OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.6 Failure mechanisms and design criteria – Page 127
12.3 Evaluation after impact testing
12.3.1 The impact tests should demonstrate that no unacceptable damage is introduced into the component.
Once the component has been exposed to impact it should be carefully inspected to ensure that no unexpected
failure mechanisms occurred that may reduce the component's performance, in particular long term
performance. If the component will be taken out of service after an impact, long term considerations do not
have to be made.
12.3.2 It shall be shown further that the component can carry all relevant loads after impact until it can be taken
out of service for repair or replacement. This can be done by analysis taking the observed impact damage into
account, by testing, or a combination of analysis and testing. Testing should be done according to Sec.10.
12.3.3 If the component may be exposed to impact but can or should not be repaired afterwards, it should be
shown that the component can withstand all long-term loads with the damage induced by the impact. The same
approach as in [12.3.2] should be used.
Guidance note:
A typical example is impact of dropped objects on a pipe.
The pipe is tested by dropping representative objects, like tools from the maximum possible height onto the pipe.
Damage analysis shows matrix cracking and delamination but no fibre failures. Since the pipe has a liner one could
assume that the capability to hold pressure is not reduced in the short term.
One pressure test is used to confirm this prediction according to Sec.10 [3].
13 Wear
13.1 General
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13.1.1 Wear is a complicated process that is influenced by the entire system. All material data used for wear
calculations shall be relevant for the system investigated.
13.2 Calculation of the wear depth
•
13.2.1 The wear depth may be calculated based on the sliding distance, using the length related wear rate w
for the corresponding wear system. The wear rate varies with the surfaces in contact, the magnitude of the
contact pressure and the environment. The wear depth dy (thickness of removed material) is given by:
•
dy
w =
dx
(m/m)
The total sliding distance dx shall be calculated assuming one contact point for the entire duration of the wear
phase.
13.2.2 Another option is to calculate the wear depth based on the sliding time, using the time related wear
•
rate w t
for the corresponding wear system. The wear rate varies with the surfaces in contact, the magnitude of
the contact pressure and the environment. The wear depth dy (thickness of removed material) is given by:
•
dy
w t =
dt
(m/s)
The total sliding time dt shall be calculated assuming the same contact point for the entire duration of the wear
phase.
13.2.3 The consequences of removing material with respect to all other failure mechanisms shall be evaluated.
13.3 Component testing
13.3.1 Refer to section on component testing: Sec.10.
Guidance note:
The performance of a wear system should ideally be assessed by a practical trial in the intended application. However,
this trial is often impractical and it is necessary to resort to laboratory testing. Accelerated laboratory tests with simpler
geometrical configurations are often used although there is still a considerable amount of controversy about the
validity of the results due to the geometry of the test samples.
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