GENERAL CORROSION RESISTANCE OF COMMON SLICKLINE ALLOYS
The corrosion resistance of common alloys in Oil & Gas production environments is complex and depends on many factors such as the environment conditions, CO2, chloride, H2S contents and downhole temperature. It also depends on the wire cold work condition and so not one single limit can be applied for each alloy. The following table gives a general guide to the areas of use.
With the Stainless steels the PRENW, (Pitting Resistance Number) is an empirical formulae used to compare alloys for corrosion resistance and gives a guide to the ranking of the different grades: In general the higher the PRENW then the better the corrosion performance.
It has been shown by a number of researchers that an austenitic stainless steel needs a higher PREN than a duplex stainless steel. For instance in seawater it has been shown that a 6Mo needs a minimum PREN of 43 for corrosion resistance whereas a Super Duplex only requires a minimum PREN of 40.
The Carbon steel grades do not have a PREN value and the MP35N does not use the same formulae as it is not a stainless steel. MP35N is a Nickel Cobalt base alloy and does have high alloy content and does have a high corrosion performance.
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|Alloy Grade||Type||Typical PRENW||Comments|
|Plain Carbon, EIPS||CS||–||Can only be used in sweet conditions with inhibitors. Will only tolerate very low levels of H2S. Wire should be cleaned after use to prevent pitting in storage.|
|UHT Carbon EEIPS||CS||–||Can only be used in sweet conditions with inhibitors. Will not tolerate any H2S. Wire should be cleaned after use to prevent pitting in storage.|
|316 SS||Austenitic SS||24||Has reasonable general corrosion resistance and can be used in sweet wells with moderate CO2 content, low chloride levels and low temperatures. Will not tolerate H2S.|
|SLICK 2205 DSS||Duplex SS||35||Has reasonable general corrosion resistance and can be used in moderate to high CO2 environments with low levels of H2S and chlorides.|
|SLICK 6MO SASS||Super Austenitic SS||43||Has excellent general corrosion resistance. Can tolerate medium levels of H2S in CO2 and chloride environments.|
|SLICK ZERON100HS SDSS||Super Duplex SS||42||Has excellent general corrosion resistance. Can tolerate medium levels of H2S in CO2 and chloride environments.|
|SLICK MP35N||Nickel Cobalt Superalloy||–||Can be used in severe environments.|
PRENW = %Cr + (3.3 x % Mo) + (1.65 x % W) + (16 x %N.
The PRENW equation relates to Stainless steels and does not cover the Carbon Steel and the Nickel Cobalt Superalloy grade and is not shown.