Pipe selection and wall thickness for Oil & Gas Industry
The type of pipe and wall thickness must be determined for each application. Following the design requirements, the pipe materials and wall thickness can be determined using the applicable formula.
the wall thickness will be determined by:
- The operating pressure (maximum and normal)
- Operating temperature
- Other design factors (depending upon the type of pipeline and applicable regulation)
- The pipe material
Steel pipe will be required in the majority of the oil and gas production and pipeline applications
ANSE/ASME A53 and A106 and API 5L seamless, ERW, and submerged arc-welded (SAW) steel pipe are commercially available and most commonly used in pipeline systems. Seamless pipe is seldom used in pipeline applications because of the higher unit cost and limited availability, From a design and regulatory perspective, pipe made with ERWs and SAW seams is equivalent to seamless pipe and is less costly
Typically, for high-pressure pipelines, higher-grade pipe (such as API 5L, Grades X42, X52, X60, and X65) is selected because much-thinner-wall pipe can be used, which significantly reduces pipe costs.
Construction-costs savings also are realized, as the welding time is reduced and material shipping/handling costs are reduced.
Pipe fittings, flanges, and valves must meet the specification and pressure class of the pipe selected for pipeline applications. The materials for pipelines commonly conform to industry codes and standards including:
ANSI/ASME Standard B16.5
ANSI/ASME Standard B16.9
ANSI/ASME Standard B31.4
ANSI/ASME Standard A105
ANSI/ASME Standard A106
ANSI/ASTM Standard A234
ANSI/ASTM Standard A420
ANSI/ASTM Standard A694
API Standard 6D
API Standard 6H
MSS Spec. 44
MSS Spec. 75
Pipe fittings can be matched to the higher grade API 5L, X Grade pipe. Detailed material information is discussed on the page on on ratings for valves, fittings and flange pressures.
Welding and pipe joining
The methods used to connect the joints or pipe segments are very important and are critical to the pipeline design. ANSI/ASME Standards B31.3, B31.4, and B31.8, as well as the DOT regulations, specify welding and joining methods for pipe. Each type of pipe material has joining or coupling methods designed to ensure that the joint is as strong as, or stronger than, pipe joint. the majority of the hydrocarbon pipeline applications require steel pipe.
For the majority of steel pipeline applications, welding is the preferred method of joining the pipe.
API Standard 1104 and ASME of the boiler and pressure vessel codes specify the requirements for the welding of steel pipe. Manual and automatic welding processes are used on pipelines both onshore and offshore. Shielded metal-arc welding (SMAW), or “stick” welding, is the most common manual process used on carbon-steel pipelines, but the development and use of higher-grade carbon-steel pipe (e.g., API 5L X65 and X70) have required the development of welding processes and metallurgy compatible with the high-carbon alloys. Stainless steels and other alloys may require special welding processes.
The WPS must be physically proved by actually welding a test “nipple” and conducting destructive testing in accordance with the API and/or ASME requirements. Once the specification is proven, a procedure qualification record (PQR) is recorded verifying the WPS. Welders must be qualified to perform the welds in accordance with either API Standard 1104 or ASME Each welder will perform a test weld using the WPS for the pipe and will qualify under the procedure. API Standard 1104, ASME Sec. IX