Exova Group - Singapore - Corrosion Testing

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Corrosion Testing

Exova Group provides one of the most comprehensive ranges of corrosion testing available. We also offer engineering and consulting of corrosion problems. Senior staff members with specific expertise are available to help and advise on corrosion problems or materials selection in laboratory or on-site inspection.

A wide variety of routine tests can be undertaken to evaluate the corrosion resistance of materials to environmental corrosion, pitting corrosion, resistance of materials to stress corrosion and intergranular attack.

Capabilities Include:

Sour Service Corrosion Testing:

A variety of corrosion problems can be encountered in industries such as oil and gas production, oil and gas transmission, energy conversion systems, and nuclear power systems. Such problems include weight loss corrosion, pitting corrosion, corrosion fatigue, stress corrosion cracking, sulfide stress cracking, and hydrogen-induced cracking.

Hydrogen-Induced Cracking (HIC) Test, NACE TMO284
:
This test method evaluates the resistance of pipeline and pressure vessel plate steels to Hydrogen Inducted Cracking caused by hydrogen absorption from aqueous sulfide corrosion.
An unstressed test specimen is exposed to a solution at ambient temperature and pressure and after a specified time, the test specimen is removed and evaluated.

Sulfide Stress Corrosion Cracking NACE TMO177,EFC16:

The polythionic acid (sulfurous acid and hydrogen sulfide) environment provides a way of evaluating the resistance of steels and related alloys to sulfide stress corrosion cracking. This practice can be applied to wrought products, castings, weld metal of steels or other materials to be used in environments containing sulfur or sulfides.

Pitting Test (ASTM G-48 Method A):

This Procedure is used to assist in the selection of test methods that can be used in the identification and examination of pits and in the evaluation of pitting corrosion to determine the extent of its effect.

The importance of this evaluation is to be able to determine the extent of pitting, either in a service application where it is
necessary to predict the remaining life in a metal structure, or in laboratory test programs that are used to select the most pitting-resistant materials for service. ASTM G48 Method A and ASTM A923 Method C are typical pitting corrosion tests performed.

Crevice Corrosion (ASTM G-48 Method B):

Crevice corrosion is a form of localised corrosion that occurs at metal surfaces shielded from the bulk environment, such as flange mating surfaces. Stainless steels and nickel base alloys are particularly susceptible to this form of attack in chloridecontaining waters.

The localised corrosion resistance of metals can be assessed by various methods such as exposure testing and
electrochemical testing (cyclic potentiodynamic polarisation curves to ASTM G61). Crevice corrosion exposure tests are undertaken in corrosive environments on specimens fitted with artificial crevice formers (ASTM G78).

Critical Pitting Temperature Test (ASTM G-48 Method C):

The critical pitting temperature (CPT) test is an accelerated test method used for ranking material resistance to pitting corrosion using an electrochemical technique. Tests are undertaken to ASTM G150 and other in-house procedures, in which a specimen is anodically polarised in the solution of interest (typically NaCl or sea water) at room temperature. The solution temperature is slowly increased until the electrochemical current rises sharply, indicating the initiation
of localised corrosion.

Intergranular Corrosion Tests:

Oxalic Acid Test
The oxalic acid test (ASTM A262 Practice A) is a rapid screening test for detecting susceptibility to intergranular corrosion in austenitic stainless steels. It is also included in ASTM A763 as Practice W for screening stabilised ferritic stainless steels.

Ferric Sulphate - Sulphuric Acid (Nickel Alloys)

This test is based on weight loss determinations and provides a quantitative measure of the relative performance of the material evaluated. The procedure includes subjecting a specimen to a 24 to 120 hour boil in ferric sulphate - 50% sulphuric acid. This procedure measures the susceptibility of stainless steels and nickel alloys to intergranular attack associated with the precipitation of chromium carbides at grain boundaries.

Ferric Sulphate - Sulphuric Acid (ASTM A262 Practice B)

This test is based on weight loss determinations and provides a quantitative measure of the relative performance of the material evaluated. The procedure includes subjecting a specimen to a 24 to 120 hour boil in ferric sulphate - 50% sulphuric acid. This procedure measures the susceptibility of stainless steels and nickel alloys to intergranular attack associated with the precipitation of chromium carbides at grain boundaries.

Nitric Acid (ASTM A 262 Practice C)

This procedure includes a boiling nitric acid test to evaluate the heat treatment or “sensitisation” of material. It may also be used to check the effectiveness of stabilising elements and of reductions in carbon content in reducing susceptibility to intergranular attack in chromium-nickel stainless steels.

Copper - Copper Sulphate 16% Sulph Acid (ASTM A 262 Practice E)

This procedure is conducted to determine the susceptibility of austenitic stainless steel to intergranular attack associated with the precipitation of chromium-rich carbides. Once the specimen has been subjected to the solution boil, it is bent through 180° and over a diameter equal to the thickness of the specimen being bent. This test is based on a visual examination of the bent specimen.

Copper -Copper Sulphate 50% Sulph Acid (ASTM A 262 Practice F)

This test is based on weight loss determination which provides a quantitative measure of the relative performance of the material evaluated. It measures the susceptibility of “as received” stainless steels to intergranular attack.

Chloride Stress Corrosion Cracking

Materials such as stainless steels and nickel-base alloys can be susceptible to stress corrosion cracking (SCC) in chloride containing environments. Exova undertakes ranking tests to determine resistance to chloride SCC including ASTM G36 (Boiling Magnesium Chloride Solution) and ASTM G123 (Boiling Acidified Sodium Chloride Solution). Specimen types commonly used are: tensile (ASTM G49, NACE), U-bend (ASTM G30), C-ring (ASTM G38), Bent beam (ASTM G39). In addition, we can undertake specialised testing in customerspecific service environments.

Full Ring Test (OTI 95 635)

The Full Ring Test is widely considered the most appropriate
test method for qualifying line pipe steels and associated welds for sour service.The Exova Corrosion Centre holds UKAS accreditation for this test - the only laboratory World Wide to hold the accreditation. The Centre has extensive facilities to undertake this type of test and has the capability to test pipes up to 52 inch diameter. 25 stations are available. Extensive strain gaging is often required to understand the load characteristics in this test. This is undertaken by Strain Measurement Services who, together with the Director of the Corrosion Centre, were heavily involved in the development of the test method. The test method being published by the UK Health and Safety Executive as OTI 95 635.

Salt Spray (Neutral / Fog), ASTM B117:

This is the most commonly used salt spray for testing of inorganic and organic coatings, especially where such tests are used for material or product specifications. Government
agencies and the automotive industries have developed standard requirements for coating testing. Salt Spray testing is a tool for evaluation the uniformity of thickness and degree of porosity of metallic and nonmetallic protective coatings. A number of samples can be tested at once depending upon their size.

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