Reliability assurance of oil production facilities electric submersible centrifugal pump parts using the metal magnetic memory
Dr. A.A. Dubov
The problem of sudden fatigue failure of electric centrifugal pump system (ESP) parts cannot be solved using conventional non-destructive testing methods (UT, MT, VT and others) since they are aimed at searching for already developed defects, which is insufficient to ensure ESPs reliability during the overhaul operation period.
The main sources of damage to ESP parts (shafts, housings, fishing heads, etc.) are stress concentration zones (SCZs), where corrosion and fatigue processes develop most intensively. Under the impact of vibration and corrosion-fatigue processes due to pumps operation, torques and bending moments due to column assembly and tripping operations, SCZs are formed in ESP parts followed by their subsequent failure. It should be noted that residual stress concentration may also occur on individual new ESP parts in the areas of metallurgical defects location. Thus, for timely identification of ESP parts susceptible to damaging, there is a need for non-destructive testing (ND) methods that have correlation with the metal's structural and mechanical heterogeneity and residual stresses.
The metal magnetic memory (MMM) method, which is becoming more widespread in practice, is an efficient method for SCZs detection in engineering products.
Russian and international standards on the MMM method are available [1, 2, 3]. The MMM method does not require artificial magnetization, parts surface dressing or any other preparatory operations.
All ESP parts in the initial state have thermo-remanent magnetization, naturally formed during their manufacture. Under operating conditions, this magnetization changes and redistributes under the effect of workloads. Due to magnetomechanical effects [4, 5, 6, 7], magnetic anomalies with abrupt local variations of the self-magnetic stray field (SMSF) occur on inspected parts surfaces in SCZs. Recording of anomalies in SMSF distribution along each part's surface using specialized sensors and instruments provides a unique opportunity to identify in the express control mode areas with limiting pre-failure metal hardening.
The Methodical Guidelines (MG) for technical diagnostics of ESP parts using the MMM method were first developed in 2002 by Energodiagnostika Co. Ltd. in cooperation with GREY LLC experts and tested at the repair facilities of OJSC TNK-Nizhnevartovsk. The MG data was approved by OJSC TNK-Nizhnevartovsk and agreed with the Rostekhnadzor Directorate for Oil and Gas Industry Supervision .
Application of the non-destructive testing methodology using the magnetic memory of metal in the repair of ESP parts resulted in sharp decrease of their accident rate at OJSC TNK-Nizhnevartovsk oil production facilities. The facilities mean time between failures during the period from 2002 to 2004 increased by 30% or more.
From 2002 to 2017 quality control of ESP parts using the MMM method has gained widespread at a number of PJSC Rosneft repair and maintenance enterprises during repair and maintenance operations at oil production facilities. Based on the gained experience in inspection of ESP parts at maintenance facilities, in 2017 Energodiagnostika Co. Ltd. developed standard "Guidelines for ESP parts inspection using the MMM method". The guidelines specify quantitative criteria for ESP parts screening, which characterize the limiting pre-failure state of the metal. These guidelines can be applied at any maintenance facilities, taking into account the design features of the ESP parts and their operating conditions.
It should be noted that since 2002, Energodiagnostika Co. Ltd. independent personnel certification body has been conducting on a regular basis training of experts in the MMM method with regard to ESP parts inspection peculiarities. Upon completion of training, certificates in the MMM method with qualifications for Level I or II are issued to certified experts in accordance with Safety Rules PB 03-440-02, which provide admission to experts work in the field of equipment and parts inspection at oil production facilities.
1. ISO 24497-1:2007(E) Non-destructive testing - Metal magnetic memory - Part 1: Vocabulary.
2. ISO 24497-2:2007(E) Non-destructive testing - Metal magnetic memory - Part 2: General requirements.
3. ISO 24497-3:2007(E) Non-destructive testing - Metal magnetic memory - Part 3: Inspection of welded joints.
4. V.T. Vlasov, A.A. Dubov. Physical bases of the metal magnetic memory method. Moscow: ZAO "Tisso", 2004, 424 p.
5. A.A. Dubov, Al.A. Dubov, S.M. Kolokolnikov. Metal magnetic memory method and inspection instruments: Training Handbook. Moscow: "Spektr" Publishing House, 2012. 395 p.
6. V.T. Vlasov, A.A. Dubov. Physical theory of the "strain-failure" process. Part I. Physical criteria of metal's limiting states. Moscow: ZAO "Tisso", 2007. 517 p.
7. A.A. Dubov, S.M. Kolokolnikov, O.A. Chukcheev. Technique for inspection of electric submersible centrifugal pump system end and tubular parts using the metal magnetic memory method // Neftyanoe Hozyaistvo, 2002, No. 12. pp. 23-26.