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	December 31,
	in Years	2014		2013
Plants, pipelines and facilities (1)	3-45 (6)	$	30,834.9	$	27,540.4
Underground and other storage facilities (2)	5-40 (7)		2,584.2		2,101.8
Platforms and facilities (3)	20-31		659.7		659.6
Transportation equipment (4)	3-10		154.2		138.9
Marine vessels (5)	15-30		796.4		744.8
Land			262.6		176.6
Construction in progress			2,754.7		2,655.5
Total			38,046.7		34,017.6
Less accumulated depreciation			8,165.1		7,071.0
Property, plant and equipment, net		$	29,881.6	$	26,946.6

(1) Plants, pipelines and facilities 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.

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

	For the Year Ended December 31,
	2014			2013			2012
Depreciation expense (1)		$	1,114.1		$	1,012.4		$	900.5
Capitalized interest (2)			77.9			133.0			116.8
(1) Depreciation expense is a component of "Costs and expenses" as presented on our Statements of Consolidated Operations. (2) Capitalized interest is a component of "Interest expense" as presented on our Statements of Consolidated Operations.

In October 2014, we recorded property, plant and equipment having a fair value of approximately $1.08 billion in connection with our acquisition of a controlling interest in Oiltanking (see Note 10). Oiltanking owns marine terminals located on the Houston Ship Channel and at Beaumont, Texas. At October 1, 2014, we recorded property, plant and equipment consisting of $395.6 million of terminal and pipeline assets (a component of plants, pipelines and facilities), $407.3 million of above ground storage assets (a component of other storage facilities), $76.3 million of land and $200.9 million of construction in progress in connection with this transaction. See Note 10 for additional information regarding our acquisition of Oiltanking, including the Oiltanking Merger completed on February 13, 2015.

In March 2013, we sold the Stratton Ridge-to-Mont Belvieu segment of the Seminole Pipeline, along with a related storage cavern, for cash proceeds of $86.9 million. As a result, net income for the year ended December 31, 2013 includes a $52.5 million gain attributable to the sale of these assets. The Seminole Pipeline remains connected to our Mont Belvieu complex through a newly constructed NGL pipeline that we own.

In April 2013, we sold certain lubrication oil and specialty chemical distribution assets for cash proceeds of $35.3 million. As a result, net income for the year ended December 31, 2013 includes a $6.7 million gain from the sale of these assets.

Asset Retirement Obligations

We record AROs in connection with legal requirements to perform specified retirement activities under contractual arrangements and/or governmental regulations. Our contractual AROs primarily result from right-of-way agreements associated with our pipeline operations and real estate leases associated with our plant sites. In addition, we record AROs in connection with governmental regulations associated with the abandonment or retirement of (i) above-ground brine storage pits, (ii) offshore Gulf of Mexico platform and pipeline assets and (iii) certain marine vessels. We also record AROs in connection with regulatory requirements associated with the renovation or demolition of certain assets containing hazardous substances such as asbestos. We typically fund our ARO obligations using cash flow from operations.

Property, plant and equipment at December 31, 2014 and 2013 includes $31.3 million and $37.4 million, respectively, of asset retirement costs capitalized as an increase in the associated long-lived asset.

The following table presents information regarding our AROs for the periods indicated:

	For the Year Ended December 31,
	2014			2013			2012
ARO liability beginning balance	$	90.2		$	105.2		$	112.0
Liabilities incurred		0.1			1.7			1.7
Liabilities settled		(2.7	)		(14.2	)		(27.8	)
Revisions in estimated cash flows		4.6			(8.6	)		13.7
Accretion expense		6.1			6.1			5.6
ARO liability ending balance	$	98.3		$	90.2		$	105.2

The following table presents our forecast of accretion expense for the periods indicated:

2015			2016			2017			2018			2019
$	6.2		$	6.4		$	6.9		$	7.5		$	7.6

Certain of our unconsolidated affiliates have AROs recorded at December 31, 2014 and 2013 relating to contractual agreements and regulatory requirements. These amounts are immaterial to our consolidated financial statements.