Marine safety service
Non-Destructive Testing (NDT)
Certified NDT on board, including visual, magnetic particle, dye penetrant, ultrasonic and eddy current testing of welds, castings, shafts and lifting equipment.
Overview
Non-destructive testing for ships
Non-destructive testing (NDT) finds cracks, lack of fusion, porosity, laminations and wall loss without damaging the component. On ships it supports class surveys, repair acceptance, damage assessment after an incident and condition monitoring of highly stressed parts such as crane pedestals, davit arms, lifting lugs, rudder stocks, propeller shafts and hull welds. A timely NDT result can turn an uncertain defect into a clear repair decision and avoid unnecessary steel renewal.
vslSafety coordinates NDT technicians at the vessel’s port with the methods and certification the job requires. Where the aim is hull or tank thickness gauging for a class survey, see ultrasonic thickness measurement; this service focuses on flaw detection in welds and components.
Regulatory requirements and standards
- Class rules specify when NDT is required during new construction, repairs and surveys, and the acceptance criteria. Surveyors may request NDT of suspected cracks, repair welds, or specific components during annual and renewal surveys.
- IACS Recommendation 20 gives guidance on non-destructive testing of ship hull steel welds, including extent of testing and personnel qualification. IACS Recommendation 47 (Shipbuilding and Repair Quality Standard) is commonly used to judge repair workmanship.
- Personnel qualification – NDT operators should hold certification to ISO 9712 or an equivalent scheme such as ASNT SNT-TC-1A, at a level appropriate to the task. Class may require the company to be an approved service supplier for certain inspections.
- Method standards – ISO 17637 (visual testing of welds), ISO 17638 (magnetic particle testing of welds), ISO 3452-1 (penetrant testing), ISO 17640 (ultrasonic testing of welds) and ISO 17636 (radiographic testing of welds) are widely referenced.
- Lifting appliances – after repair, alteration or damage, NDT may be required before load testing and re-certification under SOLAS regulation II-1/3-13 and MSC.1/Circ.1663.
When NDT is typically required
| Item | Requirement | Timing | Reference |
|---|---|---|---|
| Hull repair welds | Testing to agreed extent and acceptance level | After repair, before acceptance | Class rules, IACS Rec 20 / Rec 47 |
| Suspected cracks in structure | MPI or PT to determine extent | When found at survey or inspection | Class surveyor |
| Crane pedestals, davits, lifting lugs | MPI, UT around stressed welds | After damage or repair, before load test; per maker or class | Class / MSC.1/Circ.1663 |
| Rudder stock, pintles, shafts | Crack detection | At drydock or after grounding or contact | Class rules |
| Propeller blades | PT or MPI after damage or repair | After repair | Class rules |
What the service includes
- Visual testing (VT) of welds and components with documented findings
- Magnetic particle inspection (MPI/MT) of ferritic steel welds, lugs, hooks and castings
- Dye penetrant testing (PT) of non-magnetic materials, including stainless steel and propeller bronze
- Ultrasonic flaw detection (UT) of butt welds, fillet welds and forgings, including phased array where available
- Eddy current or ACFM crack detection through coatings where removal is not practical
- Radiographic testing arrangements where required and permitted
- Marking of indications, sizing and reporting against the agreed acceptance criteria
- Retest after repair, and support to the class surveyor
Components commonly tested
Hull structure and repair welds, hatch coaming brackets, crane pedestals and jibs, davit arms and foundations, lifting lugs and pad eyes, rudder stocks, pintles and couplings, propeller shafts and blades, anchors and chain accessories, engine components such as crankshafts, connecting rods and cylinder covers, and pressure vessel welds. For shafting and propellers see also propeller and shaft services.
Common defects found
- Fatigue cracks at bracket toes, hatch coaming ends and crane pedestal welds
- Lack of fusion and porosity in repair welds carried out without proper procedures
- Cracks in lifting lugs and pad eyes, often hidden under paint
- Cracks initiating from corrosion pits in highly stressed areas
- Propeller blade edge cracks after contact damage
- Cracks in rudder stock keyways and pintle housings
Structural cracks found during PSC or class surveys typically result in a condition of class or a requirement for repair before departure.
Certificates and documents you receive
An NDT report for each method and location, stating the procedure, standard, equipment, calibration, surface condition, acceptance criteria and results; sketches or photographs of indications; and copies of the technician’s qualification certificates. The report is signed by the qualified technician and supports the surveyor’s decision on acceptance or repair.
How to prepare the vessel
- Identify the areas to be tested and agree the extent with the class surveyor in advance
- Arrange cleaning and paint removal where the method needs a bare surface
- Provide safe access, staging, lighting and gas-free certificates for enclosed spaces
- Provide power supply for equipment, or confirm battery-operated equipment is suitable
- For radiography, arrange exclusion zones and port permissions
Information needed for a quotation
- Vessel name, IMO number, flag and class
- Port, berth, anchorage or shipyard, ETA and ETD
- Component or area to be tested, material and approximate extent (metres of weld, number of items)
- Required methods, standard and acceptance criteria, if specified by class
- Reason for testing: survey, repair, incident or planned maintenance
- Access arrangements and whether surface preparation will be done by crew
vslSafety coordinates a suitably qualified NDT provider at the vessel’s port and aligns the attendance with the surveyor.
Frequently asked questions
What NDT method is best for detecting cracks in steel welds?
Magnetic particle inspection is generally the most practical method for surface and near-surface cracks in ferritic steel welds. Penetrant testing is used for non-magnetic materials. Ultrasonic testing is needed for internal flaws in butt welds and thick sections. The class surveyor or repair specification often dictates the method and extent.
What qualifications should NDT technicians have?
Technicians should hold certification to ISO 9712 or an equivalent scheme such as ASNT SNT-TC-1A for each method they perform. Level 2 technicians can carry out testing and interpret results against the procedure, while Level 3 personnel approve procedures. Class may also expect the company to be recognised as a service supplier for particular types of inspection.
Is NDT required after welding repairs on a ship?
Usually yes for structural repairs. The extent depends on the class rules, the importance of the structure and the type of weld. IACS Recommendation 20 and the class repair procedures give guidance. Repair work can be arranged together with testing through welding and steel work.
Can NDT be done without removing the paint?
Some methods can. Eddy current and ACFM techniques can detect surface cracks through thin coatings, and some ultrasonic techniques work through paint. Magnetic particle and penetrant testing generally need a clean, bare surface for reliable results. The technician will advise on preparation for each method.
Do lifting lugs need NDT before load testing?
Where a lug or pad eye has been repaired, modified or newly installed, NDT of the welds is commonly required before load testing, and a visual and sometimes MPI examination follows the test. This is often coordinated with load testing and proof load in a single attendance.
