OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.3 Design input – Page 27
to safety issues (e.g. static electricity properties). Moreover, some structural failures may affect non-structural
performances, e.g. matrix cracking might influence acoustic performances.
7 Failure modes
7.1 General
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7.1.1 A complete list of all failure modes shall be established for every component of the product.
7.1.2 Subsequent failure scenarios shall be taken into consideration. For example, rupture of a protective
coating may in itself not be a severe event. However, subsequent corrosion of the material behind the coating
may cause serious damage.
7.2 Failure modes
7.2.1 A failure is defined as a state of inability to perform a normal function, or an event causing an undesirable
or adverse condition, e.g. violation of functional requirement, loss of component or system function, or
deterioration of functional capability to such an extent that the safety of the unit, personnel or environment is
significantly reduced.
7.2.2 A failure mode is a symptom or condition that leads to failure, in general the fashion in which the
structure fails.
Guidance note:
A failure mode is the manner in which one or several functional requirements fail. The importance of all failure modes
shall be agreed between the designer and the contractor, i.e. the associated type of limit state shall be identified for
each failure mode (see Sec.3 [7.3] below and Sec.2 [3.2] for the definition of the type of limit states).
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7.2.3 Failure shall be considered for all locations of the product taking into account all levels of detail, as
defined in [3].
7.2.4 The potential failure modes shall be listed for each location of the product. A list of failure modes that
should be considered as a minimum is given in App.A.
7.2.5 Some products may fail by other failure modes than those listed above. Such failure modes shall be
identified and documented.
7.2.6 For each location a link between possible failure modes and functional requirements shall be established.
A table describing links that should be considered as a minimum is given in App.A.
7.2.7 If a number of failure modes can cause a violation of a functional requirement all possible failure modes
shall be indicated.
7.2.8 If any of the indicated failure modes occurs for a single functional requirement the structure shall be
considered as failed. Each failure mode shall be evaluated with respect to the type of limit state it is associated
with (see [7.3]).
7.2.9 In some cases several failure modes may interact to violate a certain functional requirement. That
interaction shall be specified if relevant.
7.2.10 If a failure mode is not associated with any functional requirement it should be evaluated carefully that
this failure mode is not critical in any sense.
7.3 Identification of the type of limit states
7.3.1 For each phase and each part of the product the consequence of a failure (violation of one of the
functional requirements) shall be evaluated and it shall be decided whether the mode of failure is related to the
ultimate limit state or to the serviceability limit state.
Guidance note:
Note: the client and/or authorities should make this decision. This defines the level of severity of each failure.
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7.3.2 All possible failures of the product at each location in each phase shall be considered.
7.3.3 If a failure mode has increasing consequence of failure severity in subsequent phases, it shall be designed
for the most severe consequence of failure in all phases, unless the product can be inspected in between phases
and it can be insured that the failure mode has not occurred in the previous phase.
DET NORSKE VERITAS AS