2.3 Notch-Toughness Tests, Fillet-Weld Tests & Special Examinations

2.3 Notch-Toughness Tests, Fillet-Weld Tests & Special Examinations

Beyond standard tension and guided-bend tests, ASME Section IX Article I governs specialized test methods designed to evaluate low-temperature notch toughness, fillet weld structural integrity, and nondestructive volumetric quality. For the AWS ASME Endorsement exam, candidates must master the precise boundaries where Section IX procedural rules intersect with the external requirements of referencing construction codes such as ASME B31.1, ASME B31.3, and ASME Section VIII.

---

1. Notch-Toughness Tests (QW-170)

Brittle fracture in pressure piping and vessels occurs rapidly without significant plastic deformation, typically at low service temperatures or in thick-walled components subjected to high restraint. Notch-toughness testing evaluates the capacity of the weld metal and heat-affected zone (HAZ) to resist brittle crack propagation.

The Fundamental Code Rule (QW-171.1)

One of the most notorious traps on the AWS Endorsement examination revolves around where to find impact test acceptance criteria. Candidates often search through Section IX looking for tables of required foot-pounds ($ft\cdot lbf$) or Joules ($J$).

CRITICAL CODE FACT: ASME Section IX DOES NOT establish Charpy impact energy values, lateral expansion thresholds, or test temperatures.

Paragraph QW-171.1 explicitly dictates that:

1. The test procedures, specimen dimensions, and notch configurations shall conform to the referencing construction code or ASTM A370.
2. The test temperature and acceptance criteria (such as minimum average absorbed energy, minimum single specimen energy, shear percentage, or mils lateral expansion) are dictated solely by the referencing construction code (such as ASME B31.3 Table 323.3.5, ASME B31.1 para 124, or Section VIII Division 1 Table UG-84.1).

Role of Supplementary Essential Variables

In Article IV (QW-250 variable tables), variables are classified as Essential, Supplementary Essential, or Nonessential.

• Under standard conditions, Supplementary Essential Variables are treated as Nonessential.
• However, when the referencing construction code mandates notch-toughness testing (e.g., low-temperature service under B31.3 Fluid Service rules), all supplementary essential variables automatically become mandatory essential variables for that WPS/PQR.
• Examples include limits on heat input ($kJ/\text{in.}$), changes in welding process progression (uphill vs. downhill), changes in base metal P-Number Group Numbers, and increases in postweld heat treatment temperature or time.

Specimen Location & Removal (QW-172 & QW-463.1(f))

When impact testing is required, standard Charpy V-notch (CVN) specimens ($10\text{ mm} \times 10\text{ mm} \times 55\text{ mm}$) are extracted from the test coupon:

• Specimen Orientation: Transverse to the longitudinal axis of the weld, with the notch cut perpendicular to the surface of the plate or pipe.
• Required Locations: A minimum of one set (typically 3 specimens per set) must be taken from the weld metal centerline, and one set must be taken from the heat-affected zone (HAZ).
• HAZ Notch Placement: The notch must be positioned to sample the maximum amount of HAZ microstructure (often verified by optical macro-etching prior to cutting the notch).

---

2. Fillet-Weld Tests (QW-180)

Fillet welds represent a significant percentage of all structural, socket, and attachment welds in piping and vessels. Section IX provides dedicated qualification testing protocols for fillet welds under paragraph QW-180, utilized for both procedure qualification (QW-202.2(c) and QW-451.3) and performance qualification (QW-303.2 and QW-452.5).

                      [Fillet Weld Test Assembly: QW-462.4(a)]
                       ┌────────────────────────────────────┐
                       │          Stem / Web Plate          │
                       └──────────────────┬─────────────────┘
                                          │
                    Fillet Weld 1 ──► /\  │  /\ ◄── Fillet Weld 2
                                     /__\ │ /__\
                       ───────────────────┴───────────────────
                                    Base / Flange Plate

Fillet-Weld Fracture Test (QW-182)

The fillet-weld fracture test evaluates internal soundness and root fusion:

1. Specimen Preparation: The test assembly (T-joint) is sectioned to produce the fracture specimen; the specimen length and cut locations are fixed by the applicable QW-462.4 figure for the coupon being tested, so read the figure rather than assuming a length.
2. Loading Method: The stem plate is loaded (by hydraulic press or mechanical blow) such that the root of the weld is subjected to tension until the specimen fractures or bends flat upon itself.
3. Acceptance Criteria (QW-182):
   • The fractured surface must show complete penetration to the root of the joint.
   • The weld must be completely free of cracks and free from lack of fusion.
   • Porosity and Inclusion Limits: The sum of the lengths of inclusions and porosity visible on the fractured surface shall not exceed 3/8 in. (10 mm).

Fillet-Weld Macro-Examination (QW-183)

Macro-examination provides a cross-sectional metallurgical window into weld geometry, fusion, and profile:

1. Specimen Extraction & Number of Cuts:
   • For Procedure Qualification (QW-462.4(a)): The test assembly must be cut perpendicularly to provide five (5) cross-sections, each approximately $2\text{ in.}$ ($50\text{ mm}$) long. One face of each cross-section is prepared for examination.
   • For Welder Performance Qualification (QW-462.4(b)): A 2-cross-section cut is utilized from the end of the break coupon.
2. Surface Preparation & Etching: The cross-sections are smoothed and polished with fine emery paper, then treated with a suitable chemical etching reagent (such as 5% to 10% Nital solution for carbon steel, or ferric chloride/mixed acids for stainless steel) to provide a clear, high-contrast distinction between weld metal, HAZ, and parent metal.
3. Acceptance Criteria (QW-183): Visual examination of the etched cross-sections under optical magnification (up to 10x):
   • Must exhibit complete fusion at the root and between individual weld passes.
   • Must be completely free of cracks.
   • Must be free of lack of penetration.
   • Must demonstrate acceptable fillet leg sizing: The difference between the actual leg lengths on a single fillet weld shall not exceed $1/8\text{ in.}$ ($3\text{ mm}$) to avoid excessive convexity or severe concavity.

---

3. Visual Examination & Volumetric NDE (QW-190)

Article I also establishes the acceptance criteria for non-destructive examinations used during qualification.

Visual Examination (QW-194)

Before any mechanical test specimens are sectioned from a welder performance coupon, the coupon must undergo rigorous visual examination. Paragraph QW-194 mandates that performance coupons shall exhibit:

• Complete joint penetration across the entire root.
• Complete fusion between the weld metal and the base metal.
• Zero tolerance for cracks, incomplete penetration, or lack of fusion.
• Surface appearance must demonstrate clean workmanship and absence of severe burn-through, undercut exceeding code limits, or excessive reinforcement.

Radiographic (RT) and Ultrasonic (UT) Examination (QW-191)

Under QW-302.2, volumetric NDE (RT or UT) may be substituted for guided-bend tests to qualify a welder on groove welds, provided specific process restrictions are observed (e.g., GMAW short-circuiting transfer mode is prohibited from using RT alone without bend tests due to high susceptibility to cold-lap/lack of fusion).

Critical Distinction: Volumetric NDE can qualify welders (WPQ), but CANNOT qualify a groove welding procedure (PQR). A PQR requires destructive tension and bend tests under QW-451 to prove mechanical strength and ductility; radiography cannot measure ultimate tensile strength or elongation!

---

4. Summary Comparison: Article I Mechanical and NDE Examinations