Welcome to Hardhatengineer.com. I am Varun Patel. In this video, you will learn about the most common questions regarding piping that you may face during the interview.
You will learn about these questions;
- What is the difference between a machine bolt and stud bolt?
- What is the thumb rule to calculate spanner size for a given bolt?
- What is a steam tracing?
- Which piping items will you drop down before conducting Flushing and Hydrotest?
- Why do we provide a Dampener in the Piping of Reciprocating Pump?
- Why do we provide Full Bore Valve in connecting pipeline of Launcher / Receiver?
- What should be the relative hardness between the RTJ gasket and flange groove?
- Why do we provide Drip Leg in Steam Line?
- What is the normal upstream and downstream straight length of orifice flowmeter?
- What do you mean by Composite Flange?
So please watch this video till the end. And don’t forget to subscribe to my channel because that way you will get regular updates on a new video. You can subscribe right now by just clicking subscribe button on your screen. So let’s start with the first question.
What is the difference between a machine bolt and stud bolt?
This is sometimes confusing especially for newcomers. Bolt and stud are very frequently used in flange joint. So some people use these terms interchangeably but that is not correct. Machine bolt has a head on one side and nut on another side, but stud bolt has a thread on full body and has nuts on both sides. In the image, you can see the machine bolt and stud. Normally in piping machine bolts are used with non-metallic piping such as GRE/GRP and HDPE. For metallic piping, stud bolts are used.
What is the thumb rule to calculate spanner size for a given bolt?
A standard chart is available that shows the size of a given bolt and corresponding spanner size. Here you can see the same. But is this chart is not available, in that case, you can use thumb rule to get the spanner size. Approx spanner size is 1.5 times the diameter of Bolt.
|Wrench Sizes (in.)|
|Diameter of the Bolt||Hex Nut||Heavy Hex Nut|
|3/4||1 1/8||1 1/4|
|7/8||1 5/16||1 7/16|
|1||1 1/2||1 5/8|
|1 1/8||1 11/16||1 13/16|
|1 1/4||1 7/8||2|
|1 3/8||2 1/16||2 3/16|
|1 1/2||2 1/4||2 3/8|
|1 3/4||2 5/8||2 3/4|
|2 1/4||3 3/8||3 1/2|
|2 1/2||3 3/4||3 7/8|
|2 3/4||4 1/8||4 1/4|
|3||4 1/2||4 5/8|
What is a steam tracing?
As the name suggests, it is a tracing of steam provided to the process line. In a process plant, certain fluid such as fuel oil and intermediate feed pipeline that carries viscous fluids needs constant heating to maintain the flow in the line otherwise this fluid gets thicker and can jam the line. To prevent this constant heating of the line is required. In the image below, you can see that small tubes are attached to the main process pipeline. These tubes are known as a tracing line and stem is passed through it continuously to keep the main process line hot. Once tracing is done, the pipeline is insulated to preserve the heat loss as you can see in the last image.
Which piping items will you drop down before conducting Flushing and Hydrotest?
When you perform a hydro test or do line flushing, debris such as pipe rust, welding slag, sand will move, and it may get stuck inside the instrument and valve. This will create a problem in their function. So any item that may get impacted by this type of debris must need to be dropped while performing flushing and hydro test. Items like Control Valve, Orifice plates, Rotameters, safety valves, Thermowells are dropped or replaced with temporary spools before a hydro test.
Why do we provide a Dampener in the Piping of Reciprocating Pump?
To answer this question, you should know that the functioning of the reciprocating pump. Unlike a centrifugal pump, in a reciprocating pump, fluid get compress in a fixed volume. Here you can see how it works. Now due to this plus like effect will create in the pipeline. This will damage the line. To prevent this dampener is installed with a pump which acts as a buffer and absorbs the high-pressure pulse and releases the pressure when it is low. This way constant pressure is maintained in the line.
Why do we provide Full Bore Valve in connecting pipeline of Launcher / Receiver?
There are two types of valve available. Here is the image, you can see them both. The first is to reduce bore and second is full bore. The main difference you can see in the image. It is basically an internal diameter of the valve. In the case of full bore valve, the diameter of the valve passage is the same as a pipe. Now launcher and receiver are used to launch pig. Pigging is an activity that used to clean the line and also to inspect the line with the help of intelligent pig. Here you can see the pig. To pass this pig through a pipeline without being stuck at the valve, you have to use a full bore valve.
What should be the relative hardness between the RTJ gasket and flange groove?
In the image, you can see the RTJ flange and gasket. Now the material of the gasket should be soft enough to set inside the flange serration to prevent leakage and at the same time, it should not damage the flange face when you tighten the flange. To achieve this, the slightly soft gasket material is used then flange material. The hardness of gasket will be 20-50 BHN less than the hardness of the flange. This will make ensure smooth setting of a gasket in the flange face.
Why do we provide Drip Leg in Steam Line?
There is a chance of steam condensation inside the steam line. If you don’t remove this condensate from the line, it will create water hammer inside the line and it damages the piping system. To avoid this, you have to remove the condensate continuously from the system. Drip leg is provided to remove condensate when there is a rise in the pipe along the flow direction. Here is the image, you can see the drip leg.
What is the normal upstream and downstream straight length of orifice flowmeter?
Orifice flowmeter is used to measure the flow of the pipeline. To get an accurate result, steady flow is necessary. Any piping component will create some amount of turbulence in the line. To avoid this only straight pipe is preferred in upstream and downstream of the orifice meter. The minimum straight length preferring in upstream is 15 times the diameter of the pipe, and in downstream it is five times the diameter of the pipe.
What do you mean by Composite Flange?
The flange that is made up of more than one material is called a Composite flange. See the image of the lap flange. Lap Flange is having two components, a stub end, and a loose backing flange. Stub end is butt-welded to the pipe and Backing flange freely move over the pipe. A backing flange can be of a different material than stub material and generally of the carbon steel to save the cost.
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 a few more important questions related to piping. So keep on checking my youtube channel for a new video.
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