Studs used in a turbo pump were made from 0.35C-1.5Ni-1.0Cr-0.2Mo steel, quenche
ID: 2088455 • Letter: S
Question
Studs used in a turbo pump were made from 0.35C-1.5Ni-1.0Cr-0.2Mo steel, quenched and tempered to 400 HV hardness, cadmium-plated and baked at 200°C for 2 h. The studs used in a turbo pump failed after 3 months of assembly. A fractograph of a failed stud revealed a predominantly intergranular mode mixed with ductile failure features. Increasing the baking time to 12 h considering the low diffusivity of hydrogen across the relatively impervious cadmium coating solved the problem. Explain the cause and mode of this failure.
Explanation / Answer
The role played by hydrogen in premature failures of components protected
by electroplated coatings can be illustrated by the following example. This is because of hydrogen premature failures of components protected by electroplated coatings.
The studs used in a turbo pump failed after 3 months of assembly. The studs
were made from 0.35C-1.5Ni-1.0Cr-0.2Mo steel, quenched and tempered to
400 HV hardness, cadmium-plated and baked at 200°C for 2 h. The delayed
failure was predominantly in intergranular mode
mixed with ductile failure features characteristic of delayed failure due to
hydrogen embrittlement. Increasing the baking time to 12 h considering the
low diffusivity of hydrogen across the relatively impervious cadmium coating
solved the problem.
The examples cited indicate that innumerable defects originate during
various stages of manufacture and all of them affect the component performance
and reliability.