Pipin Material Selection Criteria 1

[ChihebG]

Experts,

What are the most important criteria to be considered in the material selection procedure of sized pipes according to ASME B31.3 ?

Chiheb Gouta
M.Eng Mechanical

 

[aliansari]

Important criteria for selection of material are,

1. Service. Type of fluid and its compatibility with the piping material
2. Operating Conditions (normal, maximum and design) like pressure, temperature and composition
3. External Environment

Appendix C of ASME B 31.3 provides general guidelines for metallic and non metallic materials. Extract from the code for metallic materials is attached. Hope it will be useful

 

[pennpiper]

Piping Material Selection Criteria

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.
• 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.
• 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.



Sometimes its possible to do all the right things and still get bad results

 

[BigInch]

Is it as simple as only sizing?

Material Specification Requirements
Yield strength / Load Resistance / Fatigue strength
Service Suitability, Temperature / Hardness / Brittleness
Quality and QA control, QA cost and QA time requirements, including both during manufacturing and construction
Compatibility with product, including HCC, SCC and chemical cross contamination
Internal / External Corrosion potential
Required treatments, internal cladding, internal & external coating requirements
Durability (life cycle cost)
Experience with its use in similar applications
Workability, Ease of assembly (glued, welded, automatically welded, PWHT)
Total Installed Cost
Environmental suitability (UV, flame resistance)
Availability (not only of your required wall thickness) length, double jointing, time to manufacture and logistics, time to deliver
Compatibility with the existing systems

 

[ChihebG]

Thank you, your contributions are very helpful.
I believed that the main criteria in selection the piping material is internal corrosion, was I right?

Chiheb Gouta
M.Eng Mechanical

 

[europipe]

not really

 

[pennpiper]

ChihebG,
You have been given a long list of issues in the combined lists above.
The "Main criteria" will be the one you did not consider.

Sometimes its possible to do all the right things and still get bad results

 

[BigInch]

I could not have used many steel types, or cladding, etc, due to high material costs, or welding difficulties. Is cost no consideration?

 

[KevinNZ]

You need to look at the internal (and external) rate of corrosion for different material options and then compare the installed cost (material costs, welding, supports etc) plus the life time cost (monitoring, NPV of replacement, shut time, risk of leak, etc) for each material option and wall thickness.

 

[rconner]

I guess could add a few other considerations, the importance of which might vary considerably depending on many factors including the experience of who is doing the considering:
1. History (and local history, good and bad) of the material and joining means in the application
2. Available experience in the area of the labor who will or might install the piping
3. Many plant environments are rather congested, often in the vicinity of working lines that do not want to shut down, and heavy items are handled in close quarters with heavy equipment and temperature in installation as well as future maintenance and service. The material's ability to tolerate some banging and clanging (aka damage resistance?) that may be inevitable in such may be helpful to safety and minimizing future plant downtime
4. Dependable service if/when? future information is needed regarding or when something goes wrong involving the material, and/or repairs/parts etc are needed