Did you tried hydrochloric acid?

The calcareoous scale is probably calcium hydroxide, a moderately strong base. It will react with acids, and this is a usual procedure in its removal. if the material is forming inside high pressure tubes, be careful with acid application; ensure the pressure is completely relieved before treatment. Typically, the formation of this scale is associated with a galvanic problem, although the movement of seawater through enclosed pipes under pressure will also cause the problem. The condition is exacerbated by heat. Cleaning requires the same procedures and materials in either case. I have good success in cleaning most bronzes with muriatic acid (30% hydrochloric acid solution). In other applications, such as stainless or hi-tensile steels, I suggest laboratory experimentation to determine a safe removal acid before actual application, if this is possible. Chuck