Sulfidic corrosion on washoil drum - extremely high rate

[Onurb85]

Hi*
On the past weeks a failure happened on a washoil drum (Vaccum unit) due to sulfidic corrosion (bottom area of the drum). This drum was never replaced (original from 1993 - P5 metallurgy) and until 2014 had very low corrosion rates even with high sulfur crudes (2.5-3.5% sulfur on washoil). Only after 2014* the corrosion rate increased up to 0.6mm/year. However* in the last 5 months* the corrosion rate increased to 6-7mm/year. Does anyone have any similar experiences on other refineries? Which kind of crudes were processed on those refineries? Any similar experiences on the HVGO section?

Based on the real process values (operating temperature* sulfur and acidity)* the McConomy curves show a corrosion rate on that area of 0.5-0.6mm/year. What could increase the corrosion to 6-7mm/year?
Thanks in advance.

[SAMEH ELSAGHER]

Dear Onurb85
What about operating temperature* are you sure that is the same for all runs.
Please check from operation charts if available * if not ask operation team because they have to inform you what upset condition happens.
Is that crude oil analysis changed or they increased operating temperature for operation purpose.
Regards

[SAMEH ELSAGHER]

Look for API RP939-C at the following link.

[link Point to another website Only the registered members can access]
Which could be good in your case.

Regards

[Onurb85]

The operating temperature was on 2013 around 320-340ºC* then increased on 2014 up to 360ºC; on 2015-2016 was around 340ºC and after Ocotober 2016 was 350ºC. All of these are far from the design operating temperature that is 385ºC. I checked if there were temperatures upsets after October 2016 and this temperature went up to 385ºC for 6 times but just after 20min it normalized to 350-360ºC.
The temperature changed for operation purpose.

[SAMEH ELSAGHER]

Look the sulfidaton corrosion in API 571where you will find how the corrosion rate increases with temperature from 350 for 5% Cr alloy (fig.5.9). You will find it increased too much.
Please check charts with operation for how long they operate the drum at 380 C