API RP 939-C

Description

This recommended practice (RP) is applicable to hydrocarbon process streams with sulfur-containing compounds, without the presence of hydrogen, which operate at temperatures above approximately 500 °F (260 °C) up to about 1000 °F (540 °C). There is considerable debate in the industry as to the correct threshold temperature for hydrogen free sulfidation and in a change in this Edition, the API 571 threshold of 500 °F (260 °C) is adopted herein. Experience has shown that little significant corrosion will occur at operating temperatures below 500 °F (260 °C) for hydrogen free sulfidation services without the influence of naphthenic acid corrosion. Mercaptan corrosion, particularly in condensate service, has been reported below this temperature, but is not explicitly covered in the 2nd Edition of RP 939-C. For hydrogen containing services, the threshold temperature is set at 450 °F (230 °C). A lower threshold limit for sulfur content is not provided because significant corrosion has occu