'part by part' is correct and can be used in written English.
It is usually used to mean piece by piece or step by step. For example, "We studied the material part by part until we had a thorough understanding of the subject."
Westchester's Doctors Are Ready to Renew You, Part By Part".
"We are not treating part by part and organ by organ," Dr. Sreelatha explained kindly.
"The idea is you can build the body part by part," said Paul Brown, DDS, consulting associate professor of anatomy.
One giant machine assembles the figures part by part – a 'skeleton' holds everything together – and cameras monitor every move.
Ruddock, like most recording engineers, would have been used to hearing music in detail, part by part, note by note.
Restoring power to the observatory will be done part by part and will take several hours, Mr. Burch said.
Some non-part-by-part sketching does arise, however, and appears to be closely linked with those parts of objects that possess multiple functionalities (i.e. multifunctional parts).
However, reliable evidence was obtained indicating that part-occlusion and part-multifunctionality were determinants of non-part-by-part production under both object-recall and object-copying instructions.
The in-line feed-forward control identifies appropriate part-by-part adjustments using these learned control actions and incoming assembly component measurements.
This blog had documented the part-by-part appearance in rebel hands of one old heat-seeking system, known as the SA-7.
Analyses failed to indicate reliable effects on levels of non-part-by-part sketching of drawing condition (recall vs. copying), part type (multifunctional vs. unifunctional), or an interaction between these factors.
