TPI July 2013

How refineries select corrosion-resistant materials By Sandvik – China

Proper material selection ensures long-term benefit Sulphur and high sulphur crude is generally identified by higher density, higher viscosity, higher metal content and higher corrosion than ordinary sweet crudes. In particular, low- grade sulphur crude may cause hydrogen sulphide corrosion at high temperatures, wet hydrogen sulphide corrosion at low temperatures and polyphonic acid stress corrosion cracking. As many refinery plants were originally designed to process sweet crude, problems arise in terms of production equipment operation, quality assurance, safety and environmental protection after processing sour crude.

I ncreasingly stringent environmental demands and crude resource deterioration are creating new challenges for refineries in the selection of corrosion- resistant materials. The fierce competition among refineries requires them to extend the service life of steel pipes and reduce maintenance workload and downtime, in order to reach the ultimate goal of increasing refinery output.

The challenges facing refineries In recent years, environmental protection regulations in many countries have been becoming increasingly stringent, and China is no exception. The nationwide promotion of national IV gasoline and diesel in big cities this year will substantially reduce emissions of sulphides, which creates even higher requirements for the quality of refinery oil products. Meanwhile, global crude quality is deteriorating, largely represented by rising sulphide content. Figures show that approximately two thirds of global crude is sulphide-containing crude, while sour crude of over 1.5% sulphide content accounts for some 70% of remaining global recoverable reserves. The percentage of crude containing sulphide processed by Sinopec reached 80.66% in 2010, a year-on-year increase of 0.68%. China’s crude imports have changed from sweet crude to sour crude and crude containing sulphide, and refineries must cater to this trend. Sulphide-containing crude processing should become a priority. The application of sulphide-containing crude certainly creates value for refineries, as it meets the need for refineries to reduce operating costs. Figures show that profit from processing sulphide-containing crude increases due to the price difference between sweet crude and sulphide containing crude, which reduces feedstock costs. Since crude cost makes up 80 - 90% of the refinery’s total costs, it has become increasingly important to improve enterprise benefit by reducing crude cost. The primary issue for a refinery is how to seek profit while avoiding disadvantages and ensuring normal operation. Selecting an appropriate anti-corrosion material is a major safety measure. The guarantees that a quality anti-corrosion material provides make it possible for a refinery to expand capacity and increase output.

The application of vacuum distillation equipment at the start of the crude refining process directly affects the normal

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