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5.2 Classification of Materials

* Materials are characterised based on several parameters including type,

strength, fracture control, corrosion resistance, chemistry,

microstructure, weldability, etc. The following are the different types of

materials used for offshore structural and production applications.

* 1. Structural steel: These are carbon and low alloy steels used for

structures and pipelines.

* 2. Production equipment steel: These are carbon, low alloy and alloy

steels used for tubulars, pipes, fittings and production/process

equipment.

* 3. Corrosion resistance alloys: These materials are used for production

and process equipment that are subjected to corrosive environments

containing CO2 and H2S. They involve stainless steels, nickel base alloys,

cobalt base alloys, nickel-kopper alloys and titanium alloys.

* 4. Non-metals: These involve elastomers, coatings, plastics and

composites.

5.2.1 Structural Steel

* Structural steels are generally specified based on the appropriate

national or industry standards such as ASTM, API, BSI, ISO, etc. In most

cases, standards provide mainly the basic requirements such as limits

on chemical composition and tensile properties.

* During the mid-1960s several in-service and structural fabrication

problems were encountered illustrating that the common pipes such as

API 5L B and structural steels such as ASTM A7 and ASTM A36 do not

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