iacs under 90 steel selection

IACS History File + TB Part A

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UR S6 Use of Steel Grades for Various Hull Members - Ships of 90 m in Length and Above

Part A. Revision History Version no. Approval date Implementation date when

applicable Rev.7 (Apr 2013) 18 April 2013 1 July 2014 Rev.6 (May 2010) 24 May 2010 - Rev.5 (Sept 2007) 18 September 2007 1 July 2008 Rev.4 (July 2003) 16 July 2003 - Rev.3 (May 2002) 6 May 2002 - Rev.2 (1996) No record - Rev.1 (1980) No record - NEW (1978) No record - Rev.7 (Apr 2013) .1 Origin for Change:

Suggestion by IACS Member .2 Main Reason for Change: A question was raised in the Hull Panel regarding the applicability of Table 2 of UR S6 to Liquefied Natural Gas (LNG) Carriers. See TB document in Part B. .3 List of non-IACS Member classification societies contributing through the TC Forum and/or participating in IACS Working Group: None. .4 History of Decisions Made: After discussion within the Hull Panel, it was decided that Table 2 of UR S6 could lead to inconsistencies when applied to LNG Carriers. Therefore, a new Table was added to provide the minimum material grades for LNG Carriers and an addition was made to Table 1, item C5.1. In addition, Table 1, items B3 and C8 were clarified and editorial changes were made to the text in UR S6.1. .5 Other Resolutions Changes None .6 Dates:

Original proposal: 23 October 2012, made by Hull Panel Chairman Panel submission to GPG: 25 January 2013

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GPG Approval: 18 April 2013 (Ref. 13039_IGe) Rev.6 (May 2010) .1 Origin for Change:

Based on IACS Requirement (Common Structural Rules for Bulk Carriers and Double Hull Oil Tankers)

.2 Main Reason for Change: Following the introduction of the IACS Common Structural Rules for Bulk Carriers and Double Hull Oil Tankers, Hull Panel were tasked to review all the UR S files to consider whether or not they are applicable to ships covered by the CSR. .3 List of non-IACS Member classification societies contributing through the TC Forum and/or participating in IACS Working Group: None. .4 History of Decisions Made: After review it was decided that for CSR ships the requirements of UR S6 are superseded by those of the Common Structural Rules and therefore do not apply. .5 Other Resolutions Changes All UR S files, except UR S8, S9, S15, S16, S19, S22, S23, S30 and S31. .6 Dates:

Original proposal: 2007, made by Hull Panel Task 50 Panel submission to GPG: 19 April 2010 GPG Approval: 24 May 2010 (Ref. 10051_IGd)

Rev.5 (Sept 2007) Hull Panel Task 17 Review of UR S6 for side shell plating exposed to low temperatures. See TB document in Part B. Rev.4 (July 2003) See TB document in Part B. Rev.3 (May 2002)

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See TB document in Part B. Rev.2 (1996) No TB document available. Rev.1 (1980) No TB document available. NEW (1978) No TB document available.

Part B

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Part B. Technical Background List of Technical Background (TB) documents for UR S6: Annex 1. TB for Rev.3 (May 2002)

See separate TB document in Annex 1.

Annex 2. TB for Rev.4 (July 2003)


Annex 3. TB for Rev.5 (Sept 2007)


Annex 4. TB for Rev.7 (Apr 2013)


Note: There are no separate Technical Background (TB) documents for the original resolution (1978), Rev.1 (1980), Rev.2 (1996) and Rev.6 (May 2010).

(UR S6, Rev.3, May 2002)Technical Background to changes proposed with respect to Table 1 of UR S6

The objective of the attached proposal is to clarify the application of the Notes of Table 1 in UR S6, inorder to avoid different interpretations on their application, in particular for what concerns the plating atcorners of large hatch openings.

It is now clarified that large hatch openings are to be intended as the cargo hatch openings in thestrength deck and the relevant requirements are now specified. A distinction is made between ships suchas container carriers and bulk/ore carriers. For these latter, less stringent requirements may be applied inthe region outside 0,6L amidships based on the fact that lower hull girder stresses occur in this area.

The application to continuous hatch coamings has been clarified by introducing a length criterium (0,15L,above which coamings are considered as being subjected to hull girder stresses). Requirements for thesteel grades of end brackets and deck house transition of longitudinal cargo hatch coamings have beenintroduced, based on damage statistics results.

The change was agreed unanimously and no unresolved issues remain..

Submitted by WP/S ChairmanDate: 14 March 2002

Zoe WrightTypewritten TextPart B, Annex 1

Technical Background S6.1 in Rev. 4 of UR S6

The objective of the attached proposal is to clarify that the minimum width requirement of single strakes (800 + 5*L mm, need not be greater than 1800 mm) applies to those strakes located at the four corners of the ships cross section, plus deck strakes on top of longitudinal bulkheads. In addition, the fact that ships geometry may impose limitations to the width of the above strakes (e.g. in some containerships), is taken into account.


TECHNICAL BACKGROUND

UR S6, REV.5 (SEPT 2007)

IACS HULL PANEL TASK 17 - Review of UR S6 for side shell plating exposed to low temperatures

1. Scope and objective Consider requirements on selection of steel grades, with a view to preventing brittle fracture in the side shell plating of ships operating in areas with low air temperatures. 2. Background Transportation Safety Board of Canada reports and correspondence with IACS concerning hull fractures in the Lake Carling and its sister ship Ziemia Gornoslaska. The TSB expressed concern over the current requirements of UR S6 for side shell plating which it did not consider adequate for ships operating near or below 0C. 3. Points of discussions/Analysis 3.1 General The brittle fracture damage of MV Lake Carling and analyses done in connection to this incident have been pointing at the following main issues:

- Application of material for side shell - Material grade requirements for materials subjected to lower temperatures - Stress level - Consequence of brittle failure

3.2 Analysis The issue of steel toughness requirements, or to be more accurate lack of measured steel toughness requirements for normal strength ship steel grade A ship steel, has been raised as a major issue within both IACS and IMO by the Transport Safety Board of Canada. They based there assumptions on the brittle fracture that occurred in 19 mm grade A plate of the side shell of MV Lake Carling which initiated at a temperature of approximately 0C (fracture initiated below the water line and is therefore assumed to be near 0C, air temperature was minus 6C). Earlier, IACS WP/MW was asked to review the IACS testing requirements for normal strength ship steel grade A, which presently has no requirement for Charpy V-notch impact testing the steel mill. The working party reported back and quite rightly confirmed that there is no need to change the current test arrangements. It is more correct to consider changes to the requirements selecting the grade of material to be used, in this case IACS UR S6.


Lloyds Register has recently taken the opportunity, with the kind permission of the Transport Safety Board of Canada, to carry out further tests on steel plate taken from the Lake Carling and its sister ship the Ziemia Gornoslaska; these have not been too encouraging, see the table shown below.

Steel Source

Lake Carling Z Gornoslaska1

Charpy V-notch 27J transition temperature

L= +10C T= +10C

L= +20C

Fracture appearance transition temperature FATT (50% Crystalline)

L= +10C

T= +15C

L= +15C

FATT (70% Crystalline) L= -5C

L= +5C

Minimum CTOD (BS 7448) @ -19C 0.01 mm

Minimum CTOD (BS 7448) @ 0C 0.25 mm

Note 1, Z Gornoslaska is a sister ship to the Lake Carling. IACS UR S6.1 was developed based on world wide service using a lowest mean daily average temperature of -10C. Areas of navigation to this temperature are given in statistical tables and charts such as the Pilot series of publications published by Hydrographer of the Navy or other authoritative reference, see Figure 1 as an example. This temperature for example, allows for navigation in the Northern Baltic and the St. Lawrence. Therefore IACS UR S6, will allow the use of grade A steel as follows; Class I, grade A up to 30 mm at temperatures down to -10C Class II, grade A up to 20 mm at temperatures down to -10C and grade B up to 25 mm at temperatures down to -10C Class III, grade A up to 15 mm at temperatures down to -10C and grade B up to 20 mm at temperatures down to -10C. This indicates that the current rule IACS UR S6 allows the use of non-impact tested steel in greater thicknesses and to a lower temperature than that involved in the Lake Carling incident. Thickness increase and lower temperature each increase the risk of brittle fracture.

Chart based on temperature data points from Admiralty Pilot Books, published by HMSO

Figure 1 Example of Navigation Chart based on Temperature 4. Proposed upgrading In the proposed revision Table 1 is revised into Tables 1 to 5 for easier interpretation. The following areas are upgraded to minimum grade B/AH regardless of Class: a) For ships with length exceeding 150 m and with single strength deck and without inner continuous longitudinal bulkhead(s) between bottom and the strength deck, single side strakes in way of cargo hold:

- High shear stresses - Serious consequences (flooding/reduced hull girder capacity) of brittle failure

b) Shell strakes in way of ice strengthening:

- High ice pressures and impacts from collision with ice resulting in high stresses, high strain rates and possible plastic deformation at temperatures close to (below or equal) 0 C.

c) For vessels with length exceeding 150 m and with single strength deck, within 0.4L amidships, for longitudinal strength members of strength deck plating and continuous longitudinal members above strength deck, excluding hatch coamings, as these members may be:

- Subjected to high hull girder tensile stresses - Subjected to temperatures down to -10 C - critical / brittle fracture may have serious consequences for the hull girder integrity

In addition is the new requirement for single side shell strakes and lower bracket in way of single side (D/DH) as given in CSR for bulk carriers also included. S6.1 Ships in normal world wide service Materials in the various strength members are not to be of lower grade than those corresponding to the material classes and grades specified in Table 1 through Table 6. General requirements are given in Table 1, while additional minimum requirements for ships with length exceeding 150m and 250m, bulk carriers subject to the requirements of SOLAS regulation XII/6.5.3, and ships with ice strengthening are given in Table 2 through Table 5. The material grade requirements for hull members of each class depending on the thickness are defined in Table 6. Table 1 Material Classes and Grades for ships in general

Structural member category Material class/grade SECONDARY: A1. Longitudinal bulkhead strakes, other than

that belonging to the Primary category A2. Deck plating exposed to weather, other than

that belonging to the Primary or Special category

A3. Side plating

- Class I within 0.4L amidships - Grade A/AH outside 0.4L amidships

PRIMARY: B1. Bottom plating, including keel plate B2. Strength deck plating, excluding that

belonging to the Special category B3. Continuous longitudinal members above

strength deck, excluding hatch coamings B4. Uppermost strake in longitudinal bulkhead B5. Vertical strake (hatch side girder) and

uppermost sloped strake in top wing tank

- Class II within 0.4L amidships - Grade A/AH outside 0.4L amidships

SPECIAL: C1. Sheer strake at strength deck (*) C2. Stringer plate in strength deck (*) C3. Deck strake at longitudinal bulkhead,

excluding deck plating in way of inner-skin bulkhead of double-hull ships (*)

- Class III within 0.4L amidships - Class II outside 0.4L amidships - Class I outside 0.6L amidships

C4. Strength deck plating at outboard corners of cargo hatch openings in container carriers and other ships with similar hatch opening configurations

- Class III within 0.4L amidships - Class II outside 0.4L amidships - Class I outside 0.6L amidships - Min. Class III within cargo region

C5. Strength deck plating at corners of cargo hatch openings in bulk carriers, ore carriers, combination carriers and other ships with similar hatch opening configurations

- Class III within 0.6L amidships - Class II within rest of cargo region

C6. Bilge strake in ships with double bottom over the full breadth and length less than 150m (*)

- Class II within 0.6L amidships - Class I outside 0.6L amidships

C7. Bilge strake in other ships (*)

- Class III within 0.4L amidships - Class II outside 0.4L amidships - Class I outside 0.6L amidships

C8. Longitudinal hatch coamings of length greater than 0.15L

C9. End brackets and deck house transition of longitudinal cargo hatch coamings

- Class III within 0.4L amidships - Class II outside 0.4L amidships - Class I outside 0.6L amidships - Not to be less than Grade D/DH

(*) Single strakes required to be of class III within 0.4L amidships are to have breadths not less than 800+5L (mm), need not be greater than 1800 (mm), unless limited by the geometry of the ships design.

Table 2 Minimum Material Grades for ships with length exceeding 150m and single strength deck

Structural member category Material grade Longitudinal strength members of strength deck plating

Grade B/AH within 0.4L amidships

Continuous longitudinal strength members above strength deck

Grade B/AH within 0.4L amidships

Single side strakes for ships without inner continuous longitudinal bulkhead(s) between bottom and the strength deck

Grade B/AH within cargo region

Table 3 Minimum Material Grades for ships with length exceeding 250m

Structural member category Material grade Shear strake at strength deck (*) Grade E/EH within 0.4L amidships Stringer plate in strength deck (*) Grade E/EH within 0.4L amidships Bilge strake (*) Grade D/DH within 0.4L amidships (*) Single strakes required to be of grade E/EH and within 0.4L amidships are to have

breadths not less than 800+5L (mm), need not be greater than 1800 (mm), unless limited by the geometry of the ships design.

Table 4 Minimum Material Grades for single-side skin bulk carriers subjected to SOLAS regulation XII/6.5.3

Structural member category Material grade Lower bracket of ordinary side frame (*),(**)

Grade D/DH

Side shell strakes included totally or partially Grade D/DH

between the two points located to 0.125l above and below the intersection of side shell and bilge hopper sloping plate or inner bottom plate (**) (*) The term of "lower bracket" means webs of lower brackets and webs of the lower part of

side frames up to the point of 0.125l above the intersection of side shell and bilge hopper sloping plate or inner bottom plate.

(**) The span of the side frame, l, is defined as the distance between the supporting structures.

Table 5 Minimum Material Grades for ships with ice strengthening

Structural member category Material grade Shell strakes in way of ice strengthening area for plates

Grade B/AH

Table 6 Material Grades Requirements for Classes I, II and III ................. 5. Source/Derivation of proposed interpretation

N.A.

6. Decision by voting

N.A.

Submitted by Hull Panel Chairman 20 July 2007

Permanent Secretariat note (September 2007): Adopted by GPG 18 September 2007, ref. 7632_IGb, with an effective date of 1 July 2008.

Part B, Annex 4

Technical Background Document for UR S6 (Rev. 7 Apr 2013)

1. Objective/Scope

The objective of this revision is to clarify the scope of application with regard to LNG Carriers, and to identify the minimum steel grades for selected structures on LNG Carriers. Table 2 is clarified and a new Table 3 is added for LNG Carriers. 2. Source of Proposed Requirements

The proposed requirements are based on the technical justifications for the current requirements, current practice within industry, and discussion within the Hull Panel (via correspondence and at Hull Panel Meetings). 3. Technical Basis and Rationale

In general, the proposed revisions reflect the industry practice. Regarding Table 2, the current practice is to not apply Table 2 to the longitudinal strength members located above the strength deck of LNG carriers. Four (4) LNG carriers with lengths greater than 150 meters were examined and a table of the material grades for plating of the strength deck and above is shown in as follows. These LNG carriers have higher grade steel in the strength deck, inner deck and deck girders that can be attributed to the need for higher grade steel along the tank boundary. However, most of the vessels have low grade steel in the trunk deck that is lower than the minimum material grade in Table 2. This indicates that Table 2 is not being applied in way of the double deck area.

Vessel A B C D Length (m) 332 278 266 205

Strength Deck Plating

E E E E

Trunk Deck Plating A, B A,D A D Inner Deck Plating DH, E E E2 E M

ater

ial

Gra

de

Deck Girders E E, E1 E, E2 E Notes: 1. Steel Quality Z25 2. Grade E Steel having improved weld toughness.

Therefore, the proposal is based on the following:

1) Although LNG carriers have a single strength deck, the trunk deck and inner deck can be considered a double deck and therefore Table 2 does not apply.

2) The inner deck will have a high material grade due to its nature as a cargo tank boundary. Similar to the inner deck, the deck girders are generally of a higher grade steel. However, in case of an unusual design, a minimum material grade should be set for the inner deck and deck girders.

3) A minimum material grade is required for the portions of the strength deck contributing to the longitudinal strength to provide a level of toughness to reduce the likelihood of crack initiation, as indicated in the Technical Background to Rev. 5.

4) As the material class indicated in Item B3 of Table 1 is acceptable and common practice, an additional minimum material grade is not required for the trunk deck.

Part B, Annex 4

5) The higher grade of the strength deck and deck girders may provide some crack arresting for the trunk deck.

An additional review of twenty-eight LNG carriers with delivery dates from 2005 to 2013 showed that the material of the trunk deck and inner deck plating at corners of liquid dome openings is E or EH grade in all vessels due to these corners being high stress areas. Therefore, a new item was added to Table 1 to account for this. 4. Summary of Changes

4.1 Clarification of the scope of application for Table 2

A note is added for Table 2, indicating that it does not apply LNG carriers which are covered by a new Table 3 (mainly membrane-type LNG carriers). 4.2 Clarification of the Structural member category

Structural member categories were modified in Tables 1 (item B3) and 2 to clarify that the steel grade applies to the plating only. The detail requirements in all Tables of UR S6 are only applicable to plating and not to the attached stiffeners. Note, the material grade requirements for stiffeners fall under the statement in UR S6 "For strength members not mentioned in Tables 1 to 6, Grade A/AH may generally be used." The only exceptions where stiffeners are explicitly covered in UR S6 are follows: (a) Table 1, C8, the hatch coaming consist of the vertical coaming plating and the horizontal coaming top plate and the top plate flange. See the following figure.

(b) Table 5 (of Rev 7), for "Lower bracket of ordinary side frame", clearly applies to vertical "stiffeners" that make up the side frame of bulk carriers. 4.3 Insertion of new table and figure

As a result of the clarification to the scope of application of Table 2 as indicated in 4.1 and 4.2 above, a new table was added to identify the minimum steel grades of LNG carriers (mainly membrane-type LNG carriers). This table has been inserted as a new Table 3. In addition, a figure was added to identify the three decks used in Table 3 to define the structural member categories. This figure has been inserted as a new Figure 1. 4.4 Addition to Table 1, item C5.1

Part B, Annex 4

A new item was added as item C5.1 to indicate that the highly stressed corners of the trunk deck and inner deck plating of the liquid dome openings of LNG carriers requires a higher class/grade of steel, similar to how higher grade steel is need at the corners of cargo hatch openings on bulk carriers. 4.5 Removal of footnote mark (*) from Table 1, item C6

The reference in Table 1, item C6 to the footnote was removed since the footnote is not applicable to this item. 4.6 Clarification of Table 1, item C8

Text was added to Table 1, item C8 to clarify that that the minimum material grade or class is also applicable to the coaming top plate and flange of longitudinal hatch coamings. 4.7 Reorganization of text for UR S6.1

Two paragraphs of UR S6.1, which were previously located after the Tables 1-7, were moved ahead of the tables to make them more visible. The first paragraph was reorganized into a list to clearly identify each table and text was added to identify the new Table 3. For clarify, the second sentence in the third paragraph of S6.1 was amended. 4.8 Correction of table and figure numbering and references

The table and figure numbering and references through the UR S6 were corrected as necessary. 5. Points of Discussion Prior to the proposed revision, points of discussion were:

(a) The applicability (or non-applicability) of Table 2 to LNG carriers (b) Technical justification of Table 2 (for ships with L>150m) (c) Technical justification of Table 3 (for ships with L>250m)

Following the proposed revision, points of discussion were:

(a) Structural member category The original wording is not clear and could be confusing. It is intended that the material grade requirements in UR S6 are applicable to the plating and not the longitudinal stiffeners. The reason for requiring the enhanced material grade of plating in certain locations is to act as crack arresters within the hull girder of the vessel.

(b) Application of Table 3 Table 3 is applicable to membrane type gas carriers only. Gas Carriers with other containment designs, such as the MOSS spherical tank design, would apply Table 2.

(c) Scope of new Item C5.1 in table 1 (d) Minimum material grade for Stiffeners on longitudinal hatch coamings of length

greater than 0.15L

Part B, Annex 4

6. Attachments, if any

None

Submitted by Hull Panel Chairman 25-Jan-2013

***

Part A. Revision HistoryPart B. Technical BackgroundAnnex 1 - TB for Rev.3 (May 2002)Annex 2 - TB for Rev.4 (July 2003)Annex 3 - TB for Rev.5 (Sept 2007)Annex 4 - TB for Rev.7 (Apr 2013)

iacs under 90 steel selection

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