'which they replaced' is correct and usable in written English.
You can use it when you are referring to a specific item or items that have been replaced with something else. For example: "The team found a solution to the problem, which they replaced with a better solution."
Agents went to a spot where Metsos stopped and found a buried package beneath a beer bottle, which they replaced and set up a camera.
Peter Cramer, a founder of the Petit Versailles garden on East Houston Street, said he was concerned that the new rules might open the door to build upon the lot, near Avenue C, where he and others hauled away garbage and auto parts in 1996, which they replaced with trees and flowering plants.
Badger swept through Chambers Street in the 1850's, and he listed a dozen projects on the street, some entire building fronts like the Cary Building, but others simply intricate ground floor storefronts -- like the one Isaac and Mary Jones put on the business building with which they replaced their house.
There is a general belief that cultivation of cacao, as traditionally practiced in Africa, has the potential to restore carbon stocks to levels comparable to that in the native forest which they replaced.
Using a particle accelerator at the Paul Scherrer Institute in Villigen, Switzerland, they generated hydrogen atoms in which they replaced the electron with a muon, a particle 207 times as massive that lasts for only 2 microseconds before decaying.
In the case of the two millets, Fuller et al. (2009) pointed out that in both cases the newer plants were similar in appearance to those which they replaced (op cit); they also probably had similar agronomic characteristics and filled similar niches in people's food habits.
One area of syntax in which the Romance languages vary widely in the extent to which they retain and in the manner in which they replace the Latin subjunctive is that of past-tense hypothetical conditional clauses.
This indicates that shortening the lifetime of passenger cars shortens the time that car owners own their cars, which they replace within a short period.
In 2007, Huang and Zhang [2] introduced the concept of cone metric space as a generalization of metric space, in which they replace the set of real numbers with a real Banach space.
Here is where I should note that CyberPower has a specific section in their warranty for DOA (Dead On Arrival), in which they replace your system in case something like this happens.
Macaroni penguins moult once a year, a process in which they replace all of their old feathers.
