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CORROSION OF APPURTENANCES

A major advantage for using composite materials versus steel for the underground propane tank design is to eliminate the need for cathodic protection of the tank and the inspections associated with that protection. However, as the appurtenances used in conjunction with the underground propane tanks are also constructed of metal, we undertook a paper study evaluation of candidate appurtenance metals, and the likelihood of corrosion without cathodic protection of the tank. Unsurprisingly, some metals are more corrosion-resistant than others under these conditions, and results are described below.

Die Cast

AA 360

Regulator

Bonnet & body

Aluminum

Die Cast

AA 360

Cylinder Valve

Hand wheel

Forged

AA 6061-T6

Regulator

Body

Forged

C37700

Cylinder Valve

Body

Brass

Wrought

C36000

Regulator

Nozzle orifice, cylinder

valve stem

Copper

Wrought

C12200

Tubing

Conduit

Ductile Iron

Cast

N/A

Pressure Relief Valve

Manifolds, Body

Stainless Steel

Wrought

Type 302

Regulator

Spring

Steel

Wrought

Piano Wire

Regulator

Spring

ASTM A228

Zinc

Die Cast

ZA-7

Regulator

Body, Bonnet

A review was conducted of the construction materials for tank appurtenances and the consequence of their interaction with an underground environment. The main sources of data for the materials of construction of the appurtenances were vendor catalogs and supplier information. The evaluated appurtenances included service valves, relief devices, level gages, regulators, and connection piping. Table 12 summarizes the alloys that are used in most of the appurtenances, and Table 13 lists the nominal composition of the alloys.

Table 12. List of Alloys Used in Appurtenances

Base Metal

Form

Alloy Name

Part

Function

Alternative Underground Propane Tank Materials, Phase II—Final Report

23

September 2009 Battelle and Lincoln Composites

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