Comprehensive reliability analysis of blistered ‘LPG wash water vessel’ in FCC unit – Part I: Failure analysis Sova Bhattacharya ⇑ , Kannan Chandrasekaran, A.K. Lahiri 1 Indian Oil Corporation Limited, Research and Development Centre, Sector-13, Faridabad, Haryana, India article info Article history: Received 11 June 2010 Received in revised form 8 February 2013 Accepted 9 February 2013 Available online 13 March 2013 Keywords: LPG wash water vessel Hydrogen blister Lamination INDMAX process Metallurgical investigation abstract LPG wash water vessel of INDMAX process unit – an improvised patented FCC technology of Indian Oil Research and Development centre experienced severe hydrogen blistering damage calling for replacement of the wash vessel. Considering the lead time of supply of new vessel, it was decided to carry out Engineering Critical Assessment (ECA) using IOC’s in-house developed software, before taking the vessel in service. The vessel was re-put into service at de-rated operating conditions for a period of more than 6 months and there after the vessel was replaced. It was desired to carry out a detailed investigation on failed vessel post replacement, to find out the root cause analysis and reconfirmation of the ECA meth- odology adopted for reliability assessment employed during the study. This paper enumer- ates the findings of the failure analysis carried out on the vessel post replacement. Part-II of the paper describes the detailed ECA analysis carried out during service as well post replacement of the vessel. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Hydrogen damage of equipment is a matter of great concern in the refining industry [1–3]. The damage is due to hydro- gen absorbed by the metal during service, both at high and low temperatures. Absorption of hydrogen at high temperatures is dependent on temperature and partial pressure of hydrogen. At lower temperatures, hydrogen absorption, is related to the process of corrosion, where hydrogen released in the course of corrosion is absorbed by the metal [4,5]. The absorbed hydro- gen diffuses in the metal under concentration gradient, resulting in various types of hydrogen damage [6,7] like Sulfide stress corrosion cracking (SSCC), blistering , Hydrogen Induced cracking (HIC) and Stress oriented hydrogen induced cracking (SOHIC). Literature reports LPG storage vessel failure by wet H 2 S cracking [8] and methods to mitigate such failures are well documented [9–11]. The present paper describes a unique case of extensive blistering observed in one of the vessel in Flu- idized Catalytic Cracking (FCC) unit of one of the refinery of Indian Oil Corporation. This unit is based on in-house developed INDMAX technology, which produces very high yield of light olefin such as pro- pylene, butylenes and high-octane gasoline (98+) from wide range of heavier petroleum fractions. The yields propylene and butylenes can be as high as 27 and 15 wt.% respectively with VGO range feed. The LPG produced (as high as 50 wt.% with VGO range feed) is first washed with caustic to remove H 2 S. This is followed by water washing in another vessel in series. After 2 years of operation, the wash water vessel was found to have developed severe blistering which progressively increased both in numbers and size. A decision was taken to replace the vessel but con- sidering the lead time of supply of new vessel, it was decided to quantify the extent of damage and to carry out Engineering 1350-6307/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.engfailanal.2013.02.027 ⇑ Corresponding author. Tel.: +91 129 2294205; fax: +91 129 2286221. E-mail address: bhattacharyas1@iocl.co.in (S. Bhattacharya). 1 Address: B1/704 Paradise Apartment, IP Extension, Delhi 92, India. Engineering Failure Analysis 32 (2013) 91–97 Contents lists available at SciVerse ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal