Final answer:
The permissible excess in pressure rating or allowable stress for a pressure design during self-limiting conditions cannot be provided without specific data or standard references. In engineering practice, systems under occasional or transient conditions may exceed their normal limits based on relevant codes and safety standards.
Step-by-step explanation:
The question relates to the engineering design of a piping system and the permissible excess in pressure rating or allowable stress. Unfortunately, without the specific data or standard reference, a numeric answer can't be correctly provided for the allowable percentage increase under the given conditions. However, as a principle in engineering under certain cases such as occasional loads or transient operating conditions, it is recognized that systems may operate beyond their standard pressure ratings or allowable stresses for a limited amount of time without compromising safety.
This will depend on the regulations, codes, and standards that govern the operation of the piping system (such as ASME B31.3 for Process Piping in the petrochemical industry). A pressure relief valve (PRV) would be set at a certain percentage above the system's maximum allowable working pressure (MAWP). The exact percentage allowed will be governed by these standards and the specific design considerations of the system in question. It's essential to consult the relevant codes and the manufacturing or design specifications for the specific system to determine the permissible excess under self-limiting conditions.