ASME Section IX qualifies the weld procedure and the welder, not the finished vessel. A TIG weld on a code vessel is “certified” when it follows a qualified WPS backed by a tested PQR, is made by a welder with a current WPQ, and then passes the inspection and pressure test that the construction code (usually ASME Section VIII, Division 1) requires.
That split matters to anyone buying pressure work in Houston, Baton Rouge or anywhere on the Gulf Coast. Section IX tells you the shop can make a sound weld. The construction code tells you how each production weld gets checked. You need both sets of records before a vessel goes into service.
What does ASME Section IX actually cover?
Section IX is the ASME Boiler and Pressure Vessel Code book for welding, brazing and fusing qualifications. It lists the variables that affect a weld, the test coupons to make, and the tests those coupons must pass. It covers two things: procedures and people.
It does not set design rules, production NDE acceptance limits or pressure-test values. Those come from the construction code that calls up Section IX
- ASME Section VIII, Division 1 for most unfired pressure vessels
- ASME Section I for power boilers
- ASME B31.3 for process piping in refineries and chemical plants
ASME Section V explains how to perform NDE methods such as radiography and ultrasonic testing. The construction code then says how much NDE to do and what passes.
Each shop must qualify its own procedures and welders. A WPS cannot be borrowed from another company. The one exception is the set of AWS Standard Welding Procedure Specifications (SWPS) that Section IX accepts under its own rules.
| Document | What it is | What it proves |
|---|---|---|
| WPS (Welding Procedure Specification) | Written instructions for making a weld | The welder knows exactly what settings and materials to use |
| PQR (Procedure Qualification Record) | Record of the test coupon and its test results | The WPS can produce a weld with the required strength and ductility |
| WPQ (Welder Performance Qualification) | Record of one welder’s test coupon and results | That person can make a sound weld using a qualified WPS |
How is a WPS developed and qualified?
Most shops follow the same path from a blank page to a qualified procedure and qualified welders. The steps below apply to manual TIG (GTAW) on stainless or carbon steel.
- Define the job. List the base metals and their P-Numbers (304 and 316 stainless are P-No. 8; common carbon steels such as SA-516 Grade 70 are P-No. 1). Add thickness, pipe diameter, weld positions, and whether the service needs impact toughness or post-weld heat treatment (PWHT).
- Write a preliminary WPS. Set target values for each variable. For GTAW, the variables are listed in the Section IX table for that process. Typical entries include filler F-Number and A-Number, shielding and backing gas, current and polarity, preheat and interpass temperature, and PWHT.
- Weld the test coupon. A skilled welder welds the coupon under the shop’s supervision. Record the actual amps, volts, travel speed, gas flow rates and interpass temperatures as you go. Many owners also ask for a third-party witness, but check whether your contract requires it.
- Test the coupon. Cut and test specimens as Section IX requires. A groove-weld PQR normally needs tension tests and guided bend tests. Add Charpy impact tests when the construction code requires toughness.
- Complete and certify the PQR. Record the real values used and the lab results. The shop signs the PQR to certify it is accurate.
- Finalize the WPS. Set the allowed ranges based on what the PQR supports. For example, the qualified thickness range comes from the coupon thickness. One WPS can cite more than one PQR, and one PQR can support several WPSs.
- Qualify each welder. Each welder welds a test coupon using the qualified WPS. The coupon is checked by bend tests or, for GTAW, by radiography in place of bend tests. Record the results on a WPQ that lists the positions, thicknesses, diameters and filler groups the welder is qualified for.
- Keep it current. Log each welder’s use of the process. A welder’s qualification lapses if they do not weld with that process for a set time. If an essential variable changes, you need a new or added PQR before you weld.
Variables come in three types. Essential variables change the weld’s mechanical properties, so changing one means a new PQR. Supplementary essential variables only apply when impact toughness is required. Nonessential variables, such as groove design details, can be changed by revising the WPS without new testing.
Which tests prove a production weld is sound?
Once the procedure and welder are qualified, the construction code decides how each weld on the vessel is checked. On a Section VIII, Division 1 vessel, the common checks are listed below.
| Test | What it finds | Where the rules come from |
|---|---|---|
| Visual testing (VT) | Surface cracks, undercut, surface porosity, weld size, misalignment | Method in Section V; acceptance in Section VIII |
| Radiographic testing (RT) | Internal porosity, tungsten inclusions, incomplete penetration, some lack of fusion | Method in Section V; full RT and spot RT rules in Section VIII |
| Ultrasonic testing (UT) | Planar flaws such as lack of fusion and cracks, especially in thick walls | Method in Section V; allowed in place of RT under set conditions |
| Liquid penetrant testing (PT) | Surface-breaking cracks in nonmagnetic stainless | Method in Section V; required where Section VIII calls for it |
| Hydrostatic test | Leaks and gross weakness in the finished vessel | Section VIII test pressure, commonly 1.3 times MAWP adjusted by the stress ratio |
The amount of radiography also changes the design. Section VIII assigns a joint efficiency to each butt weld based on how much of it is examined. A fully radiographed joint earns a higher efficiency than a spot-checked or unexamined one, which can allow a thinner shell. Ask your engineer which level the design assumed before you price the NDE.
Why do TIG welds fail qualification or inspection?
Most failures trace back to a short list of causes. Bend tests are strict: an open flaw on the stretched surface past a set size fails the specimen.
- Lack of fusion. Low amps, fast travel or a poor torch angle leave filler lying on the sidewall. It opens up in bend tests and shows on UT.
- Incomplete penetration. A tight root gap or a thick root face stops the weld from reaching through.
- Porosity. Drafts, low or overly high gas flow, dirty filler rod or oily base metal trap gas in the weld.
- Tungsten inclusions. Dipping the electrode into the puddle leaves dense bits of tungsten. They show as bright spots on a radiograph.
- Root oxidation on stainless. Without a back purge, the root side turns gray and crusty. See our guide to preventing sugaring in stainless tube welding.
- Cracking. Hot cracks can form in stainless weld metal with too little ferrite. Hydrogen cracks can form in carbon steel welded without the preheat it needs.
- Paperwork gaps. Welding outside the WPS ranges, an expired WPQ, or a missing PQR for a changed essential variable. Inspectors find these in the records, not the weld.
Dissimilar joints need their own care. A 304-to-carbon-steel nozzle is a P-No. 8 to P-No. 1 joint and needs a WPS qualified for that combination. Our post on TIG welding 304 stainless to carbon steel covers filler choice for these joints.
What should buyers ask for before awarding a code job?
Ask for these records with the quote, not after the vessel ships
- The WPS for each joint type, plus the PQR or PQRs that support it
- Current WPQs for the welders assigned to the job, with continuity records
- Proof of the ASME Certification Mark and designator the job needs, such as “U” for Section VIII, Division 1 vessels
- NDE procedures and personnel qualifications
- Material test reports for base metal and filler
- The hydrostatic test record and data report
TIGTechs welds pressure-retaining stainless and carbon steel parts through our pipe and pressure vessel welding service. Our current code credentials are listed on the certifications and compliance page.
Have a vessel, nozzle or spool that needs code welding? Request a quote and send the drawing, materials and construction code. We will tell you which qualified procedures apply and what NDE the job will need.
What are essential, supplementary essential and nonessential variables?
Section IX sorts every welding variable into categories, and the category decides what happens when that variable changes. Essential variables are the ones that change the mechanical properties of the weld. Change one beyond the qualified range and the procedure must be requalified with a new PQR. For GTAW, typical essential variables include the base metal P-number, the filler F-number, the weld metal A-number, adding or removing post-weld heat treatment, and qualified thickness limits.
Supplementary essential variables only apply when the construction code also requires notch toughness (impact) testing. Heat input, preheat and pass thickness are common examples. If the job has no impact requirement, these variables behave like nonessentials. The way Section IX lists toughness variables has been reorganized across recent editions, so check the edition your code of construction references.
Nonessential variables can be changed by revising the WPS, with no new testing. Groove design, stringer versus weave technique and cleaning method usually fall here.
Welders are qualified against a separate list of performance variables. For a welder, the process, position, backing, filler F-number and deposited thickness drive what they are qualified to weld. A procedure can be valid while the welder is not, so both must be checked.
How do the WPS, PQR and WPQ fit together?
Three records cover a code weld, and each answers a different question.
- WPS (Welding Procedure Specification): the instruction sheet the welder follows. It gives ranges for each variable, such as amperage, filler, gas and preheat.
- PQR (Procedure Qualification Record): the record of one test coupon. It lists the actual values used and the test results that proved the procedure. One PQR can support several WPSs, and it is not rewritten later except to add data or fix editorial errors.
- WPQ (Welder Performance Qualification): proof that a specific welder made a sound test weld under a WPS. It stays active as long as the welder keeps using that process. Section IX lapses it after six months without use.
When you review a vendor’s package, trace the chain. The WPS should name its supporting PQR. The production variables should fall inside the WPS ranges. The welder should hold a WPQ with a current continuity log. A gap anywhere in that chain is the most common reason an Authorized Inspector stops a job.
Frequently asked questions
A WPS is the set of instructions a welder follows on the job. A PQR is the record of the test coupon that proved those instructions make a sound weld. Every WPS used on code work must be backed by at least one PQR.
No. Section IX covers procedure and welder qualification. The construction code, such as ASME Section VIII, Division 1 or B31.3, sets how much NDE each production weld needs and what passes.
For GTAW, Section IX generally allows a volumetric test such as radiography in place of bend tests for welder qualification. Some materials and joint types have limits, so check the current QW-304 rules before planning the test.
It stays active as long as the welder keeps using the process and the shop logs that use. If the welder goes too long without using it, the qualification lapses. It can also be revoked if there is a specific reason to question the welder’s work.
It depends on the change. A different F-Number or A-Number is an essential variable for GTAW and needs a supporting PQR. A change within the same filler group may only need a WPS revision, so check the variable table for the process.
Section VIII, Division 1 commonly sets the hydrostatic test at 1.3 times the maximum allowable working pressure, adjusted by the ratio of material stress values at test and design temperature. Your vessel designer sets the final number on the data report.
A P-number groups base metals with similar composition, weldability and mechanical properties, so a procedure qualified on one metal can cover others in the same group. Austenitic stainless steels such as 304 and 316 are P-No. 8. Common carbon steels are P-No. 1.
An F-number groups filler metals by usability, meaning how they affect a welder’s ability to make a sound weld. Bare solid stainless rods and wires such as ER308L and ER316L are F-No. 6. F-numbers matter mostly for welder qualification ranges.
