How do I read a class thickness limit?

The four thicknesses, and the fifth that is not a margin

Every limit in this chapter is a statement about one of a small set of thicknesses. Get the set straight and the rest of the chapter reads itself. The names below are the ones CSR uses, because CSR is the only document in this handbook that defines all of them in one place — but the quantities exist on any ship, whether or not the society names them.

Definitions and formulae: CSR Ch 3 Sec 2 [1.2] · Ch 13 Sec 2 [2.1.1]

Two of these carry the whole argument of this page. The corrosion addition is a design quantity: it is worked out for the member from what is on each side of it, independently of the strength calculation, so that the corrosion state of the ship can be read off at any point in its life. The voluntary addition is not a design quantity at all — it is owner's or builder's steel, and CSR is blunt about where it stands: thickness the owner or the builder specified on their own account counts for nothing towards compliance with the Rules. That cuts both ways at the gauge. It does not earn the ship a thinner limit, and it does not raise one either: on a CSR ship it is subtracted before the renewal thickness is computed, so a plate with a 1 mm voluntary addition simply has 1 mm more steel to lose before it reaches the same renewal thickness as its sister without one. CSR Ch 3 Sec 2 [1.1.1] / [1.3.2]

Away from CSR ships most societies do not publish this vocabulary. They publish one number — a percentage — and leave you to work out what it is a percentage of. That is where the trouble starts, and the next two sections are the two answers you will meet.

Scheme 1 — a percentage of the as-built

This is the scheme most societies publish and the one most technicians carry in their head. The society prints a wastage allowance for the member — 20 %, 25 %, 30 % — and the limit is that fraction taken off the as-built thickness of the plate you are standing on. Two plates of different as-built thickness in the same tank therefore have two different limits in millimetres, and the thinner one reaches its limit first. ABS states that consequence directly: under a percentage limit a thin member arrives at its limit before a thick one does, when both are losing steel at the same rate per surface; and a member wasting on both faces under matching conditions runs its allowance down twice as fast. ABS 7-A1-4/17.1

The trap is the base. "Percentage of the as-built" is a fair description of what ABS, ClassNK, KR and INSB do, and a wrong description of BV and DNV. LR sits in between: it publishes percentages without naming the base in the clause. The base is written into each society's own text and the wording is not the same word twice.

Row by row: ABS Tab 1A · 7-1-1/3.64 LR §1.5.1 · Tab 1.5.5 n.6 — older edition, Nov 2016 v7.3 NK App 3.5 (1) — older edition, 2014 KR Annex 1-5 Tab 1 n.4 INSB Ch 3 Sec 13 Tab C BV Pt A Ch 2 App 3 Tab 6 DNV Sec.2 [3.1.2] Tab 1 — older edition, Jul 2022 CCS Ch 3 §II.1 · Tab 3.1 PRS Pt I §5.1.3.6

Two habits follow from this section alone. Record the as-built for every point, because under this scheme it is the whole denominator. And do not average a low reading away or report a single low reading as the plate: LR and INSB both state that the maximum diminution applies to the average thickness over the plate area, or over the length between supports for a stiffener — and ABS states that one reading is not a corrosion pattern, and that a single marginal reading calls for more readings evaluated together with a close visual examination. Those are three ways of saying the same thing to the person holding the probe. LR Tab 1.5.5 n.6 · INSB Tab C n.3 · ABS 7-A1-4/17.1

Scheme 2 — a computed renewal thickness

The second scheme starts at the other end. Instead of taking a fraction off what was fitted, it builds the limit up from the scantling. The clean case is a CSR ship. Renewal is required when the measured thickness t_m falls below the renewal thickness, and the renewal thickness is the as-built with the corrosion addition and any voluntary addition taken out: t_ren = t_as-built − t_c − t_{vol_add}. The corrosion addition is not a percentage of anything — it is looked up per side, per compartment, in a rule table, summed, rounded up to the next half millimetre, and topped with a reserve of 0.5 mm. CSR Ch 13 Sec 2 [2.1.1] · Ch 3 Sec 3 [1.2.1]

The consequence is the one thing to take away from this page. On a CSR ship the percentage is an output. You cannot start from "how much may this plate lose" — there is no such number until t_c has been assembled for that particular member in that particular pair of compartments. Two plates of the same as-built thickness in the same hold can have different renewal thicknesses because one of them has a ballast tank behind it and the other has the sea. The full corrosion-addition grid and the whole chain from the grid to t_ren are in K5.7.

DNV's scheme sits in the same family for a different reason. DNV-CG-0182 publishes a diminution coefficient k, and it hedges the limit rather than imposing it: the minimum thickness of plates and of stiffener or girder webs and flanges at a renewal survey may be determined from t_min = k · t_{gr_off} — the wording of a class guideline, which is what CG-0182 is, and not of a rule requirement. The formula comes with t_{gr_off} = t_{as_built} − t_{vol_add} and the documented owner's voluntary addition explicitly subtracted. The coefficient is a fraction, so the shape looks like scheme 1 — but the base is not the plate's as-built thickness, and the technician cannot reach the limit from the reading and the shell expansion alone. Somebody has to establish first whether a voluntary addition was fitted and how much of it. The longitudinal-strength coefficients are 0.80 for plating, girders and stringers, side and longitudinal bulkhead plating and corrugated bulkhead plating, and 0.75 for stiffeners — with the bulk carrier inner bottom plate the one plating entry that departs from 0.80, at 0.75. This is DNV-CG-0182 Edition July 2022, the newest edition held; the current edition sits behind the DNV Rules Explorer login and was not read. DNV-CG-0182 Sec.2 [3.1.2] Tab 1 — older edition, Jul 2022

Both members of this family share one practical property: the limit is derived, so it can be got wrong upstream of the gauge. A missing voluntary addition, a wrong as-built, a member assigned to the wrong compartment pair — each of those moves the limit by its own amount and none of them shows up in the reading.

The other two forms — a millimetre allowance, and four numbers at once

Two schemes would be manageable. There are four, and the remaining two are the ones that get transcribed wrongly into a report.

A flat millimetre allowance

Some limits are stated in millimetres and do not scale with the plate at all. KR's wear-limit table carries three ship classes, and for Class III — high speed craft and light craft the wear limit is a flat 1 mm, not a percentage. KR also sets its shear strength triggers in millimetres rather than percent, and there are three of them, one per ship group. A separate shear strength evaluation is called for when the average corrosion of any strake exceeds: 2.0 mm (Class I) or 3.0 mm (Class II) in the side shell or a longitudinal bulkhead of an oil tanker, chemical tankers included; 1.5 mm or 2.5 mm in the side shell only of a liquefied gas carrier; and 1.5 mm or 2.5 mm in the side shell or a longitudinal bulkhead of a bulk carrier or ore carrier intended for alternate loading. All three sit under one condition: they bite where the thickness measurement for the longitudinal strength evaluation is being carried out under the Society's separate requirements. ClassNK's first band is the hybrid form — 20 % of original thickness + 1 mm — which is neither a pure percentage nor a pure millimetre allowance, and which cannot be reported as "20 %" without changing the answer. KR Annex 1-5 Tab 1 · NK App 3.5 (1) — NK older edition, 2014

CCS writes the same kind of statement the other way up. Where the Guidelines set a figure themselves rather than referring it out, they state a minimum renewed thickness as a percentage of the as-built — 75 % of as-built for structural members in the fore and aft peak ballast tanks of ships of 90 m and above. That is the complement of a wastage percentage, not a wastage percentage, and copying it into a column headed "allowable diminution" inverts it. CCS Ch 3 Tab 3.1

PRS goes further again for one member. Publication 63/P covers the side shell frames, and their brackets, in cargo holds bounded by a single side shell — on single-deck bulk carriers with topside and hopper tanks built primarily for dry bulk cargo and not built to sub-chapter 20.5 of Part II of the PRS Rules, and, on a compliance timetable of their own, on single-deck oil-bulk-ore (OBO) carriers. Within the publication the word "ship" carries both types. The renewal thickness for the frame and bracket webs is the greatest of four figures, and the first two of them are where the reading usually goes wrong:

• t_COAT − t_C. t_COAT is not a coated or a measured thickness. The symbol list defines it as 0.75 t_20.5 — three quarters of the thickness that sub-chapter 20.5 of Part II of the PRS Rules requires for the member, taken from 20.5.3 for frame webs and from 20.5.4 for the webs of upper and lower brackets. t_C comes from a small table keyed on ship length and on whether the frame stands in No. 1 hold, and runs 2.0 to 4.0 mm.
• 0.75 t_AB — three quarters of the as-built, and the only one of the four that behaves like a plain percentage limit.
• t_REN,d/t = (web depth in mm) / R, with R between 55√k and 87√k depending on whether the member is a frame or a lower bracket and whether the flange is symmetrical. This one does not apply over the whole frame: it counts in zones A and B only, two of the four zones A to D that the publication marks out on the frame in its Figure 1.
• t_REN,S, the shear-strength thickness, where the shear check is required.

A limit that depends on the web depth of the member you are gauging is not something a technician can carry in the head, and it is not something the office can apply without the frame geometry on the sheet — nor without knowing which zone of the frame the reading came from. PRS Pub 63/P §1 · §2.1.1 · §2.1.2 · §2.2 — the file held prints July 2008

Four numbers at once: BV and RINA

BV and RINA do not publish one percentage per member. They publish up to four, in four columns, and the four are assessed in order. Taking one number out of the set and quoting it as "the BV limit" is the single most common way this table gets misread.

On an oil tanker, item 1 — deck plating, deck stringer, sheer strake and longitudinal bulkhead upper strake taken together — reads 25 / 20 / 10 across the isolated-area, item and group columns, sitting under a deck zone criterion of 10 %; the neutral axis zone is 15 % and the bottom zone 10 %. So a single deck plate may lose 25 % in an isolated area and still pass, while the deck plates as a group may not average more than 10 %. Quoting the 25 % alone makes BV look the most permissive society in the set; quoting the 10 % alone makes it the strictest. Neither is a statement about the ship. Behind the zone criterion sits a general condition BV states separately: across the middle 0,4 L of the ship, the hull girder section modulus as measured has to stay at or above 90 % of the rule value. Note 1 to the same clause then moves the goalposts for anyone applying the zone column: where the zone criterion is the one being used, the assessment is made against the ship's original modulus, not against the rule modulus. On a ship built with modulus to spare those are not the same number. The note adds one release valve: at the Owner's request the Society may run a direct calculation on the ship's current thicknesses and accept more diminution than the zone figure allows. BV Pt A Ch 2 App 3 §4.3.1 / §4.3.4 / §4.3.5 · Tab 6

RINA publishes the same four-column shape, in Tables 5 and 6 for general cargo ships, 7 and 8 for bulk carriers and 9 and 10 for oil tankers. The pairing matters: the first table of each pair covers ships whose building contract was signed on 1 June 2000 or later, the second covers ships contracted before that date, and the older table is not the same numbers. On oil tankers, Table 10 prints 25 / 20 with no group column at all, and it leaves the neutral axis zone blank where Table 9 publishes 15 %. Contract date first, table second, column third. These figures are RINA Part A Ch 2 App 2, 1 July 2024 interactive set, the newest edition held; the edition in force is later and sits behind the RINA member area. RINA Pt A Ch 2 App 2 Tab 9 / Tab 10 — older edition, 1 Jul 2024

The allowable margin, and the 75 % rule

Almost every society in the set draws the line at the same place. A member is substantially corroded once the surveyor, reading the corrosion as a pattern and not as one point, finds the loss has gone past 75 % of allowable margins while the member is still inside acceptable limits. Read the preposition. The 75 % is a percentage of the allowable margin — of the wastage the society already allows — and not a percentage of the as-built thickness. It is a percentage of a percentage, and that is why it is routinely computed the wrong way round. UR Z10.2 §1.2.11

The allowable margin is not defined by Z10 — it is whatever wastage allowance the individual society publishes for that member. ABS says so in its own definition, with a note pointing at the tables that hold them. ClassNK names them in the same appendix that defines the term: 20 % of original thickness + 1 mm for shell plates, strength deck plates, flat-bar longitudinal beams on the sheer strake and strength deck, tight bulkheads in deep tanks and inner bottom plates — the flat-bar qualifier is printed in the table and is easy to drop, and longitudinal beams appear again in the 30 % row; 25 % for floors and girders in the double bottom, primary members, hold frames and watertight bulkhead plates; 30 % for other frames, longitudinal beams, stiffeners and brackets, effective deck plates, hatch covers and hatch beams. LR names a different quantity again — 75 % of the permissible diminution, applied to individual plates and stiffeners — and adds that the maximum diminutions given already take account of additional average corrosion for a further five year period. ABS 7-1-1/3.64 · NK App 3.5 (1) · LR §1.5 — NK and LR older editions

The arithmetic, on the source's own worked example

ABS prints the example in full, which is the safest thing to work from because nothing has to be assumed. Take a transverse bulkhead plate on a tanker, individual plate wastage allowance 25 %, original thickness 12 mm:

original thickness            12.00 mm
allowable margin  25 % of 12 =  3.00 mm    <-- the 75 % is taken of THIS
75 % of the margin            =  2.25 mm

gauged 12.00 .. 9.75 mm   diminution 0 % .. 18.75 %   the plate had some corrosion
gauged  9.75 .. 9.00 mm   diminution 18.75 % .. 25 %  substantial corrosion range
gauged below 9.00 mm      diminution over 25 %        renewal limit

The band opens at 9.75 mm exactly, and the source adds no measurement margin to it. Written out in general form, with W the published allowance as a fraction: the renewal limit is t_{as_built} (1 − W), and the substantial-corrosion band opens at t_{as_built} (1 − 0.75 W). On the ABS plate that is 12 × (1 − 0.1875) = 9.75, which is the printed figure. ABS 7-A1-4/17.1

CCS draws the same arithmetic instead of writing it. Sketch Map 1.1 splits the range between the renewal thickness and the original thickness into four quarters; the quarter nearest the renewal thickness is marked "substantial corrosion areas" and labelled "75 % of allowable limits", and everything below the renewal thickness is marked "excessive corrosion areas". The picture is worth carrying: the band is the last quarter of the allowance, not the last quarter of the plate. CCS Ch 1, Sketch Map 1.1

Two conditions travel with the number and are dropped more often than the number is. First, the definition turns on a corrosion pattern: an individual reading does not constitute one, and a single marginal reading requires more readings, evaluated together with a close visual examination by the surveyor, before the extent can be called. Second, the band is bounded at both ends — "in excess of 75 % of allowable margins, but within acceptable limits". Below the renewal limit it is not substantial corrosion any more; it is renewal. IACS Rec 96 is the only source in this set that puts both ends in percentages outright: a substantially corroded structure is one whose wastage has passed 75 % of the diminution allowed for that member without having reached 100 % of it — and Rec 96 is a Recommendation, which is guidance and binds no society by itself. ABS 7-A1-4/17.1 · IACS Rec 96 §2.1.5 (guidance)

On a CSR ship none of this arithmetic runs. The band there is a fixed 0.5 mm above the renewal thickness — the reserve thickness t_res, a flat figure independent of the member and of the as-built thickness. It does not scale with the plate, so on a thick plate it is a much smaller slice of the allowance than 75 % would carve out, and on a thin one it is a larger one. CSR Ch 3 Sec 3 Symbols · Ch 13 Sec 2 [2.1.3]

t_ren or t_net: IACS does not use one name

The same band, on the same CSR ship, is written with two different symbols inside IACS's own documents. The Z10 survey series writes it with t_ren: for vessels built under the Common Structural Rules, substantial corrosion is a measured thickness between t_ren + 0.5 mm and t_ren. Recommendation 96 writes the identical sentence with t_net in place of t_ren. The 2011 ESP Code writes t_net too, at Annex B Part A §1.2.9, and it still does: Res. MSC.525(106), which amends that Code with effect from 1 July 2024, leaves §1.2.9 alone. The two definitions it does replace are §1.2.1 in each of Annex B Part A and Part B, and they define the ship type, not the corrosion. UR Z10.2/.4/.5 · Rec 96 §3.2.1 (h) · ESP Code 2011

Class documents split the same way. ABS, KR and CCS write t_ren; BV writes t_renewal; ClassNK Part B avoids a symbol and writes the band as a range of 0.5 mm above the renewal thickness stipulated in the relevant provisions; DNV-CG-0182 writes t_net. LR's guidance manages to do both in two facing pages: §1.5.7.4 defines substantial corrosion as a gauged thickness between t_renewal and t_renewal + t_reserve, and the figure on the next page labels the same band "t_net + 0.5mm and t_net". ABS · KR · CCS · BV · NK Pt B · DNV · LR — NK, DNV and LR older editions

This is not a spelling problem. CSR does not define a symbol called t_net at all. It defines t as the net thickness, t_req as the net required thickness and t_off as the net offered thickness, and those are two different numbers. The net offered thickness is t_{as_built} − t_{vol_add} − t_c, which is the same subtraction as the renewal thickness. The net required thickness is what the strength calculation demands, and compliance only requires that the offered be equal to or greater than the required. So a reader who resolves "t_net" as the net required thickness will land at or below the renewal thickness — a limit that is never stricter and can be looser, on a plate whose whole point is that it is close to the line. CSR Ch 3 Sec 2 Symbols / [1.2.3] / [1.3.2] · Ch 13 Sec 2 [2.1.1]

What to do about it is short. Never carry the symbol across documents — carry the formula. On the sheet and in the report, write the limit out as as-built − corrosion addition − voluntary addition with the three numbers beside it, and name the document the corrosion addition came from. When a class document hands you a symbol, read the definition that that document gives for it, not the one you last saw. And note the further trap in the same sentence: the CSR band and the Z10 band are stated with different inequalities in different texts — CSR and the Z10 series close the band at the lower end, t_ren ≤ t_m < t_ren + t_res, while LR writes it with strict inequalities at both ends. On a reading that sits exactly on t_ren that is the difference between a band entry and a renewal. CSR Ch 13 Sec 2 [2.1.3] · LR §1.5.7.5 — LR older edition

One plate, judged two ways

The two schemes are easiest to hold apart on one plate. Take a strength deck plate of a double hull oil tanker, in the cargo area, with a cargo oil tank directly below and the weather above. As-built 18.0 mm, no voluntary addition. Two sisters, alike in everything the scope clause asks about — self-propelled, unrestricted navigation, and a freeboard length L_LL above the 150 m at which CSR reaches a double hull oil tanker at all — and different in one thing only. One was contracted for construction after 1 July 2015 and is therefore a CSR ship; the other was contracted in 2008 and is therefore not, and is classed with ABS. Drop any one of those conditions and the first sister leaves CSR too: all four have to hold together. CSR Ch 1 Sec 1 [1.1.1] · [1.3.1]

The CSR sister — build the limit

upper face   exposed to atmosphere, weather deck plating        t_c1 = 1.7
lower face   cargo oil tank, other members, within 3 m below
             top of tank (weather deck is the tank top)          t_c2 = 1.7
                                                          sum        3.4
Roundup_0.5(3.4)                                                     3.5
+ reserve thickness t_res                                          + 0.5
                                                          t_c        4.0 mm
                                        (minimum 2 mm — satisfied)

t_ren    = 18.0 - 4.0 - 0                                          14.0 mm
band     = 14.0 <= t_m < 14.5                     alternative solutions
t_repair = 18.0 - 0                                                18.0 mm

The plate may lose 4.0 mm before renewal, which is 22 % of the as-built. Nobody wrote 22 % anywhere. It fell out of two table lookups, a rounding rule and a fixed reserve, and it would be a different percentage on a plate of a different as-built thickness in exactly the same position. The last line of the block carries a hedge that belongs to the source and should travel with the number: an area that needs renewal is in general repaired with an insert of at least the original grade and yield stress and of thickness t_repair or more. "In general" is CSR's word, not ours — the rule leaves room for the case it does not fit. worked from CSR Ch 3 Sec 3 Tbl 1 + [1.2.1] + Ch 13 Sec 2

The non-CSR sister — take the percentage off

ABS wastage allowance, strength deck plates,
non-CSR tanker 90 m and over                                 W = 20 %

allowable margin      0.20 x 18.0                                3.6 mm
renewal limit         18.0 - 3.6                                14.4 mm
75 % of the margin    0.75 x 3.6                                 2.7 mm
band opens at         18.0 - 2.7                                15.3 mm

substantial corrosion range   15.3 mm down to 14.4 mm

The 20 % is the figure ABS prints for strength deck plates on a non-CSR tanker of 90 m and over in the contract-2005-or-later double bottom column — and the same 20 % is printed in the 1962–2004 double bottom and the single bottom columns, so on this row the contract-date column does not change the answer. On other rows of the same table it does, so check the column. ABS 7-A1-4/35.3 Tab 1A · 7-A1-4/17.1

Read the 14.2 mm row twice. Same steel, same probe, same day — and on one ship it is a finding the surveyor may resolve with an alternative solution, and on the other it is an insert plate. Nothing in the reading tells you which. The ship type, the contract date and the compartment on the far side of the plate tell you.

Do not turn this into a rule about which society is more generous. It came out this way on this member. On the sloped plating of a hopper tank in a large BC-A bulk carrier the CSR one-side value is 3.7 mm against the hold, which builds a far larger allowance than any published percentage would; on a lower stool sloping plate it is 5.2 mm. The comparison has to be redone member by member, which is what the tables are for. CSR Ch 3 Sec 3 Tbl 1

What this means when you fill the sheet

Every scheme on this page needs something from the sheet that a bare thickness column does not carry. The office cannot apply any of them from a list of readings and locations. Four fields do most of the work.

• As-built, per point, not per plate name. Under scheme 1 the as-built is the whole denominator; under scheme 2 it is the first term of the subtraction. Either way a wrong as-built moves the limit by the same amount as the error, and it moves it silently. Where the drawing gives a range across a strake, record which value belongs to the point you gauged.
• The compartment on both sides. A corrosion addition is assembled from two one-side values, one for each face. "Deck, frame 62" is not enough; "weather above, cargo oil tank below" is. Ballast one side and the sea the other is a different limit from ballast one side and a hold the other, on the same plate in the same position.
• The member category. Every published table is indexed by member type before it is indexed by anything else — face plate of a primary supporting member against other members, plating against stiffener web against stiffener flange, deep tank bulkhead against watertight bulkhead. BV and RINA also need to know which item and which group the member belongs to, because the group average is one of the four criteria. Record the member as the rule names it, not as the tank is nicknamed on board.
• Where the point sits relative to the tank top. On CSR ships the band within 3 m below the top of the tank carries its own higher one-side values, and it applies only to cargo tanks, slop tanks and ballast tanks that have the weather deck as their tank top, measured vertically from and parallel to that top. A point at 2.8 m and a point at 3.2 m below the deck are two different limits. Nobody can reconstruct that from a frame number.

Two more habits pay for themselves. On a stiffener, note where it lands on the plating — CSR fixes the corrosion addition of a stiffener by the location of its connection to the attached plating, not by where the web sits. And when a reading falls in the band, whichever scheme drew it, say so on the sheet in words. A band entry is neither a pass nor a failure, and it is the one finding that has to reach the surveyor rather than sit in a column. CSR Ch 3 Sec 3 [1.2.3] · Tbl 1 note (4)

This page gives the reading. The cells give the values: the full permissible-diminution grid, eleven societies against three ship types and every member, is in handbook table T01 — Permissible diminution, class by class, and the whole CSR chain from the corrosion-addition grid to the renewal thickness is in T10 — CSR renewal thresholds. Every cell in both carries its clause and its PDF page.

Sources

1. CSR Pt 1 Ch 3 Sec 2IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version (in force 1 July 2024) — Net Scantling Approachofficial text ↗
2. CSR Pt 1 Ch 3 Sec 3IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version — Corrosion Additionsofficial text ↗
3. CSR Pt 1 Ch 13 Sec 2IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version — Ship in Operation: Acceptance Criteriaofficial text ↗
4. UR Z10.2IACS UR Z10.2 Rev.37 (Feb 2023) — Hull Surveys of Bulk Carriersofficial text ↗
5. UR Z10.4IACS UR Z10.4 Rev.18 (Feb 2023) — Hull Surveys of Double Hull Oil Tankersofficial text ↗
6. UR Z10.5IACS UR Z10.5 Rev.20 (Feb 2023) — Hull Surveys of Double Skin Bulk Carriersofficial text ↗
7. IACS Rec 96IACS Recommendation 96 Rev.2 (2023) — Double Hull Oil Tankers: Guidelines for Surveys, Assessment and Repair of Hull Structuresofficial text ↗
8. ABS Pt 7ABS Rules for Survey After Construction, Part 7 — July 2026official text ↗
9. BV NR467 Pt ABureau Veritas NR467 Rules for the Classification of Steel Ships, Part A — R26, July 2026official text ↗
10. RINA Pt A Ch 2 App 2RINA Rules for the Classification of Ships, Part A Ch 2 App 2 — 1 July 2024 interactive setofficial text ↗
11. DNV-CG-0182DNV-CG-0182 Allowable thickness diminution for hull structure — Edition July 2022official text ↗
12. LR TM GuidanceLloyd's Register Thickness Measurement and Close-up Survey Guidance, Part 1 — Version 7.3, November 2016official text ↗
13. ClassNK GuidanceClassNK Guidance for Undergoing Class Maintenance Surveys — 2014 editionofficial text ↗
14. KR Rules Pt 1KR Rules and Guidance for the Classification of Steel Ships, Part 1 — 2026 editionofficial text ↗
15. CCS TM GuidelinesCCS Guidelines for Thickness Measurement of Hull — Ver. 6.6, March 2025official text ↗
16. INSB Pt IINSB Rules and Regulations for the Classification and Construction of Steel Ships, Part I — Issue 04 Rev.03, December 2024official text ↗
17. PRS Pt IPRS Rules for the Classification and Construction of Sea-going Ships, Part I — January 2026official text ↗
18. ESP CodeIMO Res. A.1049(27) — International Code on the Enhanced Programme of Inspections during Surveys of Bulk Carriers and Oil Tankers, 2011official text ↗
19. MSC.525(106)IMO Res. MSC.525(106) — Amendments to the International Code on the Enhanced Programme of Inspections during Surveys of Bulk Carriers and Oil Tankers, 2011, adopted 10 November 2022, in force 1 July 2024official 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.

Related questions

• What counts as substantial corrosion in each class?K5.2
• What are the diminution limits for oil tankers?K5.3
• What are the diminution limits for bulk carriers?K5.4
• What are the diminution limits for general cargo ships?K5.5
• What are the pitting acceptance criteria in each class?K5.6
• At what thickness must steel be renewed on a CSR ship?K5.7
• What wastage allowances apply to ships under 90 m?K5.8
• What changes for thickness measurement on CSR ships?K3.9