FAILURE ANALYSIS ON 6 PWD P-4290 DISCHARGE LINE SUMMARY Failure analysis has been conducted to find out the root cause of the failure on 6 produced water injection on 6 Discharge line of P-4290 at Plant, where a leaking was happen on 3.00 oclock due to SRB (Sulfate reducing Bacteria) attack. SRB attack occurs on bottom wall pipe and will cause a localized corrosion. The assumption is also supported by the rotten egg / sulfur smell plus black mark, observed on corroded area, which is very common for SRB corrosion. To minimize similar SRB attack in the future, it is recommended to perform a good circulation of water regular frequently,injects Biocide with proper dosage at upstream of discharge line of pump if it applicable. DISCUSSION On November, 2011, it was reported a leak occurred on 6 Discharge line of P-4290 at Plant due to Bacterial corrosion. The pipe was made by API 5L Gr-B. This line is used to drain produced water from discharge of Produced water pump of P-4290 as shown in fig.1

Fig.1 Process Schematic The line is located on underground area, and wrapped to prevent from external corrosion attack. The position of the leak on 3.00 oclock as shown in fig.2

Fig.2 Leak Position

The actual condition of inner wall pipe is shown in fig.3

Fig.3 Internal Profile

Wall thickness measurement was performed on pipe for 6 Discharge line of P-4290 after leaking

on November 2011 (see attachment). Ultrasonic wall thickness measurement on the leaking area

shows that significant wall loss was occurred.

The presence of sulfate reducing bacteria in water may be determined by sensory perception.

Since hydrogen sulfide is a by product of their metabolism, the rotten egg odor associated with

this sulfur compound is an indication that sulfate reducing bacteria (SRB) may be present in the

sample leaking especially in a carbon steel. The rotten egg / sulfur smell plus black mark

observation is very common to determine SRB corrosion.

Fig.4 Rotten egg / Sulfur Smell Observation.

A water system naturally contains sulfate based compounds, but when sulfite is added to a closed

water system as an oxygen scavenger and corrosion inhibitor, the sodium sulfite is oxidized to

sodium sulfate as indicated (1) below.

2 Na+1 + SO3-1 + O2-2 = 2 Na+1 + SO4 -2 (1)

Excess electrons occur in a water system as a result of iron corrosion at the anode & cathode cells

as indicated in reactions (2) & (3) bellow,

4 Fe = 4 Fe+2 + 8 e-1 (anode reaction) (2)

8 H+1 + 8 e-1 = 8 H (cathode reaction) (3)

The resultant accelerated corrosion mechanism of iron by the sulfate reducing bacteria is illustrated

in equations (4), (5), (6), (7) & (8) below.

SO4-2 + 8 H = S-2 + 4 H2O (cathodic depolarization by SRB) (4)

8 H2O = 8 OH-1 + 8 H+1 (dissociation of water) (5)

2 H+1 + S-2 = H2S (reversible reaction) (6)

Fe+2 + S-2 = FeS (anode corrosion product) (7)

3 Fe+2 + 6 (OH)-1 = 3 Fe(OH)2 (cathode corrosion product) (8)

CONCLUSION The leaking on 6 Discharge line of P-4290 was occurred 3 oclock position. The failure root cause

of the leak is caused by Microbiologically Induced Corrosion (MIC) which have typical species is

Sulfate Reducing Bacteria (SRB). The assumption is also supported by the rotten egg / sulfur smell

plus black mark, observed on corroded area, which is very common for SRB corrosion. The growth

of SRB is not mitigated by Biocide and then making high population at low flow on wall pipe which

are causing leak at 3 oclock position.

RECOMMENDATION To reduce SRB attack on 6 Discharge line of P-4290, it is recommended to :

1. Perform a good circulation of water regular frequently.

2. Injects Biocide with proper dosage at upstream of discharge line of P-4290 if it applicable.

Prepared by :

References : - Corrosion threats handbook, upstream oil and gas production

- Corrosion by Sulfate Reducing Bacteria, G.F Yuzuwa, P.Eng