What does UR Z10.1 require for oil tankers, in plain language?
UR Z10.1 is the enhanced survey requirement for oil tankers that are not double hull, combination carriers included. Table I fixes the minimum close-up survey and Table II the minimum gauging at each special survey. Both grow with the survey number.
The short answer
- Who: every self-propelled oil tanker that is not a double hull oil tanker. Ore/oil and other combination carriers are in; asphalt carriers are out.
- Cycle: special survey every 5 years, annual each anniversary, intermediate at or between the 2nd and 3rd annual.
- Close-up: Table I. One web frame ring at SS1; all web frame rings in a ballast wing tank (or a cargo wing tank used primarily for water ballast) at SS2; all in every ballast tank, all web frame rings in a cargo wing tank, plus 30% in the remaining cargo wing tanks at SS3.
- Gauging: Table II. Suspect areas always; one deck section at SS1, then 1, 2 and 3 transverse sections at SS2, SS3, SS4.
- Rev.25 applies to surveys commenced on or after 1 July 2024.
Which ships it catches, and which part of the ship
Z10.1 applies to every self-propelled oil tanker other than a double hull oil tanker; the boundary is drawn by the application clause of UR Z10.4, and Z10.1 points at it rather than repeating it. An oil tanker here is a ship built mainly to carry oil in bulk in cargo tanks forming part of the hull. Ore/oil ships and other combination carriers count. Ships carrying oil in independent tanks that are not part of the hull — asphalt carriers being the named case — do not. UR Z10.1 §1.1.1
Inside the ship it governs the hull structure and the piping over a fixed set of compartments: the cargo tanks, the pump rooms, the cofferdams and pipe tunnels, the void spaces that sit inside the cargo area, and every ballast tank. The rest stays under Z7. A tank used for cargo or ballast as routine operation is treated as a ballast tank, so it comes into that count. UR Z10.1 §1.1.2
The survey cycle the rule governs
Special survey runs on a 5-year interval — the first within 5 years of the initial classification survey, then within 5 years of the credited date of the previous one. An extension of 3 months maximum is possible in exceptional circumstances and does not shift the next window. The survey may start at the 4th annual and finish by the 5th anniversary; start earlier and the whole thing has to be completed within 15 months or the early work is not credited. Nothing may be credited to the intermediate and the special survey at once, gauging included. UR Z10.1 §2.1
Annual surveys fall within 3 months either side of the anniversary date; the intermediate is held at or between the 2nd and 3rd annual. Between 5 and 10 years of age the clause fixes no figure: all ballast tanks are examined, thickness measurement and testing follow only where the surveyor considers them necessary to show the structural integrity is still effective, and suspect areas from previous surveys are examined as well. UR Z10.1 §4.2.2 Past 10 years of age the intermediate is worked to the extent of the previous special survey, minus the pressure testing of cargo and ballast tanks and minus the longitudinal strength evaluation unless the surveyor calls for them; past 15 years a dry dock survey joins it. A written survey programme is required before any part of the special survey, and before the intermediate once the tanker is over 10. UR Z10.1 §4.2 / §5.1.1
Close-up survey: how much, by special survey number
An overall survey of all tanks and spaces happens at every special survey. Table I sits on top of it, and the same three structural families run down every column — so what changes with the survey number is the count, not the kind of structure.
| Survey | Web frame rings | Deck / bottom transverses | Transverse bulkheads |
|---|---|---|---|
| SS1 age ≤ 5 | One, in a ballast wing tank — or a cargo wing tank used mainly for ballast | One deck transverse, in a cargo oil tank | Lower part only: one in a ballast tank, one in a cargo oil wing tank, one in a cargo oil centre tank |
| SS2 5 < age ≤ 10 | All, in a ballast wing tank (or a cargo wing tank used primarily for water ballast) | One deck transverse in each remaining ballast tank, one in a cargo wing tank, one in each of two cargo centre tanks | Both complete in a ballast wing tank (or a cargo wing tank used primarily for water ballast); lower part in each remaining ballast tank, a cargo oil wing tank, two cargo centre tanks |
| SS3 10 < age ≤ 15 | All in every ballast tank; all in a cargo wing tank; min 30% in each remaining cargo wing tank | Deck and bottom transverses with adjacent members, min 30% in each cargo centre tank | All complete, in all cargo and ballast tanks |
| SS4+ age > 15 | Everything at SS3, plus additional transverses where the Classification Society deems them necessary | ||
Source for the whole table: UR Z10.1 Table I "Complete" includes the girder system and adjacent members; "lower part" is the lower part of the bulkhead with the same. A 30% count is rounded up to the next whole number. SS3 also picks up additional complete web frame rings where the surveyor considers them necessary.
Two levers move this table. The surveyor may extend the close-up survey, and the rule names two cases: tanks whose arrangements or details have given trouble in similar tanks or on similar ships, and tanks approved with reduced scantlings under a corrosion control system. The other way, GOOD hard coating in a tank lets the Table I extent be specially considered. UR Z10.1 §2.3.3–2.3.4
Thickness measurement: how much, by special survey number
Two lines run through every column of Table II and are not repeated below: suspect areas are gauged at every special survey whatever the age, and every member under close-up survey per Table I is gauged for general assessment and to record the corrosion pattern. That second line is why the close-up list drives the gauging list.
| Survey | Deck / bottom | Sections | Wind-and-water strakes |
|---|---|---|---|
| SS1 | One section of deck plating, full beam, in way of a ballast tank or a cargo tank used mainly for ballast | 0 | — |
| SS2 | Each deck plate | 1 | Selected strakes outside the cargo area |
| SS3 | Each deck plate | 2 | All strakes in the cargo area; selected strakes outside it |
| SS4+ | Each deck plate and each bottom plate | 3 | All strakes, full length |
Source for the whole table: UR Z10.1 Table II
Where two or three sections are called for, at least one has to take in a ballast tank within 0.5L amidships. Sections are picked where the largest reductions are suspected or where the deck plating readings have already pointed. On tankers of 130 m and over that are more than 10 years old, the sampling for the longitudinal strength evaluation follows Annex III Appendix 3, and the evaluation itself is done at the special survey after the ship passes 10 years. As with close-up, GOOD hard coating lets the Table II extent be specially considered. UR Z10.1 §2.4.4–2.4.6
What makes the extent grow
Substantial corrosion is the switch. Z10.1 defines it as a corrosion pattern showing wastage in excess of 75% of allowable margins while still inside acceptable limits. Find it, or find structural defects, and the survey is extended, close-up survey included. UR Z10.1 §1.2.9
- At special survey: the extended pattern is Table IV — four sheets, for bottom structure, deck structure, side shell and longitudinal bulkheads, and transverse and swash bulkheads. Those readings must be taken before the survey is credited.
- History: suspect areas from previous surveys are examined again; substantial corrosion recorded at previous surveys is gauged again.
- Ballast tanks on annual watch: no hard coating from new, a soft or semi-hard coating, substantial corrosion inside, or hard coating below GOOD not repaired — any one puts the tank on annual examination, gauging as the surveyor deems necessary.
- At the annual survey: extensive corrosion in a ballast tank brings gauging; if that gauging shows substantial corrosion, the extent goes up to Table IV.
- Judgement: the surveyor may further extend the measurements as deemed necessary, and the extent must always be enough to represent the actual average condition.
Sources: §2.4.2–2.4.3 §2.2.3.1 §3.2.5.1 §7.1.4 Table IV
What Rev.25 changed, and from when
The revision history at the front gives the date directly: IACS societies apply Rev.25 uniformly to any survey that commences on or after 1 July 2024. A survey that started before that date runs on Rev.24. Three items in the marked-up text matter on the ship. UR Z10.1 Note 19
- The oil tanker definition was tightened — the oil is carried in cargo tanks forming an integral part of the hull, and ships carrying oil in independent tanks that are not part of the hull are now excluded by name. That decides whether a ship is on Z10.1 at all. §1.2.1
- A ballast tank is one used primarily for salt water ballast, where the earlier wording said solely. Tanks that see occasional other service no longer drop out of the count. §1.2.2
- Crew-performed cargo tank testing got a timing rule. To be accepted it must be done before the overall or close-up survey, inside the special survey window, and not more than 3 months before the date that survey is completed — on top of the existing conditions on the approved procedure, the absence of leakage, distortion or substantial corrosion, the logbook record, and the surveyor's own finding on the tank. §2.5.1
Nothing in the gauging chain moved: still a firm certified by the Classification Society on the principles in Table VII, still witnessed by a surveyor on board to the extent needed to control the process, still a report the surveyor reviews and countersigns on its cover page. UR Z10.1 §7
Sources
- UR Z10.1 Rev.25IACS — Hull Surveys of Oil Tankers, Feb 2023official text ↗
- UR Z10.4IACS — Double hull oil tankers; Z10.1 §1.1.1 defers to its §1.1.1 for the boundaryofficial text ↗
- UR Z7IACS — Hull classification surveys, for the parts of the ship outside the Z10.1 scopeofficial text ↗
Class-society and IMO documents are indexed and linked, never re-hosted. Where a class rule is stricter than the IACS baseline, the class rule governs.