Final answer:
Swing joints and unions should not be used where piping is subject to movement or vibration as they can fail under such conditions. Other considerations like avoiding mixing metals such as copper and iron in pipe joints are key to preventing galvanic corrosion.
Step-by-step explanation:
The student's question addresses the conditions under which swing joints and unions should not be used in piping installations. The correct answer is that swing joints and unions should not be used where piping is subject to movement or vibration. This is because these types of fittings can fail under dynamic stress, leading to leaks or pipe damage.
It is notable that swing joints and unions are frequently used in underground applications (such as irrigation systems) because they allow for some movement and make maintenance easier. However, their use in scenarios where there is significant movement or vibration, like in machinery or along fault lines, should be avoided.
Mixing different metals, such as copper (Cu) and iron (Fe), in pipe joints can indeed lead to galvanic corrosion if the metals are not properly isolated from each other. This is another important consideration in the lifespan of piping and is relevant to ensuring long-term integrity of the system.