Q & A > Question Details
My question is related with a problem of copper corrosion strip failure (ASTM-D130) in gasoline. We have two tanks of off-spec gasoline:
- Copper strip corrosion 3B; SH2=0ppm, mercaptans = 9ppm. Does not improve copper strip corrosion test adding corrosion inhibitor
- Copper strip corrosion 2C; SH2=0ppm, mercaptans = 5ppm. Improves copper strip corrosion test adding corrosion inhibitor
My questions are:
- Could the low level of mercaptans present cause a failure in copper corrosion strip?
- Could a NaOH carryover from the Merox unit cause a failure in copper corrosion test?
- Any other sulfur compound, besides SH2 and mercaptans, could cause this copper strip corrosion test failure?
- Does anyone know any commercial additive for mercaptan removal that could be useful for this problem?
 
Answers
17/12/2011 A: Ryan Crowe, No Heat Resources, rcrowe@no-heat.com
We have an excellent chemcial that removes mercaptans from gasoline. Quite different to anything on the market. It is non-organic and contains no sodium hydoxide. We regularly treat gasoline.
15/12/2011 A: Sridhar Balakrishnan, Bharat Oman Refineries Limited , laksrid@yahoo.com
Copper strip Corrosion failures are caused by Active sulphur species like Mercaptans, Hydrogen Sulphide etc. Traces of Caustic carryover into Hydrocarbon streams also can contribute to Copper Strip Corrosion Failure.
Other than Hydrogen Sulphide and Mercaptans , Elemental sulphur also contributes to copper strip corrosion failure .
Doctor Test can be performed to detect presence of Mercaptans, Hydrogen Sulphide or Elemental Sulphur .
There are many commercial Mercaptan and Hydrogen Sulphide Scavengers available in the market to mask the active sulphur species.


14/12/2011 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Caustic carryover from caustic treater can certainly cause Cu strip test failure and is a common reason for off spec products downstream of caustic treaters. Often this is due to inability of sand coalescer, mesh pad, electrostatic coalescer or other low efficiency coalscer not being to effectively enough remove entrained water /caustic from the hydrocarbon phase. This is part due to the very low IFT (Interfacial Tension) which may be as low as 0.5 dynes/cm which means this is a very stable emulsion and a difficult separation to make. High efficiency PhaseSep Liquid Liquid coalescers have been proven to remove sodium to very low levels.
What type of separation equipment do you have currently downstream of your caustic treater? I am happy to help further if you need further assistance.
13/12/2011 A: Gareth Richardson, Murphy Oil Corp, Gareth_Richardson@murphyoilcorp.com
The copper strip test I always thought was caused by sulphur compounds so the mercaptans could be a problem maybe a scavenger type chemical should help we have used it in LPG spheres so it might work in Gasoline.
13/12/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
The copper strip corrosion test is very sensitive to reactive sulfur compounds (and free sulfur). In all likelihood there is elemental sulfur dissolved in the gasoline. Test for total sulfur as for catalytic reformer feed.
Use the 'lead acetate on paper' test to detect trace H2S.
Caustic (with acidic compounds in it) carryover from a poorly operating MEROX unit will mess up corrosion tests.
Some time ago (2 years?) several major refiners produced gasoline treated with a 'new sulfur removal process' and found out by customer complaints it had undetected corrosive sulfur compounds in it which ruined the fuel level sensors in thousands of automobiles.