Piping Class / Piping Specification

Piping Material Engineering

Piping Material Selection Criteria

What are important elements and their properties to be considered while selecting a material in oil and gas industry practices keeping in view each selection criteria for materials?

The selection criteria for materials:
• Pressure - Pressure is low, neutral (atmospheric) or high. On the low end of the pressure scale you could have from just slightly below atmospheric all the way down to full vacuum. Full Vacuum or even just a moderately low pressure can collapse pipe and other piping components. You must select a wall thickness (or reinforcement Rings) to prevent the negative force of the low pressure. On the high end of the pressure scale you must prevent the pipe and other components from failing and the system turns into a bomb. Fracture failures do to high pressure can and does kill people in process plants. The Design Pressure shall be used for all Wall thickness and Flange Rating calculations.
• Temperature - Above we discussed Pressure, now if you add Temperature to the mix you compound the risk. A very low temperature even just -50 F (-45 C) and either a very low pressure or very high pressure you have an even higher risk of component failure. On the other hand High to very high Temperature can degrade the structural capabilities of the various piping components. Look at the Flange Rating Chart. As the Temperature goes up the Pressure (Containment) rating goes down. The Design Temperature shall be used for all Wall thickness and Flange rating calculations. The maximum Operating Temperature shall be used for all Stress related Thermal expansion calculations.
• Commodity - What is it? A Gas (Vapor), a Liquid or a Slurry? The State of the commodity can have an impact on the selection of Valve types, packing or Gasket materials.
• Corrosion - Is the commodity a highly corrosive fluid or gas? If so, How corrosive? What is the rate of corrosion you must use in the calculation for "Plant Life"
• Erosion - Erosion can be caused at elbows by things like sand in a Concrete Slurry mix or by Air or Gas bubbles in mixed (cavitation) flow. You would need to select an erosion resistant material or a manner/method (Flanged Crosses with built-in wear plates) for changing directions that minimize excessive erosion.
• Piping Code - ASME B31.1, B31.3, B31.8, etc all have different applications and have slightly different criteria for certain things. So the applicable Code for the Project needs to be consulted.
• Toxic Risk - There are some commodities that are so toxic that you would not do the standard, common everyday things. You would select all butt-welded construction where ever possible (Vessel nozzle to pipe, pipe to valve, etc) to eliminate the possibility of leaks. You would also select "Bellow Seal" valves so you do not run the risk of Stem leaks from packing failure.
• Purpose - The purpose of the line is important to the selection of material. The commodity in the line may be a combination of Oil and Water but the line is an Underground Oily Water Sewer. That "Purpose (or Function) makes a difference in the selection of material.