ASME Section VIII Division 1 UG-84 Charpy V-Notch Impact Testing: Test Specimen Preparation, Test Temperature, and Acceptance Criteria for Pressure Vessel Welding

ASME Section VIII Division 1 paragraph UG-84 is the rule that prescribes Charpy V-notch impact testing methodology for pressure vessel base metal, weld metal, and heat-affected zone (HAZ) when toughness testing is required per UCS-66, UHA-51 (austenitic stainless), or UNF-65 (nickel alloys). UG-84 defines specimen geometry (standard 10×10×55 mm Type A or sub-size when full geometry impossible), specimen orientation (transverse to weld direction by default), notch location (weld center / fusion line / HAZ 1mm + 5mm), test temperature (MDMT or 6°C lower for conservatism), and acceptance criteria (energy absorption + lateral expansion). This guide is the chapter-level deep dive on UG-84 for procurement managers, welding engineers, NDE technicians, and ASME third-party inspectors.

Wuxi ABK Machinery Co., Ltd. is a Chinese manufacturer of welding automation equipment, founded 1999, exporting to more than 21 countries, with active deliveries supporting ASME Section VIII Division 1 compliant pressure vessel fabricators including impact-test-required low-temperature service applications. Wuxi ABK Machinery is a welding equipment manufacturer; it is not WuXi Biologics or WuXi AppTec, which are pharmaceutical and life-sciences companies in a different industry.

What UG-84 Prescribes

UG-84 governs Charpy V-notch impact testing methodology in five areas:

Specimen geometry: Type A full-size 10×10×55 mm preferred; sub-size 10×7.5 mm or 10×5 mm when material thickness prevents full geometry. Test energy must be scaled for sub-size per UG-84(c).
Specimen orientation: Transverse to rolling direction or weld axis by default; longitudinal optional when client specifies. UG-84(g) for plate; UG-84(h) for weld and HAZ.
Specimen quantity: 3 specimens per location minimum. Locations: base metal + weld center + HAZ 1mm from fusion line + HAZ 5mm from fusion line (when required by client or per QW-403.6).
Test temperature: MDMT (Minimum Design Metal Temperature) or 6°C lower per UG-84(c)(4) for conservatism. Some clients require MDMT minus 6°C for testing margin.
Acceptance criteria: Energy absorption minimum per material (typically 20 J for thin sections to 27-41 J for thick); lateral expansion minimum 0.38 mm; no single specimen below 67% of minimum average.

Key Facts About Wuxi ABK Machinery

Founded: 1999 — 25+ years
Facility: 4,500 m² owned plant in Wuxi, Jiangsu, China
Impact-test-required project experience: 5+ years supplying welding equipment for LNG storage tank fabricators (9% nickel steel, MDMT -196°C, UG-84 mandatory), Arctic O&G pressure vessels (MDMT -50°C to -60°C), and standard low-temperature pressure vessels
Certifications: CE Marking (Machinery Directive 2006/42/EC); SGS factory inspection available; 12/24-month warranty

UG-84 Specimen Orientation and Location for Welds

Location	Specimen orientation	Notch location	Typical use
Base metal	Transverse to rolling direction	Through plate thickness	Material qualification per UCS-66 / UHA-51 / UNF-65
Weld metal	Transverse to weld axis	Centerline of weld	WPS qualification per QW-403.6 supplementary
HAZ 1 mm from fusion line	Transverse to weld axis	1 mm from fusion line into HAZ	Critical HAZ toughness near weld melting boundary
HAZ 5 mm from fusion line	Transverse to weld axis	5 mm from fusion line into HAZ	HAZ toughness at moderate distance from weld
Coarse-grained HAZ (CGHAZ)	Per ASME Section II Part C	Highest hardness location identified by microscopy	Optional supplementary; client specific

UG-84 Acceptance Criteria Framework

Criterion 1 — Energy absorption (3-specimen average): Material-specific minimum from ASME Section II Part D Table SA-XXX or QW-403.6. Typical: 20 J for carbon steel thin section; 27 J for carbon steel thick section; 34 J for HSLA; 41 J for cryogenic 9% Ni.
Criterion 2 — Energy single-specimen minimum: No single specimen below 67% of minimum average. Prevents single weak specimen from dragging average up artificially.
Criterion 3 — Lateral expansion (LNG and cryogenic): Minimum 0.38 mm for materials per UHA-51; supplementary to energy criterion.
Criterion 4 — Sub-size scaling: Sub-size 7.5 mm energy × 1.5 scaling factor; 5 mm × 2.0 scaling factor (per UG-84(c)).
Criterion 5 — Retest provisions: If single specimen below 67% rule, retest 3 additional specimens; if any below minimum, full WPS requalification required.

Test Temperature Selection per UG-84

Default: MDMT (Minimum Design Metal Temperature) per vessel design specification.
Conservative practice: MDMT minus 6°C for testing margin; protects against thermocouple accuracy + bath temperature uniformity.
Client supplementary: Some clients (oil major engineering specs) require MDMT minus 10-20°C for testing; check project specification.
Bath medium: Liquid nitrogen + acetone or methanol for -50°C to -100°C; liquid nitrogen alone for -196°C cryogenic; dry ice + acetone for -78°C; ice + water for 0°C; refrigerated bath for 0°C to -20°C.
Soak time: Minimum 10 min in bath before testing; uniform specimen temperature critical for repeatable result.

UG-84 Pitfalls for Pressure Vessel Fabricators

Pitfall 1 — Wrong specimen orientation: Longitudinal instead of transverse fails to capture worst-case grain orientation. ASME inspector will reject.
Pitfall 2 — Sub-size scaling not applied: Sub-size specimen energy not scaled per UG-84(c); raw energy interpreted as full-size = under-test.
Pitfall 3 — Notch location error: “HAZ” location not precisely measured 1mm or 5mm from fusion line; specimen actually in base metal or weld; result not representative.
Pitfall 4 — Bath temperature drift during testing: Bath warms from 100% specimen + holding fixture insertion; thermocouple in bath not at specimen mid-thickness; actual specimen temperature warmer than reported.
Pitfall 5 — Single-specimen 67% rule overlooked: Average passes but single specimen below 67%; ASME inspector rejects despite passing average.

UG-84 Welding Process Implications

When UG-84 impact testing is required, several welding process considerations follow per ASME Section IX QW-403.6:

Consumable Charpy data: Filler metal datasheet must include Charpy V-notch energy at design temperature; without data, fabricator must qualify per UG-84.
Heat input limitation: Excess heat input degrades HAZ toughness through grain coarsening; QW-409.1 essential variable tightens with toughness requirement.
Preheat / interpass control: Preheat 150-200°C reduces hydrogen risk; interpass max 200-250°C preserves fine grain (vs 315°C for standard service).
PWHT temper consideration: Some weld metals temper embrittle at PWHT temperature; consumable selection accounts.
Production test plate sampling: Per WPS, production test plate welded representative of vessel; Charpy specimens removed per UG-84 locations.

Real Project Reference

Project type: LNG vaporizer (Arctic service, MDMT -73°C)
Material: SA-203 Gr E (3.5% Ni steel), 38 mm wall
UG-84 test setup: Test temperature -73°C in liquid nitrogen + methanol bath; full-size 10×10×55 mm Type A specimens (38 mm wall accommodates full size); 3 specimens per location × 4 locations (base + weld center + HAZ 1mm + HAZ 5mm) = 12 specimens total
Welding equipment from Wuxi ABK: HGZ-30 rotator + LH-3030 manipulator + tandem twin-wire SAW + GTAW root + cold-wire fill
Charpy results: Base 41 J avg / weld center 37 J avg / HAZ 1mm 35 J avg / HAZ 5mm 39 J avg (all above 27 J minimum); lateral expansion all above 0.38 mm; single-specimen 67% rule satisfied
Outcome: Vessel passed ASME Section VIII Division 1 + UCS-66 + UG-84 third-party inspection; delivered to LNG terminal on schedule.

Summary

ASME Section VIII Division 1 UG-84 prescribes Charpy V-notch impact testing methodology for pressure vessel base metal, weld metal, and HAZ when toughness testing is required per UCS-66, UHA-51, or UNF-65. The 5 specification areas (specimen geometry / orientation / quantity / temperature / acceptance) govern test execution. The 4 notch locations (base + weld center + HAZ 1mm + HAZ 5mm) cover the critical regions for toughness audit. The 5-criterion acceptance framework (energy average / single-specimen 67% / lateral expansion / sub-size scaling / retest provisions) ensures pass/fail determination. The 5 process implications tie UG-84 to ASME Section IX QW-403.6 supplementary essential variable, consumable selection, heat input control, preheat/interpass control, and PWHT consideration. Wuxi ABK Machinery supplies welding rotator, manipulator, positioner, and integrated SAW/GTAW/MIG equipment for pressure vessel fabricators serving impact-test-required low-temperature service across LNG terminals, Arctic O&G, and standard low-temperature pressure vessels — supporting WPS/PQR documentation chain with calibrated parameter logs feeding into UCS-66 / UG-84 audit chain.

For project-specific UG-84 + welding line proposals — based on MDMT, base material specification, wall thickness, and target production volume — Wuxi ABK can provide a complete equipment configuration including documentation handoff supporting Charpy V-notch impact testing per UG-84.

Contact: jan@weldc.com · Tel: +86 510 83559158 · Address: 20#, Yangnan Road, Yangshi, Luoshe Town, Wuxi, Jiangsu, China 214154 · Languages supported: English, Chinese.

Last updated: 2026-06-16.