Specification selector

Service-Condition Ladder — Pick the Environment, Read the Callout

ASTM B633-13 publishes thickness classes in Table 1, finish types in Table 2 and zinc corrosion rates in Appendix X1, in three separate places. This chains them so you can go from where the part lives to what belongs on the drawing, and then divide one by the other to see how many years of sacrificial reserve you actually bought.

Where does the part live in service? This is the wording ASTM B633 Table 1 uses to describe each service condition. Pick the description, not the class number.

Which atmosphere is that, for the reserve calculation? Mean atmospheric corrosion rates of zinc, ASTM B633 Appendix X1. The reserve figure is arithmetic on those rates, not a service-life prediction and not a warranty.

SC3 — severe

What goes on the drawing

Coating class	Fe/Zn12
Minimum thickness	12 µm
Common finish type	Type II, colored chromate
Minimum salt spray for that type	96 h
Diametral increase on a fit	24 µm

Divide the class thickness by the corrosion rate and you get the sacrificial reserve: 12 µm ÷ 1.5 µm/yr ≈ 8 years before the zinc is spent.

Send a Drawing for a Finish-Spec Review

Salt-spray hours are an acceptance threshold agreed between purchaser and supplier, not a lifetime claim. Thread roots, blind holes and deep recesses are exempt from the minimum unless your drawing designates them (clause 7.1.2).

Source: ASTM B633-13 Table 1, Table 2 and Appendix X1. Zhenling Metal machines the component and coordinates the finishing operation; we operate no plating line, and this selector states what the standard says rather than what any one plating shop offers.

Service-Condition Ladder — Pick the Environment, Read the Callout

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