The next sassda Technical Evening Webinar will be held at sassda’s offices on Thursday, the 5th of May, 2017.
These evenings will be broadcast via webinar to the regions who will hold functions at The Master Builders Association in KwaZulu-Natal and The Building Centre in Cape Town. Outlying areas will be able to access the presentation via webinar from their offices. There is no cost to attend this evening.
sassda’s offices, First Floor, Block D, Homestead Park, 37-41 Homestead Road, Edenburg, Rivonia
The Master Builders Association in KwaZulu-Natal, 40 Essex Terrace, Berea West, Durban
The Building Centre, 7 Platinum Drive, Northgate Business Park , Ysterplaat
Time Drinks and Snacks will be served from 16:00. The presentation will commence at 17:00.
Bismuth free cored wires with a focus on cladding
In the early 1980’s, stainless steel FCAW wires from japan became very popular. These wires contained small additions of bismuth (Bi) in the form of bismuth oxide (Bi2O3) for improved slag removal to the aid of the welder. Bi levels of 180 – 200ppm in the weld metal was quite common during these early stages of stainless steel flux cored arc welding wire production.
In the early 1990’s, premature creep failures were reported in power plants in high service temperature applications. Dr Damian Kotecki from the US found that segregation of Bi to grain boundaries caused these premature creep failures.
Research has proven that the segregation of Bi to the grain boundaries at high temperatures resulted in (1) reduced ductility at temperatures above 650°C and (2) inter-granular cracks at temperatures above 700°C.
Therefore, special FCAW wires, that are free of bismuth, is required for (1) high service temperature applications and (2) applications where a post weld heat treatment 9PWHT) above 600°C of the component/vessel is specified. In fact levels of less than 10ppm are required in the weld metal in order not to be susceptible to the above degradation of the weld metal in high service temperature applications.
High service temperature applications are mostly found in the power generation and petrochemical industries. If we consider cladding, then we more specifically focus on the petrochemical industry where the majority of stainless steel cladding applications are, and where PWHT cycles above 600°C are often required.
Wiehan Zylstra – Welding Alloys South Africa