Al Safwan Marine
Al Safwan Marine
Get a quote Call +971 55 659 9860

Hull thickness and NDTLesson 3 of 5

NDT methods for hull welds and cracks, and who may do them

You will be able to pick the right NDT method for a hull weld or a suspected crack and check that the people and the procedure behind the result are acceptable to class.

14 minutes · For signed-up learners, free · Rules checked 20 October 2026

Start here

A crack in a hull weld rarely announces itself. It may start at the toe of a bracket under coating, grow a little every time the ship works in a seaway, and show only as a rust line or a weep of ballast water. When the surveyor sees that line, the question is no longer whether to test but how: which non-destructive testing (NDT) method will find the end of the crack, and whose result will class accept?

The answer depends on where the defect sits (surface or inside), the material (magnetic steel or not), the thickness, and who holds the probe. IACS answers the first three for new construction in Unified Requirement (UR) W33, and the last one in UR W33 and UR W35, with a change coming in 2028. Start by sorting the jobs below.

Continue this lesson free

The rest of this lesson, the interactive Match each job to the NDT method that suits it best and the quiz are open to signed-up learners. It's free, takes a minute, and opens every lesson in all 14 courses.

We use your details to save your progress and to understand who uses the Academy. Already signed up? Get a sign-in link.

In this lesson

  • Try it: Match each job to the NDT method that suits it best
  • In plain words
  • In detail
  • What the rules say
  • Flag and class notes
  • Key numbers
  • What inspectors find
  • Questions people ask
  • Quiz: 6 questions

Sources

  1. 1 IACS Unified Requirement W33, Non-destructive testing of ship hull steel welds, Rev.1 Corr.1 (August 2021; ships contracted for construction on or after 1 July 2021), paragraphs 1.1 to 1.6, 2.4, 2.5 and Table 1, 3.1 to 3.3, 5.1 to 5.10, 6.1 to 6.6. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2022/05/18145127/ur-w33rev1corr1.pdf
  2. 2 IACS UR W33 Rev.2 (July 2026; ships contracted for construction on or after 1 January 2028), section 3.1. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2022/05/16133333/UR-W33-Rev.2-July-2026-CLN.pdf
  3. 3 IACS Unified Requirement W34, Advanced non-destructive testing of materials and welds (December 2019; ships contracted on or after 1 July 2021; Rev.1 in force 1 January 2028), paragraphs 1.1 to 1.5. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2022/05/18145233/ur-w34.pdf
  4. 4 IACS Unified Requirement Z7, Hull Classification Surveys, Rev.29 Corr.1 (May 2024), paragraphs 1.2.3, 1.3.1, 2.2.9, 5.3.1 and 5.3.2. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2024/05/21130428/UR-Z7Rev.29Corr.1.pdf
  5. 5 IACS Unified Requirement W35, Requirements for NDT Service Suppliers, Rev.1 (October 2023, implemented from 1 January 2025), paragraphs 1.1 and 1.4; Rev.2 (February 2025) in force 1 January 2027. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2024/01/02143105/UR-W35-Rev.1-Oct-2023-CLN.pdf and https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2025/02/13122835/UR-W35-Rev.2-Feb-2025-CLN.pdf
  6. 6 IACS Unified Requirement Z17, Procedural Requirements for Service Suppliers, Rev.22, 23 and 24 (Rev.23 in force 1 January 2028), Rev.23 paragraphs 4.1.2 and 4.2 and Annex 1, section 19. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2023/05/05122440/UR-Z17-Rev.22-23-24-CLN.pdf
  7. 7 IACS Recommendation No. 20, Non-destructive testing of ship hull steel welds, deletion notice (“Deleted 1 July 2021, on implementation of UR W33”). https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2022/05/20081450/rec20del.pdf
  8. 8 IACS UR Z17 Rev.21 (January 2025, implemented from 1 July 2026), Annex 1, paragraphs 1.2, 3.2 and 8.4. https://iacs.s3.af-south-1.amazonaws.com/wp-content/uploads/2023/05/14135618/UR-Z17-Rev.21-Jan-2025-CLN.pdf

Free awareness training. Al Safwan Marine is not an approved training provider, so no certificate is given, and these courses are not a qualification. They don't replace STCW training, manufacturer training or the certification technicians need for this work. The manufacturer's manual and your flag's rules always come first.

Sign in to save your progress.

This lesson is also published by our sister site vslsafety.com.