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Thicker or controlled geometry pipe sections to improve strain capacity of pipelines

IP.com Disclosure Number: IPCOM000200916D
Publication Date: 2010-Oct-29
Document File: 2 page(s) / 164K

Publishing Venue

The IP.com Prior Art Database

Abstract

Techniques aimed at improving strain capacity of pipelines through controlled geometry of pipe sections are discussed

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Thicker or controlled geometry pipe sections to improve strain capacity of pipelines

Technical Memorandum,  18 June 2010                                                

One factor which is of great importance to achieving high strain capacity is obtaining good alignment between pipe sections.  When there is poor alignment between pipes at the girth weld, tensile strain capacity can be reduced by the lower effective pipe thickness which promotes plastic collapse. Additionally, such misalignment produces local bending and shear stress which increase the driving force for fracture at flaws which may be present, accelerating ductile flaw growth or promoting cleavage fracture. Misalignment also promotes buckling at the weld joint. The region where the greatest misalignment will be experienced is at tie-in locations, where one pipe will be sectioned in the middle (where geometry control is poor) and where the use of an internal alignment clamp is impractical (because it cannot be easily removed after welding).

Description of techniques

There are multiple techniques available to reduce misalignment, including placing tighter controls on purchased pipe, sorting pipe before welding, using high strength clamps to deform the pipes and force them into alignment during welding, or by using weld overlays in the region of misalignment. However, all of these techniques still leave the potential for significant pipe misalignment and introduce a need for additional QA/QC measures during pipe purchase or construction. The use a thicker or controlled geometry section on one side of the tie-in (the one which is cut to length) increases the remaining ligament in the region of the flaw (thus delaying plastic collapse and reducing the bending moment at the weld) and reduces local bending and shear stresses. This can be accomplished by:

1.        Using a single joint of thicker pipe or controlled geo...