Measuring sprial serrations for flamge surface finish

[cbabblingbrook]

According to ASME B16.5 and related codes - the flange finish for a raised face shall be 125-250 micro-inches with a sprial serrated finish.

QUESTION - How do you measure this roughness? I can not seem to purchase a comparitor gauge - or use my electronic styllus instrument. If I measure across the sprials using the styllus - the reading is extremely higher than 125-250.

Any suggestions?

 

[Scipio]

The only way I've ever seen to do it us using a comparison gauge, I borrowed mine from one of our inspectors (it was basically a plastic card with a number of different sections with different facings machined on it). No idea where he got it though, probably a manufacturer.

 

[cbabblingbrook]

Scipio,
Thanks for the reply! I would certainly like to get my hands on a comparitor gauge.

Please post if you find the manufacturer.

 

[bmoorthy]

Use visual comparitor which is as per B46.1. This clarity is given in B 16.5 itself. The comparators are freely available in market.

Stylus measurement is not recommended for flange surface finish verification. One of the main reason is that the stylus is very sensitive and would get spoiled (Pocket Surf). Normally stylus type M/C are used for measuring Blast clean surface (Although in case of Blast clean surface visual comparitors are available) when Painting becomes very important (Such as under ground pipes or Mounded storage tanks etc). In some of the applications such as crystalizers and in some dairy and food industry applications the internal surface of SS vessel would require polishing,here usage of stylus is appropriate.

 

[tosg]

I have a roughness comparator of Rubert & Co. Ltd. UK.
Website of the company may be of some help.

http://www.rubert.co.uk/