ALTER TABLE Recipe
ADD CONSTRAINT FK_Recipe_DuplicateOfRecipeId_Recipe_Id FOREIGN KEY (DuplicateOfRecipeId)
    REFERENCES Recipe (Id) ;

ALTER TABLE Recipe DROP CONSTRAINT  FK_Recipe_DuplicateOfRecipeId_Recipe_Id
results in the following error:
'FK_Recipe_DuplicateOfRecipeId_Recipe_Id' is not a constraint.

ALTER TABLE Recipe NOCHECK CONSTRAINT FK_Recipe_DuplicateOfRecipeId_Recipe_Id
results in: Constraint 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id' does not exist.

alter table Recipe ADD CONSTRAINT FK_Recipe_DuplicateOfRecipeId_Recipe_Id FOREIGN KEY (DuplicateOfRecipeId) REFERENCES Recipe (Id);

The ALTER TABLE statement conflicted with the FOREIGN KEY SAME TABLE constraint "FK_Recipe_DuplicateOfRecipeId_Recipe_Id". The conflict occurred in database "CrawlerDB", table "dbo.Recipe", column 'Id'.

select COUNT(*) from sys.objects where name = 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id'
select COUNT(*) from sys.all_objects where name = 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id'
SELECT COUNT(*) FROM sys.foreign_keys where name = 'FK_Recipe_DuplicateOfRecipeId_Recipe_Id'