01162 Erosion-corrosion Failures in Chemical Plant Steam Condensate Piping Systems (51300-01162-Sg)

EROSION-CORROSION FAILURES IN CHEMICAL PLANT STEAM CONDENSATE PIPING SYSTEMS

A. Kh. Bairamov, Mohammed Al-Sonidah SABIC Technology Center, Jubail,

P.O. Box 11425, AI-Jubai131961, Saudi Arabia

Ali A. AI-Beed Saudi Petrochemical Company (Sadaf)

P.O. Box 10025, AI-Jubai131961, Saudi Arabia

ABSTRACT

Carbon steel piping systems in several plants have failed under different applications, due to erosion-corrosion. This paper presents a variety of case histories where single-phase and two-phase steam flows, caused erosion-corrosion damage mainly at turn points of elbows and heat exchanger tubes. It was observed that the presence, even of a small amount, of the vapor phase can significantly increase the velocity of the condensate. The results of metallographic, SEM, elemental (EDX), X-ray Photon Spectroscopy (XPS) and Fourier Transform Infrared Spectroscopy (FTIR) analyses and corrosion rate calculated for each case are presented. The main causes of the failures are discussed and recommendations are provided to avoid similar problems in the future.

Keywords: Steam condensate, piping system, erosion-corrosion, air cooler tubes, elbows, impingement, carbonic acid, thermal conductivity.

INTRODUCTION

A typical modem chemical plant has a wide network of steam and condensate piping systems that include equipment and items such as steam condensate air coolers, pipes, bends, different elbows, pumps, valves, etc. Usually, pure steam is not aggressive from a corrosion point of view. However, if its condensates are contaminated by CO2 and dissolved oxygen it becomes rather corrosive [1-6]. When steam condenses, liquid formation results and the system becomes actually a two-phase (vapor-liquid) system. Normally, the wetter the steam (i.e., the greater the amount of condensation), the more corrosive it becomes. It is well known that the steam is acidic because of the decomposition of bicarbonates resulting in carbonic acid formation. At elevated temperatures and pressures pH of water also falls to 6.0 [4]. Naturally, temperature and oxygen content are the factors that will most aggravate the corrosion reactions.

It has been established [7] that an increase of temperature up to 180°C results in more than four fold increase of the corrosion rate of carbon steel in neutral solutions. Acidic conditions make the steel

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surface extremely susceptible to local attack at such high temperatures. Oxygen even at very small concentration as low as 50 ppb will significantly increase the corrosion rate at elevated temperatures [8].

Pitting corrosion occurs in pure water at 100-150°C in the presence of even 1 ppm of oxygen [9]. Steam generally passes through piping system at very high velocities because of economic reasons. The flow velocity is another major accelerating factor in a steam condensate system. It is well known that in a steam condensate system the most common type of damage is erosion-corrosion [2-5, 10-13]. This usually occurs when protective surface films or adherent corrosion products are mechanically removed by flowing liquid environment. The mode of damage is generally characterized by patterns such as grooves, waves, rounded holes, valleys and horseshoe-shaped depressions [2, 10, 12-17]. All these forms of damage exhibit strong directional pattern consistent with liquid flow and normally contain smooth- bottomed recesses.

Impingement corrosion is known as a severe form of liquid erosion-corrosion, which usually occurs when corrodent or solid particles bombard (impinge) the metallic surface at an angle (worst case at approximately 90°). Such damages occur frequently in elbows or turns of tubes or pipes, impellers of turbines, etc. In particular, high-velocity wet steam can cause some specific forms of impingement corrosion depicted as steam erosion with rounded surface and showing a large number of small cones [13].

In wet steam (two-phase), erosion-corrosion is similar in appearance to that which occurs in the liquid phase. However, the mechanism is complex and it involves the electrochemical corrosion process (anodic and cathodic reactions), the convective mass transport and mechanical wear effects of abrasion, droplet impingement, and/or solid particle erosion. Generally, erosion-corrosion and its prevention in steam and steam condensate systems are one of the current major problems of process industries [1-6, 12-161.

The results of failures of steam condensate carbon steel piping equipment are presented in this paper.

CASE h Failure of Steam Condensate Air Cooler Tubes

The low pressure steam condensate horizontal air cooler (fin fan cooler) experienced leakage of the heat exchanger tubes mainly at the lower (bottom) row at tube sheet after being in service for about 11 years.

Background Information: The steam temperature at the inlet was about 148°C and at the outlet was about 110°C with an operating pressure of 0.35 MPa. Heat exchanger tubes with OD of 25.4mm, wall thickness of 2.8mm and length of 10.0 meter were combined in four tube bundles, each of which contained 108 tubes (3 rows with 36 tubes in each). The material was low carbon steel ASTM A-179, containing (in wt.%) 0.06-0.18 C; 0.27-0.63 Mn; max 0.035% P and max 0.035 S.

Examinations and Analysis: Visual observation showed that local damages up to complete perforation occurred only at the portion of tube end inserted into the tube sheet opposite the steam condensate flow direction. Gradual thinning of the tube walls was also observed. Optical microscopy analysis revealed very smooth, nonuniform asymmetrical, wave-like product on the surface at the flow side (Figure la and b). No microstructural changes or cracks were observed at the damaged areas.


Scanning electron microscopy analysis clearly showed that the failed surface had become tooth shaped with a semi-circular step-like morphology and several shallow pits located mainly at the very top surface of the ratchets (Figure 2). Damages were very well aligned with flow direction. The corrosion attack was in the shape of horseshoe depressions.

Elemental analysis (from EDX spectrum) revealed the presence of Na (1.8%), Si (1.9%), AI 1.7%), Zn (1.1%), C (0.2%) and Ca (0.2%) along with high contents of oxygen (33%) and Fe (56%) (Figure 3) in the surface layer of most damaged area (all contents are given in weight percents).

All surfaces at the thinned area were covered with thin, uniform and blackish adherent layer which consisted mainly of iron oxide of stoichiometry Fe304. This was confirmed by FTIR analysis, which clearly revealed a peak at 572 cm- t assigned to Fe304 [18].

Discussion: It is clear that condensation of steam occurs more in the bottom rows of tubes where the temperature of the cooling air is lower compared to the upper rows. Possibly, there was a mixture of liquid phase with some amount of steam in vapor phase. At the given conditions, the system in the outlet area is in the saturated state. According to our calculation, by using the steam density data [19] if all flow (30 T/h or 8.34 Kg/s) was in a liquid phase, its velocity was only 0.81 m/sec, which is relatively low. However, it is supposed that if only a few percent of this flow was in vapor phase, the velocity would significantly increase and consequently increase the tendency towards liquid erosion-corrosion. The observed shape and character of attack indicate that some liquid impinging (erosion-corrosion) actions took place at the area inserted into the tube sheet.

However, the type of damage found at the portion located 16-18 cm away from the tube sheet was completely different. In particular, only severe gradual thinning occurred at the bottom half of the tube where the system was in liquid phase due to relatively higher condensation. Character of damages were typical for carbonic acid because it is well known that when the steam condenses, carbon dioxide (CO2) dissolves in the condensate and forms carbonic acid (H2CO3) lowering pH of the system [3-6, 20]. Although this is a weak acid, at elevated temperatures it accelerates the corrosion rate of carbon steel more than one thousand times [20].

It is well known that 300-series SS and harder carbon steel (containing more than 0.3% C) are more resistant to flowing wet steam [2-5, 19]. It is interesting to note that alloying with elements such as Cr, Cu, Mo can significantly (more than 10 times) improve erosion-corrosion resistance of carbon steel [2-5,9,10]. Field experience shows that 1.25% Cr-0.5% Mo or2.25% Cr - l%Mo steels are virtually immune to erosion-corrosion [9,10].

Unfortunately, it is well known that increase in carbon content or alloying with Cr, Ni and Mo significantly decreases thermal conductivity [21, 22]. For example, increase in carboncontent from 0.08% to 0.23% leads to a decrease in thermal conductivity by at least 10% at 200°C. Thermal conductivity of 300-series SS is 3 times less than that of carbon steel [21]. Alloy SA 387 Gr22 (2.25% Cr-l% Mo) has a thermal conductivity 34-35% less than that of carbon steel [22]. Therefore, the use of a little higher carbon content steel is reasonable from an energy-loss viewpoint. However, use of materials with a higher alloying content will lead to loss of heat exchange properties, or will need an increase in the number of tubes and some redesign work.

Another method to protect tube end from liquid erosion-corrosion is to use non-metallic (Nylon, PTFE, ceramics) or erosion-corrosion resistant metallic ferrules with a minimum length of 13mm [10].


Use of different types of ferrules depends on temperature, degree of damage and galvanic effect. In the case of severe damages, metallic ferrules can also be used for mechanical support of failed tubes.

Conclusion: The results of all examinations and evidences obtained make it possible to conclude that the exchanger tubes underwent liquid erosion-corrosion (portion located inside the tube sheet) attributable to impingement of steam condensate at the surface opposite to the flow direction. However, at an area away from this portion only gradual thinning occurred due to the combined action of the liquid flow and the presence of carbonic acid.

The presence of some residual stresses during fabrication may also have aggravated impingement phenomenon in the portion located inside the tube sheet.

Recommendations: Consider the use of standard Teflon or stainless steel type ferrules to protect the tube ends from impingement and carbonic acid attacks.

CASE II: Failure of Condensate Air Cooler

Leaking of the other condensate air cooler heat exchanger tubes was found after being in service for about 13 years.

Background Information: Tubes with OD of 25.4 mm and wall thickness of 2.8 mm leaked mainly at inlet pass (top row). Inlet temperature of condensate was 110°C and outlet temperature was about 56°C with a pressure of 0.883 MPa and flow of 69.5 T/h or 19.3 kg/s. The tubes were made of carbon steel SA 214 with the chemical composition (wt.%): 0.18 C; 0.27-0.63 Mn; 0.035 P, and 0.035 Si.

Examinations and results: Tubes failed mainly at the inlet portion inserted into the tube sheet due to the formation of holes with diameter of 4-5 mm (Figure 4). Knife-type damage was found along the whole diameter of tube, at the boundary between tube sheet, and tube surfaces (Figure 4). It is interesting to note that round perforations were observed at the areas opposite to the condensate flow; while on the other areas opposite to the failed surface no damage was observed. Optical microscopy showed that smooth wave-like line attack occurred at the inner surface (Figure 5).

Surface analysis revealed the presence of uniformly distributed shallow dimples (craters) with spherical bottoms (Figure 6 a). Preferential attack of pearlite within the grains was found under higher magnification (Figure 6 b).

XPS analysis of the inner surface layer at the failed portion showed the presence of peaks ofFe, O and C (Figure 7a). Peaks of C1, Si and S were also detected (Figure 7b) which were originated from the corrosion medium. Iron oxide was mainly in the form of Fe203 with binding energy of 711 eV [23].

Discussion: Calculations showed that the average corrosion rate was approximately 0.215mm/year or 8.4 mpy, which is an acceptable corrosion rate.

The ductile dimple characteristic of the surface is typical for erosion-corrosion [9, 24, 25]. The observed shape and character of damage, and its location indicate that some liquid impinging took place. Most likely the top portion of the inlet tubes underwent the liquid erosion-corrosion [2-7, 12-17] attributable to impingement of steam condensate. In this area the system is totally in liquid phase. However, practically, a small amount of vapor may also be present and cause an increase in the flow velocity in this particular area. Rough calculation showed that overall flow rate of the liquid is about 1.4


m/s. However, as was mentioned in the case I, the presence of a few percent vapor phase would be expected to increase significantly the flow velocity and promote the occurrence of local erosion.

The same limitations regarding the use of harder steels and tubes with higher alloying contents, as discussed in Case I, are also quite applicable in this case.

Conclusion: According to the examination results and the evidence obtained, the analyzed tubes ends failed due to liquid erosion-corrosion caused by impingement of steam condensate at the portion located inside the tube sheet.

Recommendation: Consider the use of standard metallic or non-metallic ferrules to protect the tube end. Taking into consideration severe damage of the tubes, it is reasonable to use stainless steel ferrules to enhance mechanical integrity of tubes.

CASE III: Failure of Steam Condensate Line Elbow

The steam condensate line experienced frequent failure at elbows being in service for only about 2 years.

Background information: A carbon steel elbow with 165ram OD and wall thickness of 8 mm was used to transport steam condensate at 160°C and a pressure of 0.5 Mpa, with steam flow of 68.76 T/h or 18.1 kg/s.

Examinations and Analysis: Severe gradual thinning up to complete perforation was observed mainly at the bend's larger radius area (Figure 8, taken from [26]) and initiated from the inner surface. No pitting, crevices or cracks were found. The type of damage was characterized by a typical horseshoe- shaped groove mark [2, 10, 12] developed up to a hole.

Discussion: Calculated erosion-corrosion rate was 4 mm/y or 158 mpy, which is an extremelyhigh corrosion rate for carbon steel in neutral environment. Handled steam flow is totally pure steam in vapor phase (superheated vapor at the given condition) with very high velocity. However, if this flow is totally in liquid phase, the calculated velocity is only 1.05 m/s. For the given conditions, the dew point is 152°C ,which is close to the operating temperature (160°C), and most likely, practically some

insignificant local (due to turbulence) condensation occurs in the bend area resulting in the formation of the very small water particles. It is clear that the presence of water droplets flowing at such high velocity will impinge the metallic surface and consequently cause local erosion-corrosion. Thus, the shape of the damage and the evidence clearly indicate that the localized thinning was caused by liquid erosion- corrosion phenomenon [26].

Conclusion: Observed thinning of the carbon steel steam condensate line elbow was caused by liquid erosion-corrosion.

Recommendation: The use of 45 ° carbon steel elbows ore replacement in similar stainless steel elbows was recommended.


CASE IV: Failure of Welded Carbon Steel Elbow

A socket welded carbon steel elbow through which dilution (purge) steam passed to the furnace outlet valve failed after being in service for only 2.5 years.

Background information: The pipe with OD of 27 mm and wall thickness of 5.4 mm were inserted into the socket elbow with length of 20 mm from the outlet side and 22.5 mm from the inlet side (Figure 9). The elbow thickness was 13 mm. Operating temperature of steam was approximately 180°C at a pressure of 0.4 MPa and a flow rate of 90 kg/h. Material of the elbow and pipe was carbon steel A 105 with chemical composition (wt. %): 0.35 C; 1.05-0.6 Mn; 0.04 P; 0.05 S and 0.35 Si.

Examinations and Analysis: Observation of the longitudinally cut assembly showed that approximately 15 mm of the outlet tube end inserted into the elbow in the upper side, was completely gone (Figure 10 a and 11). In the upper portion, at the curved position of the elbow, a gradual thinning of the elbow on depth of 5 mm (from right to the left) was also observed. Most severe failure occurred in the area at the connection of the outlet pipe with the elbow. Here, the clearance width between the edge of the tube and the inner bead of the elbow was approximately 6 mm, while the clearance at the inlet side was about 1.5 mm where no significant damage was found (Figure 10 a and b).

Taking into consideration only the thickness loss, the rate of damage for the outlet pipe reaches 4mm/yr. The elbow lost approximately 46% of its thickness. However, taking into account the loss of the pipe tube length (inserted part), which was 15 mm for the investigated sample and more than 20 mm for the sample with a hole (in the half portion), the rate of failure is extremely high (276 and 315 mpy respectively). Naturally, such high rates will never be attained due to only pure corrosion phenomenon of carbon steel in near neutral environment. Rather, a contribution of factors such as erosion and corrosion may have dominated the process.

Metallographic examination revealed that the nasal part of the outlet tube end underwent unform attack (Figure 12 a), while next portion had rounded tooth-shaped damage (Figure 12 b). The other part of the sample had a more racheted tooth-shaped appearance (Figure 13), with more slopping at the front surface (of the flow side). The failed surface of the elbow (zone D in Figure 11) underwent significant damage with the typical shape of large cavities, with relatively large diameter and depths with spherical bottoms (Figure 14).

SEM examination revealed the presence of clearly pronounced wavy feature as valleys and grooves on the surface of failed outlet tube in the portion approximately perpendicular to the flow (Figure 15 a), while other areas had more uniform ruptured surface (Figure 15 b). Surface morphology in both areas showed a typical dimpled ductile tearing [9, 24, 25]. Ferrite was most likely selectively dissolved. After chemical etching of the sample, platelet cementite was revealed (Figure 16). A typical localized damage as depressions with spherical bottoms were found in the portion of inlet tube far away from the elbow (zone A, Figure 11).

The results of elemental analysis showed the presence of mainly O (3-50%), C (30-39%), and Fe (20-30%) along with some amount of Si (0.3-0.7%), S (0.5-10%), CI (0.2%), Ca (0.2-0.5%) and Na (0.2- 0.6%) (Figure 18 a). However, in some areas high peaks of C (77%) and S (11%) were detected (Figure 18 b). It is clear that these two elements originated from the medium (DMDS (is a source for S). High concentrations of O and Fe indicate the formation of different iron oxides.


Discussion: The morphology and damage locations clearly indicate that the cause of observed failure can be generally attributed to the high turbulence in the upper region of the elbow where clearance was 6 mm. The direction and specific shapes of damages were strongly aligned with flow lines and were typical for erosion-corrosion phenomenon [2-5, 10-17]. At the given conditions dilution steam can condensate at approximately 161 °C which is close to operating temperature. Even though, the system is in a superheated vapor condition in the inlet part, some local condensation occurred in the clearance area due to turbulence and very small water droplets formed which aggressively impinged the pipe ends.

Under the combined action of relatively high velocity and temperature of steam, and probably the presence of carbon particles the removal of protective oxide film from the metallic surface in the failed area occurred. This changed the reaction properties of the fresh surface and led to rapid acceleration of damage.

Pure impingement type of attack did not occur in this case because if it had taken place the maximum failure would have been at region close to the turn point of the elbow. However, only gradual thinning of the elbow was observed. Naturally, such a high damage rate (200-300 mpy) will never be reached only due to pure corrosion of carbon steel in neutral or slightly acidic environment. Therefore, erosion-corrosion damages most likely occurred.

Conclusion: The results of the examinations and evidence obtained make it possible to conclude that the observed failure occurred due to erosion-corrosion caused by the formation ofhighturbulence zone between the inner bead of the elbow and the outlet tube butt-end.

Recommendat ions: The following remedies were recommended:

Maximum clearance between inserted tubes and inner beads of the elbow should be not be more than 1.5-1.8 mm.

Use long radius elbow.

More resistant alloys can be utilized such as cast martensitic stainless steel CA-6 NM, cast austenitic stainless steel CN-7 M, or austenitic 304 stainless steel.

GENERAL CONCLUSION

Different types of equipment in steam piping systems may undergo liquid erosion-corrosion failure at sharp turn points due to the presence of a small amount of water droplets in the steam or the presence of small volume of steam in vapor phase in the condensate. Most likely, the flow velocity of a mixture in a piping system increases significantly if the steam condensate contains some amount of steam in the flow. Gradual thinning of the air cooler tubes at portion next to the tube sheets (bottom part with the lengths of about 16-18 cm) occurred due to the influence of formed carbonic acid. The concentration of carbonic acid decreases away from this portion and, therefore, no corrosion evidence was revealed. The thermal conductivity properties should be taken into consideration with change of alloy chemistry for the air-cooler tubes. The use of metallic or non-metallic ferruls will significantly increase service life of the existing failed air coolers and will help to avoid replacement expenses. Probably, adjustment of steam temperature is also one of the solutions to avoid or minimize the condensation phenomenon.


A C KNOWLEDGEMENT

The authors are grateful to the management of SABIC R&D and Sadaf Company for extensive full support to accomplish and publish this work.

REFERENCES

1. H.H. Uhlig, The Corrosion Handbook, New York, John Willey and Sons, Inc., 1984. 2. N.S. Hirota, In Book: Metals Handbook, 9 th ED., v.13, "Corrosion",ASMI p. 964-973, 1987. 3. T.M. Laronge, In Book: Process Industries Corrosion, Ed., B.J. Moniz, W.I. Pollok, NACE, p. 215-

226, 1986. 4. P.A. Akolzin, Korrosia I Zaschita Metalla Teploenergeticheskogo Oborudovania, M., 303 p., 1982,

(in Russian). 5. C.P. Dilon, Corrosion Control in the Chemical Process Industries, MTI, Publication No. 45, 2 nd Ed.,

NACE, 420 p., 1997. 6. D.M. Cicero, Chemical Engineering, p. 78, March 2000,. 7. F. Speller, Corrosion Causes and Prevention, New York, McGraw -Hill, Inc., 168 p.1951. 8. Z. Szklarska-Smialovska, Z. Xia, R. Brebak, P. Skulta, Corrosion, v. 50, No.4, p. 279-289, 1994. 9. C.J. Czajkowski, In Book: Handbook of Case Histories in Failure Analysis. Ed., S.D. Henry, ASMI,

v.1, p. 136-139; p. 182-187, 1992. 10. H.M. Herro, R.D. Port, The NALCO Guide to Cooling Water Systems Failure Analysis, McGraw -

Hill, Inc., 420 p., 1993. 11. C.P. Dilon, Forms of Corrosion. Recognition and Prevention, v. 1, NACE, 116 p., 1982. 12. G. Kobrin, In Book: Metals Handbook, 9 th Ed.,v.13, "Corrosion", ASMI, p., 321-337, 1987. 13. Corrosion in the Petrochemical Industry, Ed., L. Garveric,ASMI, 480 p., 1995. 14. M.G. Fontana, N.D. Greene, Corrosion Engineering, McGraw-Hill, Inc., p.72-79, 1967. 15. F.J. Heymarm, Mach.Des., p.105-109, Dec., 1970. 16. I.M. Hutchings, Publication 25, Materials Technology Institute of the Chemical Process Industries,

p., 72-81, 1986. 17. L.E. Sanchez-Caldera, Ph. D. Thesis, MTI, June, 1984. 18. Kazuo Nakamoto, Infrared & Raman Spectra of Inorganic and Coordination Compounds, 3 rd Ed.,

USA, 1977. 19. J.H. Keenan, F.G. Keyes, P.G. Hill, J.G. Moore, Steam Tables, 1992. 20. Tzu-Yu Chen, C.B. Barton, D.M. Cicaro and R.D. Port, "Corrosion/98", NACE paper No. 718,

Sandiago, USA, 1998. 21. Metals Handbook, Desk Edition, ASM, Metals Park, 1997. 22. Metals Handbook, 8 th Edition, v. 1, ASM, Metals Park, 1978. 23. Handbook of Photo-electron Spectroscopy, Ed., C.D. Wagner, Perkin- Elmer, 1979. 24. P.K. Liaw, A.Saxena, J.Schaefer, In Book: Handbook of Case Histories in Failure Analysis.Ed.,

S.D. Henry, ASMI, v.1, p. 434-439, 1992. 25. ASM Handbook, v. 12, Fractography, ASMI, 1992. 26. H. Lee, Failure Analysis Report, SABIC R&T, Riyadh, KSA, 1998.


Flow Flow

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FIGURE 1. Stereo microscopy photograph of the failed tube surface (a) and its cross section (b) showing asymmetrical, protuding attack.

FIGURE 2. SEM micrograph of the failed surface showing the semi-circular, step-like shape of damage with shallow pits at the very top surface of ratchets (x25).

FIGURE 3. EDX spectnml from the failed surface (general area) showing high peaks for O, Fe, Zn, AI, Na and Si.


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FIGURE 5. Cross section of the failed part of tube inserted into the tube sheet with wave-line of damage in the inner surface (x 100).

FIGURE 6. SEM micrographs from the perforated edge showing dimples with spherical bottoms (a, x500) and preferential attack of the grains (b, x2K).


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FIGURE 8. A close up photograph of the failed elbow cut longitudinally showing the thinned area with hole.

FIGURE 9. A close-up photograph of the sectioned socket welded elbow.

FIGURE 10. Close-up photographs of the sectioned welded elbow with the outlet (a) and the inlet (b) tubes. Note the wider clearance and the most damaged areas in portion (a).


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Layout of the sectioned assembly (elbow with inserted tubes). Dashed lines show the completely gone areas.

Cross section of the failed outlet tube end showing uniform attack in the nasal part (a, x50) and the tooth-shaped damages with the sharp lines in the next portion (b, x50).


Figure 13 Figure 14


FIGURE 13. The presence of ratchets on the surface next to nasal part (x50).

FIGURE 14. Cross section of the failed elbow surface showing the large cavities with spherical bottom (xSO).

FIGURE 15. SEM micrographs of the outlet tube surface showing the wave-line feature as valleys in the area perpendicular to flow (a, x150) and more uniform attack in the next nearest area (b, x250). Note the dimpled ductile tearing surface morphology.


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FIGURE 16. SEM micrograph of the failed outlet tube surface showing selective dissolution of ferrite and the platelet feature of eementite ( x 2,5).

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FIGURE 18.

SEM micrograph from the other end of outlet tube (zone A, figure 11) showing local type of corrosion as the depressions with spherical bottoms and holes ( x 300).

EDX spectrum from the surface of the outlet tube showing high peaks of Fe and O (a) and from the surface of the inlet tube (b) showing the intense of C and S peaks.


Documents

01162 Erosion-corrosion Failures in Chemical Plant Steam Condensate Piping Systems (51300-01162-Sg)