API 1111:2021 pdf download

API 1111:2021 pdf download.Design, Construction, Operation, and Maintenance of Offshore Hydrocarbon Pipelines (Limit State Design).
4.2.3 Pressure Ratings for Pipeline Components
4.2.3.1 Components
Valves, flanges, and other components shou4d have pressure ratings that are equal to or exceed the
requirements for the pipeline or flowline. See note in 4.1.2.1
4.2.3.2 Components Without Specific Ratings
Components not manufactured to a standard specification may be qualified for use as specified in ASME 831 A or ASME B31 .8. Nonmetallic trim, packing, seals, and gaskets should be made of materials compatible with the fluid the pipeline and with the offshore environment.
4.2.3.3 Segmentation for Different MOPs
Pipelines that are segmented to operate at different MOPs should have an isolatxm valve (and any associated components) rated to the higher MOP installed at the point of pressure segmentation. The lower MOP segment should be protected from overpressure by high.pressure shutdown devices at the appropriate connected platforms or by a relief system if the segment terminates on shore. Automatic or remote operation of the valve at the point of pressure segmentation should be considered only if reliability of communication and actuating power to the valve is appropriately ensured.
For lines where there is a pressure break topside. a redundant shutdown system consisting of two independent isolation valves with independent pressure shutdown switches should be considered.
4.3 Pressure Design of Components
4.3.1 Internal Pressure (Burst) Design
4.3.1.1 General
The hydrostatic test pressure, the pipeline design pressure, and the incidental overpressure. Anduding both internal and external pressures acting on the pipelines, shall not exceed that determined by the equations (see Figure 2):
4.3.1,4 AxIal Collaps,IBurst Due to Combined Axial CompressIve Load and Internal pressure
Axial compressive load can combine with internal pressure loading to result in material stresses exceeding the yield strength of the pipe, with potential for axial collapse/burst failure due to overload and strain localization. This combination is a particular nsk for deepwater PIP construction by the J4ay or S-lay methods (see 44.1) where the internal and external pipes are not continuously structurally linked. For these PIP installation methods, the inner pipe may be non-tensioned and free standing in the outer pipe during pipe lay. All pipe lay tension loads are carried by the outer pipe. The inner pipe must support its own weight with a resultant compressive stress at touchdown on the seabed Consequently, as the PIP is progressively laid to the seabed. the inner pipe compressive load is permanently captured by contact friction with the outer pipe. At the completion of pipe lay. virtually the entire Inner pipe will have a permanent compressive stress approximately equal to (water depth x inner pipe unit weightlinner pe steel area). In deep water (>1500 m). this stress can be 25% to 50% of the axial compressive yield load.
Combined with the axial stress arising from high operating temperatures, the axial stress may exceed the yield strength of the pipe and an inner pipe weak section may accumulate excessive strains (strain localization) leading to laibire by axial collapse/burst when pipe wall strains exceed material capacity, For further details, refer to OTC 18063 171
4.3.2 External Pressure (Collapse) Design
4.3.2.1 General
During construction and operation, offshore hydrocarbon pipelines may be subject to conditions where the external pressure exceeds the internal pressure. The differential pressure acting on the pipe wall due to hydrostatic head can cause collapse of the pipe The pipe selection should provide a pipe of adequate strength to prevent collapse, taking into consideration the physical property variations, ovality, bending stresses, and external loads. The combined application of Equation (9) Equation (17) in the following sections shall be used in all external pressure design calculations.
4.3.2.2 Collapse Due to External Pressure
The collapse pressure of the pipe shall exceed the net external pressure everywhere along the pipeline as follows.