Title | Corrosion Failure of 4" Pipeline of a Gas Production Well in Egypt Western Desert |
---|---|
Author | Co. SEP |
Pages | 7 |
File Size | 563.5 KB |
File Type | |
Total Views | 18 |
www.me‐journal.org Journal of Metallurgical Engineering (ME) Volume 4, 2015 doi: 10.14355/me.2015.04.008 Corrosion Failure of 4ʺ Pipeline of a Gas Production Well in Egypt Western Desert Z. Abdel Hamid, Ibrahim M...
www.me‐journal.org Journal of Metallurgical Engineering (ME) Volume 4, 2015 doi: 10.14355/me.2015.04.008
Corrosion Failure of 4ʺ Pipeline of a Gas Production Well in Egypt Western Desert Z. Abdel Hamid, Ibrahim M Ghayad, N. Gomaa Central Metallurgical Research & Development Institute (CMRDI), P.O.Box:87 Helwan, Cairo, Egypt [email protected] Abstract A corroded part of a 4 pipe of AG which is a gas producing well came to production since July 2011. It was sent to CMRDI to investigate the failure analysis of the failed pipe. Severe corrosion was observed in the 6 O’clock position inside the pipe. Combined erosion and pitting corrosion occurred on the bottom (6 O clock) of the failed pipe. The Corrosion attack is thought to occur due to associated condensate waterwhich is relatively high (as this case).Water is mostly acidic due to the high concentration of CO2 which dissolves in water forming carbonic acid H2CO3. High corrosive nature of water is also evident from the great amounts of chloride present in the condensate water. It is suggested that proper treatment of the problem can rely on the use of suitable corrosion inhibitor and also increase the efficiency of dewatering process to decrease the amount of water associated with the flowing gas. Keywords Gas Well Pipline;Corrosion;Failure Analysis
I nt roduc t ion Major pipelines across the world transport large quantities of crude oil, natural gas, and petroleum products. These pipelines play an important role in modern societies and are crucial in providing needed fuels for vital functions such as power generation, heating supply, and transportation. In light of the hazardous properties of the products being transmitted through these pipelines, a failed pipeline has the potential to cause serious environmental damage. The risk associated with pipeline in terms of safety of people, damage to the environment and loss of income has been a major concern. Sources of failure include structural problems, corrosion problems, operator error, outside force damage and control problems. There have been a number of studies conducted by researchers on causes of oil pipeline failures in the oil and gas industry [1]. In failures resulting in product loss, leaks constituted 86.8% of failures and ruptures 13.2%. Corrosion is the predominant cause of leaks. According to the findings, the third party damage is the leading cause of line ruptures. Ndifon [2] reviewed the number of internal corrosion failures for multiphase pipelines and discovered that internal corrosion failures increased steadily while the number of external corrosion failures held steady. Moffat and Linden [3] stated that for sour gas pipelines, internal corrosion is the major cause of failure. External corrosion failures have declined, possibly as the result of improved coatings and increased inspection. Of the sour line failures, about 86% were leaks and 14% were ruptures. Natural gas pipeline sections located near to the extraction wells are more susceptible to fail. This fact is due to the high concentration of corrosive agents carried in the gas stream, such as CO2, H2S, calcium and chlorine compounds which promote the deterioration of the steel pipe, mainly due to erosion–corrosion [4‐7]. In addition to the contaminants, the presence of salt water which usually encounters inside the pipeline aggravates the corrosion process. Process variables, such as flow rate, pressure and pipeline design interact to create a synergistic effect of corrosion and erosive wear of the pipe. Corrosion products are first deposited on the internal gas pipeline surface in the form of scales. These products, which are mainly CaCO3 and FeCO3, initially, act as a protective barrier to prevent the corrosion of the steel surface [8‐9]. Once the scales have grown to a certain thickness, they will become highly brittle and easily removed by the mechanical forces of the gas stream in localized zones. Thus, the newly
62
Journal of Metallurgical Engineering (ME) Volume 4, 2015 www.me‐journal.org
exposed areas become highly susceptible to a galvanic corrosion process aggravated by the attraction of chlorine ions into these areas. This develops localized pits due to pitting corrosion until the final failure of the pipe is produced. Se rvic e H ist ory A corroded part of a 4 pipe of AG which is a gas producing well came to production since July 2011. The current production rate of the well is 9.8 MMSCFD/ Water: 31 BBL / Condensate: 103 BBL. The pipe data and gas analysis are shown below:
Material API 5L X52 grade B PSL‐2 Pipe size 4 sch.40 Nominal thickness: 6.019 mm Manufactured by : BAO steel PO‐NO: 19804/AS Heat No.: 327691‐3 Total length 2 Km TABLE 1 ANALYSIS OF CONDENSATE WATER CONDUCTED BY EGYPTIAN PETROLEUM RESEARCH INSTITUTE
Element
N2
Cl
CO2
C2
C3
I-C4
Wt.%
0.402
84.63
3.678
6.774
2.393
0.51
Element
C6+
I-C5
N-C4
N-C5
C6+
Total
Wt.%
0.48
0.653
0.28
0.202
0.48
100
TABLE 2 ANALYSIS OF MINOR ELEMENTS CONDUCTED BY EGYPTIAN PETROLEUM RESEARCH
Element
SG
H2S
C4
C5+
ppm
0.685
4
1.163
0.962
Pe rform e d I nve st iga t ions The following investigations are performed on the heat exchanger tubes:
Visual examination Chemical analysis Mechanical Testing Metallographic examination Corrosion testing
Re sult s a nd Disc ussion Visual Examination No indications of localized corrosion attack were observed at the external surface. In other words, the localized corrosion attack was confined only to the internal surface of pipe. The pipe was found to be severely corroded at 6 O’clock position. The internal surface of the pipe was covered with corrosion products. A longitudinal corrosion grooving was observed at the 6 O’clock position (Fig. 1).
63
www.me‐journal.org Journal of Metallurgical Engineering (ME) Volume 4, 2015
FIG. 1 CLOSE‐UP OPTICAL MICROGRAPH (50X) OF THE INTERNAL SURFACE OF THE PIPE, SHOWINGS SEVER LOCALIZED CORROSION AT 6 O’CLOCK POSITION
The internal surface of the pipe between 3 and 9 O’clock positions was affected by general and localized corrosion (Fig. 2).
FIG. 2 GENERAL CORROSION OBSERVED AT THE 3 AND THE 9 O’CLOCK POSITIONS USING OPTICAL MICROSCOPE (50X)
The pitting was 1.1 mm in depth, which corresponding to 18% reduction of the original wall thickness (Fig. 3).
FIG. 3 OPTICAL MICROGRAPHS (50X) OF CROSS SECTIONS TAKEN FROM 6 O CLOCK POSITION OF PIPE.
64
Journal of Metallurgical Engineering (ME) Volume 4, 2015 www.me‐journal.org
Chemical Analysis The chemical analysis of the pipe samples was performed using the Spectro‐lab (optical emission spectrometer) device to determine the main elements of manufactured material. Table 3 shows the results of chemical analysis conducted by CMRDI and compared with the required specifications. Table 3 shows that the chemical composition is confirmed with API 5L grade X‐60‐PSL2 as mentioned by the client. The chemical composition confirmed with API 5L grade X‐52 PSL2 TABLE 3 CHEMICAL COMPOSITION OF PIPE ON COMPARISON WITH STANDARD
Element, wt%
C
Mn
P
S
CMRDI
0.133
1.29
0.017
0.003
Standard (max.)
0.24
1.4
0.025
0.015
CMRDI
Si
V
Nb
Fe
Standard (max.)
0.27
0.063
0.035
Bal.
Mechanical Testing The received pipe was cut and processed for tensile and hardness tests. The tensile strength test was carried out using a Universal Testing Machine (UTM). Hardness test was carried out using a Vickers Hardness Machine (Hv). The results of tensile and hardness tests are shown in Table 4 in comparison with the standard specifications. The data reveals that the measured values are confirmed with API grade 5L X‐52‐PSL2. The mechanical test results are confirmed with API grade 5L X‐50‐PSL2. TABLE 4 MECHANICAL TEST OF TUBE MATERIAL
Sample
Yield strength (N/mm2) Ultimate strength (N/mm2)
Elongation (%)
Hardness (Hv)
CMRDI
377
552
27.2
198
Standard (min)
360 ‐ 530
490 – 760
‐‐‐‐
196
Metallographic Examination 1) Microstructure Investigation The microstructure investigation was carried out for the pipe within the corroded area, and revealed a structure which consists of ferritic‐pearlitic structure, as shown in Fig.4 {ferritic matrix (white area) and some pearlite (black area)}.There were no metallurgical defects which could result in corroded area.
FIG.4MICROSTRUCTURE OF THE PIPE WITHIN THE CORRODED AREA
2) Scanning Electron Microscopy / Energy Dispersive Spectroscopy Examination A specimen from the received pipe was cut, processed and the localized corrosion attack on the inner surface was examined using scanning electron microscope (SEM) (Fig.5).Corrosion products were distinguished from
65
www.me‐journal.org Journal of Metallurgical Engineering (ME) Volume 4, 2015
the metal surface inside the pit. The EDS spectra are shown in Fig. 6. No corrosion products were obtained on the metal surface (Fig. 6a). EDS spectra inside the pit (Fig. 6b) shows the presence of oxygen and chlorine peaks inside the pits indicate the formation of iron oxide and iron chloride as corrosion products.
FIG. 5SCANNING ELECTRON MICROSCOPE (SEM) PHOTOGRAPH SHOWING THE LOCALIZED CORROSION ATTACK ON THE INNER SURFACE OF THE FAILED PIPE
FIG. 6A EDS ANALYSIS ON THE SUBSTRATE SURFACE FIG.6B EDS SPECTRUM OF THE DEPOSIT INSIDE PIT
Corrosion T e st ing a nd M e c ha nism A specimen from the pipeline was subjected to electrochemical corrosion testing in 0.8% sodium chloride solution (simulating water associates the gas flowing in the pipe) using computerized potentiostat (see Fig. 7). The test gives important information about the susceptibility of material towards pitting corrosion attack. Current increases rapidly with increasing potential until it reaches a steady value of 13 mA/cm2. The high currents (0.13 A cm‐2) shown by the curve indicates high susceptibility of the pipe material towards corrosion in general and pitting corrosion in particular.
FIG. 7 POTENTIODYNAMIC POLARIZATION CURVE OF THE PIPE MATERIAL IN 0.8% NACL. CURRENT MEASURED IN AMPERE (A) WHILE POTENTIAL MEASURED IN VOLT (V)
66
Journal of Metallurgical Engineering (ME) Volume 4, 2015 www.me‐journal.org
Combined erosion and pitting corrosion occurred at the bottom (6 O clock) of the failed pipe. Erosion corrosion reaults from the disruption of protective passive films by erosive or abrasive processes. Once the protective or passive film is removed in an aqueouselectrolyte, the electrochemical processes for pitting corrosion will take place. The initiation of a pit occurs when electrochemical or chemical breakdown exposes a small local site on a metal surface to damaging species such as chloride ions. The sites where pits initiate include; scratches, surface compositional heterogeneities (inclusions), or places where environmental variations exist. In the present case, the sites of pit initiation are likely due to scratches formed by solid particles (sand) contained in the water associates the gas flow in the pipe. In addition, the very high concentration of chloride ions enables them to penetrate the metal surface layer and initiate pitting corrosion by themselves. Another factor intensifies pitting corrosion attack is the high CO2 content. CO2 increases the acidity of the water inside the pipe and thus facilitates and increases pitting attack. The pit grows if the high current density (the area of breakdown initiation is exceedingly small) involved in the repassivation process does not prevent the formation of a large local concentration of metal ions produced by dissolution at the point of initiation. If the rate of repassivation is not sufficient to choke off the pit growth, two new conditions will be developed. First, the metal ions produced by the breakdown process are precipitated as solid corrosion products (such as the Fe(OH)2 which usually cover the mouth of the pit. This covering traps the solution in the pit and allows the buildup of positive hydrogen ions through a hydrolysis reaction. Then, chloride or other damaging negative ions diffuse into the pit to maintain charge neutrality. Consequently, the repassivation becomes considerably difficult because the solution in the pit is highly acidic, containing a large concentration of damaging ions and metallic ions, and a low oxygen concentration. Thereby the rate of pit growth accelerates [6]. The pit is the anode of an electrochemical corrosion cell, and the cathode of the cell is the non‐pitted surface. Since the surface area of the pit is a very small fraction of the cathodic surface area, all of the anodic corrosion current flows to the extremely small surface area of the breakdown initiation site. Thus, the anodic current density becomes very high, and penetration of a metal structure bearing only a few pits can be rapid. Ex pe c t e d Ca use s of Corrosion At t a c k Associated Condensate Water Corrosion naturally occurs in pipelines wherever water wets the pipeline wall. If the amount of water is relatively high (as this case), the pipe can corrode at almost any location subjected to water replenishment. Corrosive Nature of Water Water is mostly acidic due to the high concentration of CO2 which dissolves in water forming carbonic acid H2CO3. High corrosive nature of water is also evident from the great amounts of chloride present in the condensate water. Flow Pattern The flow pattern in the pipeline is transitional in nature and gives a chance to stratification of the liquid phases. Since the water cut is about 30% (may be more or less), water will wet the pipeline even in the transition flow conditions. At low lying areas (Pipeline Crossings) where the chances of condensate water accumulations are greater, aggressive localize corrosion is expected in these stagnant areas. Conc lusion a nd Re c om m e nda t ion
Mechanical and chemical analysis is in conformity with the specifications. The pipeline failed as a result of localized pitting corrosion initiated from the internal surface in the 6 O clock position. The most significant parameters contributing to the failure by localized corrosion are the associated condensate water. The localized corrosion is influenced by some variables such as acidity, operation, water wetting, scheme depths and bacterial effect. The influences of these parameters are closely linked with each other; and the
67
www.me‐journal.org Journal of Metallurgical Engineering (ME) Volume 4, 2015
mechanism of separate action of each is shown in details in item No. 6 of this report. Dewatering treatment unit should be transferred to the well site or at least a new treatment unit should be installed in a point before gas flow in the pipeline. Biocides: Addition can be helpful for fighting bacterial corrosion. Reference to a specialist in this respect is helpful, provided that the above recommended actions were implemented. Corrosion inhibitor must be injected on the gas flow line with rapid film forming.
REFEREN CES
[1]
C.H. Achebe, U.C. Nneke, and O.E. Anisiji, Analysis of Oil Pipeline Failures in the Oil and Gas Industries in the Niger Delta Area of Nigeria, Proceedings of the International MultiConference of Engineers and Computer Scientists 2012 Vol II, IMEC 2012, March 14‐16, 2012, Hong Kong.
[2]
W.O. Ndifon, (1998); Health impact of a major oil spill: Case study of Mobil oil spill in AkwaIbom State, 9th International Conference on the Petroleum Industry and the Nigerian Environment, Abuja, pp.804 ‐ 815.
[3]
D Moffat and O. Linden, (1995); Perception and reality: Assessing priorities for sustainable development in the Niger Delta, AMBIO: Journal of Human Environment, Vol. 24, and Nos. 7‐8, pp.527‐538.
[4]
M.A.L. Hernandez‐Rodrıguez, D. Martınez‐Delgado, R. Gonzalez, A. Perez Unzueta, R.D. Mercado‐Solıs, J. Rodrıguez, Casestudy:Corrosive wear failure analysis in a natural gas pipeline, Wear 263 (2007) 567–571.
[5]
J.R. Shadley, S.A. Shirazi, E. Dayalan, M. Ismail, E.F. Rybicki, Erosion–corrosion of a carbon steel elbowin a carbon dioxide environment, Corrosion 52 (9) (1996).
[6]
Uhlig s Corrosion Handbook (2011), 3rd Edition, R. Winston Revie (Editor) ISBN: 978‐0‐470‐08032‐0.
[7]
E.S. Venkatesh, Erosion damage in oil and gas wells, in: Proceeding of Rocky Mountain Meeting of SPE, Billings, MT, May, 1986.
[8]
L.E. Newton, R.H. Hausler (Eds.), CO2 Corrosion in oil and Gas Production, NACE, 1984 (selected papers, abstracts and references).
[9]
68
C.A. Palacios, J.R. Shadley, CO2 Corrosion of N‐80 steel at 71◦C in a two‐phase flow system, Corrosion 49 (8) (1993).
...