval ranges to limit your specification, but in some cases you need
to specify accurately what will be welded on the job. The first example for this is the ​Product
type​:
This WPS is meant for piping work. Sometimes the PQR will approve welding Pipes and
Plates. This means you could technically use a WPS for piping and plating / structural work.
That is not the point of the welding procedure specification though, as you should specify the
details so that there is no room for doubts when a welder interprets this document.
The same goes for the ​weld type​, in which some standards will approve welding fillet welds
by performing a butt weld test. Like the product type, you should specify which type of weld
will be made with this WPS, and only type in a single option.
Welding Processes​ are pretty straightforward. Just type in the processes used in the PQR /
the ones to be used in production.
4. 4 Base Material Details
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4. The base material details are also quite straightforward. Keep in mind that this is WeldNote’s
WPS format and as such you do not need to place the fields exactly where we’ve put them.
First of all is the ​base materials​ themselves, which are intertwined with the groups. These
groups are what define which base materials should be welded with this WPS. These group
definitions can be found at ISO/TR 15608, but if you’d like to know what group a material
belongs to, you should check out ISO/TR 20172 and ISO/TR 20173.
In this case, the ​thickness ​range is exactly the approval range limits of the PQR. While this
is perfectly acceptable in regards to standards, you should restrict the limits of your WPS in
order for them to be accurate with the amperage, voltage and travel speed parameters (you
would not want to weld a 3 mm plate with the same parameters you would use for a 24mm
plate).
The same goes for the ​diameter​, but i’d say this one is more lenient. My suggestion would
be to use a WPS for small thicknesses and small diameters, and a WPS for bigger
thicknesses and bigger diameters (more, if the project has a lot of different pipe or plate
sizes).
Always use a range of thicknesses and diameters though, even if they are a bit strict. You
wouldn’t want an inspector to come to your shop floor and order you to stop using a 15mm
WPS because the welder is welding a 15.2mm pipe (which has already happened).
Welding positions​ are quite important, and you should plan for them ahead of time. The
safest way to go at it is to put them all in your WPS, as it is approved by the PQR, but the
best way to proceed is to define which are the positions to be used in the shop floor, which
will mostly be PA, PC and PH.
5. 5 Filler Material Details
Getting into the ​filler materials​ or consumables, in my experience there have been some
misconceptions on some of the requirements here.
The ​specification ​and ​classification​ of the filler material should be exactly as the
standards (AWS, ASME or ISO) say. This is for a 316 stainless steel and as such we’ve
chosen the ER316L for both TIG and MAG processes.
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5. The ​commercial name​ for a given filler material is not mandatory as per ISO 15614­1, it is
not an essential variable unless you are using the following processes: 111, 114, 12X, 136
and 137, so according to §8.4.5 only the “fluxed” processes require your WPS to have a filler
material ​commercial designation​ in them, and even then, it’s only when impact tests are
required, even if that is true for most cases.
In regards to the diameter or ​filler material size​, according to ISO 15614­1, you can change
it, so long as you take into consideration the heat input requirements and, as such, I would
recommend you to have 2 to 3 options here (e.g. 2.0mm and 2.4mm for the TIG rods).
You can find the ​symbol ​for the gas designations in ISO 14175, I1 means 100% Argon and
M21 means a mixture of Argon with 15 to 25% CO2. This information will probably come in
your gas certificate along with the commercial name, which is something that is not at all
required to put in your WPS, however, you probably want to put it, especially if you work with
more than one gas supplier. Why? This way your welders will know exactly which gas tank
they should pick up and avoid any problems with your client about the specified gas for the
job at hand.
Flow rates​ are important, they make the difference between a welder being able to control
the torch easily and assuring a sound weld, with no oxidation either on the root or the top
side, which means this value should be thought out and based upon previous experience, for
both the shielding and backing gases.
6. 6 Joint Details
While the joint details are only intended to give some guiding lines for the welders, their
importance should not be underestimated. It is very hard to define exactly the number of
passes on the ​weld layer configuration​, and as such you should have, at most, a range of
the maximum number of layers to be made. The ​groove design​ should have important
information such as the ​root gap​, ​root face​ and ​groove angle​ (which could mean it’s meant
for fitters and tack welders).
Preparation methods​ do not need a lot of details, you should just specify if this welded joint
is going to be grinded, machined, etc.
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6. The ​weld details ​are an essential variable so they are of the utmost importance, but you just
need to specify whether the joint will have material, gas or no backing, or if it will be welded
in a single side or both sides. You may mention the fact that it could be a single or multi layer
weld, but that is not so important, as that information will already be available on the welding
passes themselves.
7. 7 Welding Parameters
Now we’ve reached into the most important part of the WPS. The detailed description of how
each pass should be welded. This should be filled in with care, with information based upon
your company’s welding experience and your certifications.
● Pass #:​ This is pretty straightforward as you only need to specify which layer you’re
referring to. You may put a range of layers (e.g. passes 3 to 6) or if you’re referring to
the remaining passes until the capping layer you may use “passes 3 to N” or “3+”.
● Process: ​Name the processes to be used for the specific welding pass
● Filler Material: ​The filler material should always be metallurgically, physically and
chemically compatible with the base material and should be chosen prior to this WPS
elaboration. In this case you just have to associate it to the corresponding welding
process and pass.
● Diameter: ​The fact that the filler material diameter or size is not an essential variable
gives you some freedom in what to insert here, however, as the heat input is an
essential variable, you will need to take care in selecting a proper diameter. The rule
of thumb is to use a small diameter for the first passes, and raise the diameter as you
weld more layers. On higher layers you can raise the amperage, voltage and travel
speed to gain some productivity while maintaining the heat input levels, but for that
you also need a larger rod, electrode, or in the case of semi­automatic processes, a
higher wire feed speed.
● Current:​ These parameters are the most critical to assure a sound weld. Amperage
has a direct influence on the heat input and also defines how a welder will control his
puddle. In case of a semi­automatic process you will not control the current directly.
Rather you will be able to control the voltage and wire feed speed. You should either
use previous experience to define these values, or hire an experienced consultant to
help you with them.
● Voltage: ​If you are using a manual welding process, you can not control the voltage,
as this value is defined by the height of the welder’s hand, relative to the pipe being
welded, and as such you should set a considerable range of values, regarding to
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7. your welders’ skills and usual techniques. In the case of semi­automatic welding, the
voltage is a set value that will remain the same throughout the welding pass, and
should be defined, like the current, with previous experience in mind, or with the
expertise of an experienced consultant.
● Polarity ​will have a big influence on the deposit rates of your weld, but it will also
influence your penetration. Depending on the standard you may not be allowed to
change this parameter from the PQR, but if you are allowed to, you should always
use higher penetration polarities for the root passes (DC­ for TIG and DC+ for the
other processes) and higher deposit rates polarities for some of the filling passes and
or capping passes (DC+ for TIG is not really recommended in this case, but DC­ in
other processes is doable)
● Wire Feed Speed: ​Only applicable to semi­automatic and automatic processes, like
the voltage and the current, it is something that should be based on previous
experience or from an experienced consultant’s knowledge. Selecting a wire feed
speed from your PQR’s parameters is also a viable option.
● Travel Speed ​should always be accounted to an acceptable heat input, however, if
you are using manual welding, you can have a wider range of values, as you will
have to take into account that each welder has different techniques and may reach
sound welds with very different travel speeds.
● Heat Input ​is a critical value that has to be calculated. All the other parameters have
to boil down to bring this to acceptable values, as it will be a way to determine if a
weld is sound or not. Calculate this with the following formula
=IH = v
V I η* *
Travel Speed
V oltage Current Thermal Efficiency* *
V in Volts
I in Ampéres
Thermal Efficiency is a constant coefficient based upon the welding process used
○ 1 for Submerged Arc welding
○ 0.8 for MMA, MIG/MAG, Flux Cored Arc Welding
○ 0.6 for TIG
Travel speed has to be in millimeters per second in order for heat input to be in
KJ/mm
8. 8 Additional Details
There are some additional details that are, nonetheless, relevant to making WPS according
to ISO 15609­1 and ISO 15614­1. Although less important, they should be mentioned. The
most important here would be the ​Torch Angle and Number of Electrodes. ​The torch
angle will directly influence the morphology of the weld bead.
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8. The ​oscillation​ is mostly used for machine welding, but you can define the limits of the
weaving that a welder should restrict himself to. ​Details of back gouging​ are only relevant if
you are performing welding from both sides, and could have some information of the
electrode used, how much thickness and width to be gouged, etc.
Pulse weld details​ is similar, but only if you are welding with a pulsed transfer mode /
current type, and should have the current minimum and maximum peaks, with the period
between pulses, etc. ​Stick­out​ has an effect on the heat developed on the electrode,
causing it to eventually raise or decrease the deposit rate.
9. 9 Thermal Parameters
The thermal parameters are usually pretty straightforward, even if they are of the utmost
importance (they are straightforward from a WPS standpoint, but if you have to specify a
welding procedure before it is qualified it becomes a serious design issue, as it will take into
account your company’s resources and shop areas, as well as material types).
The ​preheat temperature​ is stated on your PQR, and according to ISO 15614­1 it should
not be lower than what is stated there. As such you could opt to go with the minimum value
or if you find there is an extra need for preheating, you may do so (e.g. higher thickness
requiring a higher temperature).
The ​interpass temperature​ is especially important when you’re dealing with austenitic
stainless steels, but should not be disregarded for any other material (recommend about 150
for austenitic, and 300 for carbon steels).
Post weld heat treatment​ is perhaps one of the most important aspects of your welding, if it
is verified to be necessary. In high thicknesses it is mandatory in pretty much every welding
code, in Cr­Mo steels as well, in order to prevent the forming of cracks due to three
dimensional cooling rates or the high temperability of these Cr­Mo steels.
The ​time​ field is the duration of the heat treatment at the highest temperature, usually 1 to 2
hours, depending on the steel and application. The ​method​ is dependant on your company’s
resources. If you have to perform work outdoors you won’t have an oven readily available
and as such you may have to use an oxypropane torch. The ​heating​ and​ cooling rate
should be around 100ºC / h, especially for the cooling rate, which should not be too high.
10. 10 Revisions and Approval
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9.
Finally, the ​revisions ​should be numbered (or lettered), with the signatures of the persons
responsible for writing the wps, verifying it and approving it, to be provided to your client to
sign and approve it themselves.
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Best regards,
Tiago Pereira
CEO at ​WeldNote, Welding Management Software
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