Cracking on joint lug of aluminum alloy framework of an airplane

A new interesting paper in  » Engineering Failure Analysis » published on ScienceDirect.com.

An aluminum alloy joint lug of the framework of an airplane was found to have a crack near the bolt hole after serving for a period. The failure mode is stress corrosion cracking.  The cracking of the inner surface anodic oxidation film is the main cause. Some prevention measures for such failure were proposed.

This paper brings out the detail of investigation carried out.

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Understanding the Effects of Hydrogen on SCC of Pipelines

A thesis submitted in Department of Chemical and Materials Engineering University of Alberta, © Zeynab Shirband, 2016.

Near-neutral pH stress corrosion cracks (NNpH SCC) are developed under coating disbondments on the external surface of pipelines where the surface of pipeline is exposed to the soil solution. NNpH SCC initiation and early stage of growth is mainly governed by the dissolution process of steel. …This study aimed at understanding the contribution of these important factors to NNpH SCC. In this study, the role of coating disbondment on hydrogen ingress into pipeline steels and the effects of mill-scale and hydrotesting on NNpH SCC crack initiation are investigated.

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Metallurgical investigation of cracked aluminium alloy valve

1-s2-0-s2213290213000096-gr1A case study published in « Case Studies in Engineering Failure Analysis« , July 2013.

The high strength aluminium alloy Al–5.5Zn–2.5Mg–1.5Cu (AA7075) is being widely used in realisation of aerospace components. A component ‘fill and vent valve’ used in liquid propulsion system was fabricated from AA 7075 forgings in T7352 temper condition, and subsequently undergone various functional tests, four years back. Recently, during dye penetrant test after proof pressure test at 525 bar, a valve indicated presence of a crack. Detailed metallurgical investigation indicated that failure was caused by stress corrosion cracking.

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Investigation of turbine blade failure in a thermal power plant

1-s2-0-s2213290213000333-gr2A paper published in « Case Studies in Engineering Failure Analysis« , july 2013

The present work reports an investigation of a failure in a blade in the LP stage of a thermal power plant of 310 MW. After opening the turbine casing, one blade in the LP region was found fractured. The main damage occurred in the blade row 36 which is the L-3 row of the flow in the turbine side. The key objective of this paper was to identify the root of the failure.

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An investigation of cracking causes in an outlet RTJ flange in ISOMAX unit

2016-11-16_18h55_18A paper published in « Case Studies in Engineering Failure Analysis« , available on sciencedirect.com.

Corrosion has always been a problem in the petroleum refining and the petrochemical operations. The equipment of ISOMAX unit, such as reactors, furnace tubes, valves, and pipelines are frequently performed at high temperatures and high pressure condition. This working conditions, accelerates the failures due to corrosion. Therefore, heat- and corrosion-resistant alloys, e.g., austenitic stainless steels, have been widely used in this unit because of their excellent corrosion resistance, mechanical strength and toughness.

This paper describes failure analysis procedure of a cracked high pressure 321 SS RTJ flange in ISOMAX unit. In order to get conclusions related to crack propagation mechanisms of the flange, some investigations were done on the cracked flange that is mentioned in the body of the paper.

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A failure analysis of a prestressed steel cable of a suspension bridge

AS_267786534518800@1440856693175A case study published in « Case Studies in Construction Materials », 06/2015.This paper presents results of a failure analysis study to characterize the damage phenomenon that occurred in prestressed steel cables of a suspension bridge. Results from fatigue tests and fractographic study allow to the conclusion that the main cause of cable failure, which led to a collapse of the bridge, was stress corrosion cracking (SCC).

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Stress corrosion cracking of full sized rockbolts

2016-06-04_07h48_16An article published in  « International Journal of Rock Mechanics & Mining Sciences – 81 (2016)« .

Previous studies had identified that a testing protocol was required to examine stress corrosion cracking (SCC) of full sized rockbolts under simulated in situ conditions. It was found that SSR testing provided an appropriate analogue for examining rockbolt susceptibility to SCC and was thus used to examine the effect of grit blasting, galvanising and varying steel grades on the SCC resilience of rockbolts. Of these, 300 grade steel and galvanising provided the most promising resistance to SSC, while grit blasting provided a 40% improvement in resistance compared to untreated HSAC 840 grade rockbolts.

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SCC investigation of low alloy ultra-high strength steel

An interesting paper in « Chinese Journal of Aeronautics«  published on ScienceDirect.com.

The paper reports detail of investigation carried out. SCC behavior of low alloy ultra-high strength steel 30CrMnSiNi2A in neutral 3.5 wt%NaCl solution is investigated by SSRT with different strain rates under OCP, cathodic, and anodic polarization potentials, electrochemical measurements and surface analysis technique. The effect of strain rate on SCC behavior is analyzed and SCC mechanisms at OCP, cathodic and anodic polarization potentials are discussed in detail.

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Stress corrosion cracking in 316L stainless steel

A new interesting paper in « Case studies in Engineering Failure Analysis » published on ScienceDirect.com.

There were three consecutive occurrences of bellows failure in a particular pressure safety valve (PSV) of a petroleum refinery within a time span of one week. The bellows were made of 316L grade austenitic stainless steel, and the PSV was mounted on one of the vessels of vacuum gas oil service in a hydrocracker unit. Metallurgical analysis of the failed bellows revealed that the failure had occurred by stress corrosion cracking (SCC)This paper brings out the detail of investigation carried out.

Stress corrosion and hydrogen induced cracking of a control valve body

The control valve body failed due to combination of SSC and HIC cracking in wet H2S environment. According to HIC and SSC laboratory tests the best alternative for the valve body alloy is A217-WC9 steel.Anodic polarization curves clearly shows a considerable improvement in pitting resistance.

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