What is the consequence of using cast iron flanges rated for incorrect pressures?

Using cast iron flanges rated for incorrect pressures can lead to cracking or failure due to material stress. Cast iron is a brittle material, meaning it does not handle stress well compared to ductile materials. If the pressure exerted exceeds what the flange is rated for, it can result in structural failure. This may manifest as cracks propagating through the material or even catastrophic failure under extreme conditions, which can jeopardize the entire piping system and lead to leaks, loss of containment, or even safety hazards in some scenarios. Proper matching of flange ratings with the expected service pressure is crucial for maintaining system integrity and safety.

The other options, while potentially relevant under different circumstances, do not directly stem from the issue of using incorrectly rated pressures. For instance, rust and sealing issues relate more to the material characteristics and installation rather than pressurization ratings. Additionally, weight concerns do not typically influence the decision-making regarding pressure ratings in the selection of pipe fittings.