SSCC : SULPHIDE STRESS CORROSION

CRACKING

IGC : INTERGRANULAR CORROSION

TWO IMPORTANT CORROSIONS TYPES

ENCOUNTERED 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 IMPORTANT

FACTORS.

PROCESS FLUIDS

CONTAMINANTS

SOLVENTS

CATALYSTS ETC.

HIC --

HYDROGEN INDUCED CRACKING

SSCC ---

A CRACKING PROCESS THAT

REQUIRES SIMULTANEOUS ACTION

OF A CORRODENT AND SUSTAINED

TENSILE STRESS.

WATER :

FUNCTIONS AS ELECTROLYTE

HYDROLYSES INORGANIC SALTS

COMBINATION OF AIR & WATER

IS 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 CORROSION

FAILURES 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 LENGTH

b = CRACK AREA THICKNESS

W = SECTION WIDTH

T = 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 METAL

YIELD STRENGTH.

THIS MAY BE CHANGED BY

CUSTOMER

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

FROM

METAL

FROM

ATMOSPHERE

Cr2O3 FORMS A TENACIOUS FILM

ON THE SURFACE.

MINIMUM 12 % Cr IS NEEDED

TO MAKE STEEL STAINLESS

WHEN S.S. PASSES THROUGH THE

TEMPERATURE RANGE OF 425O C

TO 850O C WE HAVE :

C + Cr -----> Cr23C6

THE REACTION OCCURS AT

GRAIN BOUNDARIES

THUS THERE IS A BAND AT THE

GRAIN BOUNDARIES WHERE

Cr IS LESS THAN 12%

THIS AREA IS NO MORE

STAINLESS

THE PROCESS FLUIDS AND

CONTAMINANTS CAN ATTACK

IN THIS AREA.

THERE ARE A LOT OF PROCESSES

OF MANUFACTURING THAT TAKE

SS IN THIS RANGE

EG. WELDING ; CUTTING ; HOT/WARM

FORMING

SERVICE TEMPERATURE CAN ALSO

BE 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 WEIGHT

LOSS IS MEASURED.

THE CORROSION RATE IS GIVEN

BY THE WEIGHT LOSS

THIS IS NOT THE CORROSION

RATE IN ACTUAL SERVICE.

THE RESULT IS A RELATIVE

MEASURE

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 NO

CRACKS. 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 hours

d = 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)

PRACTICE E

EVALUATION

FAILED MARGINAL

( DOUBTFUL )

PASSED

STEP DUAL

DITCH

As Received

After exposure

After bending

PARENT METAL

100 x

100 x

100 x

HAZ

Before exposure

After exposure

WELD

Before exposure

After exposure

PASSED

FAILED