The dynamic creep rupture of a secondary superheater tube in a 43MW coal-fired boiler by the decarburization and multilayer oxide scale buildup on both sides

Liu, William

doi:10.1016/j.engfailanal.2015.03.018

Cited by 12 publications

(5 citation statements)

References 19 publications

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“…Short-term overheating due to oxide scaling was more likely to occur in horizontal superheaters. These patterns are consistent with findings reported in the literature [2,11,4,12]. Some plant operating procedures attempt to reduce the risk of short-term overheating occurrences by constantly monitoring saturation temperatures within the boiler and ensuring that steam temperatures remain above saturation temperatures.…”

Section: Introductionsupporting

confidence: 89%

Over-attemperation and Short-term Overheating in Pendant-type Superheaters

Basson¹,

Fuls²

2021

rdj

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A water-wedge is often suspected to be the root cause for short-term overheating in fossil-fuelled boiler superheaters. However, it can be argued that evaporation of the water-wedge would cool the tube sufficiently and prevent overheating. This study aims to determine if the thermo-physical conditions occurring at low loads support this claim by studying the transient behaviour of a representative superheater segment under postulated conditions. A flow model was constructed to facilitate direct comparison with a boiler pendant superheater of a full-scale fossil-fuelled power plant. Several scenarios of water-wedges sustained by attemperation spraywater were simulated at low load operating conditions. The temperature evolution of the tube wall was tracked and, together with calculated equivalent stresses including thermal stress, was compared to the yield strength of the material. The results show that the stresses exerted over the tube wall and throughout the tube length are not sufficient to overcome the yield strength of the tube material, even for an aged tube under severe process conditions of boiler overfiring. Evaporation of the water-wedge provides sufficient cooling to the superheater tube to prevent failure. It was concluded that water-wedging alone is unlikely to be the root cause of short-term overheating at low boiler loads. Additional keywords: Short-term overheating; water-wedge; boiler superheater tube; attemperation; thermal stress, evaporation.

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Section: Introductionsupporting

confidence: 89%

Over-attemperation and Short-term Overheating in Pendant-type Superheaters

Basson¹,

Fuls²

2021

rdj

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“…In Figure 5, the pitting corrosion observed are those that are close to the surface of the outer diameter of the tube. The observations show that there is a significant difference in the contours of the corroded area, this indicates that there is a hollow in the material filled with oxides [10,11]. After the metallography testing is carried out, the hardness test is carried out with the hardness vikers (HV) unit so that the minimum hardness in normal area is 154.03 HV and the maximum hardness is 163.06 HV, minimum hardness in corroded area is 149.61 HV and the maximum hardness is 158.21 HV, minimum hardness in weld area is 155.79 HV and the maximum hardness is 177.92 HV.…”

Section: Resultsmentioning

confidence: 95%

3-Dimensional Microstructure Investigation of High Temperature Corrosion of Boiler Tube Material

Nugraha¹,

Rasgianti²

2021

KEM

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The material of the tubes has suffered localized overheating and corrosion, probably as a result of local heat flux impingement phenomenon, combined with high temperature corrosion. Boiler tubes that experienced failure indications were tubes material SA 213 T22 with the dominant alloy elements is Cr. Materials with these specifications are which should be resistant to corrosion, so it is necessary to carry out laboratory testing to answer suspected indications of failure. The methodology of analysis and identification carried out is by observing the microstructure in 3 dimensions supported by other mechanical tests, namely visual observation, hardness testing, chemical composition testing using SEM and EDAX and testing the chemical composition of the material using a spectrum analyzer. Observation using an optical microscope shows that the microstructure condition of the tube is ferritic and the results of 3D metallography observations show that the tube has undergone micro crack with a measured depth of 1853,28 μm. After the metallography testing is carried out, the hardness test is carried out with the hardness vickers (HV) unit and the minimum hardness is 149 HV and the maximum hardness is 177 HV. Testing of the chemical composition of the deposit showed that there were chemical elements found in seawater that trigger corrosion such as sodium and chlorine which enter the water vapor system. The results showed that the tube had pitting corrosion, which was indicated by the presence of microcrack at the grain boundaries and an oxide deposit had been formed which would cause an overheating phenomenon and deterioration.

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“…Furthermore, the decarburization zone in the outer surface of sample II (100 μm) is thicker than sample III (50 μm), suggesting that the failed tube suffers a higher temperature than the un-failed one. The decarburization rate increases with increasing temperature because carbon diffusion out of the surface is accelerated at a higher temperature (Liu, 2015).…”

Section: Metallographic Examinationmentioning

confidence: 99%

“…Among all of the WHB system components, boiler tubes are critical components because failure on boiler tubes might disrupt boiler performance and even plant shutdown (Ding et al, 2017). Several failure mechanisms that commonly occurred are creeps (Liu, 2015;Ray et al, 2003), thermal fatigue (Ahmad et al, 2010;Vetriselvan et al, 2018), corrosion (Daneshvar-Fatah et al, 2013;Srikanth et al, 2003) and overheating (Dhua, 2010;Duarte et al, 2017). Because of the enormous potential for economic loss and safety risk, failure of boiler tubes in the WHB system can be minimized by understanding the potential failure root cause, particularly lesson-learned from industrial practices.…”

Section: Introductionmentioning

confidence: 99%

Failure analysis of primary waste heat boiler tube in ammonia plant

Ardy

Putra²,

Anggoro

et al. 2021

Heliyon

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The primary Waste Heat Boiler (WHB) in an ammonia plant experienced cap leaking and the outer tube rupture after ten months since the last repair and replacement (total retubing). The leaking cap and the outer tube materials are low carbon steel SA-204 Gr. B and SA-209 Gr. T1a. The inappropriate vertical part of the leaked cap, which is 2.4 mm shorter than the design, might trigger turbulence flow inside the cap and lead to flow-accelerated corrosion (FAC), as suggested by the appearance of wall thinning and horseshoe pattern in the inner surface. This condition is severed by improper cap material selection with low chromium content (0.01%), which is more susceptible to FAC. The local turbulence flow might erode the oxide layer at the cap bottom and accumulate the oxide deposit around the circumference weld joint and the nearest nail spacer in the tube, represented by a thick Fe 3 O 4 deposit. The primary WHB outer tube failure might occur due to the lack of cooling from boiler water because of cap leakage combined with a thick Fe 3 O 4 scale deposit on the nail spacer that causes significant local temperature increases on the failed tube, which resulted in yielding and thin-lip rupture.

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The dynamic creep rupture of a secondary superheater tube in a 43MW coal-fired boiler by the decarburization and multilayer oxide scale buildup on both sides

Cited by 12 publications

References 19 publications

Over-attemperation and Short-term Overheating in Pendant-type Superheaters

Over-attemperation and Short-term Overheating in Pendant-type Superheaters

3-Dimensional Microstructure Investigation of High Temperature Corrosion of Boiler Tube Material

Failure analysis of primary waste heat boiler tube in ammonia plant

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