3.1 General3.1.1 There are three basic types of possible failures to be considered in connection with
development of a survey programme; corrosion, cracks and buckling. Contact damages,
however, would not normally be covered by the programme as indents are usually dealt
with as a normal routine by surveyors.
3.1.2 The development of a survey programme should in principle be as shown
schematically in figure 1. The approach is based on an evaluation of experience and
knowledge basically related to:
- design;
- corrosion.
3.1.3 The structural design should be considered with respect to structural details which
may be susceptible to buckling or cracking as a result of vibration, high stress levels or
fatigue.
3.1.4 Corrosion is related to the age of a ship, and is closely connected with the quality
of the corrosion prevention system and subsequent maintenance during the service life.
Corrosion may also lead to cracking and/or buckling.
3.2 Methods3.2.1Collection of informationBefore commencing the development of the survey programme, the following
information should be collected:
- survey status and basic ship information;
- main structural plans (scantling drawings), including information regarding use of
high tensile steels (HTS);
- previous survey reports;
- previous damage experience, including damage experience for similar ships, where
available;
- typical hull damages for the particular type of ship (as applicable/available);
- acceptable corrosion allowances;
- information regarding the use of the ship's holds and tanks, typical cargoes,
loading/unloading procedures, and other relevant data;
- information regarding the corrosion prevention system;
- information regarding the relevant maintenance level during operation.
Proper co-operation between the owner and the Administration is essential in order to
collect the necessary information for those developing the survey programme.
3.2.2 Design details3.2.2.1 Damage experience related to the ship in question and similar ships, where
available, is the main source of information to be used in the development of the survey
programme. In addition, a selection of structural details from the design drawings should
be included.
3.2.2.2 Typical damage experience to be considered will consist of:
- number, extent, location and frequency of cracks; location of buckles.
This information may be found in the survey reports and/or the owner's files. The
defects should be analyzed, noted and marked on sketches.
3.2.2.3 In addition, general experience should be utilized. For example, figure 2 shows
typical locations in bulk carriers which experience has shown may be susceptible to
structural damage or corrosion . Also, reference should be made to IACS publication
"Bulk Carriers: Guidelines for Surveys, Assessment and Repair of Hull Structure", which
contains a catalogue of typical damages and proposed repair methods for various bulk
carrier structural details. Such figures should be used together with a review of the main
drawings, in order to identify similar details which may be susceptible to damage. An
example is shown in figure 3.
3.2.2.4 The review of the main structural drawings, in addition to using the
above-mentioned figures, should include checking for typical design details where cracking
has been experienced. The factors contributing to damage should be carefully considered.
3.2.2.5 The use of high tensile steel (HTS) is an important factor. Details showing good
service experience where ordinary mild steel has been used may be more susceptible to
damage when HTS, and its higher associated stresses, are utilized. There is extensive and,
in general, good experience, with the use of HTS for longitudinal material in deck and
bottom. Experience in other locations, where the dynamic stresses may be higher, is less
favourable, e.g. side structures. In this respect, stress calculations of typical and important
components and details, in accordance with the latest classification rules or other relevant
methods, should be considered.
3.2.2.6 The selected areas of the structure identified during this process should be
recorded and marked on the structural drawings which should be included in the survey
programme document.
3.2.3 Corrosion3.2.3.1 The following information should generally be considered in order to evaluate the
corrosion risks:
- usage of tanks, holds and spaces;
- condition of coatings;
- condition of anodes;
- cleaning procedures for cargo holds;
- previous wastage;
- cargo hold/ballast tank usage (frequency/time);
- corrosion risks in cargo holds and ballast tanks;
- location of ballast tanks adjacent to heated fuel oil tanks.
The Tanker Structural Cooperative Forum (TSCF) publication "Condition Evaluation
and Maintenance of Tanker Structures, 1992" gives definitive examples which can be used
for judging and describing coating condition, for both bulk carriers and oil tankers.
3.2.3.2 The evaluation of corrosion risks for both bulk carriers and oil tankers should be
based on information contained in the above-mentioned TSCF publication, together with
relevant information on the anticipated condition of the ship as derived from the
information collected in accordance with 3.2.1 and the age of the ship.
3.2.3.3 The tanks, holds and other spaces should be listed in a table with the risk of
corrosion nominated accordingly.
3.2.4 Areas for close-up survey and thickness measurement3.2.4.1 The areas for initial close-up survey and thickness measurement (sections) should
be chosen on the basis of the table of corrosion risks indicated in 3.2.3.3 and an
evaluation of historical structural experience.
3.2.4.2 The sections subject to thickness measurement should normally be nominated in
tanks, holds and other spaces where the risk of corrosion is judged to be the highest.
3.2.4.3 The nomination for close-up survey of tanks, holds and other spaces should be
based on the highest corrosion risk.
