SOUR CRUDE OIL
SOUR CRUDE OIL
(OP)
I'm working on a 16" carbon steel pipeline that transfer crud oil at 90°C.
This Crude Oil has the following characteristics:
Specific gravity at 35°C = 0.95
Sulphur content = 3,5%
Viscosity = 220 Cst
Water sediment = 1%
I read a lot of articles that indicate 1% as a limit for sulphur on crude oil and that above this value means the necessity of NACE requirements.
The NACE ISO 15156-2 doesn't mention any limit of sulphur. How can I decide if the Oil is sour or not?
In the above mentioned case should I apply NACE materials?
Thanks in advance
This Crude Oil has the following characteristics:
Specific gravity at 35°C = 0.95
Sulphur content = 3,5%
Viscosity = 220 Cst
Water sediment = 1%
I read a lot of articles that indicate 1% as a limit for sulphur on crude oil and that above this value means the necessity of NACE requirements.
The NACE ISO 15156-2 doesn't mention any limit of sulphur. How can I decide if the Oil is sour or not?
In the above mentioned case should I apply NACE materials?
Thanks in advance





RE: SOUR CRUDE OIL
Sour service (wet H2S) requires free water and H2S (extended to wet HF and wet HCN that also produce 'wet H2S' type cracking).
The presence of free water is confirmed (1%) in your case.
If your crude has high sulfur content, can these sulfur compounds transform to H2S ? if yes I would specify NACE XXX requirements (which NACE document do you refer to?)
I ve never seen this sulfur limit 1% that you mentionned... what is the source for this 1% figure ?
Some users refer to 50ppm(w) H2S into the free water phase to start application of NACE XXX requirements, some use ppH2S > 0.003bar, some others consider NACE XXX requirements as soon as H2S is present together with a free water phase, whatever the concentration is.
You can refer to NACE MR0175 and NACE Pub 8X194 for more information on sour service environments.
Regards
RE: SOUR CRUDE OIL
But in my case having crude oil and no other indications, I have no idea about how can I compare my analysis with the above.
On the other hands I have the concern that the sulfur of 3% can generate H2S. In fact I have find some articles that considering the sulfur a potential risk, and mention 0.5% or 1% as a limit for sour crude oil. In any case I have no reference in the NACE ISO 15156-2 and NACE MR 0103 so I cannot verify this limitation as true.
RE: SOUR CRUDE OIL
if you can demonstrate that the H2S level dissolved in water remains well below 50ppm and that the partial pressure H2S remain well below 0.3kPa, also because 1% water is dispersed in HC and induces low corrosion rates and lower SSC/HIC susceptibility, then you have arguments for allowing simple carbon steel (no PWHT).
RE: SOUR CRUDE OIL
RE: SOUR CRUDE OIL
The issue here is that the H/C industry has a different meaning for the same word.
Upstream you tend to look at "Sour" as meaning H2S limits which impact on corrosion, issues with steel cracking and at high levels of H2S a toxic gas.
Downstream producers tend to look at elemental sulphur and somewhere around 0.5 to 1% is the difference between low sulphur and high sulphur crude oils which then gets translated as "sour".
The two things are completely different. To determine if the fluid is "sour" to NACE you need to know the level of H2S in your Crude Oil and water, not Sulphur.
I have to say that is some pretty heavy gloopy Crude Oil you have there.
At the end of the day deciding something is sour to NACE isn't that big a deal unless this translates into having to heat treat every weld.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: SOUR CRUDE OIL