Types of Pipe Material and Their Selection

What are Pipes and Piping materials?

Pipes are spherical conduits made of a variety of sizes and materials that may transport liquid under pressure. Circular pipes are frequently utilized for drinking water delivery and distribution. Pipes can be made from a variety of materials, including GI, DI, CI, WI, steel, cement, HDPE, PPR, PVC, and more.

Piping Engineering includes crucial piping materials. The quality of the piping materials has a significant impact on a project’s cost and success. Therefore, careful pipe material selection is crucial for project economics, and it is always preferable to use piping materials that are technically sound but less expensive. The market is filled with a wide choice of piping materials. It can be very difficult to select the most cost-effective pipe material for a particular service, which is where piping material engineers come in. They choose the best pipe material after consulting with process engineers. 

The word “piping material” is broad and does not just refer to the pipe material. It denotes the composition of all piping parts, including pipes, fittings, valves, and other objects. Therefore, we can sum up piping material by stating that it refers to the materials of every component found in a particular pipe class.

The sort of materials that the pipe transports influences the material choice of its many components. A pipeline transports a variety of liquids, some of which may be flammable, corrosive, explosive, volatile, reactive, and occasionally hazardous to human health. For this reason, choosing the right pipe material is crucial.

Requirements of good quality piping material for selection:

Good pipe materials must meet the following criteria:

1. It should be structurally strong enough to withstand the pressure that is applied both inside and externally, compressive and tensile temperature stress, load from overlapping impact stresses, and shock.
2. It ought to be impenetrable, corrosion-resistant, strong, and long-lasting.
3. It must be economical and accessible on the market for a fair price. 4. To enhance hydraulic efficiency, Hazen William’s constant should be large and the Darcy frictional coefficient should be as low as possible.
4. Water should have enough resistance to abrasion since it may contain inorganic particles like sand, silt, and other materials that, when flowing at a high velocity along the invert of a pipe, could cause material erosion.
5. It should be lightweight to be portable, manageable, and freezer-friendly.
6. It should be simple to assemble, adaptable in design, and simple to fix and keep up.
7. It must respect the environment.

Parameters important for Pipe Selection:

The right pipe material selection is crucial since pipes and pipelines transport a variety of liquids and gases under varying processing conditions. The following are the primary process variables that control as well as influence the choice of piping material is: 

• Types of fluids
• Temperature while using
• Pressure during the operation

The type of fluid it conveys is the first process condition, operating pressure, that will affect the choice of material. As opposed to non-corrosive services, corrosive fluids require higher corrosion-resistant materials.

High corrosion resistance material is necessary when working with corrosive fluids like crude oil, seawater, H2S, ammonia, acids, etc. In contrast, regular carbon steel is enough for non-corrosive fluids like a lubricant, air, nitrogen, etc.

The temperature of the fluids is the second process factor that will influence the choice of material.

• Cryogenic
• If the temperature is low
• A moderate temperature
• A high degree of temperature

One needs unique material for both high temperature and cryogenic services since a change in the service fluid temperature would significantly affect the pipe material’s mechanical qualities, such as impact resistance, elongation, and tensile strength.

The pressure of service fluids is the third process condition that will affect the choice of material. For high-pressure services compared to standard pressure services, there is a need for material with higher strength or thickness.

The following non-process variables are also taken into account while choosing materials:

• Material cost
• Whether the substance is readily available locally or if an import is necessary.
• The selection also heavily weighs the material’s weldability and manufacturability. The material that has no additional requirements for welding and production is always preferred.

Basis of Material Selection:

The process/metallurgy Engineer is responsible for choosing the fundamental piping metals and materials (such as CS, LTCS, AS, SS, etc.) for the piping specification. The primary choice is made per the process, licensee, and/or intrinsic metallurgical specifications to accommodate the process media, such as corrosion, high temperature, pressure, etc.

This fundamental choice must also take into account PWHT-specific factors, NACE-specific valve trim, corrosive services like acids and amines, as well as hazardous services like hydrogen, chlorine, phosphorus, and oxygen.

Basics of the Materials:

Since they have limited mechanical strength, metals are rarely employed in their purest form. Strength and ductility are two attributes that alloying helps to improve. (For instance, making ferritic Carbon Steel by adding carbon to iron is the easiest.) The optimization and improvement of its mechanical properties are achieved by adding alloying elements in the correct ratios and carrying out the necessary metal processing and heat treatment. Additionally, alloying aids in enhancing machinability, weldability, and corrosion and oxidation properties.

Additionally, complex alloyed materials are being developed for use in programs and applications related to aerospace. Metallic glasses and crystalline alloys have also been made and metal alloys are sometimes even joined with graphite, ceramic and biological elements as composites for wider and more complicated applications. 

Properties of Piping Material:

While choosing a pipe material for a particular application, certain mechanical features are also taken into account. Those are

• Young’s Modulus: which is determined via tension tests, is the ratio of stress to strain.
• Range of Elastic: After the load is relieved, the material resumes its original shape.
• The plastic range: even after the load has been withdrawn, the material is permanently distorted.
• Yield Strength: It determines the limiting value at which the transition from the elastic to the plastic phase occurs.
• Ultimate Tensile Strength: This property specifies the upper limit beyond which any additional loading under continual stress would stop the specimen’s elongation or thinness and cause it to fail.
• Ductility is demonstrated by the specimen’s elongation and reduction in the cross-sectional area before failure. It is determined by measuring the specimen’s minimum diameter before failure and length before elongation.
• Hardness is a material’s capacity to withstand deformation. Brinell or Rockwell tests are used to measure hardness. Both of these hardness tests are indentation-type tests.
• A material’s toughness determines its capacity to withstand abrupt, brittle fractures brought on by the quick application of stresses. Utilizing the Charpy V-Notch test to measure.
• The ability of a material to withstand failure or fracture initiation and additional crack propagation under repeated cyclic loading conditions is known as fatigue resistance.

Terms regarding Materials and their definition:

• Creep Strength: The ability of a metal to sustain steady pressure or force at high temperatures without cracking is known as creep strength. 
• Brittle Fracture: application of energy that causes the metal to fail quickly and suddenly with little distortion
• Stabilization: Adding alloying elements lowers corrosion at higher temperatures by preventing the development of carbides and carbon-chromium precipitation.
• Intergranular Corrosion (IGC): It is corrosion that happens at the edges of metal grains as a result of chromium depletion and the subsequent creation of a layer of Cr Carbide that protects against more corrosive conditions. (SS: Minimum 12% Cr). Reducing acids, oxidizing acids, and organic acids are the culprits of IGC.
• Reducing Acids: Acids that are reduced lose oxygen while gaining hydrogen; examples are hydrochloric, hydrofluoric, and hydrobromic acids.
• Oxidizing Acid: Sulfuric acid, nitric acid, and chromic acid are examples of oxidizing acids. Oxidation is a chemical process between metals and oxygen that results in the gain of oxygen and the loss of hydrogen.
• Organic Acids: Acetic acid, formic acid, and citric acid are a few examples of organic acids, which are composed of carboxyl (COOH) groups and contain hydroxide (OH).
• Stress Corrosion Cracking (SCC): It is a metal failure caused by the interaction of chemical corrosion and tensile stress. SCC is additionally influenced by metal characteristics, exposure time, solution environment, and service temperature.
• High Temp Hydrogen Attack – This causes the degradation of carbon and low alloy steel because the carbon (a strengthening agent) in the steel is depleted (decarburized) as a result of a reaction with hydrogen at high temperatures, which results in a loss of metal strength.
• Hydrogen Blistering: Atomic hydrogen diffuses into steel at low temperatures and becomes trapped as a non-metallic inclusion, creating pressure that eventually causes steel to swell and blister.
• Hydrogen-Induced Cracking: Similar to hydrogen blistering, hydrogen-induced cracking (HIC) only happens in pipelines that are used for sour services.
• Limiting the sulfur level of steel to 0.005% or 0.010% at most will prevent hydrogen blistering and HIC.
• Oxidation: It is the chemical reaction that occurs when metals and alloys are exposed to oxygen in the air, forming oxides. Scaling is the product of this process.

What are alloying elements?

To give steel benefits over conventional carbon steel, alloying elements are utilized to change the mechanical and chemical properties of steel. Even though there are several alloying elements, some are much more prevalent than others to attain certain increased qualities. These are the several alloying components, some of them known as chromium, molybdenum, vanadium, manganese, and nickel.

Effects of alloying elements:

The primary alloying components that affect the qualities of pipe materials and, consequently, the choice of those materials are:

• Strength and hardness increase with carbon content, but ductility and toughness decrease.

• High levels of phosphorus (P) make materials brittle by reducing their ductility and shock resistance.

• Silicon as Under 2%, silicon (Si) improves the metal’s stability by boosting tensile strength without causing it to become more brittle. Additionally, it is a deoxidizing agent and resists oxidation.

• Sulfur in combination with manganese (Mn) increases hardness, which enhances hot working properties.
• Nickel (Ni) – It makes steel stronger and more durable, which enhances hardenability. Impact and fatigue resistance is improved when combined with chromium. enhances low-temperature characteristics. Better resistance to chloride cracking is achieved with higher nickel content.
• Chromium (Cr) is a hardening element that increases the strength of materials at higher temperatures. improves steel’s resistance to high-temperature oxidation and corrosion.
• Molybdenum (Mo) – It increases the creep resistance of the steel at higher temperatures, making it tougher and more stable. 2% Mo in steel lowers the rate of high-temperature oxidation.
• Columbium/Titanium (Cb/Ti) is a commonly used stabilizing ingredient that reduces carbide precipitation to enhance steel’s sustained high operating temperature qualities. Types 321 and 347 of SS.

Types of Pipe Material:

Cast Iron- These pipes are frequently utilized for the conveyance of water in the water supply scheme. These pipes have excellent corrosion resistance as well as other desirable qualities including strength, longevity, durability, and the ability to withstand the highest pressure that may occur. Cast iron pipes are expensive and heavy, making them challenging to move. CI must not be employed in situations including extreme cycle conditions, high heat, or thermal shock.

When the temperature is below -29°C and over 343°C, DI and MI cannot be employed (ASTM A47, A536).

Austenitic DI (ASTM A 571) can only be utilized in temperatures no lower than -196°C.

CI pipes come in a range of diameters and lengths from 2.5 to 5.5 meters. CI pipes are divided into three classes based on their thickness: LA, A, and B. These classes can withstand pressures of 10, 12.5, and 16 kg/cm, respectively.

Some advantages of CI include, that these pipes are reasonably priced, it is simple to connect the pipes, the pipes have a high level of corrosion resistance, the pipes are robust and long-lasting, it’s simple to establish service connections, and the average lifespan is 100 years. 

Some drawbacks of this material are that since CI pipes are heavier, they are challenging to handle and carry, as the lifespan of pipes increases as a result of tuberculation, the carrying capacity of these pipes diminishes. These pipes cause the water to taste metallic because iron from the rusting of the pipe leaches into the water. Along with that, these pipes are brittle, for one as CI pipes are heavier, using greater sizes is no longer practical.

Carbon Steel- Common characteristics of carbon steel materials include that they prove to be better than CI and possess higher strength, they are used for temperatures up to 427° C (800° F) or higher and the steam piping is included in most processes services.

Low-temperature applications such as chilled brine, chlorine liquid or gas, propylene, etc. use Low Temp Carbon Steel (LTCS) ASTM A333-Gr 1, 3, 4, 6, 8, 11, etc. (Bet -45 to 485 °C). It possesses more carbon, fewer alloying elements like cr and mo, and nickel, which enhances low-temperature characteristics. Impact characteristics/values at low temperatures are superior to CS (Charpy N Notch test)

For impact test requirements for low temperature/cryogenic services, one can refer to ASTM 01.01.

Copper pipes are also often utilized in both hydronic and household applications, especially for 2-inch and smaller pipe sizes. Despite being more expensive than steel, copper has the advantage of weighing less, which could result in installation requiring fewer workers, depending on weight and union requirements. Additionally, compared to steel or galvanized steel, copper is typically nobler and corrosion-resistant.

The majority of copper used in the HVAC industry is Type L (medium thickness) and hard (tempered) copper, however, Type K is frequently used for subterranean soft (annealed) copper (thick). Thinner drain, waste, and vent (DWV) pipe (Type M).

Galvanized Steel- Steel that has been dipped into a zinc pool is known as galvanized steel pipe. There are two ways to reduce corrosion when using galvanizing, they are: 

• It covers the surface like paint and, in most cases, develops an extremely tenacious oxide coating, similar to that of aluminum and stainless steel.
• It substitutes a zinc sacrificial anode for the steel to receive corrosion.

Although slightly more expensive, galvanized steel pipe has all the benefits of steel pipe as well as improved corrosion resistance in most environments. When used in applications where it is periodically wet and dried, galvanizing works practically completely (e.g., road signs and guard rails).

It can break down in situations with a lot of salt because the sodium causes the adhering oxide film to separate and behave more like a steel pipe where the oxide flakes off (for example, softened water that was initially quite hard). The welder must be careful to grind down to the raw steel when welding galvanized pipe. The galvanizing on the inside of the pipe might be beyond repair. Consider mechanical connectors if a continuous galvanized coating is required within.

For fundamental resources like water, air, and nitrogen, use is restricted to temperatures of roughly 200° F or 93° C.

To prevent welding-related damage to galvanizing, pipe connections are typically screwed. These pipes are frequently used for after-service connections or in-home plumbing. 12mm to 25mm diameter, non-corroding pipes are used for water pipe fittings and come in lengths of 7 m. These are affordable, lightweight, simple to assemble, portable, and manageable. These pipes have a lifespan of roughly 20 years.

Lined Piping- They are typically cement-lined, metallic, glass, non-metallic, and

Are utilized for extremely corrosive services such as acids, caustics, process-limited services, etc. CS typically utilized in seawater applications is the cement-lined pipe.

Steel- These are made by rolling mild steel plates to the appropriate diameter and joining them with rivets or welding. These pipes are sturdy, affordable, lightweight, and able to withstand high pressure for up to 400 meters. The lengths and diameters of the welded steel pipes range from 12 meters to 2.4 meters. These pipes are more expensive, more prone to corrosion, and can’t withstand pressure from an external load while there is a vacuum inside.

Some advantages possessed are that since they come in lengthy lengths, there are fewer joints, and the initial cost of the pipes is low. Along with that, the pipes are robust and able to withstand tremendous pressure. The pipes are set on curves and are quite flexible. Lightweight makes for simple transportation.

Some drawbacks can be that costs for maintenance are considerable, acidic or alkaline water can cause the pipes to corrode, the pipes are not appropriate for distribution pipes since they take more time to fix when they break, and under the combined effect of external forces, the pipes may shape deform.

The different types of steel can be classified as:

Alloy steel- They are used for high-temperature applications in the CS base, such as process services, superheated steam, reformer gases, etc., above 400° C design temperature (ASTM A335 Gr P1, 5, 11, 22, etc.)

After welding, PWHT or stress relief is required since Cr-1/2Mo steels can only be utilized between -29°C and 454°C design temperatures.

Stainless Steel- This type of steel is used for cryogenic applications, high-temperature services, and process-critical operations. 

There is process-governed selection for particular service requirements.

Stainless steel grades ASTM A312 Gr TP 304 and 316 are typically used for pipes.

Compared to SS304, SS316 has greater overall corrosion resistance qualities due to the presence of 2% Mo.

In chloride conditions, SS316 offers greater resistance to pitting and crevice corrosion.

Grade L series has a reduced C content (0.035%), enhancing its use at higher temperatures up to 1100°F (600°C), as well as having improved weldability and greater resistance to IGC. improved mechanical strength at high temperatures and good high-temperature oxidation resistance up to 925 °C.

Grade H offers increased high-temperature strength above 815° C with controlled C between.04 and 0.1% and reduced Ni.

Food, steel utensils, beverages, the dairy sector, and other items are frequently made from SS304.

SS316 is frequently used in the culinary, pharmaceutical, marine, and medical implant industries.

Grade 317 – usage constrained by the process/licensor

Due to the inclusion of Columbium and/or Tungsten, Grades 321 and 347 are metallurgically particularly stable in high-temperature applications.

If C is 0.1%, impact testing is not necessary.

For impact test requirements for low temperature/cryogenic services, reference to ASTM 01.01.

Duplex SS- Grade 2205/2207 has excellent strength and corrosion resistance, enhanced resistance to acids and chlorides, and superior weldability are all characteristics of Cr-Ni-Mo steel (ASTM A928). 

Ductile iron- 

These pipes are made of ductile iron, which is frequently used for the distribution and transmission of potable water. Centrifugal casting is typically used to create the pipe in metal or resin-lined molds. To combat corrosion issues, protective interior linings and external coatings are applied to ductile iron pipes. As a result, these pipes have a high level of corrosion resistance.

The only differences between ductile iron (DI) and cast iron are that DI has a lower carbon content and uses annealing and/or additives, like magnesium, to create a distinct (nodular) matrix. This increases its strength and ductility compared to cast iron. Its corrosion resistance is quite comparable to cast irons.

Other materials include nickel, Monel, Inconel (600, 6250, 800, 800H, 825), Hastalloy, aluminum alloy, and titanium seamless pipes. 

Polyvinyl Chloride (PVC) Pipe – Vinyl and plastic are combined to create PVC pipes. These plastic pipes are widely used because they are very rigid, simple to join, powerful at withstanding pressure, lightweight and transportable, and able to withstand acids, alkalis, salts, and organic chemicals. They are also less expensive.

Due to its flexibility, this pipe needs more support because it might shatter or crack if handled improperly. PVC pipes are temperature resistant up to 60 °C. PVC pipes may be installed with only a few simple tools and expertise. These pipes are frequently utilized in water systems because they do not rust, degrade, or wear out over time. 

Pipes are affordable, strong, and adaptable. They are good electrical insulators and do not corrode. They are lightweight and versatile enough to take on any shape. Some drawbacks are that plastic has a high coefficient of expansion, and it is challenging to find plastic pipes with a consistent composition. Less heat resistance exists in the pipes. Some plastic pipes give the water a flavor.

Polypropylene random copolymer (PPR)- Thermoplastic resins called polypropylene random copolymers are made by polymerizing propylene and adding ethylene links to the polymer chain. Polypropylene comes in homopolymers, random copolymers, and block copolymers. These pipes can withstand temperatures of up to 70o C, making them suitable for the supply of hot water.

PPR pipes and fittings are now widely used in plumbing and water supply facilities because they are simple to join, have an ideal seal-tight system, have no calcification issues, are sturdy and have a long lifespan, are recyclable, are chemically resistant, etc.

Some advantages are that these pipes have strong hydraulic performance, it is lightweight and manageable, and they have great resistance to heat. Along with, it exhibiting strong chemical resistance, these pipes are tough and environmentally friendly, there is no calcification issue, and they have a lifespan of more than 50 years.

Some drawbacks are that using a fusion-welding instrument makes it possible to join and repair PPR pipes and because PPR pipes are made of plastic, prolonged exposure to sunshine could dry out the oil that is contained in all plastics.

PP, CPP, and PE Polyolefins as Pipe Materials-  

• The thinnest thermoplastic piping material is polypropylene (PP). Their characteristics are excellent tensile strength and chemical resistance; resistance to compounds containing sulfur. Up to 80°C (180°F), applications are permissible. Excellent material for demineralized water, chilled water, petroleum industry, industrial drainage, and saltwater disposal lines.

• Copolymer Propylene and polybutylene are copolymerized to form polypropylene (CPP).  It possesses superior dielectric and insulating qualities, a high level of chemical resistance, and toughness and strength between freezing and 93°C (200°F) operating temperatures along with excellent flexibility and resilience to abrasion. joining using butt or socket fusion.
• The four types of polyethylene (PE) are as follows:
• Compared to polyethylenes, low-density polyethylene (LDPE) has a less compact and more branched molecular structure. Ideal for brine tanks, food handling facilities, etc. suitable for temperatures up to 60°C (140°F). hot gas welding for joining. To a large variety of common chemicals, all polyethylenes have exceptional chemical resistance.
• A thermoplastic with a lower density than HDPE is medium-density polyethylene (MDPE). It is more stress-cracking resistant than HDPE and has superior shock and drop resistance. In comparison to HDPE, it is less rigid and hard, extensively utilized in packaging films, gas pipelines, and fittings. hot gas welding for joining.
• The molecular structure of High-Density Polyethylene (HDPE) is more compact and has fewer branches. LDPE is stiffer and less porous. Suitable for temperatures up to 71°C (160°F). used for control tubing, caustic storage tanks, and abrasion-resistant pipe, among other things. hot gas welding for joining.
• Cross-Linked A 3-dimensional polymer with a very high molecular weight and compact molecular structure is known as high-density polyethylene (XLPE). High impact strength and superior resistance to environmental stress cracking. Suitable for temperatures up to 71°C (160°F). ideal substance for use in large storage tanks for outdoor use.

Other materials comprise fluoroplastics of several forms and thermoset plastics. 

Concrete Pipe– These pipes made of reinforced or unreinforced cement are both acceptable. For heads more than 60 inches, pre-stressed concrete can be used; however, PCC pipes can only be used for heads up to 15 meters.

On situ pipes is another name for these pipes, which allows for on-site tasting. The Hume name is also used for reinforced pipe, which has a longer lifespan and is not corrosive. Cement concrete pipes require minimal maintenance, and their joints are relatively straightforward. Concrete pipes, however, are cumbersome since they are heavy and less able to endure shock and impact.