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CHEMICAL TREATMENT TABLE 1
Alloy composition by OES (wt%) Element Carbon Silicon
Manganese Phosphorous Sulfur
Chromium
Molybdenum Nickel Cobalt Copper Titanium
Vanadium Tungsten Tin
Boron
Nitrogen Iron
Plate A (wt%) 0.0114 0.544 0.902
0.0279 0.0056 16.3 2.17 9.98
0.150 0.342
<0.0030 0.0462 0.0360 0.0284 0.0012 0.0220 69.3
2.34% molybdenum, 10.7% nickel, and 17.9% chromium. These results were broadly consistent with the mill test cer- tificates of the welding consumables, which listed 0.031% C, 2.4% Mo, 11.9% Ni, and 18.9% Cr. The testing program was set up to ad-
dress the following: z Evaluate the effect of inhibitor on the pitting susceptibility of Type 316L steel.
z Identify the chloride threshold for pitting under the operating condi- tions of the acid storage tank.
z Determine the role of the weld on the pitting stability under operating conditions.
z Assess the difference between the stock synthetic solutions on the pit- ting stability results.
z Evaluate prevention methodologies. The electrochemical methods used
are: 1) cyclic polarization to evaluate the pitting and repassivation potential and 2) stepped potentiostatic polarization to evaluate the pit propagation kinetics. The test specimens were exposed to the following testing environments:
NACE International, Vol. 51, No. 4 Pitted plate sample as received, showing the locations of samples removed.
z Synthetic acid solution: 85% HAc (HPLC grade) + 15% high-purity distilled water
z Synthetic stock solution: 80% HAc
(HPLC grade) + 5% inhibitor + 15% high-purity distilled water
z Green stock solution: Sample of acid solution from the actual storage tank
April 2012 MATERIALS PERFORMANCE 47 FIGURE 1
Plate B (wt%) 0.0153 0.490 1.45
0.0245 0.0056 16.4 2.03 9.98
0.0753 0.154
0.0171 0.0908 0.0360 0.0116 0.0018 0.0483 69.1
ASTM A240 Type 316L Range (wt%) 0.03 max. 0.75 max. 2.0 max.
0.045 max. 0.030 max. 16-18 2-3
10-14 n.s. n.s. n.s. n.s. n.s. n.s. n.s.
0.10 max. balance