Flange Face Finish (Surface Finish) is refer to ANSI B16.5

There are 2 unit systems that usually used for Flange Face Finish :

a) RMS = Root Mean Square

b) AARH = Aritmetic Average Roughness Height

There are some equation we can use to measure Flange Face Finish :

a) RMS = 1.11 x Microinches (Ra) (equation 1)

b) AARH = Ra x 0.0254 (equation 2)

c) Ra = AARH / 0.0254. (equation 3)

Note :

Ra = Microinches

AARH = Micrometers

There are some requirement that usually used for Flange Face Finish :

a) Stock Finish : < 63 AARH

b) Smooth Finish : 3.2 6.3 AARH

Example :

Condition

Valve standard for flange face finish is 125 250 Ra.

Customer request for smooth finish (3.2 6.3 AARH).

Solution

We can use equation 2 to check whether Valve standard can comply customer requirement

or not.

AARH = Ra x 0.0254 AARH = Ra x 0.0254

AARH = 125 x 0.0254 AARH = 250 x 0.0254

AARH = 3.175 AARH = 6.35

AARH = 3.2 AARH = 6.3

From this equation we can find the result that 125 250 Ra is equal with 3.2 6.3 AARH,

which means Valve standard is comply with customer requirement.