What does UR Z10.3 require for chemical tankers?
Z10.3 is the enhanced-survey rule for chemical tankers with integral cargo tanks. It sets close-up extent, gauging extent, tank testing and the substantial-corrosion expansion against the Special Survey number — and it lets you waive gauging on stainless steel, which no other Z10 does.
The short answer
- Who it covers: self-propelled chemical tankers with integral cargo tanks — a ship with an IMO certificate of fitness carrying a product listed in Chapter 17 of the IBC Code.
- Cycle: Special Survey every 5 years, annual within ±3 months of the anniversary, intermediate at or between the 2nd and 3rd annual.
- Gauging extent: Special Survey No.1 is suspect areas only. No.2 adds each deck plate and 1 transverse section, No.3 2 sections, No.4 and after 3 sections plus every bottom plate.
- Stainless steel: gauging of stainless steel hull structure and piping may be waived — clad steel plating excepted.
- Substantial corrosion: wastage over 75% of the allowable margin, and it pulls in the Table IV pattern before the survey can be credited.
Read this before you quote a number
The current revision of this UR is Rev.21, August 2023, to be applied to surveys commencing on or after 1 July 2024. Every extent, table and clause number on this page is taken from Rev.20, May 2022, which applied to surveys commencing on or after 1 January 2023. This article has not been revalidated against Rev.21. Do not treat its Rev.20 extents as current requirements; verify them against UR Z10.3 Rev.21 and the vessel’s applicable class rules. IACS AR 2023 · Z10.3 R20 note 19
What Rev.21 changed, according to the change summary: the reference to the Owner's Inspection Report was added to section 6.3.1, Supporting Documents, to bring Z10.3 into line with the other Z10s. That is the whole entry. No change to close-up extent, gauging extent, tank testing or the substantial-corrosion table is recorded. IACS AR 2023 item 31
Cross-check: PRS Publication 46/P of July 2024 implements this UR and carries the same close-up and gauging extents, so the Rev.20 numbers below still stand in a current class publication. Where that is the case the PRS clause is cited alongside. PRS 46/P Tbl II
Which ships, which spaces
Z10.3 catches self-propelled chemical tankers with integral cargo tanks — in practice, a ship holding an IMO certificate of fitness for the carriage of dangerous chemicals in bulk. A chemical tanker is defined as a ship built or adapted to carry in bulk any liquid product listed in Chapter 17 of the IBC Code. UR Z10.3 §1.1.1
Two boundary cases are named. A ship built with both integral and independent tanks falls under Z10.3 only for the part of the cargo length that holds the integral tanks. A combined gas carrier / chemical tanker whose independent tanks sit inside the hull is surveyed as a gas carrier instead. Independent tanks on deck are outside the rule altogether. UR Z10.3 §1.1.1–1.1.2
Inside the ship, Z10.3 governs the hull structure and the piping across the cargo tanks and pump rooms, the cofferdams and pipe tunnels, the void spaces lying inside the cargo area, and every ballast tank. Everything else stays under Z7. A tank used for cargo or ballast as a routine part of the ship's operation counts as a ballast tank; a cargo tank that takes ballast only in the exceptional cases of MARPOL I/18.3 stays a cargo tank. What the tables give is the minimum — the survey is extended when substantial corrosion or structural defects turn up. UR Z10.3 §1.1.2–1.1.3
The survey cycle
Special Survey runs on a 5-year interval: the first within 5 years of the initial classification survey, each one after that within 5 years of the credited date of the previous. An extension of 3 months maximum can be granted in exceptional circumstances and does not move the next window. The survey may be started at the 4th annual and finished by the 5th anniversary; start it earlier than the 4th annual and the whole survey has to be completed within 15 months or the early work is not credited. Nothing may be credited to both the intermediate and the special survey — gauging included. UR Z10.3 §2.1
A dry dock survey is part of every Special Survey, and the overall survey, close-up survey and gauging of the lower portions of cargo and ballast tanks are done there if not already done. Lower portion means below the light ballast waterline. UR Z10.3 §2.2.2.1
Annual surveys fall within 3 months either side of the anniversary date. The intermediate survey is held at or between the 2nd and 3rd annual, and its extent depends on age. Between 5 and 10 years it is an overall survey of representative ballast tanks; if nothing structural is found, it drops to verifying that the hard coating is still GOOD. Past 10 years the intermediate survey is worked to the same extent as the previous Special Survey, minus the pressure testing of cargo and ballast tanks unless the attending surveyor calls for it. Past 15 years a dry dock survey becomes part of the intermediate survey as well. UR Z10.3 §3.1.1 / §4.2
A written Survey Programme, worked out by the owner with the class society, is required before any part of the Special Survey and before the intermediate survey once the tanker is over 10 years old. It has to account for and comply, as a minimum, with Tables I and II and with §2.5 and §2.6 — close-up survey, thickness measurement, tank testing and pipe testing respectively — and the Survey Planning Questionnaire is completed by the owner before the programme is developed. UR Z10.3 §5.1
Close-up survey extent, by Special Survey number
An overall survey of all tanks and spaces is done at every Special Survey. On top of that, Table I fixes the close-up extent, and Z10.3 splits it in two: Table I.1 for single skin, Table I.2 for double skin. The lettered and numbered areas in the two tables are not the same set, so check which table you are reading before you count web frame rings.
| Survey | Web frame rings (A) | Deck transverses (B) | Transverse bulkheads (C complete / D lower part) |
|---|---|---|---|
| SS1 age < 5 | One, in a ballast wing tank | One, in a cargo tank or on deck | D only: lower part of one bulkhead in a ballast tank, one in a cargo wing tank, one in a cargo centre tank |
| SS2 5 < age < 10 | All, in a ballast wing tank or double bottom ballast tank | One in each remaining ballast tank or on deck, one in a cargo wing tank or on deck, one in each of two cargo centre tanks or on deck | C: both bulkheads in a ballast wing tank. D: lower part in each remaining ballast tank, in two cargo centre tanks, in a cargo wing tank |
| SS3 10 < age < 15 | All in every ballast tank; all in a cargo wing tank; one in each remaining cargo tank | — | C: all bulkheads in all cargo tanks and in all ballast tanks |
| SS4+ age > 15 | Everything required at SS3, plus additional transverse areas where the class society deems them necessary | ||
Source: UR Z10.3 Tbl I.1 A is a complete transverse web frame ring with adjacent members; B a deck transverse with adjacent deck members; C a bulkhead complete, girder system and adjacent members; D the lower part of a bulkhead with its girder system and adjacent members. Where the ship has a centre longitudinal bulkhead and no centre cargo tanks, the wing tank bulkheads are surveyed instead.
| Survey | Ballast tanks | Cargo tanks |
|---|---|---|
| SS1 age < 5 | One web frame ring (1) in a ballast double hull tank; one transverse bulkhead (4) in a ballast tank | One deck transverse (2) in a cargo tank or on deck; one bulkhead (5) in a cargo wing tank and one in a cargo centre tank |
| SS2 5 < age < 10 | All web frame rings (1) in a ballast wing tank or ballast double hull tank; the knuckle area and the upper 3 m approx. (6) of one web frame in each remaining ballast tank; one bulkhead (4) in each ballast tank | One deck transverse (2) in each of two cargo tanks; one bulkhead (5) in two cargo centre tanks and one in a cargo wing tank |
| SS3 10 < age < 15 | All web frame rings (1) in all ballast tanks; all bulkheads (4) in all ballast tanks | All web frame rings (7) in a cargo wing tank; one web frame ring (7) in each remaining cargo tank; all bulkheads (3) in all cargo tanks |
| SS4+ age > 15 | Everything required at SS3, plus additional transverse areas where the class society deems them necessary | |
Source: UR Z10.3 Tbl I.2 A web frame in a ballast tank means the vertical web in a side tank, the hopper web in a hopper tank, the floor in a double bottom tank and the deck transverse in a double deck tank; in peak tanks it means the complete ring. In a cargo tank it means the deck transverse, the longitudinal bulkhead elements and the cross ties. The knuckle area is the web frame around the hopper-slope connections, up to 2 m from the corners on both the bulkhead and the double bottom. "Ballast double hull tank" counts the double bottom, double side and double deck tanks together even when they are separate tanks.
Two levers move both tables. 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. In the other direction, where hard coating in a tank is found GOOD, the Table I extent may be specially considered. Stainless steel tanks are the chemical tanker exception — they may be done as an overall survey with close-up added only where the surveyor wants it. UR Z10.3 §2.3
Thickness measurement extent, by Special Survey number
| Survey | Within the cargo area | Sections | Wind-and-water strakes |
|---|---|---|---|
| SS1 age < 5 | Suspect areas only | 0 | — |
| SS2 5 < age ≤ 10 | Suspect areas; each deck plate; the members under close-up survey per Table I.1 or I.2 | 1 | Selected strakes outside the cargo area |
| SS3 10 < age ≤ 15 | Suspect areas; each deck plate; all wind-and-water strakes; the members under close-up survey per Table I.1 or I.2 | 2 | All strakes in the cargo area, plus selected strakes outside it |
| SS4+ age > 15 | Suspect areas; each deck plate; each bottom plate; the members under close-up survey per Table I.1 or I.2 | 3 | All strakes, full length |
Source for the whole table: UR Z10.3 Tbl II PRS 46/P Tbl II Where two or three sections are measured, at least one must include a ballast tank within 0.5L amidships. Rev.20 struck the full-beam deck plating section that earlier editions required at Special Survey No.1 — the change marks are still printed in the Rev.20 text, and the July 2024 PRS table shows suspect areas alone in that column.
Sections are not picked at random. They go where the largest reductions are suspected, or where the deck plating readings point. Gauging of stainless steel hull structure and piping may be waived, but not on clad steel plating, and where hard coating in a tank is GOOD the Table II extent may be specially considered. The surveyor may extend the gauging as deemed necessary. UR Z10.3 §2.4
Over 10 years of age the pipework comes in as well: selected steel cargo pipes outside cargo tanks and ballast pipes running through cargo tanks are gauged at random or at selected lengths opened for internal inspection, and pressure tested to maximum working pressure. Cargo and slop discharge lines through ballast tanks and void spaces get particular attention. UR Z10.3 §2.6.1
Substantial corrosion, and what it pulls in
Substantial corrosion in Z10.3 is a corrosion pattern showing wastage over 75% of the allowable margin while still inside acceptable limits. A location showing it — or one the surveyor judges prone to rapid wastage — is a suspect area, and suspect areas are gauged at every survey from then on. PRS Publication 46/P of July 2024 carries the same 75% definition. UR Z10.3 §1.2.9
Find it and Table IV takes over. The extended readings have to be finished before the survey is credited, and the same rule bites at annual survey: if ballast tank gauging turns up substantial corrosion, the extent is increased to Table IV there and then. Table IV runs over four sheets — bottom and hopper structure, deck structure, side shell and longitudinal bulkheads, transverse watertight and swash bulkheads. The shape of it: UR Z10.3 §2.4.2 / §3.2.5.1
- Bottom, inner bottom and hopper plating: a minimum of 3 bays across the tank including the aft bay, plus readings around and under every suction bell mouth — 5-point pattern on each panel between longitudinals and floors.
- Bottom and hopper longitudinals: a minimum of 3 longitudinals in each bay where the plating was gauged — 3 readings in line across the flange and 3 on the vertical web.
- Deck plating: two transverse bands across the tank, minimum 3 readings per plate per band. Deck longitudinals: every third longitudinal in each band, minimum one — 3 readings in line vertically on the web and 2 on the flange.
- Side shell and longitudinal bulkhead plating: deckhead strakes, bottom strakes and strakes at horizontal girders get a reading on the plating between each pair of longitudinals in a minimum of 3 bays. All other strakes: every third pair of longitudinals in those same bays.
- Upper and lower stool, where fitted: a transverse band within 25 mm of the welded connection to the inner bottom or deck plating, and another within 25 mm of the connection to the shelf plate — 5-point pattern between stiffeners over 1 m of length.
- Webs, brackets and stringers: 5-point pattern over roughly 1 to 2 square metres depending on the member, with single readings on flanges. Deep webs and girders take 3 readings across the face flat.
Source: UR Z10.3 Tbl IV/1–4 The list above is the pattern for the members most often gauged; Table IV also covers bottom girders and floors, deck girders and brackets, deck transverse webs, cross ties, horizontal girders and stringers, corrugated bulkhead strakes and panel stiffening.
The firm, the points, the paperwork
Gauging is done by a firm certified by the class society under Table V. The route is documents, then audit, then an onboard demonstration with satisfactory reporting; the certificate is renewed or endorsed at intervals not exceeding 3 years. Operators have to be qualified to a recognised industrial NDT standard, and the firm submits its equipment and calibration procedures, its operator guide, its training programme and its record format. Approval may be cancelled where the measurements were improperly carried out or improperly reported, where the Society's surveyor finds deficiencies in the approved system, or where the firm failed to inform the Society of an alteration to it. UR Z10.3 §7.2 / Tbl V
On the job: unless the society does the gauging itself, a surveyor witnesses it and stays on board to the extent needed to control the process. The firm sits in the survey planning meeting held before the survey starts. Gauging of structure in areas where close-up survey is required is done at the same time as the close-up survey, not afterwards. Whatever the tables say, the extent must be enough to represent the actual average condition. UR Z10.3 §7.1
Where the measuring points themselves are defined is the part that catches people out. Z10.3 Annex II is a pointer, not a procedure, and it is recommendatory: for single hull chemical tankers it sends you to Annex II of UR Z10.1, and for double hull chemical tankers to Annex II of UR Z10.4. That is where the recording forms and the point patterns live. PRS Publication 46/P does the same thing, pointing at its oil tanker and double hull oil tanker publications. The report itself must give the location of each measurement, the thickness measured, the corresponding original thickness, the date, the equipment type, and the names and qualifications of the personnel, and it is signed by the operator. The surveyor reviews the final report and countersigns the cover page. UR Z10.3 Annex II / §7.3
Section 6 fixes what has to be on board, kept for the life of the ship, and checked by the surveyor for completeness before the survey starts. The Survey Report File holds the structural survey reports, the Executive Hull Summary and the thickness measurement reports, and the same file is held in the owner's and the society's offices. The Supporting Documents are the Survey Programme, held on board until the Special or Intermediate Survey has been completed; the scantling plans for the cargo and ballast tanks; what has been repaired before; what the ship has carried and where she has ballasted; how far the inert gas plant is used and how the tanks are cleaned; the inspections the ship's own personnel carry out, covering structural deterioration, leakage in bulkheads and piping, and the state of the corrosion prevention system; and anything else that helps pin down critical structural areas and suspect areas. UR Z10.3 §6
That bullet on inspections by the ship's personnel is the one Rev.21 touched — it added the reference to the Owner's Inspection Report, the form printed as Annex IIIC. In Rev.20 the form already exists and is already referenced, but from the survey programme clause, where the owner's inspections over the last 3 years are listed as input to the programme and Annex IIIC is named as the guidance for reporting them. Rev.21 puts the same pointer into section 6.3.1 so the two agree. PRS Publication 46/P of July 2024 already reads that way — its supporting-documents list carries the Annex IIIC pointer under the ship's-personnel bullet. Z10.3 §5.1.2.11 · PRS 46/P §6.3.1
Sources
- UR Z10.3 Rev.20IACS — Hull Surveys of Chemical Tankers, May 2022 (one revision behind current)official text ↗
- IACS AR 2023IACS Annual Review — summary of UR changes published in 2023, entry 31 (Z10.3 Rev.21)official text ↗
- PRS Pub 46/PPolish Register of Shipping — Hull Surveys of Chemical Tankers, July 2024official text ↗
- UR Z10.1 / Z10.4IACS — Annex II thickness measurement procedures that Z10.3 Annex II points to (single hull / double hull)official text ↗
- UR Z7IACS — Hull classification surveys, the base rule Z10.3 sits on top of (Z10.3 §1.1.2)official 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.