The present study reports the hot corrosion behaviour of Hastelloy X weldment joined through gas tungsten arc (GTA) and pulsed current gas tungsten arc (PCGTA) with ERNiCrMo-2 (Mo-2) and ERiCrCoMo-1 (CoMo-1) filler materials in molten salt I (75% Na2SO4 + 25% V2O5) (MS I) and molten salt II (75% Na2SO4 + 20% V2O5 + 5% NaCl) (MS II) conditions at 900 °C for 250 h (50 cycles). The highest weight gain is found in MS II compared to MS I. The GTA CoMo-1 weldment of MS II showed the highest parabolic constant (Kp) of 5.455 × 10-6 mg2 (cm4.s)-1 and PCGTA CoMo-1 weldment of MS I revealed the lowest Kp of 0.109 × 10-6 mg2/(cm4.s). The hot corrosion resistance of MS I and II weldments is arranged in the increasing order of, GTA Mo-2 < PCGTA Mo-2 < GTA CoMo-1 < PCGTA CoMo-1. The protective phases such as Cr2O3, NiCr2O4, NiFe2O4, NiO and Al2O3 are providing the better corrosion resistance by protecting the surface and sub-surface layer from further oxidation, whereas the non-protective phases like MoO3, Fe2O3 and Cr2S3 are the reason for acidic fluxing, spallation, cracking and exfoliation of oxide scale. The PCGTA CoMo-1 of both MS I and MS II are giving the best corrosion resistance at 900 °C. © 2019 IOP Publishing Ltd.