The Challenger space shuttle’s structure was made of aluminum alloy. Titanium was first suggested but deemed too expensive. The aluminum alloy bottom for the spacecraft was covered with silicon tiles (pasted on by hand) that protected the spacecraft from the 2,500 degree temperatures encountered on reentry into the earth atmosphere. One of them fell off and the heat seeped in and blew up the craft.
The ocean gate Submersible was made up mostly of carbon fiber with the end caps titanium.
The standard in the industry was titanium but the company CEO (who died in the explosion) sought to cut costs.
The entire industry accepts inspections because the metal “fatigues” over time. Each dive puts tremendous pressures on the hull and weakens the craft. Ocean Gate never accepted inspections.