THE EVALUATION OF THE OILFIELD EQUIPMENT`S CAPABILITY BY TECHNICAL INSPECTION, USING THE DYNAMIC ANALYSIS

The dynamic loads, often occurring in the case of drilling rigs, lead to the most dangerous stress for these equipments, involving their life time reducing and, also, their premature wear. In order to evaluate and reduce the damage risks of the drilling rigs, taking into account the real dynamic loads is strongly recommended. The technical expertises point out the equipment’s damages that occur during their functioning. The authors make obvious that the methods used until now can show only partially the really behaviour of the drilling rigs. Using the dynamic analysis during technical inspections, their real life time, load-bearing capacity and reinforcement measures can be established, in order to increase the analyzed equipments` capability and durability. 1. GENERAL CONSIDERATIONS A metallic structure (mast, metallic derrick) is a slender metallic construction, made of straight bars (rolled shapes) with welded ends, which has many issues regarding its stability not yet solved. These issues relate to the study in terms of dynamic stability and are consistent with recent research showing that only study in terms of static stability behaviour is not enough. Thus, studying the stability of metallic structures submitted to dynamic loads, as the masts or metallic derricks from oilfield industry are, should also include the dynamic stability problems. The studies made in this paper are the result of current trends manifested in the construction of oilfield equipment: technical expertise, extending oilfield equipment’s life and upgrades (increasing the technical characteristics) of the existing oilfield equipment, wherever is possible. The specific dynamic loads of the drilling/intervention rigs (both on-shore and off-shore) produce the most dangerous stress and lead to their premature wear, reducing their life time. In order to decrease the failure risk assessment of these resistance structures is imperative to take into account the real dynamic loads. Hence, is necessary to develop a general algorithm for dynamic analysis, by dynamic calculus, using the finite element method which results can be applied in real time during the technical expertise, and verified by experimental measurements with modern devices, on the real structures. Technical expertise is insistently required by beneficiaries, because many drilling rigs have accumulated a long service time, showing many structural damages. In the present, many of the technical expertise have made only visual findings or non-destructive measurements on the wall thickness and on the metallic elements` wear (ultrasonic methods and penetrating liquids/magnetic particles measurements). Thus, a performant dynamic algorithm, supplemented by direct measurements in real time, in the frequency domain, is a rigorous, fast and efficient method for detecting any structural defects. On this basis, during the technical expertise, the remaining life time and the actual load-bearing (load-carrying) capacity can be determined. Also, measures to enhance the examined structure’s capacity and durability can be immediately taken. ANNALS of the ORADEA UNIVERSITY. Fascicle of Management and Technological Engineering, Volume IX (XIX), 2010, NR3