WULC_14_1100-C v Venugopal OMIFCO Failure Analysis of HP Ammonia Pumps Suction Line Weld Joint

7/24/2019 WULC_14_1100-C v Venugopal OMIFCO Failure Analysis of HP Ammonia Pumps Suction Line Weld Joint

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OMIFCO PROJECT SPONSORS

OOC - Oman Oil Company S.A.O.C, Oman

(50 % shareholder)

KRIBHCO - Krishak Bharati Cooperative Limited, India

(25 % shareholder)

IFFCO - Indian Farmers Fertiliser Cooperative Limited, India

(25 % shareholder)

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PROCESS UNITS

(i) Total installed capacity

Ammonia : 11,90,000 MT/year

Urea : 16,52,000 MT/year

(ii) Plant Capacity Licensor

Ammonia* 2 x 1750 MTPD M/s Haldor Topsoe

Urea** 2 x 2530 MTPD M/s Snamprogetti

* For CO2 removal system, the process licensor : M/s Giammarco Vetrocoke

** For Urea granulation, the process licensor : M/s Hydro Fertiliser Technology

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FAILURE ANALYSIS OF

COMMON SUCTION LINE WELD JOINT

OF HP AMMONIA PUMPS OPERATING AT 23 BAR

IN

UREA PLANT.

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Site Photograph that indicates weld joint atthe pipe has broken and snapped off from itslocation during operation


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Investigation byTCR Advanced Engineering Services Pvt. Ltd., Vadodara, INDIA

Visual Examination

Low Magnification Examination

Wet Fluorescent Magnetic Particle Inspection ( WFMPI ) Chemical Analysis

Scanning Electron Microscopy ( SEM ) Analysis

Energy Dispersive Spectrum ( EDS ) analysis

Microstructure Examination ( Metallography )

Tensile Test

Impact Test

Hardness Test

Micro - Hardness Test

Micro Hardness Profile Measurement

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Visual Examination

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OMIFCO - Oman8

Rust marks in the areaadjacent to the weld ofpainted pipeline.

ID surface of the pipe looksblackish brown indicatinggeneral form of corrosion.

Fracture surface is flat andin transverse direction. Atone location weld material hadpeeled off.

The counterparts of the

failed joint displaced off-centre.

Weld joint failed from theHAZ region as well as

from the weld region.


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OMIFCO - Oman

view near fast fracture surface.

The weld bead had come out on either side of the pipe, Somepitting/dent marks are seen on ID.

Rust marks are noticed on the fracture surface. No thinning or deformations observed at the failed location.

At all region fracture surface displayed flat surface with coarsestriations.

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LOW MAGNIFICATION EXAMINATION

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low magnification view at the

fracture surface.

Multiple origins are observedfrom OD as well as ID Surface.

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Indicates that the fracture has

taken place precisely at the

fusion zone and perhaps

moved into the weld.

ID surface shows general form

of corrosion having blackish

grey color.

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Photographs at low magnification( 33 X ) shows multiple originsin form of ratchet marks.

Presence of corrosion products observed at the crackedsurface.

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The fracture surface is fully covered with adherent corrosiondeposits.

Photographs indicates that initial crack movement is in fatiguemode.

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NON - DESTRUCTIVE TEST

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Photograph indicates theID surface Weld HAZview in WFMPI (WetFluorescent Magnetic

Particle Inspection) testedcondition.

Secondary Transverse

Hairline Cracks wereobserved at HAZ.

No other defectsobserved either at OD

or at ID.

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CHEMICAL ANALYSIS

pipe specimen and weld zone.

It conforms to the material specification

A 333 Gr. 6

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SCANNING ELECTRON MICROSCOPY ( SEM )

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SEM reveals crack

initiation in fatiguemode and movement inperipheral direction inhigh cycle fatigue

mode. corrosion marks on the

fracture surface.

crack propagated under

combined influence ofcorrosion and fatigue.

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ENERGY DISPERSIVE SPECTRUM ( EDS ) ANALYSIS

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Result of EDS Analysis.

Presence of Oxygen, Sodium, Magnesium, Chlorine, and Calciumconfirm that the corrosion is induced by the salty marineatmosphere.

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Energy Dispersive Spectrum ( E D S )

57.74Iron

0.87Calcium

1.07Chlorine

0.93Silicon

0.87Magnesium

1.31Sodium

37.22Oxygen

% ageElements


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MICROSTRUCTURE EXAMINATION

METALLOGRAPHY )

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corrosion fatigue crackinghaving trans-granular nature

of propagation. It is having mild branching

nature.

Matrix is banded ferriteand pearlite.

crack observed adjacent tofracture surface on pipeindicating another origin of

fatigue crack.

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corrosion damage entering the metal surface from the pittinglike surface damage at weld location.

Matrix is ferrite dendrites with carbides.

It also indicates corrosion fatigue crack moving preciselyalong the fusion zone of the weld.

The nature of crack is trans-granular.

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EDS ANALYSIS AFTER METALLOGRAPHY

EDS Analysis carried out after metallography inside the crack.

The presence of Oxygen, Sulphur and Chlorine on OD crackconfirm that it is a corrosion product induced by marine

atmosphere.

Presence of Oxygen, Sodium, Sulphur and Calcium at ID crackindicates that there is a water based corrosion product.

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TENSILE TEST

Tensile Test results meet the requirements of ASTM A 333 Gr.6for tensile properties.

V NOTCH CHARPY IMPACT TEST

V notch charpy test was carried out on the sample drawn at ()56 C.

Impact Test results meet the requirement of ASTM A 333Gr.6.

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HARDNESS TEST


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HARDNESS TEST

General hardness was measured at different locations.

Hardness results meets with the requirements of ASTM A 333

Gr.6.

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MICRO - HARDNESS TEST Micro-hardness test conducted at different locations. indicating a

normal trend. Values at OD and ID are little on higher side as slight cold deformationis given during pipe making.

The lower values at crack tip and fracture surface indicate that the

welded joint had slight inherent stresses which were relieved after thefracture.

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207 , 215 , 213I D

170 , 168 , 172Core

207 , 209 , 208OD

191 , 186 , 209At Fracture Surface

194 , 198 , 207At Crack Tip

196 , 212 , 213Origin of Crack

Micro - Hardness in VPN @ 100 gm

Load

Location I D


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MICRO - HARDNESS PROFILE

The result of micro-hardness profiled is shown in table.

The profile does not indicate any severe abnormality. Values at weld

and HAZ are on slightly higher side.

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SUMMARY

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The butt weld joint failed circumferentially during the serviceafter 39 months of operation in February 2008.

The pipe material is ASTM A 333 Gr. 6. The pipe dimensions were8 X Sch. 20.

A Leak was observed from the same weld joint during first week ofSept., 2007 and again in the first week of Jan., 2008 and the same

was arrested by injecting sealing compound using clamp. Visual Examination indicates complete snapping of the pipe at the

failure location from the weld joint.

Circumferential corrosion damage is seen near to the failure

location where the paint has peeled off precisely at the region ofclamp.

Fracture has occurred perpendicular to longitudinal directionand in a single plane from the weld / HAZ region.

Fracture surface comprises of both fatigue and brittle nature. Low Magnification View confirms cracking both from OD and ID

and in the weld zone near Weld HAZ.

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SEM Analysis confirms that the cracking is a typical fatigue

damage starting both from ID and OD and Assisted by mildcorrosive atmosphere.

Crack movement is in combined influence of high cycle fatigueand corrosion mode.

Secondary cracks were also noticed on the fracture surfaceswhich were also having corrosion fatigue nature along withcorrosion products.

EDS Analysis confirms that the corrosion damage on fracturesurface is due to salt containing Moisture from marineatmosphere.

Overall microstructure of weld metal, HAZ and parent metal is

normal and acceptable for the service. Pitting like corrosion damage at OD surface.

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Tensile Test results and Charpy V Notch Impact Test at (-)56C results were satisfactory.

Micro Hardness Values indicated normal trend in theirvariation. Slightly higher hardness observed at HAZ but whichis normal.

Micro Hardness profile was also normal.

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CONCLUSIONS

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Visual Examination clearly indicates that the fracture has taken place intransverse direction perpendicular to the pipe axis.

The failure has taken place both from weld and HAZ.

From Visual and Low Magnification Examination multiple origin of thecracks all over the circumference starting from both OD as well as ID.

The pipe is exposed to the sea water atmosphere and the paint hadpeeled off at some places near welding and corrosion has taken place.

Optical metallography indicates pitting like damage on OD surface of thepipe.

Both SEM Analysis and Optical Metallography confirm that the failure is onaccount of high cycle fatigue assisted by corrosion.

The cracking has taken place in the weld and HAZ zone as seen in WFMPI

and Optical Metallography. All the cracks are filled with corrosionproducts. Even the secondary cracks seen on the fracture surface werehaving corrosion fatigue nature.

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HAZ microstructure shows slight inclination towards having some internalstresses which is reflected from micro-hardness values.

Pipe has been supported especially at elbow joint where the change in

the direction of the Liquid Ammonia takes place. Pipe line connectingthe pump, hence some vibrations induced on it. In this case the vibrationstresses induced appear more severe in nature.

The surface corrosion in form of tiny pits has provided favorable sites for

stress concentration to take place both from OD and ID. The humid salty marine atmosphere provided the climate for corrosion to

take place.

The prevailing vibrations on the pipe line induced the fluctuating

stresses. Thus, naturally the most vulnerable site for corrosion fatigue damage to

take place is weld and HAZ

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CAUSE OF FAILURE

The failure has taken place on account of fatigue crackingassisted by corrosion initiated at weld and HAZ both from OD andID.

The prevailing marine atmosphere, the vibration stresses duringservice and the surface corrosion that acted as stressconcentration site resulted as corrosion fatigue.

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RECOMMEDATIONS BY M/s TCR Advanced Engg.Services Pvt., Ltd., Vadodara, INDIA

Stress Analysis of pipe line both from fluid dynamics as well as

transmitted vibrations from pump.

Quality of the painting on the pipe surface especially near weldedjoint has to be improved to avoid peeling and subsequent

underneath corrosion damage.

All other vulnerable weld joints may be evaluated with WFMPI, andIn-Situ Metallography for preventive measure.

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ACTIONS TAKEN BY OMIFCO

Engaged M/s Project & Development India Limited to carry outthe

Flexibility Analysis of the Line from the Ammonia Receiver ( V 105 ) to the Ammonia Booster Pump ( P 105 A/B ) and from thedischarge of Ammonia Booster Pump ( P 105 A/B ) to the suctionof HP Ammonia Pump ( P 101 ).

The report indicate that there is no over stressing at any point inthe pipe line and no alarming forces and moments at the restrainpoints.

Also engaged M/s ELECTROWATT ENGINEERING , Muscat to carryout similar stress Analysis.

The report also indicate that stresses are within the allowablelimits and hence, failure of welding in the piping is not due to

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MOST PROBABLE CAUSE

Finally, it is concluded that this failure might bedue to corrosion , material defect and internal

stresses owing to welding joint.The stresses may have developed on welding due to

injection of sealing compound & clamping.

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FUTURE COURSE OF ACTIONS BY OMIFCO

To carry out WFMPI or Fluorescent Dye Penetrant Testing and in Situ Metallography of other vulnerable weld joints for preventive

measure on available opportunity.

Quality of painting on the pipe surface especially near welded jointshall be shall be improved to avoid peeling and subsequent

underneath corrosion damage.

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WULC_14_1100-C v Venugopal OMIFCO Failure Analysis of HP Ammonia Pumps Suction Line Weld Joint