Structural plastics have long shown exceptional performance in products used for fluid transport and containment, such as pipes, tanks, and drainage structures. The development and use of plastics enhances the versatility and durability of these important infrastructure components, as well as their economy. However, like all materials, plastics have performance limitations, and serious failures can occur as the result of improper design, fabrication, or installation. Understanding failure mechanisms of plastics can provide valuable insight into those limitations and aid the designer, manufacturer, and installer in optimizing structural and functional performance. We review forensic techniques, including field investigation, material and mechanical laboratory tests, optical and scanning electron microscopy, and stress analysis. The example cases highlight mechanical, environmental and installation issues. These include failure to account for material creep and fatigue, defects in fusion bonding, incompatibility of solvent cement, strength limitation of joint elements, and improper installation techniques. The case studies suggest ways to avoid similar mistakes in the future.