Accelerating naval technology from ironclads to dreadnoughts

Did navies expect ironclads and pre-dreadnoughts to remain in service for as long as sailing warships?

Not really; the pace of technological change was already accelerating so rapidly that long-term relevance was much less certain.

The ironclad period marks the beginning of an accelerating technological curve. Steam machinery, armour, naval guns, and hull construction were all changing at once. A newly commissioned ship could therefore be overtaken by a different combination of technologies far sooner than an earlier sailing warship. Navies understood that long physical survival did not guarantee continued front-line relevance. Their recurring effort to slow the cycle through standardization or incremental modernization could not remove the underlying pace of change. This is why the ironclad and pre-dreadnought eras produced so many short-lived design stages on the way to Dreadnought.