NiDl Nickel Development Institute Guidelines for the welded fabrication of nickel-containing stainless steels for corrosion resistant services A Nickel Development Institute Reference Book, Series No 11 007 Table of Contents Introduction ........................................................................................................ i PART I – For the welder ...................................................................................... 1 Physical properties of austenitic steels .......................................................... 2 Factors affecting corrosion resistance of stainless steel welds ....................... 2 Full penetration welds .............................................................................. 2 Seal welding crevices .............................................................................. 2 Embedded iron ........................................................................................ 2 Avoid surface oxides from welding ........................................................... 3 Other welding related defects ................................................................... 3 Welding qualifications ................................................................................... 3 Welder training ............................................................................................. 4 Preparation for welding ................................................................................. 4 Cutting and joint preparation .................................................................... 5 Weld joint designs ................................................................................... 5 Cleaning in preparation for welding .......................................................... 7 Oxides and other surface layers .......................................................... 7 Contamination elements ..................................................................... 8 Chlorinated solvents ........................................................................... 9 Health hazards ................................................................................... 9 Fixturing, fitting and tack welding ............................................................. 9 Fixtures and positioners ...................................................................... 10 Backing materials ............................................................................... 10 Tack welding ...................................................................................... 10 Fitting pipe joints for GTAW root welds ................................................ 11 Purging during pipe root welding ......................................................... 11 Welding Processes ....................................................................................... 12 Shielded metal arc welding ...................................................................... 12 Electrode types .................................................................................. 13 Other guides in SMAW ....................................................................... 13 Electrode handling and storage ...................................................... 13 Welding current ............................................................................. 15 Arc starting and stopping ............................................................... 15 Gas tungsten arc welding ......................................................................... 15 GTAW equipment ............................................................................... 16 Consumables ..................................................................................... 16 Operator technique guides .................................................................. 17 Gas metal arc welding ............................................................................. 18 Arc transfer modes ............................................................................. 18 GMAW equipment .............................................................................. 18 Consumables ..................................................................................... 19 Other welding processes .......................................................................... 19 Post-fabrication cleaning ............................................................................... 19 Surface contaminants .............................................................................. 20 Detection ........................................................................................... 20 Removal ............................................................................................. 20 Embedded iron ........................................................................................ 20 Detecting embedded iron .................................................................... 21 Removing embedded iron ................................................................... 21 Mechanical damage ................................................................................. 22 Safety and welding fumes ............................................................................. 22 PART II – For the materials engineer ....................................................................23 Stainless steel alloys .......................................................................................23 Austenitic stainless steels ................................................................................23 Effect of welding on corrosion resistance ....................................................23 Role of weld metal ferrite ............................................................................27 Measuring weld metal ferrite ..................................................................27 Duplex stainless steels ....................................................................................28 Characteristics of duplex stainless steels ....................................................30 High temperature exposure ....................................................................30 Effect of welding on duplex stainless steels .................................................30 Nickel-enriched filler metal ....................................................................31 Heat input control ..................................................................................31 Interpass temperature control ................................................................31 Preheat .................................................................................................32 Other stainless steels ......................................................................................32 Martensitic stainless steels .........................................................................33 Ferritic stainless steels ...............................................................................33 Precipitation hardening stainless steels .......................................................34 Corrosion resistant stainless steel castings ......................................................34 Heat treatment of stainless steel ......................................................................35 Alternate 1 ............................................................................................35 Alternate 2 ............................................................................................35 Material procurement and storage guides ........................................................ 36 Surface finishes ...............................................................................................36 Purchasing guidelines ......................................................................................38 PART III – For the design engineer .......................................................................39 Design for corrosion services ...........................................................................39 Tank bottoms ........................................................................................39 Tank bottom outlets................................................................................40 Bottom corner welds ..............................................................................40 Attachments and structurals ................................................................. 40 Heaters and inlets .................................................................................42 Pipe welds ............................................................................................42 Appendix A: Specifications for stainless steel for welded fabrication ........................45 Additional requirements ....................................................................................46 Bibliography ..........................................................................................................46 Acknowledgement ................................................................................................ 46 Tables Table 1 – Influence of physical properties on welding austenitic stainless steels compared to carbon steel ................................................................ 1 Table 2 – Stainless steel cutting methods ........................................................ 5 Table 3 – Melting temperatures of metals and metal oxides ............................. 7 Table 4 – Suggested filler metals for welding stainless