High Carbon Steel - Ammonia corrosion

[thorgrim]

Greetings everyone, recently we have been repairing the Journal bearings of a twin screw Ammonia compressor .  The repair was done spraying the journals with an arc spray NiCr bond coat layer and as a rebuilding material we used a Sprasteel 80 Metco Wire (0.8% Carbon Steel,commercially known as High Carbon Steel) with a  high velocity wire flame spray gun.  The ground finished dimensions were perfectly in OEM tolerances and all the compressor working parameters were OK as oil Viscosity,working discharge pressure and temperatures,Screws RPM and everything else, but after some 8 hours of operation the bearings temperature begun to rise and the compressor was stopped and dismounted.  The Journals and the Babbitt bearings were completely worn out. As we have repaired a lot of Journal bearings in turbines,electrical motors,crankshafts and a lot of other rotary mechanical equipments, all working in lubricated hydrodynamics Journals and we never have found any kind of problems with the job, we guess if in this twin screw compressor, working with Ammonia gas the High Carbon Steel sprayed coating could have suffered a chemical attach corrosion trouble and the repaired journals are being damaged for this reason.  Could some one please help with this issue_?  Thanks

[Vadim Verlotski]

Greetings everyone, recently we have been repairing the Journal bearings of a twin screw Ammonia compressor .  The repair was done spraying the journals with an arc spray NiCr bond coat layer and as a rebuilding material we used a Sprasteel 80 Metco Wire (0.8% Carbon Steel,commercially known as High Carbon Steel) with a  high velocity wire flame spray gun.  The ground finished dimensions were perfectly in OEM tolerances and all the compressor working parameters were OK as oil Viscosity,working discharge pressure and temperatures,Screws RPM and everything else, but after some 8 hours of operation the bearings temperature begun to rise and the compressor was stopped and dismounted.  The Journals and the Babbitt bearings were completely worn out. As we have repaired a lot of Journal bearings in turbines,electrical motors,crankshafts and a lot of other rotary mechanical equipments, all working in lubricated hydrodynamics Journals and we never have found any kind of problems with the job, we guess if in this twin screw compressor, working with Ammonia gas the High Carbon Steel sprayed coating could have suffered a chemical attach corrosion trouble and the repaired journals are being damaged for this reason.  Could some one please help with this issue_?  Thanks

Ammonia is not a corrosive agent for steel coatings, so I think it is not about corrosion but about lack of lubrication (dry friction). Perhaps the grease from the bearing is washed out by the stream of ammonia and this leads to its destruction.