CORROSION TESTS

PITTING CORROSION

The test method covers procedures for the determination of the resistance of stainless steels and related alloys to pitting and crevice corrosion when exposed to oxidizing chloride environments.

ASTM G48 Standard Test Method for Pitting and Crevice Corrosion, Ferric Chloride Test involves exposing a specimen to a highly oxidizing acid chloride environment. The importance of Ferric Chloride Test 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.

INTERGRANULAR CORROSION

Intergranular corrosion in stainless steels may result from precipitation of carbides, nitrides or intermetallic phases. Only in the most highly oxidizing solutions can intergranular attack be caused by intermetallic phases. When a test is to be restricted to carbides, in a material containing nitrides or intermetallic phases, a less oxidizing solution is chosen. To conduct these tests, a carefully chosen method that is suitable for the steel grade and grain boundary composition to be tested is applied.

This test cover the following five methods: Practice A to F. Susceptibility to intergranular attack associated with the precipitation of chromium carbides is readily detected in all five tests. Sigma phase in wrought chromium-nickel molybdenum steels, which may or may not be visible in the microstructure, can result in high corrosion rates only in nitric acid. Sigma phase in titanium or columbium stabilized alloys and cast molybdenum-bearing stainless alloys,which may or may not be visible in the microstructure, can result in high corrosion rates in both the nitric acid and ferric sulphate-sulphuric acid solutions.

HYDROGEN INDUCED CRACKING (HIC) NACE TM0284

Professional Testing performs HIC test to evaluate the resistance of pipeline and pressure vessel plate steels, pipes, fittings and flanges 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.

The test specimen are cut into sections and examined under a microscope for hydrogen-induced cracks. The dimensions of any such cracks are recorded and used to compute the values in percentage for Crack Length Ratio (CLR), Crack Thickness Ratio (CTR) and Crack Sensitivity Ratio (CSR).

SULFIDE STRESS CRACKING ( Four Point Bent Test & Proof Ring Test ) NACE TM0316 / NACE TM0177

Sulfide stress corrosion cracking (SSC) is a form of hydrogen embrittlement cracking which occurs when a susceptible material is exposed to a corrosive environment containing water and H2S at a critical level of applied or residual tensile stress.

SSC FOUR POINT BEND TEST

The SSC Four-Point Bend Test (SSC-FPBT) is a constant displacement test that is performed using four point loading jigs where one face of the specimen is bent and stressed in tension and the other face is bent in compression and then immersed in NACE Solution “A” for a period of 720 hours (30 days) in accordance with NACE TM0316 requirements.

SSC PROOF RING TENSILE TEST

The SSC Proof Ring Tensile Test is a simple constant load device for round tensile specimens used to evaluate metal for environmental cracking resistance under uniaxial tensile loading. A tensile specimen is loaded to a particular stress level to give a failure/no-failure test result after 720 hours (30 days) testing in sour service environment consisting of chloride containing solution saturated with H2S gas, as specified in NACE TM0177 Method A.