Materials

Common materials used in pipe fittings:

Pipe fittings are made of various types of steel like Carbon Steel, Alloy Steel, Stainless Steel, Duplex/ Super Duplex, Nickel Alloy, etc.

 

Based on carbon %, steel can further classify as

• Low carbon steel: in which Carbon is in range from 0.05% to 0.25%

• Medium Carbon Steel: in which Carbon is in range from 0.25% to 0.5%

• High Carbon Steel it is in range from 0.5% to less than 2%

Application of Carbon steel:

Fittings made of carbon steel are used in pipe systems that carry liquids or gases, such as oil, water, natural gas, or steam. Apart from that, carbon steel fittings are highly demanded in construction and maintenance activity in the residential construction, commercial construction, electric-power generation, petroleum refining, shipbuilding and other industrial-use sectors.

Application of Galvanized Steel:

Galvanized steel pipe fittings are for all types of piping inside a building. They are also used in water supply lines, but not in gas pipelines.

For many low-alloy steels, the primary function of the alloying elements is to increase hardenability in order to optimize mechanical properties and toughness after heat treatment. In some cases, however, alloy additions are used to reduce environmental degradation under certain specified service conditions.

As with steels in general, low-alloy steels can be classified according to:

• Chemical composition, such as nickel steels, nickel-chromium steels, molybdenum steels, chromium-molybdenum steels

• Heat treatment, such as quenched and tempered, normalized and tempered, annealed

The HSLA steels have low carbon contents (0.05-0.25% C) in order to produce adequate formability and weld-ability, and they have manganese contents up to 2.0%. Small quantities of chromium, nickel, molybdenum, copper, nitrogen, vanadium, niobium, titanium and zirconium are used in various combinations.

Duplex Stainless Steel

Austenitic-Ferritic stainless steels, also called duplex stainless steels, were developed more than 70 years ago in Sweden for the paper industry in order to combat corrosion problems caused by chloride-bearing cooling waters and other aggressive chemical process fluids.

Due to the high content of chromium, nitrogen, and molybdenum, these steels offer good resistance to localized and uniform corrosion. The duplex microstructure contributes to the high mechanical strength, good abrasion, erosion and fatigue resistance. Duplex steels also possesses good weld-ability properties.

Super Duplex Stainless Steel

First used in the 1980s, Super- Duplex refers to highly alloyed, high performance Duplex stainless steel with an improved pitting and crevice corrosion resistance.

Super duplex steels were designed for specific applications where both high mechanical strength and good corrosion resistance are required. Super Duplex Stainless Steel is noted for its high level of chromium, which gives the alloy excellent resistance to acid chlorides, acids, caustic solutions and other harsh environments.

Selection criteria for pipe fittings:

The pipe fittings “bodies” are most often of the same base material as the pipe or tube in which they are to be connected, e.g., steel, polyvinyl chloride (PVC), copper or other plastic or metal. Besides this, any material that is allowed by a code or a standard can also be used. For example, a pipe fitting made of brass is common in otherwise copper piping and plumbing systems. The materials of construction of pipe fittings must satisfy certain criteria like as follows:

• The material of construction must be compatible with the other materials in the system.

• It must be compatible with the fluids or solids being transported.

• It should withstand fluctuating temperatures inside and outside of the system.

• It should also be compatible with different pressure levels.

• Fire hazards, earthquakes, and other unforeseen factors also influence pipe fitting materials.

• Pipe fitting material specifications and construction are application-dependent.

• For optimization of component selection, user consultation with fitting suppliers is a must.

• The materials of construction should also conform to certain standards like BSP, NPT, ASME, ASTM, DIN, JIS etc.

• Surface finish is equally important. It is to be noted that all pipe fittings should have a proper finish as pipe fittings are constantly in harsh environments. Corrosion resistant property of the materials is an essential requirement.

ASTM International: American Society for Testing and Materials

This is one of the largest voluntary standards development organizations in the world. ASTM standards define the specific manufacturing process of the material and determine the exact chemical composition of pipe fittings, through percentages of the permitted quantities of carbon, magnesium, nickel, etc., and are indicated by "Grade". This is a reputed scientific and technical organization that develops and publishes voluntary standards on the basis of materials, products, systems and services. This is a trusted name for standards. The standards covered by this organization covers various types of pipes, tubes and fittings, especially made of metal, for high-temperature service, ordinary use and special applications like fire protection. The ASTM standards are published in 16 sections consisting of 67 volumes.

UNS: Unified Numbering System

The Unified Numbering System (UNS) for identifying various alloys is also quoted. This is not a specification, but in most cases, it can be cross-referenced to a specific ASTM specification.

Alloy numbering systems vary greatly from one alloy group to the next. To avoid confusion, the UNS for metals and alloys was developed.

The UNS number is not a specification, because it does not refer to the method of manufacturing in which the material is supplied. The UNS indicates the chemical composition of the material. An outline of the organization of UNS designations follows:

Some ASTM materials are compatible with specifications from other countries, such as BS (Britain), AFNOR (France), DIN (Germany), and JIS (Japan). If a specification from one of these other countries either meets or is superior to the ASTM specification, then it is considered a suitable alternative, if the project certifications are met.