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Combatting Liquid Metal Attack by Mercury in Ethylene and Cryogenic Gas PlantsTask 1 - Non-Destructive Testing


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CONCLUSIONS
Based on the experimental program presented in this report, the following conclusions were made:
  1. Differences in the performance of Al-alloy 5083-0 were observed when mechanically tested in inert environments (i.e. air, water, oil) and when exposed to Hg in the presence of either air, water or oil. The material was subject to Hg attack and liquid metal embrittlement (LME). This behavior was manifested by embrittlement and reductions in the strength of the material when tested in the form of either stressed 1T compact tension (CT) specimens and pressurized pipe specimens.
  2. Maximum susceptibility to Hg attack was noted under conditions of (a) prolonged load cycling of the pressurized pipe specimen which produced the low failure pressures relative to similarly cycled control (Hg-free) specimens, and (b) when surface wetting agent was used to promote surface contact of the Al-alloy and Hg which produced increased Hg attack, LME and strength loss.
  3. Acoustic Emission (AE) monitoring of both CT specimens and pipe specimens was successful in observing characteristic emission from most specimens. These emissions can be characterized as indicated below:
Control (Hg-free) Specimens
  1. AE was observed to occur during periods of load or pressure increase.
  2. The emissions ware of highest amplitude during the onset of yielding and final fracture.
  3. AE decreased rapidly during hold periods of constant maximum load and were not observable during periods of partial or total unloading or during hold periods following these unloading events.
  4. The Kaiser effect was exhibited indicating an re-initiation of AE only after the maximum load or pressure from a previous cycle was reached or exceeded.
  5. MONPAC severity analysis of control specimens indicated maximum intensity in the location of final fracture during pressure/load cycles corresponding to yielding of the material.

Hg Contaminated Specimens
  1. The AE characteristics were more complex than those observed for the control specimens.
  2. Most specimens exposed to Hg exhibited an increase in low amplitude AE over comparable control specimens.
  3. The low amplitude AE was most prevalent during the initiation of the tests during periods of low loads in the CT specimens or low pressure (<500 psi) in the pipe specimens. The AE was somewhat random but also increased during hold periods following partial or total unloading of the specimen.
  4. Higher amplitude AE appear to occur during hold periods at maximum load in a particular loading cycle. By comparison, this behavior was very limited and attenuated rapidly in the control specimens.
  5. The AE response was difficult to evaluate in terms of Kaiser or Felicity effects. The AE described for Hg contaminated specimens in Items b and c above resulted in emissions occurring at loads and/or pressures less than the previous maximum. However, the response could not be determined to be categorized as either Kaiser or Felicity effects.
  6. MONPAC severity analysis for Hg-contaminated specimens were difficult to interpret. However, maximum intensity index occurred in the location of final fracture during load/pressure corresponding to yielding of the material. However, significant intensity ratings were obtained even at very low pressures (0 - 500 psi) in pipe specimens.

REFERENCES
  1. Kamdar, M.W., "Liquid-Metal Embrittlement", Metals Handbook, Ninth Edition, Vol. 13, Corrosion, pp 171-189.
  2. McIntyre, D. R., & Oldfield, J.W., "Environmental Attack of Ethylene Plant Alloys by Mercury", presented at NACE Corrosion Prevention in the Process Industries Conference, Amsterdam, The Netherlands, Nov. 8-11, 1988.
  3. Yuyama, S., "Fundamental Aspects of Acoustic Emission Applications to the Problems Caused by Corrosion", Corrosion Monitoring in Industrial Plants Using Nondestructive Testing and Electrochemical Methods. ASTM STP 908, G.C. Moran and P. Labine, Eds., American society for Testing and Materials, Philadelphia, 1986, pp 43-74.
  4. Fowler, T. J., "Acoustic Emission Testing of Vessels", Chemical Engineering Process, September, 1988, pp 59-70.
  5. Fleischmann, P. & Rouby, D., "Continuous Acoustic Emission during the Deformation of Pure Aluminum", pp 39-51.
  6. Wadley, H.N.G., Scruby, C. B. & Speake J.H., "Acoustic Emission for Physical Examination of Metals", International Metals Reviews, No. 2, pp 41-64.
  7. Pollock, A. A., "Acoustic Emission Capabilities and Applications in Monitoring Corrosion", Corrosion Monitoring in Industrial Plants Using Nondestructive Testing and Electrochemical Metals. ASTM STP 908, G. C. Moran and P. Labine, Eds., American Society for Testing and Materials, Philadelphia, 1986, pp 30-42.
  8. Arora, A., "Acoustic Emission Characterization of Corrosion Reactions in Aluminum Alloys", CORROSION, Vol. 40, No. 9, Sept. 1984, pp 459-464.
  9. Jones, R.H., Arey, B.W., Baer, D.R., and Friesel, M. A., "Grain-Boundary Chemistry and Intergranular Stress Corrosion of Iron Alloys in Calcium Nitrate", CORROSION, Vol. 45, No. 6., June, 1989, pp 494-502.
  10. Martin, P., Dickson, J.I., & Bailon, J. P., "Monitoring Stress Corrosion Cracking by Acoustic Emission", Corrosion Monitoring in Industrial Plants Using Nondestructive Testing and Electrochemical Methods. ASTM STP 908. G.C. Moran and P. Labine, Eds., American Society for Testing and Materials, Philadelphia, 1986, pp 75-88.
  11. Schmitt-Thomas, Kh. G., "Application of the Kaiser Effect in Acoustic Emission (AE) to Detect Hydrogen Embrittlement", copyright 1982 by the American Society for Metals, Metals Park OH 44073, pp 472-476.
  12. Kudryavtsev, V.N., Schmitt-Thomas, Kh. G., Stengel, W., & Waterschek, R., "Detection of Hydrogen Embrittlement of a Carbon Steel by Acoustic Emission", CORROSION, Vol. 37, No. 12, Dec. 1981, pp 691-695.
  13. Tonolini, F., Sala, A., & Villa, G., "General Review of Developments in Acoustic Emission Methods", Int. J. Pres. Ves. & Piping 28, 1987, pp 179-201.
  14. Wilhelm, S.M., Wu, D., "Combating Liquid Metal Attack by Mercury in Ethylene and Cryogenic Gas Plants", Task 3 - Surface Treatments, Final Report, Cortest Laboratories, Inc., Jan. 1991.

Effect of Metallurgical and Environmental Variables Upon Acoustic-Emission Energy per Unit Area of Crack Advance during Fracture of Three Steels

Grain Size 10-6m

Fracture Path

Environment

dE/dA 10-2Jmm-2

817 M40

17

Intergranular

3.5% NaCl

9

100

Intergranular

3.5% NaCl

108

17

Intergranular

H2 at 200 torr

31

897 M39

10

Transgranular

3.5% NaCl

5

10

Transgranular

H2 at 190 torr

2

10

Transgranular

H2 at 760 torr

1.5

AISI 4340

11

Intergranular

3.5% NaCl

31

200

Intergranular

3.5% NaCl

210

11

Intergranular

H2 at 200 torr

37



Nominal Chemical Composition and Tensile Properties of Al-Alloy 5083-0

Alloy 5083-0

Mn

Mg

Cu

Al

0.7

4.4

0.15

Bal.

Alloy 5083-0

Y.S. (ksi)

U.T.S. (ksi)

% Elong.

% RA

18.0*/22.8+

40.0*/45.3+

20+

32+

* = Minimum Values
+ = Maximum Values


Figure 1: Influence of electrochemical and mechanical factors in SCC

Figure 2: Embrittlement and non-embrittlement couple involving solid/liquid metals
Figure 3: Crack growth rates of Al-alloy 5083-0 in Hg at 75 F

Figure 4: Acoustic Emission (AE) aources in metals related to corrosion or SCC processes


Figure 5: AE response during tensile strain of copper


Figure 6: Relationship between AE and crack growth rate (velocity) in Al-alloy during SCC.



Figure 7: Compact Tension (CT) fracture mechanics specimen

Figure 8: Aluminum pipe specimen with butt weld and internal backing ring



Figure 9: Schemctic of compact tension specimen test frame and AE monitoring



Figure 10: Setup for pipe tests with AE monitoring

Figure 11: Precracked Compact Tension and pipe specimens in contact with Hg













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