Note 8. Property, Plant and Equipment

The historical costs of our property, plant and equipment and related accumulated depreciation balances were as follows at the dates indicated:

	Estimated Useful Life in Years	December 31,
	Estimated Useful Life in Years	2011		2010
Plants, pipelines and facilities (1)	3-45 (6)	$	22,354.4	$	19,388.4
Underground and other storage facilities (2)	5-40 (7)		1,388.6		1,477.8
Platforms and facilities (3)	20-31		637.5		637.5
Transportation equipment (4)	3-10		151.5		119.1
Marine vessels (5)	15-30		615.9		560.0
Land			136.1		123.4
Construction in progress			2,145.6		1,607.2
Total			27,429.6		23,913.4
Less accumulated depreciation			5,238.0		4,580.5
Property, plant and equipment, net		$	22,191.6	$	19,332.9

(1) Plants and pipelines include processing plants; NGL, natural gas, crude oil and petrochemical and refined products pipelines; terminal loading and unloading facilities; office furniture and equipment; buildings; laboratory and shop equipment and related assets. (2) Underground and other storage facilities include underground product storage caverns; above ground storage tanks; water wells and related assets. (3) Platforms and facilities include offshore platforms and related facilities and other associated assets located in the Gulf of Mexico. (4) Transportation equipment includes tractor-trailer tank trucks and other vehicles and similar assets used in our operations. (5) Marine vessels include tow boats, barges and related equipment used in our marine transportation business. (6) In general, the estimated useful lives of major assets within this category are: processing plants, 20-35 years; pipelines and related equipment, 5-45 years; terminal facilities, 10-35 years; office furniture and equipment, 3-20 years; buildings, 20-40 years; and laboratory and shop equipment, 5-35 years. (7) In general, the estimated useful lives of assets within this category are: underground storage facilities, 5-35 years; storage tanks, 10-40 years; and water wells, 5-35 years.

In October 2011, we announced the execution of definitive agreements to sell the equity interests of a wholly owned subsidiary, Crystal Holding L.L.C. (“Crystal”), which owns two underground salt dome natural gas storage facilities and associated pipelines located near Petal and Hattiesburg, Mississippi. The facilities have a combined 28.8 Bcf of total storage capacity (of which 18.6 Bcf is total working gas capacity) and are owned by Petal Gas Storage, L.L.C. (“Petal”) and Hattiesburg Gas Storage Company (“Hattiesburg”). We completed the sale of Crystal on December 1, 2011 and received $547.8 million in cash, net of working capital adjustments. We recorded a $129.1 million gain on the sale of Crystal. At December 1, 2011, the net carrying value of our investment in Crystal was approximately $411.9 million, of which $356.2 million was the total net carrying value of Crystal's property, plant and equipment.

We determined that the financial results of Crystal did not meet the criteria to be classified as discontinued operations. Following the sale, we continue to have significant commercial contracts and operational arrangements at the Petal and Hattiesburg facilities, which are adjacent to and currently share operating assets with our retained Petal, Mississippi NGL storage facility.

The following table summarizes our depreciation expense and capitalized interest amounts for the periods presented:

	For Year Ended December 31,
	2011		2010		2009
Depreciation expense (1)	$	776.6	$	745.7	$	678.1
Capitalized interest (2)		106.7		47.2		53.1
(1) Depreciation expense is a component of “Costs and expenses” as presented in our Statements of Consolidated Operations. (2) Capitalized interest reduces interest expense during the period it is recorded and increases the carrying value of the associated asset, which will subsequently increase depreciation expense once the asset is placed in service. See Note 20 for information regarding cash payments for interest during the years ended December 31, 2011, 2010 and 2009.

Our consolidated results of operations for the years ended December 31, 2011, 2010 and 2009 included $19.7 million, $30.5 million and $33.4 million of depreciation, amortization and accretion expense related to the Crystal assets.

Asset Retirement Obligations

We record AROs related to legal requirements to perform retirement activities as specified in contractual arrangements and/or governmental regulations. In general, our contractual AROs primarily result from right-of-way agreements associated with our pipeline operations and leases of plant sites. In addition, we have recorded AROs based on government regulations triggered by the abandonment or retirement of (i) certain underground storage facilities and related above-ground brine storage pits, (ii) offshore Gulf of Mexico assets and (iii) certain marine vessels. Our AROs may also result from regulatory requirements associated with the renovation or demolition of certain assets containing hazardous substances such as asbestos. We fund our ARO obligations using cash flow from operations, borrowings under credit agreements, or a combination thereof.

The following table presents information regarding our AROs since December 31, 2009:

ARO liability balance, December 31, 2009	$	54.8
Liabilities incurred		0.1
Liabilities settled		(7.6	)
Revisions in estimated cash flows		45.6
Accretion expense		4.2
ARO liability balance, December 31, 2010		97.1
Liabilities incurred		0.7
Liabilities settled		(7.3	)
Revisions in estimated cash flows		15.0
Accretion expense		6.5
ARO liability balance, December 31, 2011	$	112.0

The increase in our ARO liability during 2010 and 2011 primarily reflects revised cost estimates and/or settlement date assumptions for pipeline and platform abandonment projects in the Gulf of Mexico and certain onshore natural gas gathering systems. Revised estimates of the cost to comply with regulatory abandonment obligations associated with above-ground brine storage pits also contributed to the increase in our ARO liability balance during 2010.

Property, plant and equipment at December 31, 2011 and 2010 includes $37.7 million and $34.1 million, respectively, of asset retirement costs capitalized as an increase in the associated long-lived asset. The following table presents our accretion expense forecasts for AROs for the periods presented:

2012				2013				2014				2015				2016
$	5.4			$	5.6			$	6.0			$	5.7			$	6.0

Certain of our unconsolidated affiliates have AROs recorded at December 31, 2011 and 2010 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our consolidated financial statements.