Understanding the Welding Procedure Specification (WPS)

You will thoroughly learn the production of test pieces for welding procedure qualification tests (PQR), mechanical testing, and passing criteria.

WPS Cannot Stand Alone

Even if the WPS states "preheat 100℃, heat input 2.0 kJ/mm or less," there is no guarantee that condition is safe. There must be a record of actual welding, cutting, and bending tests conducted under those conditions. That is called PQR (Procedure Qualification Record, Procedure Qualification Record).

[Welding Test Implementation]  →  [Test Specimen Collection and Testing]  →  [PQR Recording]
                                              │
                                              ↓ Backing
                                           [WPS Issuance]
                                              │
                                              ↓ Using This WPS
                                        [Welder Qualification Test (WQT)]
                                              │
                                              ↓
                                          [Actual Product Welding]

A WPS without a PQR is not a document, but a wish. The first requirement during the main contractor and classification society audit is "show us the PQR that supports this WPS."

Understand the 3-Layer Structure

Document	What is it Recognizing	Target
PQR	Welding under these conditions produces performance	Procedure
WPS	Therefore, weld like this	Procedure (Instruction Manual)
WQT / WPQ	This person can perform the procedure	Person (Welder)

Even if a welder is qualified, if the company does not have a PQR, the welder cannot perform the joint. Even if there is a PQR, if there is no welder who has passed the qualification test under that procedure, the joint cannot be performed either. Both are required.

Essential Variables / Non-Essential Variables / Supplementary Essential Variables

A core concept in PQR. This is the standard to determine whether retesting is required when conditions change.

Classification	When Changed	Example
Essential Variable	PQR Retesting Required	Base metal group change, welding process change, filler metal classification change, thickness range exceeded, significant drop in minimum preheat temperature, PWHT condition change
Non-Essential Variable	Possible with WPS revision only	Improved weld shape details, presence or absence of backing, cleaning method, weaving width, etc. (depending on standard)
Supplementary Essential Variable	Promoted to essential variable when impact testing is required	Heat input, position, upper temperature limit between passes, etc.

Position is treated differently by each standard

ASME Sec.IX: Position is generally a non-essential variable for groove welds. However, it becomes an additional essential variable when notch toughness (impact test) is required.
AWS D1.1 / ISO 15614-1: Position is managed as an recognized range item.

> If you don't know this difference and apply "ASME doesn't require position" to shipyard drawings, accidents can occur. Determine the applicable standard first, and then check the variable table of that standard.

PQR Test Sequence

1. Test Plan Development (pWPS creation) — Preliminary WPS, conditions are written in advance
2. Test Specimen Material Preparation — Ensuring MTC (Mill Test Certificate) is essential
3. Test Welding Implementation — If under inspection, the inspector must be present
4. Visual Inspection + Non-Destructive Testing (RT/UT, MT/PT)
5. Specimen Cutting and Machining — The sampling location is specified by the standard
6. Mechanical Testing (Tensile, Bending, Impact, Hardness, Macro)
7. Result Evaluation → PQR Creation and Signing
8. Issue WPS Based on PQR

Record the actual values used in step 3 exactly as they are. PQR is not a record of planned values, but a record of actual measured values. WPS is used for ranges, and PQR is used for a single value from that day.

Test Items and Evaluation

Test	Purpose	Evaluation Criteria (General Trend)
Tensile Test	Joint Strength	Minimum tensile strength of base metal as specified. If the fracture occurs in the base metal and is at least 95% of the specified value, it is accepted (ASME)
Bending Test	Ductility and Fusion Condition	No defects exceeding 3mm on the convex surface after bending (ASME series). Edge cracking is judged separately
Impact Test (CVN)	Low-Temperature Toughness	Average of 3 samples at the specified temperature must be above the required value. ISO 15614-1 series allows 70% or more of the average required value for 1 sample
Hardness Test (HV10)	Hardening of Heat-Affected Zone	For carbon steel and low-alloy steel, the upper limit is often 380 HV10 in the welded condition and 320 HV10 after post-weld heat treatment
Macro Test	Penetration, Fusion, Shape	No cracks or fusion defects, and confirmation of fillet weld throat thickness
NDT (RT/UT/MT/PT)	Internal and Surface Defects	Acceptance criteria according to the applicable standard

> The number and type of bending test specimens (surface bending, back bending, side bending) depend on the plate thickness. Thin plates use surface and back bending, while thick plates use side bending instead. Check the relevant standard table for the exact number (ASME Sec.IX QW-451, etc.).

What the Bending Test Reveals

The location where the specimen cracks during bending provides diagnostic information.

Location of Crack	Suspected Cause
Center of Weld Metal	Porosity, slag inclusion, filler metal incompatibility
Fusion Line (Bond Area)	Poor fusion, insufficient heat input, insufficient cleaning of the root face
Heat-Affected Zone	Hardening, hydrogen, insufficient preheat

Acceptance Range — How Far Does One Test Cover?

The practical value of PQR lies in its range. The key is whether a test conducted at 20mm thickness can be applied to 8mm thickness.

Thickness Range (Varies by Standard)

ASME Sec.IX Series
  Test Specimen Thickness T → Generally accepted up to 2T (thicker specimens have separate tables)
  Example) T = 20mm test → Covers up to about 40mm

ISO 15614-1 Series
  Multi-pass (Multi-run) Welding → Range specified as 0.5t to 2t
  Single-pass (Single-run) Welding → Narrower range
  Example) t = 20mm, multi-pass → Approximately 10 to 40mm

※ This is a conceptual explanation. When applying, always check the relevant standard table.

There is a well-known rule regarding pipe welding position acceptance range.

If accepted as 6G (45° fixed) → Covers all positions
2G + 5G combination → Covers a range similar to 6G
1G (rotating) only accepted → Can only be used for below

That's why it's beneficial to conduct the test under the most difficult conditions once. If accepted as 6G, it reduces the need for retesting for other positions later.

Classification Society Approval — One More Layer for Shipbuilding and Marine

Because Busan, Ulsan, and Gyeongnam have a high proportion of shipbuilding, marine, and plant industries, classification society (Classification Society) approval is an additional requirement. Rules from the designated classification society, such as Korean Register of Shipping (KR), must be followed.

Item	General Industry	When Classification Society Applies
PQR Testing	In-house or certified testing institution	Classification society inspector attendance is often required
WPS Approval	In-house welding technical responsible person	Classification society WPS approval is required
Welder	In-house qualification test or national qualification	Classification society approved welder qualification is required
Filler Metal	Standard compliance	Classification society approved filler metal only can be used
Base Metal	Mill Test Certificate	Classification society approved steel (with classification society stamp)

> The most common mistake among subcontractors is not having classification society approval for filler metal. Even if the standard is the same, using products without classification society approval will result in rework due to lack of document recognition, even if the welding itself is fine. Obtain and keep the classification society certificate (Certificate) during the procurement phase.

Actual Issues Raised During Audits and Inspections

Issue	Description
WPS without PQR	Taking another company's WPS and just changing the company name
Exceeding Thickness Range	Constructing a 30mm joint with a 10mm PQR
Filler Metal Classification Mismatch	Not knowing that the classification symbol changed when the brand changed
Arbitrarily Lowering Preheat Temperature	Violation of essential variable → Procedure invalid
Welder Qualification Expired	Missing management of validity period and extension records
No Measured Records	Blank pages for preheat and interpass temperature measurements
Missing PQR Signatures	No signatures from test witnesses or technical responsible persons

PQR File Checklist

Conditions in pWPS (preliminary WPS) and PQR correspond to each other
Mill Test Certificate (MTC) for base metal is attached
Test report and approval certificate for filler metal is attached
Actual measured values for preheat and interpass temperature are recorded
Heat input calculation is based on actual measured current, voltage, and speed
Original mechanical test report from a certified institution or with witness is present
Recognized range (thickness, diameter, position, material group) is specified
Signatures and dates from test witnesses and technical responsible persons are present
A list of WPS numbers referencing this PQR is managed