Instructions Related to the Steel Renewal Criteria of Side Shell Frames and Brackets Of

Instructions related to the steel renewal criteria of side shell frames and brackets of single side skin bulk carriers (ref: UR S 31 as per BV Rules Part A, Ch 6, Sec 2, [6] and Ch 6, App 1, [5])

The compliance with such requirements is to be carried out initially at the limit date as detailed in BV Rules Pt A, Ch 6, Sec 2, [6.2] and then at each subsequent intermediate and class renewal surveys.

I) Pre-calculation by DT1 or by the LPO when delegated:

Before the scheduled survey date, a pre-calculation of the required thicknesses is carried out by DT1/LPO, upon request from the Connecting District (CD).

This pre-calculation is carried out with the software “Bulk 32”which has been specifically redesigned for the purpose of:

-calculating the minimum required thicknesses before the survey is started

-allowing the Surveyor to take appropriate actions during the survey, with respect to steel renewal or repairs or reinforcements of the frames and brackets, by comparing the measured thicknesses on-board to the pre-calculated thicknesses.

To this end, after the calculations have been carried out, DT1/LPO sends the relevant datasheetsand calculation sheets “Survey (S31)”to the CD.

The CD is to send both these datasheets and calculation sheets to the Shipowner and to the Survey Centre when known, in advance of the survey.A model of letter to the Owner is attached in Annex 1.

One calculation sheetis available for each frame which has been pre-calculated.Each pre-calculated frame is representative of a group of frames in each hold, as established by DT1/LPO.The group of framesto which the pre-calculated frame belongs is then indicated on the calculation sheet.

The calculation sheet also indicates the concerned hold No for each pre-calculated frame.

II) How to read the calculation sheets “Survey S31”:

An example of calculation sheet is given in Annex 2.

a) Headings:

The hold No is indicated on top of the page.

Ex: “Hold 3”

The frame No is also indicated , as well as the group of frames it represents.

Ex: “frame No 15 for group [10;20]” means that the calculation sheet is related to the frame No 15, and that these calculations are also relevant for frames Nos 10 to 20 inclusive.

b) 1st Table : “web thickness criteria”

This table indicates the different nominal thicknesses involved, the action to be taken depending on the value of the measured thicknesses and the replacement thickness required in case of renewal.

1st Column:

it indicates the zone A or B or C or D.

Zone A is the “lower bracket”.

Zone D is the “upper bracket”.

Zones B and C are the “frame” itself.

Zones A and B are the “lower part of frame” and are considered to be the most critical zones.

Refer to drawing 1 in Annex 3.

2nd column:

tasB: as-built thickness, for each zone.

3rd column:

tCoat: thickness as defined in Pt A, Ch 6, App 1, [5.1.2], for each zone.

4th column:

tRend/t: thickness as defined in Pt A, Ch 6, App 1, [5.3.2], for zone A and B and C. (not applicable for zone D)

5th column:

tabd : the greatest of (tCoat-tC) ; (0.75 tasB); trens

where tC is defined as per BV Rules Pt A, Ch 6, App 1, [5], table 1.

and trens is defined as per BV Rules Pt A, Ch 6, App 1, [5.3.3] (trens being only applicable in zones A and B)

6th column and 7th column:

These columns indicate the actions to be taken, depending on the value of the measured thickness of the web, for each zone.

tMweb : measured thickness on the web, for each zone (Refer also to III)).

Examples:

“If tMweb between [9.75 , 99.00[ No action required” means that if theaverage ofthe measured thicknesses is greater or equal to 9.75 mm, then no action is required on the concerned zone of the subject frame.

“If tMweb between [0.00 , 7.75[ renewal” means that if the average ofthemeasured thicknesses is less than 7.75 mm, then steel renewal is required on the concerned zone of the subject frame.

“If tMweb between [7.75 , 9.75[ other measures” means that if theaverage ofthe measured thicknesses is less than9.75 mm and greater or equal to 7.75 mm, then “other measures”, as defined in Pt A, Ch 6, App 1, [5.3.5], are required on the concerned zone of the subject frame.

Refer also to para. IV.1) for the details of the different actionsthat can be taken.

8th column:

TRepl: minimum replacementthickness required for renewal of webs, in case such webs are to be renewed.

c) 2nd Table : “Bending strength check of lower bracket”

This table is used when the lower bracket (zone A) length or depth does not meet the requirements in Pt E, Ch 4, Sec 3, [3.2.6] (corresponding to UR S 12 rev. 3).In this case, a modulus calculation is carried out by DT1/LPO.Refer to drawing 2 in Annex 3.

1st Column:

it indicates the zone A or B.

2nd Column:

Za(or Zb):is the modulus calculated at section a) (or section b)). Refer to drawing 3 in Annex 3.

3rd Column:

Zcorr : is the modulus calculated with the maximum acceptable corrosion, for each zone A and B.

4th Column:

Results: This column indicates the different kind of actions to be taken, for each zone.

Refer also to para. IV.2) for the details of the different actions that can be taken.

5th Column:

ZRepl:

minimum replacementmodulus required in case renewal or reinforcements are needed.

d) 3rd Table : “Web thickness criteria”

This table indicates the overall extent of renewal and of sand blasting & coating, when required in connection with the 1st Table.

It takes into account whether the frame is of integral type or separate type.

In case of integral brackets, if renewal is required on zone A, then it is to be carried out on zones A+B.

In case of separate brackets, if renewal is required on zone A, then it is to be carried out on zone A.

In case of integral brackets, if renewal is required on zone B, then it is to be carried out on zones A+B.

In case of separate brackets, if renewal is required on zone B, then it is to be carried out on zone B.

If renewal is required on zone C, then it is to be carried out on zones B+C.

If renewal is required on zone D, then it is to be carried out on zone D.

In case of integral brackets, if sand blasting & coating is required on zone A, then it is to be carried out on zones A+B.

In case of separate brackets, if sand blasting & coating is required on zone A, then it is to be carried out on zone A.

In case of integral brackets, if sand blasting & coating is required on zone B, then it is to be carried out on zones A+B.

In case of separate brackets, if sand blasting & coating is required on zone B, then it is to be carried out on zone B.

If sand blasting & coating is required on zone C, then it is to be carried out on zones B+C+D.

If sand blasting & coating is required on zone D, then it is to be carried out on zones C+ D

e) 4th Table : “Bending strength check of lower bracket”

The fourth table indicates the overall extent of renewal or of flange reinforcement , when required in connection with the 2nd Table, as follows:

If renewal or flange reinforcement is required on zone A, then it is to be carried out on zones A+B.

If renewal or flange reinforcement is required on zone B, then it is to be carried out on zones A+B.

III) How to gauge on-board the ship, during the survey:

The gauging methodology is detailed in the Annex V of IACS Unified Requirement UR Z 10.2 rev. 15, as detailed in the BV Rules leaflet (NR 467 December 2003 edition) to the November 2003 edition, Pt A, Ch 6, Sec 2, [6.3].

The number of side frames to be measured is to be the same as the number required for the intermediate survey or class renewal survey corresponding to the ship’s age (ref: BV rules Pt A, Ch 4, Sec 2).

From the 1st January 2004,the close-up survey and thickness measurements are to be taken for all shell frames in the forward cargo hold and one other selected cargo hold and 50% of frames in each of the remaining cargo holds, including upper and lower end attachments and adjacent shell plating, for the class renewal survey of ships between 10 and 15 years of ageand for the intermediate survey of ships between 15 and 20 years of age.

When the structural members show no thickness diminution with respect to the as-built thickness(tasB) and when the coating is found in “as-new” condition (i.e without breakdown or rusting), the exent of thickness measurements may be reduced.

When the thickness measurements show readings close to the acceptable criteria, the extent of thickness measurements is to be increased.

If steel renewal or repairs/reinforcements are applied on one or more frames in ahold, then all frames in that hold are to be gauged.

It is to be noted that, for a given calculation sheet, i.e for a given pre-calculated frame which is representative of a group of frames in a hold, the frames of this group will be subject to different possible actions, due to the different gauging readings from one gauged frame to another gauged frame.

Thickness measurements are to be taken for each zone, as follows:

Web of Zone A:

5 points to be measured, over the depth of the web and heightof the zone A.The average of these 5 points is the tMweb, which is to be compared to the required thicknesses on the calculation sheet, i.e on 1st table.

Web of Zone B:

5 points to be measured, over the depth of the web and a vertical distance equal to the frame web depth.The average of these 5 points is the tMweb, which is to be compared to therequired thicknesses on the calculation sheet, i.e on 1st table.

Web of Zone C:

3 points to be measured over the length of the Zone C.The average of these 3 points is the tMweb, which is to be compared to therequired thicknesses on the calculation sheet,i.e on 1st table.

This 3 point pattern may be extended to a 5 point pattern when considered necessary by the Surveyor.

Web of Zone D:

Same as Zone A.

When the lower bracket (zone A) length or depth does not meet the requirements in Pt E, Ch 4, Sec 3, [3.2.6] (corresponding to UR S 12 rev. 3), the bending strength check of the lower bracket is required.Gaugings are to be taken as follows, in order to calculate the actual section modulus in sections a) and b):

-at least 2 points are to be measured on the flange in way of each section a) and b).

-at least one point is to be measured on the attached shell plating on each side of the frame , i.e fore and aft of the frame, in way of each section a) and b).

Refer to drawing 3 in Annex 3.

IV) How to renew, repair or reinforce:

The different possibilities of action, listed in the 1st Table, are as follows:

-“No action required”: means that no specific action is needed on the subject zone of the frame.

-“Renewal” : means that steel renewal of the web is required .The replacement thickness is given by TRepl.

The associated flange is normally renewed at the same time, according to the as-built conditions.

-“Other measures” : means that the 3 following actions are required

sand blasting and coating

and

fitting tripping brackets

and

maintaining the coating in as-new condition (without breakdown or rusting) at subsequent class renewal and intermediate surveys

However, these “other measures” may be waived if the structural members show no thickness diminution with respect to the as-built thickness (tasB) and coating is in “as-new” condition.

-“stiffeners” : means that fitting of stiffeners on the lower bracket (zone A) , is required.

-“tripping brackets” : means that fitting of tripping brackets is required.

The different possibilities of action, listed in the 2st Table, on the column “results” are as follows, for each zone A or B:

-“Bending strength not required”: means that the verification of the section modulus is not required, as the lower bracket length and depth meet the requirements in Pt E, Ch 4, Sec 3, [3.2.6] (UR S 12 rev.3).

-“Bending strength successful for max. acceptable corrosion”: means that, as Zcorr is greater or equal to Za (or Zb), no further action is required with respect to the bending strength check, which is considered satisfactory in this case.

-“If (tMweb >= xx.xx) and (tMfl>= yy.yy) No action required” :means that if the average of the gauged thicknesses on the web (tMweb) is greater or equal to xx.xx and the average of the gauged thicknesses on the flange (tMfl) is greater or equal to yy.yy, then no further action is required for the corresponding zone.

-“If (tMweb <xx.xx) or (tMfl<yy.yy) Renewal or Flange reinforcement or Section modulus to be checked with measured thicknesses” :means that if the average of the gauged thicknesses on the web (tMweb) is less than xx.xxorthe average of the gauged thicknesses on the flange (tMfl) is less than yy.yy, then, there are 3 alternative possibilities:

-a flange reinforcement is to be carried out on zones A+B in order to obtain ZRepl.

-a renewal is to be carried out on zones A+B in order to obtain ZRepl

-the actual section modulusis to be calculated with the actual average of the gauged thicknesses and compared with Za (or Zb).

If the actual section modulus is greater or equal to Za (or Zb), then no further action is required.

If the actual section modulus is less than Za (or Zb), then flange reinforcement or renewal in zones A+B is to be carried out as mentioned above.

Note: another solution is to carry out a renewal according to the length and depth criteria for the lower bracket as detailed in Pt E, Ch 4, Sec 3, [3.2.6] and with Z Repl as section modulus.The advantage of this solution is that the bending strength check will not be required anymore at subsequent verifications on this renewed lower bracket.

-“As built modulus not OK; Renewal or Flange reinforcement”: means that the as-built modulus is not satisfactory.In this case, there are 2 alternative possibilities:

-a flange reinforcement is to be carried out in zones A+B in order to obtain ZRepl.

-a renewal is to be carried out on zones A+B in order to obtain ZRepl

V) Requirements for fitting tripping brackets, when required:

Refer to drawing 4 of Annex 3 of this document.

When tripping brackets are required, always two tripping brackets are to be fitted: one at lower part and one at mid-span of the side frames.

Tripping brackets may be located at every two frames, but lower and midspan brackets are to be fitted in line between alternate pair of frames.

The thickness of the tripping brackets is to be greater or equal to the as-built thickness (tasB) of the frame webs to which they are connected.

The tripping brackets are to be connected to the frames and plating by double continuous welding.

VI) Requirements for coating, when required:

Sand blasting, or equivalent, is to be carried out before coating.

Epoxy coating, or equivalent, is to be applied.

The part to be coated includes:

.The web and the face plate of the frames and brackets.

.The hold surface of side shell, hopper tank and topside tank plating, as applicable over a width not less than 100 mm from the web of the side frame.

VII) Other Requirements:

The UR S31 does not cover all ESP requirements.In this respect:

-The thickness measurements of flanges and side shell plating not covered in III) above are to be carried out in accordance with the gauging requirements of BV Rules Pt A, Ch 2, App.3, figure 7 and the measured thicknesses assessed against the criteria stipulated by the BV Rules Pt A, Ch 2, App.3, table 6.

-The same applies to the intermediate frames which are fitted for reinforcement in order to comply with ice class notations.This additional structure required to meet ice strengthening notation, is not included in the scope of the UR S 31, and the thickness measurements and assessment of this additional structure is consequently to be carried out according to the BV Rules Pt A, Ch 2, App. 3.

-In addition, all other ESP requirements, as per UR Z 10.2 and BV Rules Pt A, Ch 4, Sec 2, are still to be applied, when performing the intermediate survey or the class renewal survey.