Effect of the Purging Gas on Properties of Ti Stabilized AISI 321 Stainless Steel TIG Welds

Emel Taban; Erdinc Kaluc; T. Serkan Aykan

doi:10.3139/120.110655

Article

Effect of the Purging Gas on Properties of Ti Stabilized AISI 321 Stainless Steel TIG Welds

Emel Taban , Erdinc Kaluc and T. Serkan Aykan

Published/Copyright: November 20, 2014

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From the journal Materials Testing Volume 56 Issue 11-12

Abstract

Gas purging is necessary to provide a high quality of stainless steel pipe welding in order to prevent oxidation of the weld zone inside the pipe. AISI 321 stabilized austenitic stainless steel pipes commonly preferred in refinery applications have been welded by the TIG welding process both with and without the use of purging gas. As purging gases, Ar, N₂, Ar +N₂ and N₂ + 10% H₂ were used, respectively. The aim of this investigation is to detect the effect of purging gas on the weld joint properties such as microstructure, corrosion, strength and impact toughness. Macro sections and microstructures of the welds were investigated. Chemical composition analysis to obtain the nitrogen, oxygen and hydrogen content of the weld root was done by Leco analysis. Ferrite content of the beads including root and cap passes were measured by a ferritscope. Vickers hardness (HV10) values were obtained. Intergranular and pitting corrosion tests were applied to determine the corrosion resistance of all welds. Type of the purging gas affected pitting corrosion properties as well as the ferrite content and nitrogen, oxygen and hydrogen contents at the roots of the welds. Any hot cracking problems are not predicted as the weld still solidifies with ferrite in the primary phase as confirmed by microstructural and ferrite content analysis. Mechanical testing showed no significant change according to the purge gas. AISI 321 steel and 347 consumable compositions would permit use of nitrogen rich gases for root shielding without a risk of hot cracking.

Kurzfassung

Gasspülung ist notwendig, um eine hohe Qualität von Rohrschweißungen aus Edelstahl zu erzielen und eine Oxidation der Schweißzone im Rohrinneren zu vermeiden. Rohre aus AISI 321 stabilisierten austenitischen Edelstahl werden häufig für Raffinerie-Anwendungen favorisiert. Sie wurden mit dem WIG-Schweißverfahren mit und ohne Verwendung von Spülgas geschweißt. Als Spülgase wurden Ar, N₂, Ar + N₂ sowie N₂ + 10% H₂ verwendet. Das Ziel dieser Untersuchung ist es, die Wirkung von Spülgas auf die Schweißnahteigenschaften wie Mikrostruktur, Korrosion, Festigkeit und Kerbschlagzähigkeit herauszufinden. Makroschliffe und Mikrostrukturen der Schweißungen wurden untersucht. Der Stickstoff-, Sauerstoff- und Wasserstoffgehalt der Schweißnahtwurzel wurde mittels dem Leco-Analysesystem ermittelt. Der Ferritgehalt der Schweißlagen, einschließlich der Wurzel und Decklagen, wurde mit dem Ferritscope gemessen. Darüberhinaus wurde die Vickers-Härte (HV10) analysiert. Intergranularer Korrosionstests und Lochfraßtests wurden angewendet, um die Korrosionsbeständigkeit aller Schweißnähte zu bestimmen. Die Art des Spülgases beeinflusst die Lochfraßkorrosion sowie den Ferritgehalt und die Stickstoff-, Sauerstoff- und Wasserstoffgehalte in den Wurzelschweißungen. Heißrissprobleme sind nicht zu prognostizieren, solange die Schweißung primärferritisch erstarrt. Dies wurde durch Analyse des Ferritgehaltes und der Mikrostruktur bestätigt. Mechanische Tests zeigten keine signifikanten Änderungen in Abhängigkeit vom Spülgas. Die Kombination von AISI 321 Stahl und 347 Schweißzusatz würde die Verwendung von stickstoffreichen Gasen als Wurzelschutz ohne Heißrissgefahr erlauben.

Keywords: TIG welding; gas purging; austenitic stainless steel; microstructure; corrosion

*Correspondence Address, Assoc. Prof. Dr. Emel Taban Kocaeli University, Faculty of Engineering, Department of Mechanical Engineering, 41380 Kocaeli, Turkey. E-mail: emel.taban@yahoo.com

Dr. Emel Taban, born in 1980, received her BS, MSc and PhD from the Department of Mechanical Engineering of the University of Kocaeli, Turkey, in 2002, 2004 and 2007, respectively. She has been working as Associate Professor in that department and is the Vice Director of the Welding Research Center. Her major interests and expertise include welding and weldability of stainless steels, high alloyed steels and aluminum alloys using conventional and advanced welding processes.

Dr. Erdinc Kaluc, born in 1958, received his BS, MSc and PhD degrees in Mechanical Engineering in 1980, 1982 and 1988, respectively. He has 30 years of experience in welding, metallurgy and welding of stainless steels, HSLA steels and aluminum alloys. He has been working as Professor in the Department of Mechanical Engineering of the University of Kocaeli, Turkey, and serves as Director of the Welding Research Center.

T. Serkan Aykan, born in 1982, received his BS degree in Metallurgical and Materials Engineering in 2006 and his International Welding Engineer Certificate in 2008. He has eight years of experience in welding metallurgy and welding of stainless steels as well as in advanced NDT methods. He has been working as Quality Control Superintendent at Tupras (Turkish Petroleum Refineries Corporation) in Kocaeli, Turkey, since 2008.

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Published Online: 2014-11-20

Published in Print: 2014-11-17

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Articles in the same Issue

https://doi.org/10.3139/120.110655

Keywords for this article

TIG welding; gas purging; austenitic stainless steel; microstructure; corrosion