Material Properties

The differences have to be taken into consideration by both designer and welder. The high thermal expansionand low thermal conductivity of the austenitic steels lead to higher shrinkage stresses in the weld thanwhen carbon and ferritic steels are used. Thin sections of austenitic steels may therefore be deformed when an abnormally high heat input is used

These steels are mainly used in wet environments. Withincreasing chromium and molybdenum contents, the steels become increasingly resistant to aggressive solutions. The higher nickel content reduces the risk of stress corrosion cracking. Austenitic steels are more or less resistant to general corrosion, crevice corrosion
and pitting, depending on the quantity of alloying elements.
Resistance to pitting and crevice corrosion is very important if the steel is to be used in chloride-containing environments. Resistance to pitting and crevice corrosion increases with increasing contents of chromium, molybdenum and nitrogen.

Material of Construction

In pressure Part Industry we use various type of material.

Typically in industry like this, we mainly classify material as Mild Steel also known as Carbon Steel, we also use low & high alloy steel & yes stainless steel!

What diffrentiate staineless steel from Carbon steel is its corrosion resistance properties, whcih comes because of its alloy elements.

In my blog hence onward, we will discuss about the material of constrution that we use in this industry.

I’ll come back soon.

Good Websites

Hello friends,

After long time I’m updating my blog.
Please find here some shortcut to useful websites. For Conversion for Conversion For World Sesmic/Wind Chart! Great india IIT website for earthquake and wind load calculations Good site for pipe fittings details

I’ll update more links soon..


Lets start this session with some overview on Control Valves.

A power operated device, which modifies the fluid flow rate in a process control system. It consists of a valve connected to an actuator mechanism that is capable of changing the position of a flow controlling element in the valve in response to a signal from the controlling system.

Mainly control valves, which are used for the flow control (with some turn down) are Globe valve

Before we start on valve sizing part, lates start with the main terminology used for the Control Valves

TRIM: The internal parts of a valve which are in flowing contact with the controlled fluid.
Examples are the plug, seat ring, cage, stem and the parts used to attach the stem to the plug.
The body, bonnet, bottom flange, guide means and gaskets are not considered as part of the

Closure member: A movable part of the valve which is positioned in the flow path to modify the rate of flow through the valve.

Plug: A cylindrical part which moves In the flow stream with linear motion to modify the flow rate and which may or may not have a contoured portion to provide flow characterization.

Seat ring: A part that is assembled in the valve body and may provide part of the
flow control orifice. Seat Ring also can be an integral part of the body or cage material or may be
constructed from material added to the body or cage.

Cage: A part in a globe valve surrounding the closure member to provide alignment and
facilitate assembly of other parts of the valve trim. The cage may also provide flow
characterization and/or a seating surface for globe valves and flow characterization for some
plug valves.

Globe valve plug guides: The means by which the plug is aligned with the seat and held stable throughout its travel. The guide Is held rigidly in the body or bonnet.

Stem guide: A guide bushing closely fitted to the valve stem and aligned with the seat.
Disadvantage: Higher pressure drops and minor cavitation can excite vibrational modes that are
very destructive and can result in valve failure.

Post guide: Guide bushing or bushings fitted to posts or extensions larger than the valve stem
and aligned with the seat.

Boiler Design Life

Most of the cases.. Custumer ask for expected boiler life & we tend to say approx 10 years..

How one arrive at this figure? I’ve asked this question so many time to may expert inthis field but not able to get any satisfactory answer.

Recently i went thru ASME VIII Division1 , where the Fatigue requirements are discussed.

If the boiler pressure variation is less than 20% then we need not to consider those variation in fluctuating load. Only boiler cold stat-up & shut down need to be considred while calculating the fluctuating cycle.

i.e for 12 bar(g) design pressure boiler, the maximum operating pressure is 90% of design pressure i,e 10.8 bar(g) 20% of pressure variation means , pressure below 8.6 bar(g) will be counted for fluctuating load.

also delta temperature is important while calculating the fluctuation temperature.
for Delta of 200 (Star-up condition) the equivalent cycle is 4 per star-up & for
delta of 100 (Shut-down condition) the equivalent cycle is 1 per shut down, i.e if boiler is closing 15 time per month, it 12 per year, the cycle it will go thru is (4+1) x 15 x 12 = 900 cycles.

Approx, 10000 cycle boiler can take by design, i.e boiler design life will be = 10000/900 = 11.11 year approx.

Convection Continuied..

Now the big question.. the flow parameter Re & thermal parameter Pr, how they connects to HEAT TRANSFER???

So for our help.. Mr. Nusselt has created Nusselt Number!!

The traditional dimensionless form Nusselt number Nu, which may be defined as the ratio of convection heat transfer to fluid conduction heat transfer under the same conditions.

Nusselt number Nu can be calculated as

Nu = X . Re^y.Pr^z

Where X , y, z parameters are depends upon geometry, nature of flow, flow regime etc

Nusselt Number can also calculated as

Nusselt number

So equating these two equation.. one can find heat transfer co-efficient on fluid side.

Hope you have understood the above co-relations..

Heat Transfer : CONVECTION At Glance

Heat transfer occur when there is Delta T Across the two bodies.. heat always flow from hot side to cold side. Heat transfer may occur under natural draft or under forced circulation.

Industrial heat transfer equipment are mostly occur under forced condition.

As discussed above, one can conclude that the flow characteristics of the fluid on any side will pay an important role!!

We may recall our old books and some jargon like ‘ boundary layer’, ‘Lamina Flow’ , ‘Turbulent Flow’ etc.

Lay-Mann says: As we break the boundary layer.. more new fluid molecule come in contact with the surface & more heat they will carry.. So in Laminar flow the heat transfer will be less as fluid wall touching the heating surface is not leaving the place & core will remain unaffected! while in turbulent flow the boundary wall will brake & better heat transfer will occur.

This ‘Turbulent’ thing can be identified scientifically using Reynolds analogy . Same is represented with Reynold’s Number.

Reynold’s number can be calculated as:

While there is one more parameter which plays an important role in heat transfer which is ‘Prandtl number’, which shows how heat will diffuse in fluid during convectio heat transfer..

Prandtl Number can be calculates as

Where v is Kinematic Viscosity & k is thermal conductivity of fluid

As you have noticed, Reynold’s number is depends on carrier geometry & fluid properties, while Prandle number is depends on fluid property only.

Now how to use these number to evaluate heat transfer??

Wait for my next Scrap..

About Shell & Tube heat Exchangers

The discussion is IS 4503 Oriented.
IS 4503 is the code for heat exchanger ..

Type of heat exchanger

  1. Fixed Tube Plate
  2. U Tube
  3. Floating head

Classification on Pressure

  1. 2.5 kg/cm²(g)
  2. 6.3 kg/cm²(g)
  3. 10 kg/cm²(g)
  4. 16 kg/cm²(g)
  5. 25 kg/cm²(g)
  6. 40 kg/cm²(g)

Classification on Temperature
Max. Allowable Metal Temperature

  • Carbon Steel : 250ºC
  • SS : 120ºC
  • Non-ferrous : 65ºC

Max. Fluid Temperature

  • Carbon Steel : 540ºC
  • SS : 590ºC
  • Non-ferrous : 200ºC

Corrosion allowance : 3mm minimum

Tube Pitch : 1.25 times the diameter of the tube

Tube Plate thickness is depend on the Tube outside diameter

Spacing of tube plate support (baffle) : minimum 50mm (varies from 0.6m to 2.5m)

Baffle distance to be decided to avoid any flow induced vibration which will lead to tube to tube plate cracking. TEMA has very indepth calculation to avoid these kind of ‘ harmonic’ vibrations.

Something About Pressure Vessel/Heat Exchanger Codes

In day to day life we have to deal with Pressure vessel / heat exchanger manufacturing code.
These codes are not performance oriented code, these are safety oriented code. The basic approach of the code is from user point of view.. more the hazard stringent will be the code.

The Category of the pressure vessel are depends upon hazard the pressure vessel failure will lead to..

The classification depends upon pressure/volume/ liquid category (lethal or normal) .

European directive for the Pressure vessel is PED 97/23 EC (Pressure equipment directive)

Famous Code of construction used world wide are
EN 13445 : UNFIRED Pressure Vessel
BS 5500/ PD 5500 : UNFIRED Pressure Vessel
IS 2825 : UNFIRED Pressure Vessel
IS 4503 : Heat Exchanger
ASME VIII Div1 : UNFIRED Pressure vessel
BS 2790 : SHELL BOILER (replace with EN code)
BS 1113 : COIL / TUBE BOILER (replace with EN Code)
TEMA : Heat exchanger code
TRD : German Code for Fired Vessel / BOILER
GOST : Russian Code for Fired/ unfired vessel / BOILER