RETAINING RING MATERIAL ADVANCES

摘要

ETE's records about non-magnetisable retaining rings date back to 1901; material had a high carbon, low silicon/manganese and high nickel but no chrome content. Twenty-seven years later, content of carbon was reduced, silicon was doubled, manganese was almost unchanged, nickel was substantially decreased and chrome almost 5 per cent, being the first cold expanded retaining ring with a 0.2 per cent proof stress of 700mpa. Another 27 years later, content of silicone was doubled, manganese tripled and nickel deleted, resulting in the widely-known UKR material code-named P 750 used for almost 30 years by many generator manufacturers world-wide. Today's retaining rings or end bells have several unique features : 0.2 per cent proof stress of up to 1400mpa, adequate cold and hot ductility combined with high thermal expansion potential and non-magnetisable for improved efficiency of the generator. Being a highly stressed component of the turbo-generator the material used, code named P 900, is produced in an electro slag melting furnace and consists of low carbon (0.12 per cent), high chromium (up to 20 per cent), high manganese (up to 20 per cent) and nitrogen (min, 0,5 per cent) contents, which make it resistant against stress corrosion cracking offering an optimum combination of strength, toughness and resistance.