The nozzle-to-shell weld is structurally the most complex and inspection-critical joint in any pressure vessel. Its geometry — the intersection of a cylindrical nozzle and a curved vessel shell or head — creates a weld cross-section that varies continuously around the nozzle circumference, with a fusion line that changes orientation through the wall in a way that no single UT beam angle can intercept at normal incidence across the full joint.
The PAUT Approach to Nozzle Weld
Inspection
Multi-Zone Focal Law Development
Each nozzle weld inspection programme begins with a geometric model of
the specific nozzle configuration — OD, wall thickness, weld preparation
geometry, and the curvature of the vessel shell or head at the nozzle
intersection. From this model, focal laws are developed to optimise beam
coverage for each critical zone: the weld root, the mid-wall fusion line, the
outer surface cap, and the heat-affected zone on both the nozzle body and the
vessel shell.
Simultaneous Scanning Positions
Nozzle weld coverage typically requires scanning from multiple positions
— from the nozzle body, from the vessel shell on both sides of the nozzle, and
from the nozzle bore where access permits. Each position addresses zones that
the other positions cannot efficiently reach. Our scanning plans document every
required position, the focal laws deployed at each position, and the coverage
contribution of each scan before inspection begins.
Conventional UT as a Complement to PAUT
For specific nozzle zones — particularly the nozzle bore examination for
inner diameter cracking and the creep-wave examination for near-surface outer
diameter defects — conventional UT techniques complement the PAUT programme.
Our procedures specify the complete examination technique set required to
achieve full coverage of the nozzle weld in accordance with the applicable
code.
Code Qualification and Demonstration
PAUT procedures for nozzle weld inspection are qualified in accordance
with ASME Section V Article 4, ASME Code Case 2235, or EN ISO 13588, as
required by the applicable design code and jurisdictional requirements.
Procedure qualification includes demonstration of detection on a representative
nozzle mock-up with fabricated reference reflectors at the target sensitivity
level.
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Pressure vessel nozzle weld inspection — in-service and
new construction
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Reactor vessel nozzle inspection — including dissimilar
metal nozzle welds
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Heat exchanger nozzle and manway weld inspection
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Storage tank shell nozzle inspection
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Piping branch connection weld examination
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Set-on and set-in nozzle weld configurations — all
geometries
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Nozzle
weld fitness-for-service assessment — defect characterisation and sizing
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Post-weld repair nozzle acceptance inspection
Reports include zone-by-zone coverage maps, encoded S-scan and B-scan
data at all scanning positions, indication tables with location referenced to
the nozzle clock position and through-wall depth, and accept/reject disposition
against the applicable examination code. Nozzle geometry sketches and scan
position diagrams are included to support engineering review of inspection
coverage.