The present work proposes to evaluate the actual roughness impact of machined pipe body outer surfaces on fatigue performance. For this aim, a testing program has been defined comparing the fatigue performance of machined surfaces on high-strength steel pipes. Eight full scale fatigue tests have been performed with two different outer surface roughness targets. No appreciable difference in fatigue behavior has been observed between the different targeted surface statuses, showing that machined surfaces on these high grade steels results to be suitable for fatigue applications even with higher roughness values.
The possibility to manufacture heavy and ultra-heavy wall seamless pipes opens new perspectives to machine pipe body outer surfaces for the production of rigid riser's connections (i.e. upsets, flanges, connections, J-lay collars …). This option allows to avoid costly forged pieces and allows to guaranty a better manufacturing quality. From this perspective, a question to be faced is the definition of the OD manufacture quality requirement, which directly impacts the pipe manufacture productivity and, consequently, the product cost. On the other hand, among the products that could be subjected to surface machining there are pipes destined to fatigue loading during service. As a consequence, concerns arise about the fatigue resistance of machined pipes. In this framework, the present paper proposes to evaluate the actual roughness impact of machined pipe body outer surfaces on fatigue performance. For this aim, a testing program has been defined comparing the fatigue performance of machined surfaces on steel pipes of grade Q125 and TN125 (the TN125 is similar to Q125 grade with a different chemistry). Eight full scale fatigue tests have been performed. Seven pipes have been machined with two different providers and one pipe was tested as manufacture (grade TN125). The first provider manufactured specimens using pipe on steel grade Q125 and the second one using pipe on steel grade TN125.
