Annex 11 - Guidelines for Technical
Assessment in Conjunction with the Planning of Enhanced Surveys for Oil Tankers Renewal
Figure 1 Technical Assessment and the Survey Planning Process
Figure 2 Typical Damage and Repair Example (Reproduced from Ref. 2)
These Guidelines contain information and suggestions concerning
technical assessments which may be of use in conjunction with the
planning of renewal surveys of oil tankers. As indicated in 5.1.5,
these Guidelines are a recommended tool which may be invoked at the
discretion of an Administration, when considered necessary and appropriate,
in conjunction with the preparation of the required survey programme.
2 Purpose and principles
The technical assessments described in these Guidelines
should assist in identifying critical structural areas, nominating
suspect areas and in focusing attention on structural elements or
areas of structural elements which may be particularly susceptible
to, or evidence a history of, wastage or damage. This information
may be useful in nominating locations, areas and tanks for thickness
measurement, close-up survey and tank testing.
2.2 Minimum requirements
These Guidelines may not be used to reduce the requirements
of annexes 1, 2 and 3 for close-up survey, thickness measurement and
tank testing, respectively, which are, in all cases, to be complied
with as a minimum.
As with other aspects of survey planning, the technical
assessments described in these Guidelines should be completed out
by the owner or operator in co-operation with the Administration well
in advance of the commencement of the renewal survey, i.e., prior
to commencing the survey and normally at least 12 to 15 months before
the survey’s completion due date.
2.4 Aspects to be considered
Technical assessments, which may include quantitative or
qualitative evaluation of relative risks of possible deterioration,
of the following aspects of a particular ship may be used as a basis
for the nomination of tanks and areas for survey of:
.1 design features such as stress levels on various
structural elements, design details and extent of use of high-tensile
.2 former history with respect to corrosion, cracking,
buckling, indents and repairs for the particular ship as well as similar
vessels, where available; and
.3 information with respect to types of cargo
carried, use of different tanks for cargo/ballast, protection of tanks
and condition of coating, if any.
Technical assessments of the relative risks of susceptibility
to damage or deterioration of various structural elements and areas
should be judged and decided on the basis of recognized principles
and practices, such as may be found in references 1 and 2.
3 Technical assessment
3.1.1 There are three basic types of possible
failure which may be the subject of a technical assessment in connection
with the planning of surveys: corrosion, cracks and buckling. Contact
damages are not normally covered by the survey plan since indents
are usually noted in memoranda and assumed to be dealt with as a normal
routine by surveyors.
3.1.2 Technical assessments performed in conjunction
with the survey planning process should, in principle, be as shown
schematically in figure
1 which depicts how technical assessments can be carried out
in conjunction with the survey planning process. The approach is basically
an evaluation of the risk, based on the knowledge and experience related
to design and corrosion.
3.1.3 The 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 ageing process
and is closely connected with the quality of corrosion protection
at newbuilding and subsequent maintenance during the service life.
Corrosion may also lead to cracking and/or buckling.
3.2.1 Design details
188.8.131.52 Damage experience related to the ship
in question and similar ships, where available, are the main source
of information to be used in the process of planning. In addition,
a selection of structural details from the design drawings should
be included. Typical damage experience to be considered will consist
.1.1 number, extent, location and frequency of
.1.2 location of buckles.
184.108.40.206 This information may be found in the survey
reports and/or the owner’s files, including the results of the
owner’s own inspections. The defects should be analysed, noted
and marked on sketches.
220.127.116.11 In addition, general experience should
be utilized. For example, reference should be made to reference 1,
which contains a catalogue of typical damages and proposed repair
methods for various tanker structural details.
18.104.22.168 Such figures should be used together with
a review of the main drawings, in order to compare with the actual
structure and search for similar details which may be susceptible
to damage. An example is shown in figure 2. In particular,
chapter 3 of reference 1 deals with various aspects specific to double
hull tankers, such as stress concentration locations, misalignment
during construction, corrosion trends, fatigue considerations and
areas requiring special attention, which should be considered in working
out the survey planning.
22.214.171.124 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.
126.96.36.199 The use of 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 structures. Experience in other locations,
where the dynamic stresses may be higher, is less favourable, e.g.
188.8.131.52 In this respect, stress calculations of
typical and important components and details, in accordance with relevant
methods, may prove useful and should be considered.
184.108.40.206 The selected areas of the structure identified
during this process should be recorded and marked on the structural
drawings to be included in the survey programme.
220.127.116.11 In order to evaluate relative corrosion
risks, the following information is generally to be considered:
.1.1 usage of tanks and spaces;
.1.2 condition of coatings;
.1.3 condition of anodes;
.1.4 cleaning procedures;
.1.5 previous corrosion damage;
.1.6 ballast use and time for cargo tanks;
.1.7 corrosion risk scheme (see reference 2, table
.1.8 location of heated tanks.
18.104.22.168 Reference 2 gives definitive examples
which can be used for judging and describing coating condition, using
typical pictures of conditions.
22.214.171.124 The evaluation of corrosion risks should
be based on information in reference 2, together with the age of the
ship and relevant information on the anticipated condition as derived
from the information collected in order to prepare the survey programme.
126.96.36.199 The various tanks and spaces should be
listed with the corrosion risks nominated accordingly. Special attention
should be given to the areas where the double hull tanker is particularly
exposed to corrosion. To this end, the specific aspects addressing
corrosion in double hull tankers indicated in 3.4 (Corrosion trends)
of reference 1 should be taken into account.
3.2.3 Locations for close-up survey and thickness
188.8.131.52 On the basis of the table of corrosion
risks and the evaluation of design experience, the locations for initial
close-up survey and thickness measurement (sections) may be nominated.
184.108.40.206 The sections subject to thickness measurement
should normally be nominated in tanks and spaces where corrosion risk
is judged to be the highest.
220.127.116.11 The nomination of tanks and spaces for
close-up survey should, initially, be based on highest corrosion risk
and should always include ballast tanks. The principle for the selection
should be that the extent is increased by age or where information
is insufficient or unreliable.
1 Tanker Structure Co-operative Forum (TSCF),
"Guidelines for the Inspection and Maintenance of Double Hull Tanker
2 Tanker Structure Co-operative Forum (TSCF),
"Guidance Manual for Tanker Structures, 1997."