published last reviewed 2026-08-04 reviewer — rev 1 9 sources

At what thickness must steel be renewed on a CSR ship?

Steel renewal is required when the measured thickness falls below t_ren = t_as-built − t_c − t_{vol_add}. Everything else on this page is how t_c is built for the member in front of you, and what the ship has to satisfy on top of the individual plate.

The short answer

The threshold: t_ren = t_as-built − t_c − t_{vol_add}. Steel renewal is required if the measured thickness is less than t_ren. It covers local supporting members and primary supporting members.
Building t_c: two one-side values from the rule grid, added, rounded up to the next half millimetre, plus a reserve t_res = 0.5 mm. Never less than 2 mm in total, or 1.5 mm for the web and face plate of stiffeners and in way of internals of dry spaces. Stainless and aluminium members take the reserve alone, 0.5 mm, and the minimums do not apply to them.
Which ships: bulk carriers of L_LL ≥ 90 m and double hull oil tankers of L_LL ≥ 150 m, self-propelled, unrestricted navigation, contracted for construction on or after 1 July 2015 — with ore carriers, combination carriers, woodchip carriers, self-unloaders and (conditionally) cement, fly ash and sugar carriers excluded.
The band: t_ren ≤ t_m < t_ren + 0.5 mm — closed at the bottom, open at the top, fixed width whatever the plate. Not a renewal and not a clean reading: it is where alternative solutions may be adopted under the Society's rules incorporating UR Z10.2, Z10.4 and Z10.5. An insert goes back at t_repair = t_as-built − t_{vol_add}, not at t_ren.
The global check: at special surveys, over 10 years of age. Section modulus at deck and bottom at or above 90 % of the value at gross offered thickness, or the zone-area alternative at 90 %; neutral axis zone area not below the gross figure less 0.5 t_c. A screening rule at 10 % and 0.5 t_c passes a section without the zone-area calculation.
What CSR does not carry: no acceptance criteria for pitting, edge corrosion or grooving, and no use of the term "substantial corrosion". The survey requirements are those of the individual Society which incorporate UR Z10.2, Z10.4 and Z10.5.

Read this before you quote a number

Every value on this page was read from the CSR 1 January 2024 version, which entered into force on 1 July 2024. Each clause is cited from that text.

The edition in force is the Consolidated 1 July 2025 edition, being this same text with Corrigenda 1 applied. Those corrigenda are not held and are not reflected here. Cite these figures as "CSR 1 Jan 2024 version" with the clause, never as "Consolidated 2025".

One cross-reference in the source is loose and is worth knowing before you chase a clause: the symbols list of Pt 1 Ch 13 Sec 2 defines t_c as the corrosion addition "as defined in Ch 3, Sec 2", while the corrosion additions and Table 1 actually sit in Ch 3 Sec 3. Every value on this page is taken from Ch 3 Sec 3.

Which ships the criteria apply to

The renewal criteria in this chapter apply only to ships in operation that are classed in accordance with the Common Structural Rules. That is a narrower set than "bulk carriers and tankers", and getting it wrong at the top of the sheet invalidates every judgement below it. Three conditions have to be met together. CSR Ch 13 Sec 1 [1.1.2]

a) the ship is a bulk carrier or a double hull oil tanker; and
b) it is self-propelled and has unrestricted navigation; and
c) it was contracted for construction on or after 1 July 2015.

Two notes attach to that clause and both settle arguments. Unrestricted navigation means the ship is not subject to any geographical restriction — any ocean, any season — except one limited by the ship's capability for operation in ice. Contracted for construction is the date the building contract was signed between the prospective owner and the builder, and IACS Procedural Requirement PR No.29 settles the edge cases. It is the contract date that decides, not the keel date and not the delivery date. The Rules also assume a particular structural arrangement: welded steel, stiffened plate panels, longitudinally or transversely framed with full transverse bulkheads and intermediate web frames, a double bottom to the applicable statutory depth, and the engine room aft of the cargo tank or hold region. CSR Ch 1 Sec 1 [1.1.1] / [1.1.2]

Then the size limit, which is different for the two ship types. Bulk carriers, single side skin and double side skin alike, are caught at a freeboard length L_LL of 90 m or above; the bulk carrier definition used is a ship built generally with a single deck, double bottom, hopper side tanks and topside tanks, single or double side skin in the cargo hold region, intended primarily to carry dry cargoes in bulk. A hybrid bulk carrier — at least one hold with hopper and topside tanks, other holds without — is required to comply with the strength criteria of these Rules. Double hull oil tankers are caught at 150 m or above, an oil tanker being a ship that has to comply with Annex I of MARPOL 73/78. CSR Ch 1 Sec 1 [1.2.1] / [1.3.1]

Five bulk carrier types are named as outside the Rules even when they meet the length. Four of the five are absolute; the fifth carries a condition on how the ship is worked, and the condition is the requirement:

ore carriers
combination carriers
woodchip carriers
ships with inner bottom construction adapted for self-unloading
cement, fly ash and sugar carriers — but only where the ship is not loaded or discharged with grabs over 10 tons, with power shovels, or with anything else able to damage the cargo hold structure. If she is worked that way, the exclusion does not hold.

Ships for which the Rules are not applicable comply with the relevant Rules of the Society instead. Read the ship's particulars and the class notation before you assume. If the ship is not a CSR ship, nothing on this page applies to it — the limits then come from the society's own diminution tables, and those are in K5.3 and K5.4. CSR Ch 1 Sec 1 [1.2.1] / [1.1.3]

The one-side corrosion addition grid

This is the grid the whole renewal threshold is built from. Every value in it is a one-side figure in millimetres: what the rule expects a single face of a member to lose over the ship's life, given what is on that side of it. Two of them make a member. The columns are the three ship categories the rule uses, and a value printed in one column says nothing about the other two.

Corrosion addition for one side of a structural member, t_c1 or t_c2, in mm — all 24 rows the source prints. Bracketed numbers are the table notes, set out below the grid.
Compartment type	Structural member	Oil tankers	BC-A / BC-B, L_LL ≥ 150 m	Other BC
Ballast water tank, bilge tank, drain storage tank and chain locker ⁽¹⁾	Face plate of a PSM — in the 3 m band below the tank top ⁽⁴⁾	2.0
	Face plate of a PSM — anywhere else in the tank	1.5
	Other members ^{(2) (3)} — in the 3 m band below the tank top ⁽⁴⁾	1.7
	Other members ^{(2) (3)} — elsewhere	1.2
Cargo oil tank, slop tank	Face plate of a PSM — in the 3 m band below the tank top ⁽⁴⁾	1.7	N/A
	Face plate of a PSM — anywhere else in the tank	1.4	N/A
	Inner-bottom plating / bottom of tank	2.1	N/A
	Other members — in the 3 m band below the tank top ⁽⁴⁾	1.7	N/A
	Other members — elsewhere	1.0	N/A
Dry bulk cargo hold ⁽⁵⁾	Transverse bulkhead — in the upper part ⁽⁶⁾	N/A	2.4	1.0
	Transverse bulkhead — lower stool: sloping plate, vertical plate and top plate ⁽⁷⁾	N/A	5.2	2.6
	Transverse bulkhead — other parts	N/A	3.0	1.5
	Sloped plating of hopper tank, inner bottom plating	N/A	3.7	2.4
	Other members — upper part ⁽⁶⁾, plus the webs and flanges on the upper end brackets of side frames in single side bulk carriers	N/A	1.8	1.0
	Other members — webs and flanges on the lower brackets of side frames in single side bulk carriers	N/A	2.2	1.2
	Other members — other parts	N/A	2.0	1.2
Exposed to the atmosphere	Weather deck plating	1.7
Exposed to the atmosphere	Other members	1.0
Exposed to seawater	Shell plating in the band between two waterlines: the minimum design ballast draught, and the scantling draught	1.5
Exposed to seawater	Shell plating elsewhere	1.0
Fuel and lube oil tank	The compartment type carries one value; the source names no member breakdown.	0.7
Fresh water tank	The compartment type carries one value; the source names no member breakdown.	0.7
Void spaces ⁽⁸⁾	Spaces not normally accessed: entry only through bolted manhole openings and the like, pipe tunnels, and those faces of a stool space that do not bound either a dry bulk cargo hold or a ballast cargo hold.	0.7
Dry spaces	Internals of a machinery space, of the pump room, of a store room, of the steering gear space and the like.	0.5

Source for the whole grid: CSR Ch 3 Sec 3 Tbl 1 · PDF pp. 102–103

Three points on the grid itself, before the notes. Fuel and lube oil tank, fresh water tank and void spaces are three separate rows that happen to print the same value, 0.7. They are not one row and they are not one compartment type. The "spaces not normally accessed" description belongs to void spaces only; a fuel oil tank or a fresh water tank takes 0.7 whether or not it is normally accessed. N/A means the column does not apply to that compartment, not that the value is zero — a cargo oil tank does not occur on a bulk carrier and a dry bulk cargo hold does not occur on an oil tanker. And the two bulk carrier columns diverge sharply: on a lower stool the BC-A / BC-B figure is exactly double the other-BC figure, and on a transverse bulkhead upper part it is more than double.

The three additions — notes (1), (2) and (3)

These are not alternative values. They are added on top of the grid value for the surface concerned, and they are easy to miss because they hang off the compartment heading rather than off the member row.

Note	Added	To which surface
(1)	+1.0 mm	The plate surface within 3 m above the upper surface of the chain locker bottom.
(2)	+0.5 mm	The plate surface exposed to ballast, on the plate boundary between water ballast and a heated cargo oil tank or a heated slop tank. A tank counts as heated once it carries any form of heating capability, most commonly heating coils.
(2)	+0.3 mm	Each surface of a stiffener web and its face plate, where that stiffener stands inside a ballast tank and lands on a boundary carrying water ballast on one face and, on the other, a heated cargo oil tank, a heated fuel or lube oil tank, or a heated slop tank.
(3)	+0.7 mm	The ballast-side face of any plate whose far side is a heated fuel oil or lube oil tank.

The five definitions — notes (4) to (8)

Four of these decide which row of the grid a point belongs to, so they bite before any arithmetic starts.

(4) The 3 m band. It applies only to cargo tanks, slop tanks and ballast tanks that have the weather deck as their tank top. Take the 3 m vertically down from the tank top, and the lower edge of the band then runs parallel to that top. A ballast tank whose top is not the weather deck does not get the band at all, and every member in it takes the "elsewhere" value.
(5) Dry bulk cargo hold. The category takes in any hold built for dry bulk cargo, including one that can also be filled with water ballast. A ballast-capable hold is still read from the dry bulk cargo hold rows.
(6) Upper part. Everything in the hold that lies above the joint where the topside tank lands on the inner hull, or on the side shell. Where the ship has no topside tank, the upper part is instead the top one third of the cargo hold height — and a plane bulkhead standing at a dry bulk cargo hold has its own upper part set the same way.
(7) The lower stool zone where no stool exists. Where no lower stool is fitted — an engine room bulkhead or fore peak bulkhead — or where the bulkhead is plane, the rule says the lower-stool corrosion addition should still be carried up the bulkhead, as high as the stool on the bulkhead facing it across that hold. If that facing bulkhead has no stool either, the zone starts at the inner bottom and stops level with the top of the hopper sloping plate next to it, and in no case does it have to be taken higher than 3 m. This is the note that puts a 5.2 mm one-side value on a plate that has no stool anywhere near it.
(8) Pipe tunnel, outer shell side. When the value for the outer shell plating is being fixed, a pipe tunnel counts as though it were a water ballast tank — so the shell plate bounding a pipe tunnel does not take the void-space 0.7 on its inboard face.

Notes (1) to (8): CSR Ch 3 Sec 3 Tbl 1, notes (1)–(8) The same grid cell by cell, each with its own clause and PDF page, is in handbook table T10 — CSR renewal thresholds, together with the assembly rules, the renewal criteria and the scope conditions.

How t_c is assembled from the grid

Two grid lookups, one rounding step and one flat addition. The order matters: the rounding is applied to the sum of the two one-side values, before the reserve thickness goes on. Rounding after the reserve, or rounding each side separately, gives a different answer.

member between two compartments
    t_c = Roundup_0.5 (t_c1 + t_c2) + t_res

internal member wholly within one compartment
    t_c = Roundup_0.5 (2 t_c1)      + t_res

    Roundup_0.5 (t)  rounds t to the UPPER half millimetre
    t_res            reserve thickness, 0.5 mm flat

Then the floors. Whatever the two lookups give, t_c in total may not come out below 2 mm, and there are two places where that floor drops to 1.5 mm: the web and face plate of stiffeners, and internals of dry spaces. Those minimums do not apply to members made of stainless steels, stainless clad steels or aluminium alloys. CSR Ch 3 Sec 3 [1.2.1] / [1.2.2]

Materials change the arithmetic rather than adjusting it. The corrosion additions cover carbon-manganese steels, stainless steels, stainless clad steels and aluminium alloys; anything else is set by the Society. For compartment boundaries and internal members made from stainless steel or aluminium, the total corrosion addition is the reserve alone, t_c = t_res = 0.5 mm — the grid is not used at all. For stainless clad steel the two sides are treated differently: the exposed carbon steel side takes the Table 1 value for the corresponding compartment, and the stainless side takes t_c2 = 0. CSR Ch 3 Sec 3 [1.1.1] / [1.2.1]

Two allocation rules decide which grid row a member is read from, and both catch people out.

A stiffener follows its plating. The corrosion addition of a stiffener is determined by the location of its connection to the attached plating — not by where the web or the flange sits. A longitudinal whose flange projects into a different notional band is still read from where it lands.
The heaviest value takes the whole strake. Where more than one corrosion addition value could be read for a single plate or local structural member, the heaviest of them governs, and it governs the whole strake. There is one exception, and only one: on an oil tanker, where vertical corrugations are arranged with vertical seams, the part of the corrugation above the 3 m line and the part below it may each take the value that actually belongs to it.

Allocation rules: CSR Ch 3 Sec 3 [1.2.3] / [1.2.4]

Worked: inner bottom plating of a BC-A bulk carrier

upper face  dry bulk cargo hold, inner bottom plating,
            BC-A column                                     t_c1 = 3.7
lower face  double bottom ballast tank, other members.
            Note (4) does NOT apply: the tank top is the
            inner bottom, not the weather deck, so the
            "elsewhere" value is used                       t_c2 = 1.2
                                                     sum         4.9
Roundup_0.5(4.9)                                                 5.0
+ t_res                                                        + 0.5
                                                     t_c         5.5 mm
                                   (minimum 2 mm — satisfied)

as-built 20.0 mm, no voluntary addition
t_ren    = 20.0 - 5.5 - 0                                      14.5 mm
band     = 14.5 <= t_m < 15.0
t_repair = 20.0 - 0                                            20.0 mm

That is 5.5 mm of allowance on a 20 mm plate — 27.5 %, well beyond anything a percentage table publishes for an inner bottom. Move the same plate to a bulk carrier outside the BC-A / BC-B category and the hold-side value drops from 3.7 to 2.4, the sum becomes 3.6, rounds to 4.0, and t_c becomes 4.5 mm — a metre of plate lower down the same class of ship, a millimetre of difference in the limit. The ship category is not a formality on the cover sheet. worked from CSR Ch 3 Sec 3 Tbl 1 + [1.2.1] + Ch 13 Sec 2

t_ren, t_repair and the half-millimetre band

The acceptance criterion for local corrosion is one line. Steel renewal is required if the measured thickness t_m, in mm, is less than the renewal thickness. It applies to local structural elements, which the rule defines as local supporting members and primary supporting members.

t_ren    = t_as-built - t_c - t_vol_add      renew if t_m < t_ren
t_repair = t_as-built - t_vol_add            insert not less than this
band     = t_ren <= t_m < t_ren + t_res      alternative solutions
t_res    = 0.5 mm

Where the reading falls	What the rule says
t_m ≥ t_ren + 0.5	Outside the acceptance criterion for local corrosion. The global criterion still has to be satisfied separately.
t_ren ≤ t_m < t_ren + 0.5	The band. Not a renewal and not a clean reading. This is the range in which something other than renewal can be agreed, and what that something is comes from the attending society's own rules — whichever of UR Z10.2, Z10.4 and Z10.5 it has incorporated — not from CSR.
t_m < t_ren	Steel renewal is required.

Note where the band is closed. It is closed at the bottom and open at the top: a reading of exactly t_ren is inside the band and is not a renewal; a reading of exactly t_ren + 0.5 is above it. And the width is fixed — 0.5 mm, whatever the member, whatever the as-built thickness and whatever the corrosion addition. On a 20 mm plate with t_c = 5.5 it is under a tenth of the allowance; on a 10 mm plate with t_c = 2.0 it is a quarter of it. CSR Ch 13 Sec 2 [2.1.1] / [2.1.3] · Symbols

When an area is renewed, the insert does not go back at the renewal thickness. Areas needing renewal are in general to be repaired with inserted material of the same or greater grade and yield stress as the original, and of a thickness t_repair not less than t_as-built − t_{vol_add} — that is, the gross offered thickness. The voluntary addition is the only thing the owner is not obliged to put back. CSR Ch 13 Sec 2 [2.1.2]

One thing the criterion buys the ship is worth knowing, because it explains why the number is treated as decisive. Assessment against the newbuilding requirements — the full set of loads and limit states, yielding, buckling, fatigue — is not required during the operational life of the ship, provided the measured thickness of every structural member stays greater than the renewal thickness. The renewal thickness is the operational stand-in for the whole design check. CSR Ch 13 Sec 1 [1.2.2]

The global check: the hull girder

The corrosion allowance has two halves and both are acceptance criteria. Local corrosion is the uniform wastage of one local structural element — a single plate, a single stiffener. Global corrosion is wastage averaged over something larger, a primary supporting member or the hull girder itself. Assessment against both is required during the operational life of the ship, and steel renewal is required if either the local or the global corrosion allowance is exceeded. A sheet full of readings that each clear t_ren can still fail the ship. CSR Ch 3 Sec 2 [1.1.2] · Ch 13 Sec 1 [1.2]

The global check does not run at every survey. Longitudinal strength is evaluated from the thicknesses as they stand after measurement, after any renewal and after any reinforcement, and it is evaluated at special surveys, once the ship is over 10 years old. Below that age, and outside a special survey, the criterion is not triggered by the Rules themselves. CSR Ch 13 Sec 2 [2.2.1]

The three global criteria. The base for every comparison is the **gross offered** thickness, t_{as_built} − t_{vol_add}, not the as-built.
Check	What must hold
Deck and bottom zones section modulus route	Work the hull girder section modulus at deck and at bottom out of the measured thicknesses. Neither of the two figures may fall below 90 % of the same modulus computed per Ch 5 Sec 1 on the gross offered thickness.
Deck and bottom zones zone-area alternative	As an alternative, add up the measured item areas that make up the bottom zone, and separately those that make up the deck zone. Each of the two sums has to reach 90 % of the area that same zone has when it is worked out on the gross offered thickness.
Neutral axis zone	The current sectional area of the neutral axis zone — the sum of the measured plating areas of that zone — is not to be less than the sectional area of the zone calculated with the gross offered thickness minus 0.5 t_c. This one is an absolute deduction, not a percentage.
Screening rule	Take a transverse section and look at every item in it that contributes to hull girder strength. If each one has lost less than 10 % of its gross offered thickness in the deck and bottom zones, and less than 0.5 t_c in the neutral axis zone, that section already satisfies the criteria, and the zone areas need not be worked out from the measured thicknesses at all.

All four: CSR Ch 13 Sec 2 [2.2.2] · Ch 3 Sec 2 [1.2.2]

Zone membership is geometric: a member is in a zone because of where it sits, not because of what it is called. The deck zone and the bottom zone are listed separately for bulk carriers and for oil tankers; the neutral axis zone has one list covering both. None of the three lists is closed — the deck zone lists open with "such as" and the neutral axis zone with "as for example" — so an item the rule does not name still belongs to the zone if it contributes to hull girder strength. Side shell plating is in all three zones on a bulk carrier, depending on its height; on an oil tanker it is in the bottom and neutral axis zones, and the deck zone list names the sheer strake in its place. A longitudinal strength member that makes up part of the hull girder web and stands at an angle to the vertical does not bring its whole area with it. What enters the zone area is its projected area on the vertical plane.

Zone membership, as the rule sets it out
Zone	Bulk carriers	Oil tankers
Deck zone items above or crossed by the 0.9 D level line above the baseline	Plating of the strength deck · the deck stringer · the sheer strake · side shell plating · plating of the inner hull and of any other longitudinal bulkhead · sloped plating of the topside tank, its horizontal and vertical strakes included · every longitudinal stiffener, girder and stringer landing on the plating listed here	Plating of the strength deck · the deck stringer · the sheer strake · uppermost strake of the inner hull and of any other plane longitudinal bulkhead · sloped plating of the topside tank, its horizontal and vertical strakes included · the longitudinal upper stool · every longitudinal stiffener, girder and stringer landing on the plating listed here
Bottom zone bulk carriers: everything as high as the top of the hopper sloping plating — and on a ship with no hopper tank, as high as the inner bottom plating, that plating included	The keel plate · bottom plating · bilge plating · bottom girders · inner bottom plating · sloping plating of the hopper tank, with its horizontal plating where fitted · side shell plating · lower strake of a plane longitudinal bulkhead · every longitudinal stiffener landing on the plating listed here	The keel plate · bottom plating · bilge plating · lower strake of a plane longitudinal bulkhead · bottom girders · inner bottom plating · sloping plating of the hopper tank, with its horizontal plating where fitted · side shell plating · the longitudinal lower stool · every longitudinal stiffener landing on the plating listed here
Neutral axis zone items between the deck zone and the bottom zone	Side shell plating · plating of the inner hull and of any longitudinal bulkhead · sloped plating of the topside tank. The rule gives these as examples rather than as a closed list.

Zone definitions: CSR Ch 13 Sec 2 [1.2.1]–[1.2.3]

What CSR does not contain

The renewal chapter is short and it is finished. Ch 13 is two sections: principles and survey requirements, then acceptance criteria — and the acceptance criteria are the two on this page, local corrosion against t_ren and global corrosion against the hull girder figures. The stated purpose of the chapter is to provide criteria for the allowable thickness diminution of the hull structure, and that is all it does.

So there are no CSR acceptance criteria for pitting, for edge corrosion or for grooving. No pit depth, no pitting intensity diagram, no criterion for a wasted free edge or a groove along a weld. CSR does not use the term "substantial corrosion" either — it states the band and heads the consequence "Alternative solutions". Anyone quoting a CSR pitting limit is quoting something that is not in the document. Those criteria live in the class rules and in the IACS survey URs; the class-by-class picture is in K5.6. CSR Ch 13 Sec 1 [1.1.1] · Ch 13 Sec 2, whole section

CSR says where they do live, twice, in plain terms. For the hull survey requirements it points, as applicable, at whichever rules or documents the individual Society has issued to carry the relevant UR: UR Z10.2 where the ship is a single side skin bulk carrier, UR Z10.4 where it is a double hull oil tanker, UR Z10.5 where it is a double side skin bulk carrier. Those same society documents also carry the minimum survey scope for keeping class, thickness measurement included. And the band above t_ren hands its consequence back to the same three URs. CSR supplies the arithmetic; the Z10 series supplies the survey. On a CSR ship you work to both at once. CSR Ch 13 Sec 1 [1.1.4] / [2.1.1] · Ch 13 Sec 2 [2.1.3]

One more boundary, because it changes what a reading means. Some items are determined directly in gross scantlings and do not follow the net scantling approach at all — they already include additions for corrosion, but without any owner's extra margin, and they are identified in the Rules by the suffix "gr". The named examples are the scantlings of superstructures and deckhouses, and massive pieces made of steel forgings and steel castings. There is no t_ren to compute for them from this chapter, which is also why the onboard plans for superstructures, deckhouses and casing carry the newbuilding thickness only. CSR Ch 3 Sec 2 [1.1.3] · Ch 1 Sec 3 [2.2.3] a)

What the office needs, and what the plans must carry

CSR requires the ship to carry the answer, so the first move is not to compute anything. The ship has to carry one copy of each of these plans — midship sections, construction profiles, shell expansion, transverse bulkheads, the fore and aft part structures, the machinery space structures — and each of them has to show, item by item, the newbuilding thickness and the renewal thickness. The renewal chapter repeats that requirement in its own words and adds one more: where a voluntary addition exists, its thickness has to be marked clearly on the plans as well. The midship section plan carried on board has to show something further — for the representative transverse section of every cargo hold, the hull girder sectional properties that Ch 5 Sec 1 sets as the minimum. That is what the office needs for the global check. Plans of superstructures, deckhouses and casing carry the newbuilding thickness only. CSR Ch 1 Sec 3 [2.2.3] a) · Ch 13 Sec 1 [1.3.1] / [1.3.2]

Ask for those plans before the first tank. When they carry the renewal column, the job is comparison and nothing else. When they do not — and they often do not, particularly the voluntary addition marking — the office has to rebuild the number from scratch, and it needs the following on the sheet to do it. None of these can be reconstructed later from a frame number and a reading.

What has to be on the sheet before t_ren can be built for a point
Field	Why the office cannot proceed without it
As-built at the point	First term of the subtraction. An error here moves t_ren by the same amount and is invisible in the reading.
Voluntary addition, and whether it is documented	Subtracted from the as-built for both t_ren and t_repair, and it is the base of the whole global check. "None marked on the plans" is itself a usable answer; a blank is not.
Compartment on both sides	Two grid lookups, one per face. Ballast one side and sea the other is a different t_c from ballast one side and a hold the other.
Member category as the rule names it	Face plate of a primary supporting member against other members; upper part against other parts; lower stool plating against the rest of the bulkhead. These are separate grid rows: on one BC-A transverse bulkhead the one-side values run from 2.4 to 5.2 mm.
Height relative to the tank top — and what the tank top is	The 3 m band applies only where the weather deck is the tank top. Record both the distance and the fact, because a point 2.8 m below a weather-deck tank top and the same point in a double bottom tank take different values.
Where a stiffener lands	Its corrosion addition is set by the location of its connection to the attached plating, not by where the web sits.
Ship category	Oil tanker, BC-A / BC-B at L_LL ≥ 150 m, or other bulk carrier. The two bulk carrier columns differ by a factor of two on several rows.
Heated boundaries, and the chain locker	Notes (1) to (3) add 0.3 to 1.0 mm on named surfaces. Whether the adjacent cargo, fuel or lube oil tank is heated is a fact from the ship, not from the drawing.
Whether the opposing bulkhead has a stool	Note (7) sets the vertical extent of the lower-stool value where no stool is fitted, and it is the single largest one-side value in the grid.
Material, where it is not carbon steel	Stainless and aluminium members take t_c = 0.5 mm and are outside the minimums. A stainless clad plate is read differently on each face.
Height above the baseline, for hull girder points	Zone membership is geometric — the 0.9 D line, the top of the hopper sloping plating. Side shell plating can land in any of the three zones, and the office cannot assign it without knowing where the point was.

Two entries change how the sheet is written rather than what goes on it. Where a reading lands in the 0.5 mm band, say so in words, not by leaving the office to notice. It is neither a pass nor a failure, and it is the finding on which the surveyor has a decision to take under the Z10 series. And where a plate has already been renewed at a previous survey, the insert went in at t_as-built − t_{vol_add} and not at the original as-built, so the as-built column for that plate is no longer what the shell expansion says. Note the renewal and the date.

This page carries the thresholds and the arithmetic. What changes in the survey on a CSR ship — the reading of the plans, the difference from a pre-CSR sister at the gauge — is in K3.9, and the vocabulary that every class limit is written in is in K5.1. The full grid cell by cell, with the assembly rules, the renewal criteria and the scope conditions each carrying its own clause and PDF page, is in handbook table T10 — CSR renewal thresholds.

Sources

CSR Pt 1 Ch 1 Sec 1IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version (in force 1 July 2024) — Applicationofficial text ↗
CSR Pt 1 Ch 1 Sec 3IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version — Documentation, plans supplied onboardofficial text ↗
CSR Pt 1 Ch 3 Sec 2IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version — Net Scantling Approachofficial text ↗
CSR Pt 1 Ch 3 Sec 3IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version — Corrosion Additionsofficial text ↗
CSR Pt 1 Ch 13 Sec 1IACS Common Structural Rules for Bulk Carriers and Oil Tankers, 1 January 2024 version — Ship in Operation: Principles and Survey Requirementsofficial text ↗
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 ↗
UR Z10.2IACS UR Z10.2 Rev.37 (Feb 2023) — Hull Surveys of Bulk Carriersofficial text ↗
UR Z10.4IACS UR Z10.4 Rev.18 (Feb 2023) — Hull Surveys of Double Hull Oil Tankersofficial text ↗
UR Z10.5IACS UR Z10.5 Rev.20 (Feb 2023) — Hull Surveys of Double Skin Bulk Carriersofficial 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.