zheng_Outsourcing_book_temp.qxd 12/11/2009 13:32 Page 99
Corrosion Failures of Components in Electro-hydraulic Control Systems
pressure is so high that seawater ingress is hard to avoid. Earlier, in
Figure 4: The Schiehallion Layout Showing the Floating Platform,
1997, the subsea control modules of the Foinaven oilfield supplied by
Umbilical Connections and Subsea Equipment
ABB Seatec Ltd. failed when they were connected and tested. This field
FPSO
is approximately 180km west of the Shetland Islands and the
Drilling rig
Support vessel
Shuttle tanker
subsea system is located at 464m water depth. The installation
of subsea equipment on Foinaven, including manifold trees and control Anchor chains
modules, commenced in the second quarter of 1995 to meet the Loyal 1x10” Production
scheduled project completion date in the fourth quarter. The necessary
1x8” Production/test
1x8” Water injection
and unplanned recovery of the subsea manifolds delayed the 1x6” Gas lift
completion date and first oil date to November 1997.
West1x10” Production
North 1x10” Water
1x8” Production/test
Flexible risers
injection
1x8” Water injection
Central 1x10” Production
Flowlines
Subsequent investigation found evidence of control module
1x6” Gas lift
1x8” Production/test
Anchor piles
1x8” Water injection
component damage, also primarily within direction control valves, in
Gas disposal 1x8”
1x6” Gas lift
association with fluid degradation consistent with long-term
exposure to seawater.
15
The unusually long-term static presence of
Figure 5: Direction Control Valve
seawater from ingress during the initial installation operation was
identified as the dominating cause of both the inter-granular
corrosion of 440C stainless steel and the biodegradation of the
HW540 hydraulic control fluid.
The DCV components, in particular the pilot-stage valve spindles
and the balls that allowed the flow of hydraulic fluid when it
was displaced from its seat, suffered from loss of material, resulting
in fluid leak paths and in some cases failure of the tip. Individual leak
rates of 35 litres/hour were observed, with a combined maximum
leak rate of 70 litres/hour. properties and control the contamination issue associated with fluid
contamination. The task of delivering seawater-tolerant systems was
Erosion–corrosion is the
further compounded and then led to the success of the Thunder
Horse project.
cumulative damage induced by
the joint action of
The Consequences of a Corrosion Failure in an
Electro-hydraulic System
electrochemical corrosion and
As stated previously, corrosion failure in an E/H system can have
mechanical erosion and is
serious consequences for the operation of an entire subsea oil
controlled by a number of
recovery system. It will not only result in stoppage of production,
which causes huge economic losses, but also induce environmental
basic processes. safety incidents. Leakage of hydraulic fluids and oil from subsea
equipment poses the threat of serious pollution to the sea, which may
A martensitic (SS440C), a cobalt tungsten carbide cermet also cause fire and explosion.
(WC-6%Co) and a precipitation-hardened (SS17-4PH) stainless steel
were also used in the pilot stage of the valve. They all suffer from Conclusion
pitting corrosion in the hydraulic fluid/seawater environment, This article introduced most of the corrosion matters in the offshore oil
especially the WC-6%Co. industry and emphasised specific failures in E/H control systems, which
have caused tremendous problems as described from industry
From 2000, improvements in DCV materials and advances in water- experience. They are identified as one of the main concerns to be
based hydraulic fluid were sought to both improve the anticorrosion addressed when establishing a new oilfield. n
1. Foroulis ZA, Corrosion and corrosion inhibition in the 6. Srdjan N, Key issues related to modelling of internal Corrosion Science, 2002;44(10):2199–2208.
petroleum industry, Materials and Corrosion, 2004;33(3): corrosion of oil and gas pipelines – A review, Corrosion 12. Khalid SE, Al-Malahy, Hodgkiess T, Comparative studies of
121–31. Science, 2007;49(12):4308–38. the seawater corrosion behaviour of a range of materials,
2. Brondel D, Edwards R, Hayman A et al., Corrosion in 7. Totten GE, Hydraulic failure analysis: fluids, components, and Desalination, 2003;158(1–3):35–42.
the oil industry, Oilfield Review, 1994;6(2):4–18. system effects, American Society for Testing & Materials, 13. Malik AE, Siddiqi NA, Andijani IN, Corrosion behavior of
3. Ollivier B, Petroleum Microbiology, ASM Press, 2001;592. some highly alloyed stainless steels in seawater,
2005;378. 8. Henke RW, Cavitation. In: Fontana M, Corrosion Engineering, Desalination, 1994;97(1–3):189–97.
4. Buckley SE, Petroleum Conservation, New York: McGraw-Hill, 1986;105. 14. Malik AU, Mayan Kutty PC, Siddiqi NA, et al., The influence
American Institute of Mining and Metallurgical 9. Sedriks AJ, Corrosion of stainless steels, Wiley, 1996;437. of pH and chloride concentration on the corrosion
Engineers, 1951;304. 10. Kvaerner Oilfield Products and BP Amoco, Schiehallion behaviour of AISI 316L steel in aqueous solutions, Corrosion
5. Ayazi M, Mirfenderski S, Alizadeh Moghadam A, subsea hydraulic control fluid leakage investigation, Science, 1992;33(11):1809–27.
Monavarian M, Study of the corrosion factors in Revision 2, 2000. 15. Fleming R, BP Amoco subsea control system lessons,
offshore oil production units, Petroleum & Coal, 11. Guilminot E, Dalard F, Degrigny C, Mechanism of iron Measurement and Control, 2000;33(7):207–13.
2006;48(2):6–10. corrosion in water-olyethylene glycol (PEG 400) mixtures,
EXPLORATION & PRODUCTION – VOLUME 7 ISSUE 2
99
Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164