Key Construction Risks from Systems Outside the Boundary Wall of the Plant

Generally all systems outside the boundary wall of a thermal power plant carries a huge construction risk.

These systems include:

1. Cross Country Pipeline for delivering the water to the thermal power plant

2. Transmission Line  for delivering the electricity produced at the plant to the nearest point in the grid

3. Railway Siding for delivering coal to the power plant

Generally the amount of risk is directly proportional to the length of system. For instance, a cross country pipeline of 60kms carries a much bigger risk than a cross country pipeline of 20 kms.

 

Generally for Cross Country Pipeline and Transmission Line, we only need to get Right of Way (ROW) which is sort of lease model and need not actually acquire the land. However for Railway Siding, we have to actually purchase the land. Land acquisition is a long and cumbersome process as there maybe more than 2000 individual land owners for a railway track of 20 km length.

For Cross Country Pipeline, its a better strategy is run your cross country pipelines  parallel to the road or a national highway and offset it from the highway by 10 to 30 metres. Generally the land around the highways is owned by Highway Authority or other Government bodies and getting the ROW is much simpler. However, as there maybe plans to make the highway from 2 lanes to a 4 lane highway in a few years and you maybe asked to relocate your pipeline. The plant owner must protect himself against this by leaving sufficient distance from the edge of the road or highway.

Additionally our pipeline may also be crossing local roads, national highways, rivers, canals, railway lines, other pipelines, petroleum pipelines etc. While finalizing the route of the cross country pipeline we must have a very clear strategy for overcoming all these challenges.

About Pipes - Part 2

ASME and ASTM have defined the dimensional standards and material standards respectively for all pipes used in process plants. These bodies publish various codes/standards so that engineers can select pipes suitable for their application based on these internationally accepeted standards.

Carbon Steel Pipe is the most common type of pipe and is mostly specified according to ASTM 106. Within the ASTM A106, carbon steel pipe is available in Grades A,B and C based on increasing tensile strength.

Galvanized Carbon Steel Pipe is mostly specified as per ASTM A53

Stainless Steel Pipe upto 200mm Nominal Bore is mostly specified as per ASTM A312. Within ASTM A312, eighteen different grades of stainless steel pipe are specified with grade 304L as the most commonly used grade in industry. Stainless Steel pipes above 200 Nominal Bore are specified as per ASTM A358

*In India its very difficult to obtain seamless pipes above 350 NB from any of the vendors

* ASTM - American Society for Testing and Materials
*ASME - American Society of Mechanical Engineers

Weight of Pipe in terms of Kg per meter

The weight of pipe in terms of Kg per meter is = Diameter *Thickness * 16

For example a 10 inch pipe with 0.25 inch thickness has a weight of  = 10 *.25 * 16 = 40 kg per meter.

This calculation is only a thumbrule with very good accuracy. For actual billing, the weight of the pipe from pipe tables should be taken.

Calculating Electrode Consumption for Pipe Per Weld

Lets say we have a 12 inch pipeline which needs to be welded. 

Kg of Electrode Required per Weld = (Dia of Pipe/2) * 0.1 =  (12/2)* 0.1 = 0.6 kg

This is only a rough thumbrule calculation for calculating the quantity of electrode per weld.

About Pipes - Part 1

Pipes are generally made of  metal, plastic or concrete.

Metallic pipes are of Cast Iron, Galvanized Iron, Carbon Steel, Mild Steel, Stainless Steel, etc
Plastic Pipes maybe of PVC, HDPE, FRP etc
Concrete Pipes are made of various concrete mixes

Mettalic pipes maybe manufactured by extrusion (also called seamless pipes), centrifugal casting and spinning or welding.

Pipes generally are classified by their Nominal Bore which is their Outer Diameter and by Pipe Schedule which is the thickness of the pipe shell.

Pipes may be joined together by Welding, Flanging or Threading.

If pipe is joined by welding ( either Butt Welding or Socket Welding) then radiographic inspection of the welded joint would be required by the client.

If a mettalic pipe is to laid underground then the pipe must be protected from corrosion by wrapping and coating and also by cathodic protection.

Types of Valves

lvelvvBasically there are 4 types of mechanical valves:

1. Flow Regulating Valve - The purpose is to control the amount of flow in the pipe. Eg Butterfly or Globe Valve

Butterfly Valve

 

Globe Valve

 

2. Stop Valve - To completely stop or start the flow of fluid. These valves are good for "On" and "Off" application but poor in controlling the amount of flow. Eg Ball Valve or Gate Valve

3. Check Valve - Allows the fluid to flow in only one direction and prevents backflow of fluid

4. Pressure Regulating Valve - If the pressure in the piping system exceeds a certain amount, then the valve opens to relieve the pressure in the sytem. Eg Steam bypass valve

Generally the valves are color coded as per the fluid they are carrying
White Color - Steam
Blue Color - Water
Yellow - Fuel/oil
Dark brown- Sewage

Galvanizing

Galvanizing is process of depositing a layer of zinc coating on top of steel or iron to prevent rusting and improve the lifespan.
The thickness of zinc coating is measured in microns.

The two basic methods of achieving galvanizing are:
1. Electroplating
2. Hot-dip Galvanizing

Hot-dip galvanizing is preferred as it gives better quality of coating.
Ducts, pipes, fixtures, etc are some of the common items which are galvanized.

Components of a Centralized Air Conditioning System:

1. Chillers
   
   
2. AHU
    
3. Ducts
   
   
4. Water Pipes
   
   
5. Pumps
   
   
6. Cooling Towers
   
   
7. Diffusers, Grills, Registers etc
   
   
8. Mechanical Dampers, Fire Dampers, Smoke Dampers, Thermostats