L & T HAZIRA L & T HAZIRA WORKS SURATWORKS SURAT
NAME :- RAMNIK RATHOD
FABRICATION TECHNOLOGY
RG. NO. :- 1121004029
APPROVED BY. Mr. ANIL R. BONTADKAGUIDED BY.Mr. G.D.ACHARYA
CHECKED BY.Mr. S.Y.MARCHANT
SSCC : SULPHIDE STRESS CORROSION CRACKINGIGC : INTERGRANULAR CORROSION
TWO IMPORTANT CORROSIONS TYPESENCOUNTERED BY US ARE COVERED:
BROADLY CLASSIFIED AS :
LOW TEMPERATURE CORROSION ---- CORROSION AT ROOM TEMPERATURE AND BELOW
HIGH TEMPERATURE CORROSION ---- ELEVATED TEMPERATURE CORROSION INCLUDING THAT BY MOLTEN METALS
MEDIA
ONE OF THE MOST IMPORTANTFACTORS.
PROCESS FLUIDS CONTAMINANTS SOLVENTS CATALYSTS ETC.
HIC -- HYDROGEN INDUCED CRACKINGSSCC --- A CRACKING PROCESS THAT REQUIRES SIMULTANEOUS ACTIONOF A CORRODENT AND SUSTAINEDTENSILE STRESS.
WATER :
FUNCTIONS AS ELECTROLYTEHYDROLYSES INORGANIC SALTS
COMBINATION OF AIR & WATERIS DANGEROUS --- AIR SUPPLIES O2
WATER ACTS AS ELECTROLYTE
SOURCES : ALMOST EVERY PART OF PROCESS
MEDIA :
EXCLUDED : FAILURES DUE TO REDUCED SECTION AS A RESULT OF CORROSIONFAILURES DUE TO INTER - CRYSTALLINE OR TRANS - CRYSTALLINE CORROSION
H2S SOUR WATER
COMMON SOURCES : CRUDE OIL DECOMPOSITION OF ORGANIC COMPOUNDS OF SULPHUR PROCESS WATER CARRYING H2S WITH NH3 HCN ETC.
H2S REACTS WITH STEEL TO GIVE A BLACK SULPHIDE FILM
C.S. HAS GOOD RESISTANCE TO AQUEOUS SULPHIDE CORROSION
SOUR WATER
COMMON SOURCES
PROCESS WATER CARRYING H2S WITH NH3 HCN ETC
AQUEOUS H2S C.S. AND LAS ARE USED
AQUEOUS H2S + NH3 ETC CONDITION MORE SEVERE
C.S. & LAS NOT USED
DEPENDING ON SEVERITY S.S OR TITANIUM USED
HIC NACE STANDARD TM - 02 84
SSCC NACE STANDARD TM - 01 77
HIC TESTING :
SPECIMEN SIZE : 20 X 20 X 100 mm
SOLUTION :A -- SODIUM CHLORIDE + ACETIC ACID ( pH 2.7 ) SATURATED WITH H2S
B -- SYNTHETIC SEA WATER ( AS PER ASTM D 1141 ) pH 8.1 - 83 SATURATED WITH H2S
TEST DURATION : 96 HOURS ( 4 DAYS )
FINAL pH SOLUTION A -- 4.0 SOLUTION B -- 4.8 - 5.4
TEST RESULT :
THREE SECTIONS OBSERVED
BLISTERS SHALL BE NIL
CSR , CLR AND CTR SHALL BE WITHIN SPECIFIED LIMITS
CSR =100 [ (a x b) / ( W x T) ]
CLR =100 [ a / ( W x T) ]
CTR =100 [ b / ( W x T) ]
a = CRACK LENGTHb = CRACK AREA THICKNESSW = SECTION WIDTHT = TEST SPECIMEN THICKNESS
SSCC TESTING :
SPECIMEN SIZE :
ROUND BAR TENSILE SPECIMEN GAUGE DIA. 6.35 mm GAUGE LENGTH 25.4 mm ( OVERALL LENGTH 200 mm)
SOLUTION :A -- SODIUM CHLORIDE + ACETIC ACID ( pH 2.6 - 2.8 ) SATURATED WITH H2S
B -- SODIUM CHLORIDE + SODIUM ACETATE + ACETIC ACID ( pH 3.4 - 3.6 ) SATURATED WITH H2S TEST DURATION : 720 HOURS ( 30 DAYS )
FINAL pH SOLUTION A -- 4.0 SOLUTION B -- 4.0
TEST LOAD :
GENERALLY LOADED TO 72% OF STANDARD METALYIELD STRENGTH.
THIS MAY BE CHANGED BYCUSTOMER
TEST IS DEEMED PASSED IF
SPECIMEN DOES NOT BREAK
EXAMINATION AT 10 X DOES NOT REVEAL CRACKS
SUSCEPTIBLE MATERIALS : STAINLESS STEELS
PROCESS :
CORROSION RESISTANCE OF STAINLESS STEELS IS DERIVED FROM
Cr + O2 --------> Cr2O3
FROMMETAL
FROMATMOSPHERE
Cr2O3 FORMS A TENACIOUS FILM
ON THE SURFACE.
MINIMUM 12 % Cr IS NEEDEDTO MAKE STEEL STAINLESS
WHEN S.S. PASSES THROUGH THETEMPERATURE RANGE OF 425O C TO 850O C WE HAVE : C + Cr -----> Cr23C6
THE REACTION OCCURS ATGRAIN BOUNDARIES
THUS THERE IS A BAND AT THEGRAIN BOUNDARIES WHERE
Cr IS LESS THAN 12%
THIS AREA IS NO MORE STAINLESS
THE PROCESS FLUIDS AND CONTAMINANTS CAN ATTACKIN THIS AREA.
THERE ARE A LOT OF PROCESSESOF MANUFACTURING THAT TAKESS IN THIS RANGE
EG. WELDING ; CUTTING ; HOT/WARM FORMING
SERVICE TEMPERATURE CAN ALSOBE IN THIS RANGE
THUS THERE IS A NEED TO TEST THE SUSCEPTABILITY TO IGC
THIS NEED IS GOVERNED BY SERVICE CONDITIONS
APPLICABLE STD. ASTM A262
THERE ARE 5 PRACTICES
PRACTICE SOLUTION APPLICATION
A OXALIC ACID RAPID ETCH TEST IDENTIFICATION OF MATERIALS
WHICH WILL FAIL
B FERRIC SULPHATE DETECTS IGC BUT + SULPHURIC ACID NOT SIGMA PHASE SUSCEPTABILITY
C 65 % NITRIC ACID DETECTS IGC BUT AND SIGMA PHASE SUSCEPTABILITY
E Cu +CuSO4 + DETECTS IGC BUT 16 % H2SO4 NOT SIGMA PHASE SUSCEPTABILITY
F Cu +CuSO4 + DETECTS IGC BUT 50 % H2SO4 NOT SIGMA PHASE SUSCEPTABILITY
PRACTICE TEST CONDITIONS
A ETCHING AND EXAMIN AT 250 x AND 500 x
B BOILING SOLUTION 120 HOURS
C BOILING SOLUTION 240 HOURS
E BOILING SOLUTION 24 HOURS
F BOILING SOLUTION 120 HOUR
NORMALLY PRACTICE B ; C AND E
ARE USED
IN PRACTICE B AND C WEIGHTLOSS IS MEASURED.THE CORROSION RATE IS GIVENBY THE WEIGHT LOSS
THIS IS NOT THE CORROSIONRATE IN ACTUAL SERVICE.
THE RESULT IS A RELATIVEMEASURE
IN PRACTICE E SPECIMEN IS BENT THROUGH 180O OVER A FORMER OF 1T RADIUS.
THE BENT SURFACE IS EXAMINED AT 100 x AND 250 x
TEST IS PASSED IF THERE ARE NOCRACKS. CRACKS FROM EDGE ,WRINKLES AND ORANGE PEEL EFFECT ARE DISREGARDED.
PRACTICE B EVALUATION
Millimeter Per Month = 7290 x W
A x d x t
W = Weight Loss in gms.A = Total Area of the Sample in cm2
t = Time of Exposure in hoursd = Density of sample in gms / cc
Millimeter Per Month x 0.04 = Inches Per Month
Millimeter Per Month x 0.47 = Inches Per Year
Millimeter Per Month x 12 = Millimeter Per Year
Millimeter Per Month x 472 = mpy
Millimeter Per Month x Density / 3 = Milligram Per Square Decimeter Per Day
PRACTICE C EVALUATION
3440880 (W)( A ) ( d ) ( t )
MPY =
A= Total Specimen area (cm2 )W= Weight loss ( gms)
d= Density of sample ( gms / cm3 )t = Time of exposure ( hrs)