Use of fillets as primary welds on in-service welded branch connections

Full encirclement split tees along with plugging machines are used to add branch connections to piping in the petroleum industry without shutdowns or process interruptions. The additional branch connections may be necessary to bypass problematic equipment or provide tie-ins for unit modifications. A split tee is an extruded style, carbon steel fitting, fabricated and tested to ASME regulations. ASME regulations require that any branch connections which are inserted in an opening in the run be attached by full penetration groove welds. To use fillet welds as primary welds, ASME regulations require calculations to be substantiated by testing and simulation. This thesis presents the results of tension test, pressure test and metallographic tests performed to cover ASME requirements for the particular case of an actual in-service welded branch connection. Results show what has been proven in the field for years, that the use of fillet welds as primary welds on in-service welded branch connections is a safe practice and technically acceptable, benefiting an industry where process interruptions create considerable losses every year.