Numerical investigation of superheater tube failure (original) (raw)

Root-cause analysis of superheater-tube failure

Materiali in tehnologije

Superheater-tube failure is listed among the major causes of a fossil-fuel-fired boiler outage. Therefore, it is necessary not only to identify and repair it in the case of failure but also to eliminate the root cause of this problem. As there may be multiple reasons of failure in exposed equipment such as a superheater, a thorough investigation of more than one probable cause is usually required. This article focuses on a failure analysis of a boiler located in a chemical plant. After a leak was discovered, several cracks on the superheater tubes were identified as its main cause. It was necessary to assess the extent of the damage, detect the root cause and propose corrective actions. Two problematic locations with cracks were identified during the visual inspection: the first was on the superheater-tube bends and the other was the weld joint between the superheater and the transition pipe. As the first step, the material-microstructure and composition analyses of the tubes in these critical locations were carried out. Even though small weaknesses were found in the microstructure, the main cause of the tube failure was not identified. As the next probable cause, thermal-dilatation stresses were investigated using the finite-element analysis (angl. FEA). The support system, consisting of fixed and spring supports, as well as the compensator were included in the analysis that confirmed the thermal-dilatation stresses as the major cause of the failure. Based on the results, a new technical solution for the supports was suggested and verified with the FEA.

Analysis of superheater tubes failure

E3S Web of Conferences, 2019

Failures of boiler pressure parts, which working in high temperature and pressure conditions are often caused by overheating or corrosion. These two parameters are decisive, but not the only ones. Local stress concentration also depends on the type of headers support and external loads from pipelines. Boiler pressure parts subjected to all loads mentioned before are steam superheaters. Thermal expansion, high pressure and temperature lead to shortening superheaters lifetime. In the places with significant stress caused by all load combinations it is difficult to predict creep strains and material structure changes. This paper shows superheater in which considering external loads from pipeline and their influence on the stress concentration in the superheater tubes. This article also shows steel S304H creep analysis for 100k [h] results and creep equation with experimental developed constants.

Failure analysis on a primary superheater tube of a power plant

Engineering Failure Analysis, 2010

In this paper failure analysis on the SA213-T12 superheater tube by visual inspection, in situ measurements of hardness and finite element analyses is presented. A primary superheater tube has failed with a wide open burst after running at around 28,194 h. Heavy clinkers were found to almost entirely cover the primary superheater region. In situ hardness measurements were carried out on the selected primary superheater first row tubes at the middle region between furnace rear screen tube and primary superheater blower flow path. Hardness measurements are also taken on the as-received failed tube. Finite element analyses on possible features prior to failure are also conducted in order to illustrate and deduce the failure mechanism and failure root cause. Localized short-term overheating of the tube due to localized and concentrated flue gas flow resulted in a failure of the primary superheater tube.

Investigation into Cause of High Temperature Failure of Boiler Superheater Tube

The failure of the boiler tubes occur due to various reasons like creep, fatigue, corrosion and erosion. This paper highlights a case study of typical premature failure of a final superheater tube of 210 MW thermal power plant boiler. Visual examination, dimensional measurement, chemical analysis, oxide scale thickness measurement, microstructural examination are conducted as part of the investigations. Apart from these investigations , sulfur print, Energy Dispersive spectroscopy (EDS) and X ray diffraction analysis (XRD) are also conducted to ascertain the probable cause of failure of final super heater tube. Finally it has been concluded that the premature failure of the super heater tube can be attributed to the combination of localized high tube metal temperature and loss of metal from the outer surface due to high temperature corrosion. The corrective actions have also been suggested to avoid this type of failure in near future.

Failure analysis and retrofitting of superheater tubes in utility boiler

The extreme spray water mass flow rate deviation was observed to occur in the middle temperature superheater of Sahand 2 Â 325 MW Power Plant utility boiler, which severely affected its economic performance and safe operation. Boilers operating in these conditions led to failure in superheater tubes at the same place for two consecutive times in a three year span. Thus, the failure analysis of superheater tubes by investigating the visual inspection, chemical, scale and creep analysis was carried out. The brittle failure occurred in the superheater tubes after the fuel was changed from natural gas to heavy oil. Failure analysis showed that tubes were suffering from long term overheating which was instigated by high spray water flow rate. In order to rectify the boiler operating conditions, some modifications were applied in the boiler unit 1 and operating parameters on this boiler were compared with boiler unit 2. The results showed that the 8.33% reduction in heating surface area corresponds to 52.84 and 17.80% reduction in spray water mass flow rate for capacities equal to 300 and 260 MW, respectively.

Failure Investigation of Superheater Through Investigate the Nearest Component

E3S Web of Conferences

The failure of the superheater (SH) tube can cause the power plant to stop operating. A study was conducted to detect the cause of tube leak at the failure of the superheater in HRSG. This study investigated the mechanism of degradation and leak of SH HRSG by examining the SH tube adjacent to the failed SH tube. Because the failed sample was not found, this investigation was essential for the failure prevention of the recurring problem. This problem was analyzed through metallography examination, hardness test, Finite Element Method (FEM) simulation, SEM/EDS review, and tensile testing. The analysis showed that the cause of the superheater tube bending was the presence of a hotspot, which was assumed to happen when the lower flue gas flap was opened for a long time while the fluid circulation system in the superheater tube was not functioning perfectly. As a result, the thermal stress that occurs exceeds the yield strength.

Failure analysis on high temperature superheater Inconel® 800 tube

Engineering Failure Analysis, 2010

This paper presents failure analysis on a super alloy Inconel Ò 800 superheater tube in Kapar Power Station Malaysia. Visual inspection, microscopic examinations and creep analysis utilizing available related data are carried out to evaluate the failure mechanism and its root cause. The failed high temperature superheater (HTSH) tube was found snapped into two parts, heavily distorted shape and bent at several points. Microstructures of the failed tube showed that creep crack initiated at both external and internal surfaces of the tube and propagated as grain boundary creep cavities coalesced to form intergranular cracks. The severe geometry of tube causing steam flow starvation is identified to have caused increasing tube metal temperature resulting in overheating of the failed tube. Creep rupture is revealed as the cause of failure of the superheater tube.

Analysis of a Failed Primary Superheater Tube and Life Assessment in a Coal-Fired Powerplant

Journal of Failure Analysis and Prevention, 2015

The paper presents results of failure analysis of a primary superheater tube in a steam powerplant boiler. The boiler has been in service for around 52,000 h (6 years) and failure occurred on one of the primary superheater tubes in the form of a wide-open burst with appreciable wall thinning. The location of failure was first determined by on-site visual examination. Subsequently, specimens were taken from a region near the fracture surface for chemical analysis, microstructural examination using optical microscopy, and scanning electron microscopy equipped with energy-dispersive X-ray analysis to determine the probable cause of failure; whereas the lifetime of the superheater tubes was assessed using stress rupture test. Results suggest that the cause of failure was overheating due to deposit buildup inside the superheater tube which acted as thermal barrier and wall thinning resulted from direct impingement of flue gases. The lifetime of the superheater tubes is estimated and is discussed in the present investigation.

Failure investigation of secondary super-heater tubes in a power boiler

Engineering Failure Analysis, 2009

The super heater is heart of any boiler system main duty of which is to supply desired amount of steam regularly at rated temperature and pressure. Frequent tube failure in super heaters is found to be crucial problem which is directly related with boiler operation, performance and design parameters. Aim of this paper is to predict possible causes of super heater tube failure. It deals with the failure investigation of secondary super heater tube panel of SA213-T11 grade steel. The primary observations made with visual inspection and then metallurgical investigation has been carried out by microstructure analysis. The temperature distribution on the tube walls of the super heater is analyzed using computer aided engineering tools. From CFD results and metallurgical examination, localized overheating was seen in failed region of super heater tubes. High erosion areas were also seen from computational fluid dynamics. The uneven temperature distribution over the super heater tubes leads to localized overheating, chilling and development of excessive thermal stresses. This analysis is carried out using multiphysics environment which is very useful tool for analysis of many industrial systems like heat exchangers, chillers, cyclones etc.