Annex 15 – Thickness Measurements of Side Shell Frames and Brackets in Single-Side Skin Bulk Carriers Required to Comply with Resolution MSC.168(79)
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - International Codes - 2011 ESP Code – International Code on the Enhanced Programme of Inspections During Surveys of Bulk Carriers and Oil Tankers, 2011 – Resolution A.1049(27) - Annex A – Code on the Enhanced Programme of Inspections During the Surveys of Bulk Carriers - Part A – Code on the Enhanced Programme of Inspections During Surveys of Bulk Carriers having Single-Side Skin Construction - Annex 15 – Thickness Measurements of Side Shell Frames and Brackets in Single-Side Skin Bulk Carriers Required to Comply with Resolution MSC.168(79)

Annex 15 – Thickness Measurements of Side Shell Frames and Brackets in Single-Side Skin Bulk Carriers Required to Comply with Resolution MSC.168(79)

Parent topic: Part A – Code on the Enhanced Programme of Inspections During Surveys of Bulk Carriers having Single-Side Skin Construction

1 General

 Thickness measurements shall be conducted to determine the general condition of the structure and to define the extent of possible steel renewals or other measures for the webs and flanges of side shell frames and brackets for verification of the compliance with resolution MSC.168(79).

2 Zones of side shell frames and brackets

  2.1 For the purpose of steel renewal, sand blasting and coating, four zones A, B, C and D are defined as shown in figure 1.

  2.2 Zones A and B shall be considered the most critical zones.

Figure 1 – Zones of side shell frames and brackets

3 Pitting and grooving

  3.1 Pits can grow in a variety of shapes, some of which shall be ground before assessment.

  3.2 Pitting corrosion may be found under coating blisters, which shall be removed before inspection.

  3.3 To measure the remaining thickness of pits or grooving the normal ultrasonic transducer (generally 10 mm diameter) will not suffice. A miniature transducer (3 to 5 mm diameter) shall be used. Alternatively the firm conducting the thickness measurement shall use a pit gauge to measure the depth of the pits and grooving and calculate the remaining thickness.

Assessment based upon area

  3.4 This is the method specified in paragraph 2.5 of annex 2 to resolution MSC.168(79) and is based upon the intensity determined from figure 2 below.

Figure 2 Pitting intensity diagrams (from 5 to 25% intensity)

  3.5 If pitting intensity is higher than 15% in an area (see figure 2), then thickness measurements shall be taken to determine the extent of the pitting corrosion. The 15% is based upon pitting or grooving on only one side of the plate.

  3.6 In cases where pitting is evident as defined above (exceeding 15%) then an area of 300 mm diameter or more (or, where this is impracticable on the frame flange or the side shell, hopper tank plating or topside tank plating attached to the side frame, an equivalent rectangular area), at the most pitted part, shall be cleaned to bare metal, and the thickness measured in way of the five deepest pits within the cleaned area. The least thickness measured in way of any of these pits shall be taken as the thickness to be recorded.

  3.7 The minimum acceptable remaining thickness in any pit or groove shall be equal to:

  • .1 75% of the as built thickness, for pitting or grooving in the cargo hold side frame webs and flanges.

  • .2 70% of the as built thickness, for pitting or grooving in the side shell, hopper tank and topside tank plating attached to the cargo hold side frame, over a width up to 30 mm from each side of it.

4 Thickness measurement methodology

  4.1 The number of side frames to be measured shall be equivalent to those required at the renewal survey or intermediate survey corresponding to the ship's age. Representative thickness measurements shall be taken for each zone as specified below.

  4.2 Special consideration to the extent of the thickness measurements may be given by the Administration, if the structural members show no thickness diminution with respect to the as built thicknesses and the coating is found in "as new" condition (i.e. without breakdown or rusting).

  4.3 Where thickness measurement readings close to the criteria are found, the number of hold frames to be measured shall be increased.

  4.4 If renewal or other measures according to resolution MSC.168(79) shall be applied on individual frames in a hold, then all frames in that hold shall have thickness measurements taken.

  4.5 There is a variety of construction methods used for side shell frames in bulk carriers. Some have faceplates (T sections) on the side shell frames, some have flanged plates and some have bulb plates. The use of faceplates and flanged sections is considered similar for thickness measurement purposes in that both the web and faceplate or web and flange plate shall be measured. If a bulb plate has been used, then the web of the bulb plate shall be measured in the normal manner and the sectional modulus shall be specially considered if required.

Gaugings for Zones A, B and D

Web plating

  4.6 The pattern for thickness measurements in Zones A, B and D should be a five-point pattern. See figure 3. The five-point pattern should be over the depth of the web and the same area vertically. The thickness measurement report should reflect the average reading.

Figure 3 - Typical five-point pattern on the web plate

Thickness measurements for Zone C

Web plating

  4.7 Depending on the condition of the web in way of Zone C, the web may be measured by taking three readings over the length of Zone C and averaging them. The average reading shall be compared with the allowable thickness. If the web plating has general corrosion then this pattern shall be expanded to a five-point pattern as noted above.

Thickness measurements for section a) and b) (flanges and side shell plating)

  4.8 Where the lower bracket length or depth does not meet the requirements in annex 1 to resolution MSC.168(79), thickness measurements should be taken at sections a) and b) to calculate the actual section modulus required in paragraph 3.4 of annex 2 to resolution MSC.168(79) (see figure 4). At least two readings on the flange/faceplate shall be taken in way of each section. At least one reading of the attached shell plating shall be taken on each side of the frame (i.e. fore and aft) in way of section a) and section b).

Figure 4 – Sections a) and b)

5 Report on thickness measurement of cargo hold frames

 See form TM7-BC(ii) as contained in appendix 2 to annex 8A.

Reference

  Resolution MSC.168(79) on Standards and criteria for side structures of bulk carriers of single-side skin construction.

Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.