SUDDEN LEAKS INVESTIGATION 2

[Alaa1992]

Hello guys

We are in the middle of an investigation to determine the reason leading to the appearance of a ponctual corrosion phenomena inside a newly installed 3'' SCH40 ASTM A106 process piping carrying a produced water stream inside a petroleum processing facility (water with hight amounts of H2s and salt).

The duration of line service before a COUPLE of leaks started to appears was 100 days only!!!!

Ps:the metal loss was huge in some points and leaks were been detected basically near to weld joints.

As a priliminary action we started to radiographically re-inspect all weld joints existing in this line by putting spots on the fusion and HAZ areas. The results have showed many corroded points with a huge metal loss in some of them, and this was in the base metal and/or HAZ and maybe in the rest of pipe structure! (SEE RADIOGRAPHY FILMS)
An API 570 engineer will continue this inspection by doing an overall B-SCAN to detect any other corroded areas. (mechanical/chimical analysis to pipe material and water fluid will be performed in an other step)

Meanwhile, I'm starting to search about this type of corrosion through API574 and I found myself confused between two reasons/possibilities

1) base metal manufacturing failure/default. (the pipe was manufuctered in an API certified mill and within europeans standards/requirements)
2) a Mic phenomena (microbiological influenced corrosion) or other type caused by the fluid nature and/or its non compatibility with the choosed metal nuance!

By looking at the attached photos, and according to your experience, which possibility might be the most likely to happens?
Thanks in advance for your help

Alaa Edine SMAALI
Energy (Oil&Gas) Project Engineer

 

[SJmetallurgist]

from the discussions, few things i can make out. In my experience, elimination approach is the best to work towards root cause:

1. There are pits waiting to leak - possibility that pits are available before use too - pits which are breeding ground for corrosion.

2. Doesn't look like MIC, but you can always rule it out by conducting an SRB test - contact yr labs/expert for what they can offer - SRB is particularly important as you have already mentioned that you could "find/see" contaminants near the sites - though these sites can also become deposition ground without the visible deposits being actually responsible for the leak. Thus below point is important.

3. Go for an SEM analysis with EDM - but do it on a raw UNCLEANED sample - difficult to get if you have flushed the line out or anything of this sort - this will tell you what deposits are actually available at the defect site and will help you a great deal in narrowing down the reason.

Keep us posted. Wish you the best.

 

[Alaa1992]

HY SJmetallurgist.

Thanks for your Post. We are starting to narrowing down causes. The only disturbing parameter for us is the short period of corrosion (High corrosion rate value, How this can be possible);it took only 1 mounth for a 6'' line and 4 mounths for the 3'' pipe before leaks started to appear. (FYI: Both line are carrying a produced water to a tank storage battery).
Reagrding to the poor separation process with a hight amounts of salt & H2S existing in the produced water (only 1 operating vessel working among 6 in total), We are thinking about 3 possibilities:

1) A MIC due to bad fluid properities: this possibility seems the most likely, espeacialy when we cutted longitudinally the 6 inch pipe and observed a possible bacterial phenomina(see photos). Samples of internal contaminated surfaces besides to the produced water itself, have been taken to a specialized lab in order to perform an SBR tests and figure out for wich degree this can be possible. Did you encountered such event/ any comments here ??

2) A bad pipe quality (Mech & Chem properities) or a bad steel nuance selection: Personnaly i exclude this for many reason:
a) We used the same pipe (nuance, diameters, Heat numbers) in other process purposes (Processed oil lines, well head crude oil riser piping & fresh water lines)and no problems at all.

b) Our pipe supplier is well reconized
in Europe.

c) if we assume that propirities are
bad, the period of leaks appearance
would'nt be within 4 mounths only
and, if so, many other leaks would
appears intensively in different
locations.

d) According to my knowldge, Carbon
steel in general (e.g, A106, PSL1/2,
A53) with a composition of ''99% iron
and 1% = %C, %Al, %Mn etc..'', cannot
be cheated. For the mill itself, it is
not benificial and redicilious to
cheat in carbon steels.

E) The removed A106 pipe was in
operation scince 1992. It contains
many metal loss areas and this is
normal with years but never
had similar failures in its first
years. We can explain this with the
fact that old piping was operating
with 6 speration units in full
service. however, the new replacement
is working with a produced water
comming from only 01 seprator which
make product very corrosive.

Through all of the above, i strongly suspect to the fluid/service conditions (Point 1). But any way, we are conducting some of this pipe samples to the lab in order to confirm material certificates analysis.

3) Existing Pits as you said: Yeah, Maybe the reason was the hydraulic test or are existing previously (quality check didn't mentionned any problem). But saying pits, is pertaining to a small metal loss. Such a leaks, with the observed holes diameters and shapes,(see previous photos), are big within a short period.? this is where the pardox!
PS: the Majority of pits (including all leaks) were localized intensively at the lower part of the pipe (06 O'clock position).



Alaa Edine SMAALI
Energy (Oil&Gas) Project Engineer