Metallurgical Integrity of Auto-Exhaust Oxy-Acetylene Welds and Welding Practice in Western Nigeria: A Case for Regulation and Quality Development of the Artisanal Workforce

Abstract

Often times, auto-exhaust oxy-acetylene maintenance weld by local artisans hardly serve more than a wet season. The aim here is to study and document why artisanal oxy-acetylene auto-exhaust welds generally have very short service lives, and be able to propose standard practice guide for obtaining durable welds during exhaust repair. The study focus area is Ondo, Ogun and Lagos Southwestern states of Nigeria. A structured questionnaire was developed and administered to respondents, along with field observations, and interviews bothering on practicing standards. Sample artisanal and original auto-exhaust manufacturers (OAM) materials and welds were sourced from welder shops selected randomly. These samples were sectioned and comparative assessment of composition, strength and electrochemical behaviors was carried out. The result showed that virtually all the welders studied do not comply with different basic requirements such as safety and procedural standards covered by ISO 15615:2013 and EN ISO 15609 respectively. Excessive weld bead/excess penetration, pores, weld bead overlap, uneven weld bead, inclusions and spatters were some of the physically observed weld defects in the weld, and these do not bug them. Many of the welders never heard of any standard procedure for post weld quality assessment, heat treatment or basic workshop weld integrity test such as dye penetrant test. The OAM alloys compositions conform closely with standard material specification of AISI 316 stainless steel austenitic for auto exhausts. AISI409 ferritic stainless steel is also a standard material specification in this application, but the compositions of the artisan alloys on the welds deviates clearly from these. The OAM alloys and welds shows more noble electrode potentials compared with the artisan's alloys and welds, while the Rockwell hardness values shows that artisan weld joints are remarkably weak. Artisan oxyacetylene welds and practices in these focused areas, therefore, show poor compliance to material and procedural standards. Operations and certification of local welders are not well monitored by professional and regulating bodies. Towards improving the quality of this artisanal workforce, relevant welding professional bodies and Standard Organization of Nigeria needs to accept the challenge to organize workshops for these artisans, covering standard operation and quality assessment, and certain standard enforcement measures put in place.