investigation report on the failure of makkah-taif water tr

8/3/2019 Investigation Report on the Failure of Makkah-taif Water Tr

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AN INVESTIGATION REPORT ON THE FAILURE OF

MAKKAH-TAIF WATER TRANSMISSION SYSTEMDr. Anees U. Malik

Research & Development Center

Saline Water Conversion CorporationP.O.Box 8328, Al-Jubail -31951, Saudi Arabia

Tel: + 966-3-343 0333, Fax: + 966-3-343 1615

Email: [email protected]

March 1989

INTRODUCTION

Makkah- Taif Water Transmission line is about 140 km long. Water is transmitted from

Shoiba (Pumping Station 1, PSI), in 2 pipelines A and B (56" diameter each) to PSII near

Makkah about. 97 km away. From PSII, the water is carried to Taif through a single 42"

diameter line (Line C). Makkah- Taif Water Transmission System was commissioned in 1988

(Line A&B: end of May 1988 & Line C: end of Aug 1988). The underground water

transmission lines have inside cement-mortar lining on carbon steel pipes except at the

pumping stations where the pipes have epoxy lining.

During my two visits to MTWTS pipe lines (A and B at PSI in April 1989 for inspection, the

water was drained off and I went inside the pipe lines and carried out a thorough examination

of the lines covering various distribution lines and valve systems. I also examined closely the

valve systems under open and close positions. Epoxy lining and corrosion product samples

were collected from the different locations of the pipe lines and valve systems and were

analyzed subsequently in the Lab.

OBSERVATIONS

Epoxy Lining

The pipelines have inside polyamide-cured epoxy lining at the pumping stations otherwise,

the whole lengths of buried transmission lines have inside cement-mortar lining. The erosion

or deterioration of the epoxy is widely distributed but not continuous. It is predominant at the

joints of pipelines and still more at the areas in the vicinity of the valves. The disturbed areas

of lining are identified either by the appearance of innumerable small bubbles/blisters and/or

cluster of reddish brown corrosion products. The reddish brown corrosion product is
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Some photographs (courtesy: ILF) taken at the sites reveal the severity of corrosion of the

valve system (Fig. 8 to 19).

RESUL TS & DISCUSSION

Epoxy Lining

The properties of the epoxy coating derive both from the type and molecular weight of the

epoxy resin and from the copolymer-curing agent (polyamide) that is used to cross link with

it. In general, polyamide-cured coating has good moisture resistance and excellent adhesion

over steel and concrete. Polyamide-cured epoxies have been widely used as industrial and

marine maintenance coatings. The polyamide-epoxy lining can be applied either using a

water-soluble organic solvent (hydrophilic) or by heating (thermally treated). The off whiteepoxy material used in pipe lining is a polyamide-cured epoxy applied inside the steel pipe

surface using a hydrophilic solvent like n-butanol or n-propyl glycol. The solvent present at

the steel/lining interface evaporates resulting in the formation of blisters or bubbles inside the

paint. A large number of bubbles are therefore appeared inside the epoxy lining. The

dissolved oxygen and water permeate through the bubble. The bubble is subsequently broken

and the steel is exposed to water and oxygen. An electrochemical cell is established and in

consequence, corrosion occurs giving rise to corrosion products like FeOOH. Fe2O3 and

Fe3O4. The voluminous corrosion products underneath the bulged and crack coating produce

local stresses resulting in the emanation of the reddish brown products through lining. Due to

exposition of the pipe to high turbulence in the vicinity of the valve or at the joints, the

bubbles are bursted exposing directly the steel to water and oxygen and therefore, corrosion

attack is much more aggressive at these locations. This type of attack is characterized by a

cluster or cobweb like pattern and may be named as Filiform Corrosion. Under he present

conditions, with increasing operational time, the increase in the intensity and magnitude of

the corrosion of the pipe line would be phenomenal resulting in the replacement of lining

with the corrosion products. This has been observed in some locations of the pipeline.

The application of liquid in the polyamide-cured epoxy lining seems to be the main reason

for the unsatisfactory performance of the lining. In existing conditions, the use of thermally

applied lining perhaps would have been more appropriate. There is no information about the

chemical formulation of the polyamide-cured epoxy lining used in MTWTS, However,


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specially formulated polyamide-cured epoxies are now available which have the capability to

displace water. From the substrate surface. Such materials can even be applied and cured

Underwater to form corrosion-resistant coatings.

Valve System

The valve body, ball plug bore edge and the balls were found moderate to heavy corroded.

The corrosion is uniform and scales are easily exfoliable. Exposure of valve system to

stagnant water at some stage of operation might have provided conditions for the corrosion or

alternatively, mechanical non-alignment of the valve system to the pipeline might have

created conditions favorable for initiation of corrosion. Crevices/gaps between ball plugs bore

edge and polyamide coating on one side and ball plug bore edge and internal valve body on

the other side seem to be ideal sites for corrosion. The water is held up between the

gaps/crevices and caused corrosion of ball plug bore edge and internal valve body surface.

Since ball plug bore edge is more corroded initially it acts as a cathode in the later stage and

therefore, caused enormous corrosion of valve body. Cavities formed as a result of the

exfoliation of the corrosion products are the attractive sites for local corrosion and this would

further aggravate the situation.

The probable materials used for the valve systems (cast steel and cast iron) are perhaps not

able to cope with the mildly corrosive environment sustaining in the stagnant pipe line

otherwise the effect of corrosion would not have been so deleterious.

CONCLUSIONS

Epoxy Lining

The failure of the epoxy lining may be attributed to the use of liquid-applied polyamide-cured

epoxy material. This has resulted in the blistering of lining and subsequent corrosion.

Valve System

The severe corrosion attack on valve system is initiated either due to the exposure of valve

system to stagnant water at some stage of operation or due to mechanical non alignment of

the valve system and the pipe line. If former is the cause of corrosion then this attack would

have been prevented by the use of better valve materials.


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RECOMMENDATIONS

Epoxy Lining

The replacement of the existing liquid-applied polyamide-cured epoxy lining by a thermally

applied one would have been the best course. However, this provision seems to be almost

impracticable. Therefore, the measures should be taken to replace the existing lining with a

different epoxy material that has a formidable capability to displace water from the substrate

(steel pipe) surface.

Valve System

Competent design/mechanical experts should test the mechanical alignment of all the valves

and their working. If the system is malfunctioning then acting up on expert's opinion

appropriate action could be taken. Considering the severity of corrosion, the best course will

be to replace all the valves of the pipelines by new valves of superior materials and better

mechanical specifications. Alternatively, all the valves may be cleaned and cleared from the

corrosion products and then performance should be watched for 2-3 months on a trial basis

till a final decision regarding the replacement is being taken.


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Figure 1. Formation of blisters/bubbles in epoxy-lined MTTS at PSII

Figure 4. Appearance of corrosion products emanated from the bubbles in epoxy linedPipeline A at PS 1.


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Figure 3. Cluster/cobweb like appearance of corrosion products in epoxy

lined pipeline A at PS-I

Figure 2. Severe corrosion in the epoxy lined pipe line A at PSI at the locations

near the valve.


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Fig. 5. Corrosion on the walls of epoxy lined pipe line A

Fig. 6. Poorly adhered epoxy lining came out on application of pointed edge of

screw driver


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Fig. 7. Off green color epoxy lining usually does not show bubble/blister

formation

Fig. 8. a typical photograph showing corrosion of (a) ball plug bore edge and

(b) internal surface of valve body


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Fig. 9. Corrosion of ball valve MOV-1569A in epoxy lined to Fig. 11 pipe A at

PS I.

Fig.10. Corrosion of ball valve MOV-1569A in epoxy lined to Fig. 11 pipe A at

PS I.


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Fig. 11. Corrosion of ball valve MOV-1569A in epoxy lined to Fig. 11 pipe A at

PS I.

Fig. 12 Corrosion at ball plug bore edge isolation valve SV 01 at PS I line A


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Fig. 13a. Condition of corroded valve (ball plug bore edge and internal surface

of valve body) after clearance of corrosion products by means of

power brush

Fig. 13.b Condition of corroded valve (ball plug bore edge) after clearance

Of corrosion products by means of power brush


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Fig. 14. Photograph showing internal surface of valve body in corroded SV-01

Isolation valve in PSI line A (a)

Fig. 15. Photograph showing condition of corroded valve (SV-01) in close

position. Chrome polished surface of the ball shows reflection


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Fig. 16. Corroded ball valve MOV-2501 (partially closed): Suction line isolation

Valve PS II line A; valve body corroded

Fig. 17. Corroded ball valve MOV-2501 (opened): Suction line isolationvalve PS II line A; full internal surface view of the corroded body.


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Fig. 18. Corrosion of discharge line isolation ball valve MOV-2501 (closed

position): PS II line A; Note the corrosion of chrome polished ball.

Fig. 19. Same as above, Closer view of corroded ball shows deposition of oxides

investigation report on the failure of makkah-taif water tr

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