Note 6 — Property, Plant and Equipment and Intangible Assets
| | | | | | | | Estimated useful life | |
| | December 31, 2013 | | | December 31, 2012 | | | (In Years) | |
Gathering systems | | $ | 2,230.1 | | | $ | 1,975.3 | | | 5 to 20 | |
Processing and fractionation facilities | | | 1,598.0 | | | | 1,251.6 | | | 5 to 25 | |
Terminaling and storage facilities | | | 715.2 | | | | 462.0 | | | 5 to 25 | |
Transportation assets | | | 294.7 | | | | 292.5 | | | 10 to 25 | |
Other property, plant and equipment | | | 121.3 | | | | 84.6 | | | 3 to 25 | |
Land | | | 89.5 | | | | 87.1 | | | | - | |
Construction in progress | | | 702.8 | | | | 548.1 | | | | - | |
Property, plant and equipment | | | 5,751.6 | | | | 4,701.2 | | | | | |
Accumulated depreciation | | | (1,406.2 | ) | | | (1,168.0 | ) | | | | |
Property, plant and equipment, net | | $ | 4,345.4 | | | $ | 3,533.2 | | | | | |
| | | | | | | | | | | | |
Intangible assets | | $ | 681.8 | | | $ | 681.9 | | | | 20 | |
Accumulated amortization | | | (28.4 | ) | | | (1.1 | ) | | | | |
Intangible assets, net | | $ | 653.4 | | | $ | 680.8 | | | | | |
Intangible assets consist of customer contracts and customer relationships acquired in business acquisitions. The fair value of these acquired intangible assets was determined at the date of acquisition based on the present value of estimated future cash flows. Key valuation assumptions include probability of contracts under negotiation, renewals of existing contracts, economic incentives to retain customers, past and future volumes, current and future capacity of the gathering system, pricing volatility and the discount rate.
Amortization expense attributable to these intangible assets is recorded using a method that closely reflects the cash flow pattern underlying the intangible asset valuation. Amortization of these assets was $27.3 million in 2013. The estimated amortization expense for these intangible assets is approximately $61.4 million, $80.1 million, $88.3 million, $81.5 million and $67.8 million for each of years 2014 through 2018.
