Welding Procedure Specifications

On code work, you do not choose your settings. A written document called a Welding Procedure Specification (WPS) tells you how the weld must be made, and it exists because someone proved those settings make a sound weld. Knowing how to read one keeps your work from being cut out, even if your weld looks great.

What You Will Be Able to Do

• Explain the difference between a WPS, a PQR and a welder qualification.
• Find the settings you need on a WPS.
• Tell essential variables from non-essential variables.
• Recognize when a job does not match the WPS.
• Know what to do when the WPS cannot be followed.

Three Documents, Three Jobs

Think of baking. The WPS is the recipe. The PQR is the record of the test batch that turned out well. The WPQ shows that you, the cook, can follow the recipe. All three have to be in place. A good procedure does not qualify you, and a good welder does not qualify the procedure.

What Is on a WPS

The layout changes from shop to shop, but the content is similar. A WPS is a complete set of variables, including:

• ID: The WPS number, revision and date.
• Process: SMAW, GMAW, FCAW, GTAW or SAW.
• Base metal: The grade or group and the thickness range.
• Filler metal: The classification and diameter.
• Shielding gas: The type and flow rate.
• Joint design: Joint type, groove angle, root opening and root face, usually with a sketch.
• Backing: Whether backing or back gouging is required.
• Position: The allowed positions and the direction of travel, uphill or downhill.
• Preheat and interpass: The minimum and any maximum temperatures.
• Electrical settings: Polarity, and ranges for amps, volts and wire feed speed.
• Travel speed: Often given as a range for each pass.
• Technique: Stringer or weave, cleaning, and maximum bead size.
• Post-weld heat treatment: Required or not.

How a WPS Gets Approved

The approach depends on the code.

Qualified by testing. Someone welds a test coupon using proposed settings. The coupon is cut and tested, usually with tensile and bend tests. The actual values and results go on a PQR. A WPS is then written, and its limits must stay within what the PQR supports. One PQR can support more than one WPS. ASME Section IX, used on boilers and pressure piping, works this way.

Prequalified. Some codes accept certain combinations without testing, because long experience has shown that they work. Under AWS D1.1, a WPS is prequalified when it uses listed base metals, fillers, processes and joint details, and stays inside the limits the code gives. No qualification test is required, but the WPS still has to be written down and followed, and the welders still have to be qualified. A single change outside the limits means it is no longer prequalified.

Essential and Non-Essential Variables

Not every setting carries the same weight.

Essential variables are changes that can affect the mechanical properties of the weld, such as its strength or toughness. If you go beyond the limit, the procedure has to be requalified with a new PQR. Depending on the code, these can include:

• Changing the process
• Changing the filler classification
• Changing the base metal group
• Going outside the thickness range
• Reducing preheat by more than the allowed amount
• Changing the shielding gas

Non-essential variables can be changed by revising the WPS, with no new test. These can include things like the groove design details and the method of cleaning, depending on the code.

Some codes add supplementary essential variables for jobs where toughness is required. Each code has its own tables, so a change that is non-essential under one code might be essential under another. That decision belongs to the welding engineer or the person responsible for the procedure, and not to the person on the machine.

Working Inside the WPS

Your job is to stay inside the ranges. Here is how that works on the floor:

1. Find the WPS for the joint. A print or weld map may give the number.
2. Check that it covers your material, thickness, position and process.
3. Check that your qualification covers the same job.
4. Check your filler against the WPS, and confirm the diameter.
5. Set polarity, amps, volts and gas inside the ranges.
6. Set up preheat, and check the joint against the sketch.
7. Weld in the stated direction, and with the stated technique.
8. Clean and check each pass, and keep interpass temperature within limits.

Inspectors can check your amps, volts and travel speed while you weld and compare them to the WPS. They do this by reading a clamp meter, timing a pass, or checking a machine readout. Machine dials are not always accurate.

Worked Example: Reading WPS Ranges

A WPS for E7018 stick welding says:

You are asked to weld a vertical joint on 1 inch carbon steel with 1/8 inch E7018 at 125 amps, with the plate at 70 F.

• Material and thickness: inside the range.
• Electrode and polarity: match.
• Amps: 125 is inside 110 to 140.
• Position: vertical is allowed, but only uphill, so vertical down is not covered.
• Preheat: 70 F is above the minimum.

Now the foreman asks you to switch to 5/32 inch rods to go faster. That electrode is not on this WPS. You need a WPS that allows it before you change.

What to Do When the WPS Does Not Fit

Sooner or later you will meet a joint that does not match the paperwork. The gap is wider than the sketch, the plate is thicker than the range, or the filler in the crib is a different classification. Do not improvise.

1. Stop before you weld.
2. Tell your lead, foreman or quality contact what does not match.
3. Wait for an answer: a fix to the joint, a different WPS or an engineering decision.
4. Get it in writing if it changes the job.

A nonconforming weld may need to be cut out even if it looks fine, because the record no longer shows it is sound. Speaking up costs you a few minutes.

Your Own Qualification

A WPS covers the procedure, and your qualification covers you. Your record shows what you may weld, including the process, position, thickness and other limits. It is usually kept by your employer or a test facility, and it has to be current. Under most major codes, a welder who has not used a process for more than six months must requalify on that process. Keep track of what you hold, and tell your employer if you think it has lapsed.

Common Mistakes

• Turning up the amps to go faster. You may leave the range and break the procedure.
• Grabbing whatever filler is close. A different classification can mean a nonconforming weld.
• Welding downhill on an uphill WPS. Direction is often an essential variable.
• Assuming that a good-looking weld is acceptable. A weld is judged by the procedure as well as by its appearance.
• Assuming your test covers the job. Check the WPS and your record against each other.

Check Your Understanding

A foreman says, "You passed the test, so you can use any procedure." Is that right?

No. Your qualification shows you can weld within certain limits, and each job also needs a valid WPS that fits it. Both must apply to the work.

The WPS calls for 75/25 argon-CO2, and the shop is out. The foreman says to hook up 100 percent CO2 instead. What do you do?

Stop and raise it. A change of shielding gas can be an essential variable, so a different WPS or a new qualification may be needed.

What is the difference between a PQR and a WPS?

A PQR records what was actually done and tested on one coupon. A WPS is the working instruction, with ranges supported by a PQR, or by the code's prequalified limits.

Your WPS says amps 110 to 140, and an inspector measures 150. The weld looks good. Is this a problem?

Yes. You are outside the range, so the weld is not conforming, and it may need review or removal. Bring your settings back into range and tell your lead.

Key Takeaways

• A WPS says how to make the weld. A PQR proves it works. A welder qualification proves you can do it.
• The WPS is a complete set of variables, and you must stay inside its ranges.
• Changing an essential variable beyond its limit requires requalification.
• Prequalified procedures skip the test but must stay fully inside the code's limits.
• If the job does not match the WPS, stop and ask.
• Keep your own qualification current.