3.3 Test Coupons, Preparation & Required Test Specimen Allocations

3.3 Test Coupons, Preparation & Required Test Specimen Allocations

Core Principle: Procedure qualification under Article II requires physical destruction of standardized specimens to quantify ultimate tensile capacity, ductility, and sound fusion. Unlike Welder Performance Qualification (Article III)—where volumetric radiography or ultrasonic examination can frequently substitute for mechanical bending—procedure qualification mandates destructive mechanical testing. Nondestructive examination cannot replace tension and bend tests under QW-202.

---

1. Mandatory Mechanical Tests for Procedure Qualification (QW-202)

Paragraph QW-202 defines the specific mechanical tests required to qualify a groove or fillet welding procedure:

1. Tension Tests (QW-150): Conducted to evaluate the ultimate tensile strength of the groove joint. Two tension test specimens are required for every standard procedure qualification coupon per Table QW-451.1.
2. Guided-Bend Tests (QW-160): Conducted to evaluate the soundness and transverse ductility of the groove weldment. Four guided-bend test specimens are required for every standard coupon per Table QW-451.1.
3. Notch-Toughness Tests (QW-170): Charpy V-notch impact tests are mandatory only when specified by the referencing construction code (e.g., ASME Section VIII Division 1, ASME B31.1, or ASME B31.3).

+-----------------------------------------------------------------------------------------+
|                   CRITICAL CODE CONTRAST: PROCEDURE VS. PERFORMANCE                     |
+-----------------------------------------------------------------------------------------+
| ATTRIBUTE             | PROCEDURE QUALIFICATION (WPS/PQR)| PERFORMANCE QUALIFICATION (WPQ)|
|-----------------------+----------------------------------+------------------------------|
| Governing Article     | Article II (QW-200 series)       | Article III (QW-300 series)  |
| Primary Objective     | Verify joint mechanical integrity| Verify welder manual skill   |
| Volumetric NDE (RT/UT)| STRICTLY PROHIBITED AS SUBSTITUTE| PERMITTED IN LIEU OF BENDS   |
|                       | (Must pull tension & bends!)     | (For most processes per QW-304)|
| Minimum Specimen Count| 2 Tension + 4 Guided Bends       | 2 Bends (or volumetric NDE)  |
+-----------------------------------------------------------------------------------------+

---

2. Test Coupon Geometry: Plate vs. Pipe & Position Rules

ASME Section IX maintains unique foundational rules that streamline procedure qualification testing compared to welder qualification:

Plate Qualifies Pipe (QW-211)

Per paragraph QW-211, base metal test coupons may be plate, pipe, or other product forms. Qualification on plate qualifies pipe in all diameters, and qualification on pipe qualifies plate.

• In sharp contrast to Welder Performance Qualification (where pipe diameter is an essential variable under QW-452.3, and testing on small-bore pipe is mandatory to weld small diameters), a procedure qualified on a flat plate coupon is legally qualified to weld on any pipe diameter, from 1/8-inch micro-tubing to 48-inch pipeline.

All Positions Qualified by Any Position (QW-203)

Under paragraph QW-203, qualification in any position qualifies the procedure for all positions (Flat, Horizontal, Vertical, and Overhead), subject to one critical exception:

• The Notch-Toughness Exception (QW-405.2): When notch-toughness testing is mandated by the construction code, position becomes a supplementary essential variable. Specifically, an addition of a vertical-uphill progression requires requalification, because uphill progression typically introduces higher heat input (slower travel speed, wider weaving) that degrades notch toughness.

---

3. Specimen Allocation Table: Table QW-451.1 Breakdown

Table QW-451.1 governs the type and quantity of test specimens required for groove weld procedure qualification based on coupon thickness $T$:

Note 1: Side bends are permitted for coupon thicknesses $T \ge 3/8$ in. (10 mm). For thicknesses below 3/8 in., transverse face and root bends are mandatory.

Why Side Bends Replace Face and Root Bends at $T \ge 3/4$ Inch

In coupons 3/4 in. and thicker, attempting to bend a full-thickness specimen across its face or root would generate extreme outer-fiber tensile elongation that tears sound steel, or would exceed the capacity of standard guided-bend testing jigs. A transverse side bend slices the coupon crosswise into a standardized 3/8-inch (10 mm) wide specimen. Bending the specimen on its side exposes the entire depth of the weldment—from the root face through the center passes to the cover pass, including both heat-affected zones (HAZs)—to maximum strain simultaneously.

---

4. Specimen Removal Locations (QW-463)

Paragraph QW-463 establishes the exact physical locations from which test specimens must be extracted from the welded test coupon.

Plate Specimen Layout: Figure QW-463.1(a)

When qualifying on a plate coupon, specimens are removed in a balanced symmetrical order:

1. Top Discard Area: Minimum 1.0 inch (25 mm) removed and discarded to eliminate weld starts, thermal transients, and unstable edge conditions.
2. Tension Specimen #1: Transverse reduced section (QW-462.1(a)).
3. Root Bend Specimen #1 (or Side Bend #1).
4. Face Bend Specimen #1 (or Side Bend #2).
5. Tension Specimen #2: Transverse reduced section.
6. Root Bend Specimen #2 (or Side Bend #3).
7. Face Bend Specimen #2 (or Side Bend #4).
8. Bottom Discard Area: Minimum 1.0 inch (25 mm) removed and discarded to eliminate crater crack risks and termination anomalies.

Pipe Specimen Layout: Figure QW-463.1(b)

When qualifying on a pipe coupon (welded in the fixed 5G or 6G position), specimens must be removed from all four quadrants to evaluate the distinct welding dynamics of each orientation:

• Top Quadrant (Flat position, ~12 o'clock): Tension specimen and root/side bend.
• Bottom Quadrant (Overhead position, ~6 o'clock): Tension specimen and root/side bend.
• Side Quadrants (Vertical uphill/downhill, ~3 and ~9 o'clock): Face/side bend specimens.

---

5. Mechanical Testing Execution & Acceptance Standards

Tension Test Standards (QW-150 & QW-153)

Tension specimens are machined to standardized reduced-section profiles per Figure QW-462.1. Acceptance criteria under QW-153.1 require:

1. Tensile Strength Criterion: The specimen must display an ultimate tensile strength not less than:
   • The specified minimum tensile strength (SMTS) of the base metal, or
   • The specified minimum tensile strength of the weaker of the two base metals if dissimilar metals are joined, or
   • The specified minimum tensile strength of the weld metal when the Section IX code specifically permits weaker weld metal.
2. The 95% Base Metal Fracture Rule (QW-153.1(d)): If the specimen breaks in the base metal outside of the weld and weld interface (fusion line), the test is acceptable provided the tensile strength is not more than 5% below the specified minimum tensile strength of the base metal (i.e., at least 95% of SMTS).

+-----------------------------------------------------------------------------------------+
|                    MATHEMATICAL EXAMPLE: THE 95% TENSILE RULE                           |
+-----------------------------------------------------------------------------------------+
| Given: Test coupon welded on ASTM A106 Grade B pipe.                                    |
| - Base Metal SMTS: 60,000 psi (415 MPa)                                                 |
|                                                                                         |
| Case A: Specimen breaks IN THE WELD at 58,500 psi.                                      |
| -> RESULT: REJECTED (Failed). Must meet 100% of SMTS (60,000 psi) when failing in weld. |
|                                                                                         |
| Case B: Specimen breaks IN BASE METAL at 58,500 psi.                                    |
| -> CALCULATION: 95% of 60,000 psi = 0.95 * 60,000 = 57,000 psi.                        |
| -> RESULT: ACCEPTED (Pass). 58,500 psi >= 57,000 psi; failure occurred in base metal.   |
+-----------------------------------------------------------------------------------------+

Guided-Bend Test Standards (QW-160 & QW-163)

Guided-bend specimens are bent around a standardized mandrel in a test jig conforming to QW-466. For standard P-No. 1 carbon steel, the plunger radius ($A$) is 1.5 inches (38 mm) and the die width ($B$) is 0.75 inches (19 mm), imparting approximately 20% outer-fiber strain.

Acceptance Criteria (QW-163):

• The guided-bend specimen must have no open discontinuity in the weld or heat-affected zone exceeding 1/8 inch (3.2 mm), measured in any direction on the convex surface of the specimen after bending.
• Corner Cracks: Open discontinuities that develop along the corners of the specimen during bending are disregarded, unless there is definite evidence that they result from lack of fusion, slag inclusions, or internal defects.

6. Fillet Welds and Base Metal Repair Qualifications

The Groove-to-Fillet "Golden Rule" (QW-202.2(c))

One of the most powerful and frequently tested provisions in Section IX is paragraph QW-202.2(c): Qualification of a groove weld procedure qualifies the WPS for all fillet welds on all thicknesses of base metal, all sizes of fillet welds, and all diameters of pipe or tube.

• If a manufacturer has qualified a complete-penetration groove weld on 3/8-inch plate, that single qualification permits the contractor to write a fillet-weld WPS for welding a 1/8-inch fillet weld on 4.0-inch thick plate, or a 1.0-inch fillet weld on a 2-inch pipe socket fitting!

Fillet-Only Qualification (QW-180 & QW-202.2(c))

If an organization chooses not to weld a groove coupon, it may qualify a procedure strictly for fillet welds by welding a fillet-weld coupon per QW-180 and Table QW-451.3:

• Specimens Required: 5 macro-etch specimens cut from the coupon.
• Acceptance Criteria: Visual inspection of cross-sections must show complete fusion at the root and no cracks.
• Crucial Restriction: A fillet-weld test coupon qualifies the WPS for fillet welds only. It can never qualify groove welds under any circumstance.

Base Metal Repairs and Buildup (QW-202.3)

WPSs for repairing base metals or depositing weld metal buildup prior to joint fitup must be qualified using groove weld test coupons. When weld buildup is deposited to restore base metal thickness, the qualified base metal thickness range is based on the thickness of the test coupon base metal per Table QW-451.1.