Mechanical Engineer Basic Test (Piping/Tank)Full Marks: 50; Time: 60 mins

1. Write down about basic engineering design, details engineering design and commissioning for process plant project. --------5

2. What do you mean by P&ID?? What kind of information/data you can get from P&ID for piping final design and installation works???------5

3. Draw down stress-strain curve of steel.----54. Describe various types of heat exchangers with diagrams.----55. What is pressure vessel? Name some parts and accessories of Pressure

vessel.----56. What is the difference between welding and brazing?----27. What is to be inspected before and after welding?------68. Which design will create least stress on pipe due to thermal expansion and

why?---4

9. Write Bernoulli Equation with figure. -----310. Write short note on -----------6

a) hoop stressb) Renold’s numberc) Pipe schedule number

11. What types of data sheet you will be needed to design a Pressure vessel?----4

4. Describe various types of heat exchangers with diagrams.

ANS: There are many different types of heat exchanger available, the three main types are;

Shell and Tube; Shell and Tube Heat Exchangers consist of a large number of small tubes which are located within a cylindrical shell. The tubes are positioned into the cylinder using a tube bundle or "tube stack" which can either have fixed tube plates (permanently fixed to the body) or, in the case of Thermex Heat Exchangers a floating tube stack which allows the tube bundle to expand and contract with varying heat conditions as well as allowing the tube bundle to be easily removed for servicing and maintenance.

Plate Type; Plate Heat Exchangers operate in very much the same way as a shell and tube heat exchanger, using a series of stacked plates rather than tubes. Plate heat exchangers are usually brazed or gasketed depending on the application and fluids being used. Their compact stainless steel construction makes them an ideal choice for use with refrigerants or in food and beverage processing.

Air Cooled: Air Cooled Heat Exchangers are commonly used in vehicles or other mobile applications where no permanent cool water source is available. Thermex designs and supplies combination cooling packs (or combi-coolers) which combine an engine jacket water cooler, oil cooler and charge air cooler into a single unit reducing space requirements and improving efficiency. Cool air is provided either by a fan or by air flow caused by the movement of the vehicle.

5. ANS: A pressure vessel is a container designed to hold gases or liquids at a pressure substantially different from the ambient pressure.

The pressure differential is dangerous, and fatal accidents have occurred in the history of pressure vessel development and operation. Consequently, pressure vessel design, manufacture, and operation are regulated by engineering authorities backed by legislation. For these reasons, the definition of a pressure

vessel varies from country to country, but involves parameters such as maximum safe operating pressure and temperature, and are engineered with a safety factor, corrosion allowance, minimum design temperature (for brittle fracture), and involve nondestructive testing, such as ultrasonic testing, radiography, and pressure tests, usually involving water, also known as a hydrotest, but could be pneumatically tested involving air or another gas. The preferred test is hydrostatic testing because it's a much safer method of testing as it releases much less energy if fracture were to occur (water does not rapidly increase its volume while rapid depressurization occurs, unlike gases like air, i.e. gasses fail explosively). In the United States, as with many other countries, it is the law that vessels over a certain size and pressure (15 PSIg) be built to Code, in the United States that Code is the ASME Boiler and Pressure Vessel Code (BPVC), these vessels also require an Authorized Inspector to sign off on every new vessel constructed and each vessel has a nameplate with pertinent information about the vessel such as maximum allowable working pressure, maximum temperature, minimum design metal temperature, what company manufactured it, the date, its registration number (through the National Board), and ASME's official stamp for pressure vessels (U-stamp), making the vessel traceable and officially an ASME Code vessel.

MAIN COMPONENTS OF PRESSURE VESSELFollowing are the main components of pressure Vessels in general

a) Shell

b) Head

c) Nozzle

d) Support 

6. ANS:

S.NoWelding Brazing

1 Welding joints are strongest joints used to bear the load. Strength of the welded portion of joint is usually more than the strength of base metal.

Brazing are weaker than welding joints but stronger than soldering joints. This can be used to bear the load up to some extent.

2 Temperature required is 3800 degree Centigrade in Welding joints.

Temperature may go to 600 degree Centigrade in Brazing joints.

3 Work piece to be joined need to be heated till their melting point.

Work pieces are heated but below their melting point.

4 Mechanical properties of base metal may change at the joint due to heating and cooling.

May change in mechanical properties of joint but it is almost negligible.

5 Heat cost is involved and high skill level is Cost involved and sill required are in between

required. others two.

6 Heat treatment is generally required to eliminate undesirable effects of welding.

No heat treatment is required after brazing.

7 No preheating of workpiece is required before welding as it is carried out at high temperature.

Preheating is desirable to make strong joint as brazing is carried out at relatively low temperature.

7. ANS:

Distribution: Weld material is distributed equally between the two materials that were joined. Waste: The weld is free of waste materials such as slag. The slag after cooling should peel away

from the project. It should be removed easily. In Mig welding, any residue from the shielding gas should also be removed with little problem. Tig, being the cleanest process, should also be waste free. In Tig, if you see waste, it usually means that the material being welded was not cleaned thoroughly.

Porosity: The weld surface should not have any irregularities or any porous holes (called porosity). Holes contribute to weakness. If you see holes it usually indicates that the base metal was dirty or had an oxide coating. If you are using Mig or Tig, porosity indicates that more shielding gas is needed when welding.  Porosity in aluminum welds is a key indicator of not using enough gas.

Tightness: If the joint is not tight, this indicates a weld problem. In oxyacetylene welding if using autogenous welding, where there is no filler material, the weld must be tight.Same for Tig autogenous welding. The gap is not as critical in other types of welds since any gap is filled in by the filler material.That said, gaps in general indicate a potential quality problem.

Leak Proof: If you are repairing an item that contains liquid, a leak is a sure fire way (and obvious way) to see that there is a problem. Same for something that will contain a gas. One testing method is to use soap bubbles to check for problems (can be easily applied with a squirt bottle.

Strength: Most welds need to demonstrate the required strength. One way to ensure proper strength is to start with a filler metal and electrode rating that is higher than your strength requirement. 

9. ANS:

10. ans:

a) Hoop stress is a stress in a pipe wall. It is represented by the forces inside the cylinder acting towards the circumference perpendicular to the length of the pipe

b) The Reynolds number is an experimental number used in fluid flow to predict the flow velocity at which turbulence will occur. It is described as the ratio of inertial forces to viscous forces. For flow through a tube it is defined by the relationship: The parameters are viscosity η, density ρ and radius r.

c) Pipe Schedule is the term used to describe the thickness of a pipe. The outside diameter of a pipe is the same for all Schedules in a particular nominal pipe diameter. Standard standard pipe schedules or pipes sizes as given by ANSI / ASME B36.10M and API 5L.