Det Norske Veritas - Germanischer Lloyd

FRACTURE CONTROL FOR PIPELINE INSTALLATIONS METHODS INTRODUCING CYCLIC PLASTIC STRAIN
 N DNV-RP-F108

Annotation

Scope and application

This Recommended Practice considers plastic straining during the installation phase.

The plastic straining shall be limited to typical reeling situations (around 3% nominal strain)

In addition to installation, the commissioning and operation phases must be considered in order to assure safe operation during the whole life of the pipeline.

Although some advice is given in the Recommended Practice, more specific requirements are given in e.g. DNV-OS-F101 [1].

The Recommended Practice describes:

— tests for characterisation of the materials fracture resistance

— Engineering Critical Assessment (ECA) procedures for determination of acceptable flaw sizes in girth welds

— a test program for validation of the assessment procedure.

The Recommended Practice assumes that the weld strength (combined effect of tensile properties and geometry of both the weld and HAZ) over-matches or even-matches the parent pipe.

If the strength of the weld under-matches that of the parent pipe, the advice and recommendations of this Recommended Practice may not be sufficient and specialist advice is recommended.

Guidance note 1:

This Recommended Practice is mainly based on experience from tests and finite element analyses as well as practical installation experience from modern linepipe steels of type API 5L X52 to X65 welded by modern, well proven, welding methods giving ductile weldments. Pipe dimensions have typically been 6 to 16 inch OD and wall thickness of 15 to 25 mm. The methodology is also considered to be applicable for X70, 13Cr Martensitic Steels and 22Cr / 25Cr Duplex Stainless Steels provided ductile weldments are documented.