Pipe material selection for various components depends on the types of materials they transport. Various liquids that can be flammable, corrosive, explosive, volatile, reactive, and sometimes hazardous to human health are transported through pipelines, which is why selecting the proper pipe material is critical for safe industrial operations.
Process Conditions for Pipe Material Selection
Piping material selection mainly depends on process conditions such as:
· Types of fluid
· Service temperature
· Operating pressure
Let’s try to understand these conditions in depth.
1. Type of Fluid
The first process condition that impacts material selection is the type of fluid transported. For corrosive fluids, you must select a material with higher corrosion resistance than for non-corrosive services. Corrosive fluids such as crude oil, seawater, H2S, ammonia, and acids require high-corrosion-resistant materials (e.g., Stainless Steel, Duplex, or Clad piping). On the other hand, normal carbon steel is generally sufficient for non-corrosive fluids such as lube oil, instrument air, and nitrogen.
2. Temperature of Fluids
The second condition impacting selection is the service temperature. Service temperatures are generally categorized as:
· Cryogenic (e.g., LNG systems)
· Low temperature
· Medium temperature
· High temperature
An increase or decrease in the service fluid temperature significantly affects the pipe material’s mechanical properties, including impact resistance, elongation, and tensile strength. Therefore, specialized materials (like austenitic stainless steels for cryogenic applications and chrome-moly alloys for high-temperature applications) are required.
3. Operating Pressure
The third process condition is the pressure of the service fluids. High-pressure services demand high-strength materials or increased wall thickness. Wall thickness is typically determined in accordance with ASME B31.3 (Process Piping) using the material’s maximum allowable stress at the design temperature.
Other Non-Process Factors
Other non-process factors considered during material selection include:
· Cost of material and overall project budget.
· Availability – whether the material is locally available or requires importing.
· Weldability and Manufacturability – preference is given to materials that do not require highly specialized, expensive welding procedures or post-weld heat treatment (PWHT) unless mandated by code.
Pipe Material Properties
Similar to process fluid conditions, specific mechanical properties are evaluated when selecting pipe material:
| Property | Definition |
| Ultimate Tensile Strength | A material’s capacity to withstand a maximum load when subjected to tension. |
| Yield Strength | The load at which plastic deformation or permanent deformation starts. |
| Elasticity | A material’s ability to resume its normal shape after the load is removed. |
| % Elongation | A measure of the material’s ductility. |
| Hardness | The ability of a material to resist surface indentation and plastic deformation. |
| Toughness | The ability of a material to absorb energy before fracture (crucial for low-temp). |
| Creep Resistance | Ability to resist distortion under constant load over an extended period at high temperatures. |
| Fatigue Resistance | A material’s ability to withstand cyclic loading for a given number of cycles before failure. |
Classification of Piping Materials
Considering both process and material properties, process piping is broadly classified into three categories: Metals, Non-Metals, and Composite/Lined materials.
| Category | Sub-Types & Examples |
| Ferrous Metal | Carbon Steel, Alloy Steel, Stainless Steel, Cast Iron |
| Non-Ferrous Metal | Copper Alloys, Nickel Alloys, Aluminum Alloys, Titanium Alloys, Zirconium |
| Non-Metal | PVC/CPVC, HDPE, GRE/GRP, Cement Pipes |
| Lined & Clad Pipe | Composite pipes made of two materials (e.g., PTFE-lined carbon steel) to improve reliability cost-effectively. |
ASTM Material Grades for Pipe Materials
The following list represents critical ASTM specifications utilized alongside ASME B31.3 standards in process piping design:
Carbon Steel & General Purpose
· A53/A53M-02: Pipe, steel, black and hot-dipped, zinc-coated, welded, and seamless.
· A105/A105M-02: Carbon steel forgings for piping applications (flanges/fittings).
· A106-02a: Seamless carbon steel pipe for high-temperature service.
· A134-96(2001): Electric-fusion (arc)-welded steel pipe (NPS 16 and over).
· A135-01: Electric-resistance-welded steel pipe.
· A524-96(2001): Seamless carbon steel pipe for atmospheric and lower temperatures.
· A530/A530M-03: General requirements for specialized carbon and alloy steel pipe.
High-Temperature & High-Pressure Services
· A182/A182M-02: Forged or rolled alloy-steel pipe flanges, forged fittings, and valves for high-temp.
· A193/A193M-03: Alloy-steel and stainless-steel bolting materials for high-temperature service.
· A194/A194M-03b: Carbon and alloy steel nuts for bolts for high-pressure/temp service.
· A234/A234M-03: Piping fittings of wrought carbon and alloy steel for moderate/high-temperature.
· A335/A335M-03: Seamless ferritic alloy-steel pipe for high-temperature service.
· A376/A376M-02a: Seamless austenitic steel pipe for high-temperature central-station service.
Low-Temperature Services
· A320/A320M-03: Alloy-steel bolting materials for low-temperature service.
· A333/A333M-99: Seamless and welded steel pipe for low-temperature service.
· A350/A350M-02b: Carbon and low-alloy steel forgings requiring notch toughness testing.
· A420/A420M-02: Piping fittings of wrought carbon steel and alloy steel for low-temperature.
Stainless Steel & Corrosive Services
· A312/A312M-03: Seamless and welded austenitic stainless steel pipes.
· A403/A403M-03a: Wrought austenitic stainless steel piping fittings.
· A789 / A790: Seamless and welded ferritic/austenitic (Duplex) stainless steel tubing and pipes.
Supplementary Data: ASME B31.3 Temperature Guidelines
To assist in selecting the appropriate ASTM grade, refer to the general allowable temperature ranges derived from ASME B31.3 Process Piping standards:
| ASTM Grade | Material Type | Typical Service Temp Range |
| A106 Grade B | Carbon Steel (Seamless) | -29°C to 427°C |
| A333 Grade 6 | Low-Temp Carbon Steel | -45°C to 371°C |
| A312 TP304L / TP316L | Austenitic Stainless Steel | -196°C to 427°C |
| A335 P11 / P22 | Alloy Steel (Chrome-Moly) | -29°C to 593°C |
