Flanges to Replace DMW

I’m looking at replacing a dissimilar material weld (DMW) for Alstom’s HP OTC with flanges. Can anyone offer advice on this procedure?


We have used a 2500# special class “compact flange” from LTS Energy , Houston. Bolts and seal ring are inconel 718 to ensure all parts are in asme sect II. We used belleville washers on each bolt. Bolts may not use lubricants that include chloride, flouride, or sulphur. Should use baked on graphite lubricant on the wireloc seal ring. Also, the root pass to be inspected and ground or repair welded at the ID prior to F91 PWHT.

Others are using NORSOK 2500 HT flanges, but used F91 for one flange face and inconel 625 mating flange with an inconel 625 seal ring , with forged pipe extensions provided on both flanges. This allows the field weld to be distant from the flange face. They used higher strength bolts that are not in asme sect II.

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