Combatting Liquid Metal Attack by Mercury in Ethylene and Cryogenic Gas PlantsTask 1

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CONCLUSIONS
Based on the experimental program presented in this report, the following conclusions were made:

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.
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.
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

AE was observed to occur during periods of load or pressure increase.
The emissions ware of highest amplitude during the onset of yielding and final fracture.
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.
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.
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

The AE characteristics were more complex than those observed for the control specimens.
Most specimens exposed to Hg exhibited an increase in low amplitude AE over comparable control specimens.
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.
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.
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.
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.

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