We produce stainless steel Collars used in the centre bore of carbon steel flanges. When carbon steel flanges joint to stainless steel pipe or vessel, take the stainless steel collars to the centre bore and joint to the stainless steel pipe or vessel to prevent corrode. Use this stainless steel collars in carbon steel flanges can instead of stainless steel flanges to be economical in some situation, but can not completely replaced of stainless steel flanges.