A bit of googling turns up some info that indicates that it should be
possible to get decent longevity for buried aluminum radial fields:
Al-alloys in Soil : Corrosion Hazards
which has this:
Corrosion of the copper-containing 2XXX and 7XXX series alloys in moist
low-resistivity soils, measured by weight loss and pitting depth, is
several times greater than corrosion of the more resistant 1XXX, 3XXX,
5XXX, and 6XXX series alloys. Use of cathodic protection or Alclad products
effectively reduces corrosion or limits penetration.
In actual service, alloys 3003, 6061, and 6063 (which are most frequently
used for pipelines) showed corrosion attack ranging from almost none to
deep pitting after many years of service in unprotected conditions.
Cathodically protected sections of some of the same pipes in corrosive soil
showed no attack or only mild etching.
--- This seems to say that picking the right alloy AND some cathodic
protection might be a good way to do it. Note that one can create the
protection current either with a sacrificial electrode (so the current is
produced by galvanic action) OR by externally applying a suitable current
to an inert electrode. Seems to me that the latter scheme, with a solar
panel, might be the way to go, depending on the current required.
And also this:
CORROSION RESISTANCE OF ALUMINUM DRAINAGE PRODUCTS: THE FIRST 25 YEARS
Abstract:A description is provided of laboratory and field evaluation
procedures used to evaluate the corrosion resistance of aluminum culverts,
storm drains, structural plates, and retaining walls. Relationships of the
physical and chemical properties of waters and soils with the performance
of aluminum pipe are discussed. Results indicate that there is a
qualitative relationship between corrosion resistance of aluminum and the
water and soil pH and resistivities, with good performance of unprotected
aluminum pipe observed in the pH range of 4 to 9 and minimum resistivities
greater than 500 ohm-cm. The extent of localized corrosion on the soil side
of pipe can be accurately measured by portable ultrasonic metal thickness
instruments. The low pitting corrosion rates of the thin wall Alclad 3004
culvert are demonstrated to be the results of the galvanic protection
provided by the cladding alloy.
Supplemental Notes: This paper appeared in Transportation Research Record
N1001, Symposium on Durability of Culverts and Storm Drains.
TRIS Files: HRIS
Pagination: p. 77-87
<http://pubsindex.trb.org/document/view/default.asp?lbid=269730>Summerson, T J
Features: Figures (12); References (15); Tables (4)
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