Ethical issues in engineering design - 3TU.Centre for Ethics and ...

Piping and equipment
decide what the possible and probable accident scenarios are and to what load
levels these scenarios will lead. This is related to the point made above about load
scenarios. However, accident scenarios are not limited to mechanical loads, they
also include human failure. An operator might, for example, forget to close a
valve. The accident scenario “forget to close a valve” should predict what happens
in such a case. In some cases an accident scenario can lead to a specific load
scenario. For example, if it is possible that a small scale explosion occurs in a
pressure vessel then the explosion inside the vessel should also be a load scenario
for the vessel. The decision as to what accident scenarios to include is ethically
relevant because an accident or incident not considered during the design process
can lead to a disaster. For example, a failure to close a valve could lead to an
explosion which could lead to the complete destruction of an installation. Some
accident scenarios are easy to decide to use because they are specified in the
codes. This, however, is not the case for all accident scenarios. An example of an
accident scenario that is not included in regulation is the water hammer scenario.
Accumulation of water in a steam line can lead to a build up of pressure released
as a sudden small explosion. This can cause a line to come loose from its
supporting structure if the attachment to the supporting structure is too weak for
such loads. Accidents due to a water hammer can lead to employees being stuck
under collapsed construction parts or employees being burned by hot steam or
water. Within the codes and regulations there are no explicit rules about how to
deal with water hammer hazard. The design team, especially the stress engineer,
has to decide whether or not to take it into account.
The calculations and load scenarios are checked by the Notified Body, but the
Notified Body is not allowed to check the risk analysis made by the engineering
design company under official PED rules. The Stoomwezen, however, checks risk
analyses and advises engineering companies on them.
The codes prescribe a lot of small details in the design process. If it is not
possible to follow the detailed rules of the codes then the codes give alternative
and less detailed ways of designing a pipe or pressure vessel. If the formulas
cannot be used in a specific case, then the use of finite element methods is
prescribed by the code. If the method of finite element calculation is also not
possible, the vessel can be designed and put through a pressure test. This last
alternative only prescribes the pressure test to which the vessel must be
subjected.
Following codes should lead to the minimum level of safety required by law.
In the European Union, the decision whether the design is indeed safe enough
from a legal point of view is made by Notified Bodies. There are possibilities to
deviate from codes if this is approved by the Notified Body and the customer.
Deviation from the codes and regulation could lead to unsafe installations. Such
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