Try this procedure Welding guide for Old Furnace tubes The following suggestions can be made for reducing restraint and the prevention of solidification cracking: %EF%83%9E Preheat may be beneficial in reducing the risk of cracking in the parent metal. Even the use of relatively high preheat temperatures would be acceptable because HP alloys do not usually precipitate %C3%B3-phase which is harmful to other austenitic steels. However, a risk of solidification cracking was also found when preheat was employed. %EF%83%9E To reduce the effect of heat input, the use of lower heat input may be favourable to avoid solidification cracking and of less restraint caused by the thermal expansion and reduced dilution. %EF%83%9E The use of a narrower root-gap is beneficial (the last applied procedure= 6GR=), but care is required to ensure adequate back shielding. %EF%83%9E The use of a more ductile filler metal is beneficial as it is able to absorb more of the contract ional strains. ER NiCrMo-3 filler metal has lower high temperature properties than 34/45 tubes, however, it is expected to be better than Alloy 800. %EF%83%9E The sensitivity to solidification cracking in repair welding seemed higher than in original welding so that the general requirements when welding austenitic steels such as lower heat input, lower preheat and interpass temperature and good joint cleanliness should be adhered to.