7 Procedures for thickness measurements

7.1 General

7.1.1 The required thickness measurements, if not carried out by the Administration, shall be witnessed by a surveyor of the Administration. The surveyor shall be on board to the extent necessary to control the process.

7.1.2 The thickness measurement firm shall be part of the survey planning meeting to be held prior to commencing the survey.

7.1.3 Thickness measurements of structures in areas where close-up surveys are required shall be carried out simultaneously with close-up surveys.

7.1.4 In all cases the extent of the thickness measurements shall be sufficient as to represent the actual average condition.

7.1.5 Procedural requirements for thickness measurements are set out in annex 14

7.2 Certification of thickness measurement firm

The thickness measurements shall be carried out by a qualified firm certified by the Administration according to principles stated in annex 8.

7.3 Number and locations of measurements

7.3.1 Application

This section only applies to ships built under the IACS Common Structural Rules^footnote (CSR). For ships not built under the IACS Common Structural Rules, the requirements for the number and locations of measurements shall be according to the requirements of the individual classification society recognized by the Administration depending on the ship's age and structural elements concerned.

7.3.2 Number of measurements

Considering the extent of thickness measurements according to the different structural elements of the ship and surveys (renewal, intermediate and annual), the locations of the points to be measured are given for the most important items of the structure.

7.3.3 Locations of measurements

7.3.3.1 Table 1 provides explanations and/or interpretations for the application of those requirements indicated in the IACS CSR, which refer to both systematic thickness measurements related to the calculation of global hull girder strength and specific measurements connected to close-up surveys.

7.3.3.2 Figures 5 to 8 are provided to facilitate the explanations and/or interpretations given in table 1, to show typical arrangements of double-hull oil tankers.

Table 1 – Interpretations of requirements for the locations and number of points to be measured

Item	Interpretation	Figure reference
Selected plates	"Selected" means at least a single point on one out of three plates, which shall be chosen on representative areas of average corrosion.
Deck, bottom plates and wind-and-water strakes	At least two points on each plate which shall be taken either at each 1/4 extremity of plate or at representative areas of average corrosion.
Transverse section	Measurements shall be taken on all longitudinal members such as plating, longitudinals and girders at the deck, side, bottom, longitudinal bulkheads, inner bottom and hopper. One point shall be taken on each plate. Both web and flange shall be measured on longitudinals, if applicable. For tankers older than 10 years of age, within 0.1D (where D is the ship's moulded depth) of the deck and bottom at each transverse section to be measured, every longitudinal and girder shall be measured on the web and face plate, and every plate shall be measured at one point between longitudinals.	Figure 5
Transverse rings^footnote in cargo and ballast tanks	Including plates and stiffeners	Locations of points are given in figure 5
Transverse section of deck plating outside line of cargo hatch openings	At least two points on each plate in a staggered pattern and two points on the corresponding flange where applicable. Minimum four points on the first plate below deck. Additional points in way of curved parts. At least one point on each of two stiffeners between stringers/longitudinal girders.	Figure 6
Transverse bulkheads in cargo tanks	At least two points on each plate. Minimum 4 points on the first plate below main deck. At least one point on every third stiffener shall be taken between each stringer. At least two points on each plate of stringers and girders, and two points on the corresponding flange. Additional points in way of curved part. Two points of each diaphragm plate of stools if fitted.	Figure 7
Transverse bulkheads in ballast tanks	At least four points on plates between stringers/longitudinal girders, or per plate if stringers/girders not fitted. At least two points on each plate of stringers and girders, and two points on the corresponding flange. Additional points in way of curved part. At least one point on two stiffeners between each stringer/longitudinal girder.	Figure 8
Adjacent structural members	On adjacent structural members one point per plate and one point on every third stiffener/longitudinal.

Figure 5: Transverse section

Figure 6: Transverse rings in cargo and ballast tanks

Figure 7: Transverse bulkheads in cargo tanks

Figure 8: Transverse bulkheads in ballast tanks

7.4 Reporting

7.4.1 A thickness measurement report shall be prepared and submitted to the Administration. The report shall give the location of measurements, the thickness measured as well as the corresponding original thickness. Furthermore, the report shall give the date when the measurements were carried out, type of measuring equipment, names of personnel and their qualifications and be signed by the operator. The thickness measurement report should follow the principles as specified in the recommended procedures for thickness measurements set out in annex 11A/annex 11B.

7.4.2 The surveyor shall review the final thickness measurement report and countersign the cover page.