In-House Weld Inspection (NDT) for a Production Aluminum Catamaran

Overview & Key Takeaways

Aluminum is a great boatbuilding material but an unforgiving welding material: welds are prone to hot (solidification) cracking, lack of fusion, and porosity, and the heat-affected zone is the weak point for fatigue in service. Because aluminum is non-magnetic, Magnetic Particle Testing (MT) cannot be used at all — which is why Dye Penetrant and Eddy Current carry the "cheap surface crack" role that MT plays in steel yards.

Foundation: VT + PT + Leak testA few thousand dollars of gear covers 100% of welds visually, critical seams with penetrant, and every compartment/tank with air-and-soap or water fill.

Inside the weld: UT or PAUTUltrasonics verify full-penetration butt joints in primary structure. PAUT adds speed, imaging, and digital records at a much higher price.

Radiography: skip it in-houseSafety, licensing, and poor sensitivity to thin cracks in aluminum make RT a poor fit. Contract it out on the rare occasion it's demanded.

Don't stop at deliveryCats flex constantly in seaways. Annual visual checks plus ET/PT on high-stress joints every 2–5 years catches fatigue cracks before they matter.

At a Glance

Method	What it sees	Equipment cost	Training	Best use on a catamaran	Role
VT Visual	Surface & geometry	$100–$2,000 (videoscopes to $60k)	1–3 days	100% of all welds, fit-up checks	Foundation
LT Leak test	Through-wall leaks	$500–$3,500 (helium optional)	½–1 day	Tanks, watertight compartments, decks	Mandatory
PT Dye penetrant	Surface-breaking cracks	$100–$500 + lamps	1–2 days	Critical seams right after welding	Primary
ET Eddy current	Surface/near-surface, through paint	$10,000–$35,000	3–5 days	In-service fatigue cracks at weld toes	Lifecycle
UT Ultrasonic	Internal defects	$8,000–$30,000	1–2 weeks + months OJT	Butt joints in primary structure	Primary
PAUT Phased array	Internal, imaged & recorded	$50,000–$150,000	UT base + 1–3 weeks	Production QA, class records	Premium
RT Radiography	Internal volumetric	$50,000–$150,000 + licensing	1–2 weeks + RSO	Rarely justified; contract out	Avoid in-house

The Seven Methods in Detail

All figures are approximate USD, mid-2020s pricing, new equipment. Used/refurbished gear often runs 30–60% less, and OEMs frequently bundle training with instrument purchases.

Visual Testing (VT)

The foundation of every program — and a prerequisite before any other method anyway.

Equipment & Cost

Weld gauge set (fillet size, undercut, hi-lo, V-WAC/Cambridge style): $150–$600
5x–10x magnifier + quality flashlight: $50–$200
USB/budget borescope for tanks and bilges: $100–$800
Optional industrial videoscope for remote internals: $15,000–$60,000

Training

VT course: 1–3 days, ~$600–$1,800
Weld-inspection seminar (AWS-CWI style): ~1 week, $1,200–$2,600 (CWI exam ~$900–$1,600 extra if you want the credential)
Annual vision check required (Jaeger-1 acuity + color contrast)
Easiest method to staff; hardest to master — most missed defects are things people never learned to look for

Defects Detected

Surface cracks, undercut, overlap, surface porosity
Underfill / poor reinforcement / bad weld profile
Undercut at the weld toe (fatigue starter), burn-through
Dimensional: wrong weld size, misalignment, distortion, arc strikes, spatter

Top Sources

Weld gauges: NDT Supply, Mills Supply, AWS-authorized distributors (Cambridge-type, V-WAC, hi-lo gauges)
Borescopes/videoscopes: Evident (IPLEX line), Baker Hughes Waygate (XL Vuor)
Reference: AWS D1.2 Structural Welding Code — Aluminum (visual acceptance criteria)

Fit for your yard: Non-negotiable baseline. Inspect fit-up before welding and 100% of finished welds. Aluminum hot cracks can be hairline and oxidize over quickly — best caught fresh.

Leak Testing (LT)

The functional proof: the boat floats, the tanks hold, the compartments are tight.

Equipment & Cost

Shop air compressor (likely already owned): $300–$2,500
Low-pressure regulator, gauges, hoses, bung kit: $150–$600
Bubble solution (Snoop-type): $20–$100/bottle
Hand hydrostatic test pump: $150–$800
Vacuum box for flat deck/panel seams: $500–$2,500
Optional helium mass-spectrometer detector: $15,000–$60,000 (rarely needed for boats)

Training

½–1 day in-house on written procedure is usually enough
Formal LT course if desired: 1–2 days, ~$800–$1,500
Critical lesson: keep air test pressures LOW (typically ~3–7 psi / 0.2–0.5 bar). A pressurized compartment stores dangerous energy and can oil-can thin plate — many specs prefer water fill for larger volumes

Defects Detected

Only defects that penetrate the full wall: cracks, pinholes, porosity channels, lack of penetration that leaks
Perfect for fuel/water tanks, watertight bulkheads, sealed hull compartments, pipework, hatches
Tells you nothing about weld quality that doesn't leak — a weld can pass LT and still harbor internal defects

Top Sources

Compressors: any industrial supplier (Ingersoll Rand, Quincy, etc.)
Test pumps: RIDGID, Rothenberger
Bubble solutions: Nupro/Swagelok "Snoop" and NDT suppliers
Helium (if ever needed): INFICON, Pfeiffer Vacuum

Fit for your yard: Mandatory on every boat before delivery — pressurize and soap every compartment and tank. Cheap, simple, and the most convincing demonstration of quality for an owner or surveyor.

Ultrasonic Testing (UT)

Handheld probe, sees inside the weld, one-sided access.

Equipment & Cost

Portable flaw detector: $8,000–$30,000 (Evident EPOCH series, Waygate USM Go+, Sonatest, SIUI); budget brands $4,000–$8,000 (e.g., Dakota Ultrasonics)
Angle-beam transducers 45°/60°/70°, typically 2.25–5 MHz: $250–$800 each (use lower frequencies + twin-element probes — aluminum's coarse weld grain is noisy)
Calibration blocks (IIW V1/V2, aluminum step wedges per AWS D1.2): $300–$1,500
Couplant, cables, case: $100–$400

Training

Steepest learning curve of the practical methods
UT Level II course: 40–80 hours (1–2 weeks), $2,000–$4,500
Then hundreds of documented supervised scan-hours; realistic path to full qualification: 3–12 months
Smart approach: retain a UT Level II/III consultant to write procedures and sign off early work while your team trains under them

Defects Detected

Internal planar defects — cracks, lack of fusion, incomplete penetration (UT is actually better than X-ray at these if the operator is good)
Porosity clusters, inclusions, undercut
Measures defect depth and length for engineering assessment

Top Sources

Evident (formerly Olympus NDT)
Baker Hughes / Waygate Technologies (Krautkrämer lineage)
Sonatest, SIUI, Dakota Ultrasonics, Zetec
Couplant: Sonotech; blocks and probes from the same OEMs or NDT distributors

Fit for your yard: Your workhorse for verifying full-penetration butt joints in primary structure — keel/longitudinals, cross-beam connections, hull-shell seams. Cheaper entry than PAUT; expect a real ramp-up in operator skill.

Phased Array UT (PAUT)

UT with multi-element probes: live sector images, encoded scans, permanent digital records.

Equipment & Cost

Instrument + weld scanner + encoder: $50,000–$150,000
Probe and wedge sets sized to your plate thicknesses: $2,000–$8,000
Analysis software workstations for record review: $0–$5,000 (often included)

Training

Assumes conventional UT competence first
PAUT-specific course: 1–3 weeks, $3,000–$7,000
OEMs typically bundle setup and technique training with purchase — negotiate it
Realistic ramp to production confidence: 6–18 months

Defects Detected

Everything UT finds, with superior sizing and imaging
Excellent on fillet and T-joints (which dominate catamaran structure) and thick multi-pass welds
Multiple angles in one pass = faster coverage of many welds
Digital records a class society, insurer, or future buyer can re-review years later

Top Sources

Evident (OmniScan series)
Zetec (TOPAZ series, owned by Eddyfi Technologies)
Sonatest (Veo+), Doppler (Phasor series), SIUI (SyncScan)

Fit for your yard: The premium production-QA choice. If you're building serial boats, the per-weld speed and permanent records can justify the price. If budget is tight, start with conventional UT and upgrade later — skills transfer directly.

Dye Penetrant Testing (PT)

Spray-can crack detection for bare aluminum. The cheapest serious NDT there is.

Equipment & Cost

Aerosol kit — solvent remover, red penetrant, developer: $60–$250 per set; consumable cost per weld is pennies
Visible red dye needs no lamp (works in daylight)
Fluorescent penetrant option: UV-A LED lamp $200–$1,500 + a darkened area (higher sensitivity)

Training

Easiest of the serious methods to bring in-house
PT Level II course: 1–2 days (16–24 hrs), $500–$1,500
Annual vision check required
A team member can be doing useful work within days

Defects Detected

Anything open to the surface: solidification/hot cracks (the classic aluminum defect), crater cracks, surface porosity, lack of penetration at the toe
Requires clean bare metal — paint, oil, heavy oxide kills it
Sees nothing below the surface

Top Sources

Magnaflux (Spotcheck line, ITW)
Sherwin Industries, Chemsearch (Ardrox), Met-L-Chek
UV-A lamps: Spectroline, LuvoLux

Fit for your yard: Because MT is impossible on aluminum, PT is your default low-cost surface-crack method. Check critical welds immediately after welding and after any weld repair. Fast, cheap, and convincing.

Eddy Current Testing (ET)

Electromagnetic surface/near-surface inspection — works through paint. The periodic-survey superpower.

Equipment & Cost

Handheld ET flaw detector: $8,000–$35,000 (Zetec MIZ series, Evident Nortec/23 series, Fischer FISCHERSCOPE, Karl Deutsch)
Pencil, surface and weld probes: $400–$3,000 each
Optional eddy-current array (ECA) probes + scanner: +$15,000–$40,000

Training

ET Level II course: 3–5 days (24–40 hrs), $1,500–$3,000
Signal interpretation (phase/amplitude) takes practice — weeks to months to feel confident
Much gentler ramp than UT

Defects Detected

Surface and slightly sub-surface cracks — especially fatigue cracks at weld toes, the #1 in-service risk on a working catamaran
Can detect cracks through thin paint/coatings — no stripping required
Near-surface porosity; conductivity techniques can also flag corrosion thinning
Aluminum's high electrical conductivity makes ET unusually well suited to it

Top Sources

Eddyfi Technologies / Zetec
Evident (Nortec line)
Fischer Technology, Karl Deutsch

Fit for your yard: Buy or contract it once you have boats in service. It becomes the most valuable method at year 3+, finding fatigue cracks at stressed joints without removing paint — exactly what periodic surveys need.

Radiographic Testing (RT) — X-ray / Gamma

A radiographic image of the weld interior. Powerful record, heavy regulatory burden.

Equipment & Cost

Portable X-ray generator: $25,000–$90,000 (Golden XRS-3, YXLON, Vidisco, Waygate)
Imaging: film + processor $5,000–$30,000; CR scanner $20,000–$60,000; DR flat panel $40,000–$120,000
Survey meters, dosimeters, barriers, signage: $2,000–$6,000
Gamma alternative (Ir-192): $15,000–$40,000 + source replacements + even heavier regulation

Training

RT Level II course: ~40 hrs (1–2 weeks), $2,000–$3,500
Plus radiation-safety training, a designated Radiation Safety Officer, licensing (NRC / agreement-state in the US or national equivalent), ongoing dosimetry and compliance costs every year

Defects Detected

Volumetric internal defects: porosity, inclusions, incomplete penetration
Cracks only when the beam is nearly parallel to them — and cracks are exactly what aluminum welds produce
Permanent image record

Top Sources

Vidisco, Comet YXLON, Baker Hughes/Waygate, Golden Engineering
Imaging: Carestream, DÜRR NDT, Fuji, AGFA

Fit for your yard: Not recommended in-house — see the next section for why and what to do instead.

Can We Skip Radiography Entirely?

Yes — and for an aluminum boatbuilder, you probably should.

Most aluminum boatyards run complete, class-acceptable inspection programs with zero radiography in-house. Reasons:

Codes accept substitutes. AWS D1.2 (Structural Welding Code — Aluminum) and classification society rules (DNV, ABS, Lloyd's for high-speed/light craft) accept or even prefer UT/PAUT for volumetric examination of full-penetration welds. RT is rarely mandated for this product class.
RT is weak where aluminum fails. Aluminum welds fail by thin, planar cracking (hot cracks, fatigue cracks). X-ray only sees a crack if the beam is nearly parallel to it; UT/PAUT are inherently better at planar defects.
Low contrast in aluminum. Aluminum absorbs little radiation, so image contrast is poor and fine defects are hard to resolve compared to steel.
Safety and logistics. A production yard has electricians, riggers, and painters everywhere. Clearing a radiation exclusion area repeatedly is disruptive, and the licensing, RSO, dosimetry, and inspection obligations never stop.

If RT is ever demanded (a class surveyor, a flag-state requirement, or a dispute), hire a contract NDT firm — they arrive with licensed equipment and crew. Expect roughly $1,000–$3,000/day or per-weld pricing. That's far cheaper than owning it.

The recommended no-RT package: VT 100% + PT on critical seams + UT or PAUT on full-penetration butt joints in primary structure + air/water leak test on every compartment and tank + ET for in-service fatigue checks.

When to Inspect: Build Only, or Periodically?

Both — but the emphasis shifts. At build, you're catching manufacturing defects (cracks, porosity, lack of fusion). In service, you're hunting fatigue cracks at stress concentrations. A catamaran is a fatigue machine: two hulls twisting in a seaway constantly load the cross-beam/bridge-deck connections, and aluminum has no "infinite life" freebie — cracks grow with every cycle.

When	Method	Coverage	What you're looking for
Before welding	VT	100% of joints	Fit-up, root gap, cleanliness, bevel quality
After welding	VT	100% of welds	Profile, undercut, size, surface cracks, distortion
After welding	PT (or ET)	10–100% of critical fillet welds per your quality plan (100% on cross-beam, engine foundations, chainplates)	Hot cracks, crater cracks, toe cracks
After welding	UT or PAUT	Full-penetration butt joints in primary structure (percentage per AWS D1.2 / class; typically 100% on keel, cross-beam, shell seams on the first hulls, sampling thereafter once rates stabilize)	Internal cracks, lack of fusion, porosity
Before delivery	Leak test	100% of tanks and watertight compartments (air + soap at ~3–7 psi, or water fill); vacuum box on flat deck seams if specified	Any through-wall leak
Annually	VT by a knowledgeable person	High-stress zones + coating condition	Visible cracks, coating breakdown, pitting, galvanic corrosion at fittings
Every 2–3 years (charter/commercial) or 3–5 years (private use)	ET (+ PT on bare metal)	High-stress weld toes: cross-beam/bridge-deck connections, hull-to-deck joints, bulkhead connections, engine foundations, chainplates, rudder stocks	Fatigue cracks — through paint, no stripping needed
After an event (grounding, collision, severe storm)	VT + PT + ET, UT as indicated	Affected areas and adjacent structure	Impact damage, new cracks

Two habits that pay off enormously

Keep a weld map. Number every significant weld and record who welded it, when, and the NDT result. Periodic surveys become "compare against baseline" instead of archaeology.
Buy digital where you can. PAUT data files and even photos create the baseline that makes year-5 comparisons meaningful — and they're gold during warranty discussions, class surveys, and resale.

When Will a Humanoid Robot Do This?

Honest answer: this is forecasting, so treat dates as informed speculation with wide error bars. The harder problem isn't walking around the boat — it's consistent probe pressure, couplant management, scan patterns, and judgment about acceptability.

Now – ~2030: Purpose-built automation, not humanoids Encoded PAUT weld crawlers, tank-inspection drones, and robotic UT scanners already exist and will keep spreading. Humanoids (Figure, Tesla Optimus, Agility Digit, Apptronik, Unitree) are in pilots for material handling and simple, repetitive tasks — not skilled NDT.
~2030 – 2035: Supervised humanoid pilots Expect the first shipyard demos of humanoids doing guided VT and simple PT under close human supervision, likely teleoperated or semi-autonomous. Messy, cramped, one-off boat interiors are the last place this lands — but a production catamaran line (repeatable geometry, known weld map) is exactly where it lands first.
~2035 – 2040: Practical robotic NDT on production lines Semi-autonomous inspection of routine production welds becomes plausible — though probably via dedicated arms and crawlers driven by the same PAUT software a human uses, not a humanoid.
2040+: General-purpose humanoid inspectors A robot that can be handed "survey this 15-year-old cat" with human-level judgment may be this far out — or may never beat cheaper specialist tools. The judgment side (accept/reject against code, knowing what matters) is the bottleneck, not the locomotion.

Design your process now so robots can inherit it later

Numbered weld maps, consistent access to critical joints, digital PAUT records, and written procedures are exactly what an automated inspector will need. Automation-friendly documentation costs almost nothing today and future-proofs you either way.

Three Starter Budgets

Tier	What you get	Equipment	Training (team of 2–3)	Covers
1. Start now	VT kit, PT kits, leak-test kit	~$1,500–$7,000	~$2,000–$5,000	VT 100%, PT on critical seams, leak test everything. The irreducible minimum.
2. Structural capability	Tier 1 + conventional UT instrument, probes, blocks (+ consultant Level II)	~$25,000–$60,000	~$8,000–$15,000	Everything in Tier 1 plus internal verification of primary-structure butt joints.
3. Production-grade	Tier 2 replaced/augmented with PAUT system + ET instrument + part-time Level III	~$100,000–$200,000	~$15,000–$25,000	Full in-house program with digital records; in-service survey capability with ET.

Certification & Standards Notes

How your team gets certified

In the US, most employers certify their own NDT personnel under a written practice based on ASNT SNT-TC-1A: documented training hours + on-the-job hours + written/practical exams.
International alternative: ISO 9712 (third-party certification bodies).
You'll need a Level III (by exam or by hire) to approve your written practice and procedures — commonly contracted part-time for a small yard.
Annual vision screening (near-vision + color contrast) is a formal requirement for most methods.

Codes & standards worth knowing

AWS D1.2 — Structural Welding Code, Aluminum (visual & UT criteria)
ISO 10042 — quality levels for fusion welds in aluminum
ISO 23277 — PT acceptance levels; ISO 17640 / 11666 — UT technique & acceptance
Classification society rules (DNV, ABS, Lloyd's) if the boat will be classed or commercially flagged — their surveyor requirements drive your acceptance criteria, so engage them early.