Property, Plant and Equipment

Our property, plant and equipment consists of the following at the dates indicated:



	Estimated	March 31,
Description	Useful Lives	2018			2017
		(in thousands)
Natural gas liquids terminal and storage assets	2-30 years	$	238,487		$	207,825
Pipeline and related facilities	30-40 years	243,616			248,582
Refined products terminal assets and equipment	15-25 years	6,736			6,736
Retail propane equipment	2-30 years	197,113			239,417
Vehicles and railcars	3-25 years	184,273			198,480
Water treatment facilities and equipment	3-30 years	601,139			557,100
Crude oil tanks and related equipment	2-30 years	218,588			203,003
Barges and towboats	5-30 years	92,712			91,037
Information technology equipment	3-7 years	38,564			43,880
Buildings and leasehold improvements	3-40 years	167,472			161,957
Land		63,600			56,545
Tank bottoms and line fill (1)		20,118			24,462
Other	3-20 years	13,145			39,132
Construction in progress		77,450			87,711
		2,163,013			2,165,867
Accumulated depreciation		(443,066		)	(375,594		)
Net property, plant and equipment		$	1,719,947		$	1,790,273


(1)	Tank bottoms, which are product volumes required for the operation of storage tanks, are recorded at historical cost. We recover tank bottoms when the storage tanks are removed from service. Line fill, which represents our portion of the product volume required for the operation of the proportionate share of a pipeline we own, is recorded at historical cost.

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



	Year Ended March 31,
	2018		2017		2016
	(in thousands)
Depreciation expense	$	128,808	$	119,707	$	136,938
Capitalized interest expense	$	182	$	6,887	$	4,012

We record losses (gains) from the sales of property, plant and equipment and any write-downs in value due to impairment within (gain) loss on disposal or impairment of assets, net in our consolidated statement of operations. The following table summarizes losses (gains) on the disposal or impairment of property, plant and equipment by segment for the periods indicated:



	Year Ended March 31,
	2018			2017			2016
	(in thousands)
Crude Oil Logistics (1)	$	(3,144	)	$	8,124		$	54,952
Water Solutions	8,117			7,169			1,485
Liquids	639			92			(2,992		)
Retail Propane	1,136			(287		)	(137		)
Refined Products and Renewables	15			91			3,080
Corporate	8			(1		)	—
Total	$	6,771		$	15,188		$	56,388

(1)

Amounts for the year ended March 31, 2018 primarily relate to losses from the disposal of certain assets and the write-down of other assets, offset by a gain related to the sale of excess pipe. Amounts for the year ended March 31, 2017 primarily relate to losses from the sale of certain assets, including excess pipe. Amounts for the year ended March 31, 2016 primarily relate to the write-down of pipe we no longer expected to use in our originally planned pipeline from Colorado to Oklahoma.