"a number of failures" is a correct and usable phrase in written English.
You can use it when you are referring to more than one failure. For example: Despite a number of failures, the student ultimately passed the course.
BP listed a number of failures committed onboard the rig, which was operated by Transocean.
"Incentives are needed to help address a number of failures in the market for these products.
At the time of the exchanges, Chinese-made kick motors had suffered a number of failures.
A Metropolitan police investigation into an armed assault by Kevin Hutchinson-Foster, who went on to provide the gun to Duggan, was found by the police watchdog to have had "a number of failures".
After a number of failures in the mid-1960s, the Soviet Union scored several notable achievements: the first successful lunar soft landing by Luna 9 and the first lunar orbit by Luna 10, both in 1966.
So while the Virgin Group has had a number of failures, such as Virgin Cola and Virgin Brides, the crash of Little Red hasn't affected the strength of the Virgin brand or its reputation, but rather enhanced its decisiveness and boldness.
A number of failure modes which are not addressed sufficiently in the certificate guidelines are presented.
Along with the remarkable growth of the ERP market, we have seen a number of failure cases of ERP adoption.
While a number of failure modes have been studied, the neuroinflammatory response, in particular, has received significant attention.
Full field strain analysis and visual observations show a number of failure mechanisms between the different core thicknesses.
The methodology employs an iterative design process with respect to a number of failure criteria to ensure optimal structural and material performance of the blade.
