PetroStreet

Please explain to me the applicability of carburization check of tubes intended for ethlylene or when they are put in service. When it is needed, and how it is done?

NACE TM0498 is the right reference for alloy carburization check for the tubes to be used in ethylene furnace.
It provides the guidelines to perform pack bed testing or the etching test as needed to understand the damages from carburization. Refer to that to have more insights.
These tests are applicable both to the new tubes and the ones when they are put in service. Field examination does not apply as tests mentioned in NACE TM0498 are to be applied on the actual material taken from the tube.

dlew,
Would you please share some more details as how the in-process tubes are checked for alloy carburization?

NACE TM0498 implies that the evaluation of the carburized specimens will be performed through methods that examine the material's altered state. Historically, assessing carburization often involves:
Metallurgical Analysis: This can include examining the microstructure, phase identification, and chemical composition of the carburized layer. For instance, NACE TM0498 references the use of an NACE etchant for evaluating carburization, which is a destructive metallographic technique.
Hardness Testing: Measuring hardness at various depths into the material is a common method to determine the extent of carburization.
Microstructural Examinations: Techniques like Scanning Electron Microscopy (SEM) can be used to characterize the changes in the material's structure due to carburization.
These methods require samples to be cut, polished, etched, or otherwise altered, classifying them as destructive.

While TM0498 focuses on a specific test procedure that leads to destructive analysis, it's important to note that other methods exist for evaluating carburization, particularly in operating tubes. These non-destructive testing (NDT) techniques, such as magnetic analyzers, eddy current testing, and ultrasonic testing, are used for in-situ inspection and do not damage the component. These NDT methods complement the data obtained from destructive tests like those described or implied by TM0498.

Hope this helps.