Piping Interview Question Part -5 (Flange Face and Serration)
Piping Interview Question Part -5 (Flange Face and Serration)


Welcome to Hardhatengineer.com. I am Varun
Patel. In this video, you will learn about most common questions regarding pipe flanges
that you may face during the interview. You will learn about these questions;
1. What is the height of the face in the raised face flange?
2. What is serration on the flange face? 3. What types of serration are used on flange
face? 4. What are AARH and RMS?
5. How to measure the serration? So please watch this video till the end. And
don’t forget to subscribe my channel because that way you will get regular updates on a
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So let’s start with the first question. 1. What is the height of the face in the raised
face flange? In the last video, I have explained to you
about flange faces. Now, look at this image of a flange. You can see the height of the
face. It is not random height, but it is based on the flange ratings. For 150# & 300# height
of the raised face is 1/6” that is approx. 4.25 mm and above 300# it is 1/4” that is
6.35 mm. Let’s move to the second question. 2. What is serration on the flange face?
Flange face can be a smooth or serrated type. Which type of face to use, is depends on the
type of the gasket and service of the fluid. The flange face with small grooves as you
can see in the image, this machining is known as a serration. This serration is very critical
to prevent the leak from the flange. Even small damage of the face can lead to a plant
shutdown. So, if you are working with flange, you have to take measures to protect the flange
while handling. Next question is; 3. What types of serration are used on flange
face? Serration can be spiral or concentric rings
as you can see in the slide. Concentric rings type finishing is used when fluid is of very
low density. If you use spiral type finish with very low-density fluid, it may find a
leakage path through the spiral cavity. 4. What are AARH and RMS?
In the previous question, you learn about serration. Now, this machining is not random,
and it has to be perfect to prevent a leak. Small grove will not let gasket material seat
in and large grove will damage gasket and increase corrosion of face. Now the measurement
value of Serration of flange face is specified in RMS (Root Mean Square) or AARH (Arithmetic
Average Rough Height). These two are the units that used to measure the roughness of the
flange face. The most common value of serrated face is 120-250 AARH.
5. How to measure the serration? Measuring the serration of the flange required
special gauge. This gauge is known as a comparator gauge. Comparator gauge is used to check serration
of the flange. In the image, you can see the how gauge is used to verify the value of serration.
You can see that gauge has actual machining samples of different value. As the name suggests,
you match this sample with your flange machining. This way you can measure actual value, but
it will tell you that you machining is acceptable or not. To measured actual value of machining,
you can use roughness gauge. This is the end of the video. I hope that
you have learned from this video. In the next video, I will explain to you about gasket
related question. So keep on checking my youtube channel for new video.
Visit my website hardhatengineer.com for free study materials and don’t forget to subscribe
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you soon goodbye take care.

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