Goodwill and other identifiable intangible assets

Changes in goodwill during the years ended December 31, 2018 and 2017 were as follows:



In millions	Gas Cylinders			Elektron			Total
At January 1, 2017	$	27.0		$	40.9		$	67.9
Exchange difference	2.0			1.3			3.3
At December 31, 2017	$	29.0		$	42.2		$	71.2
Impairment	(1.3		)	—			(1.3		)
Exchange difference	(1.4		)	(0.9		)	(2.3		)
Net balance at December 31, 2018	$	26.3		$	41.3		$	67.6

Accumulated goodwill impairment losses were $9.6 million as of December 31, 2018 and $8.3 million as of December 31, 2017, with the difference due to an impairment of goodwill in 2018 associated with our Superform business.

In 2018, a goodwill impairment loss of $1.3 million has been recognized in our Gas Cylinders segment in relation to our Superform business unit. As part of the annual impairment review, the present value of future cashflows of the business unit were below the carrying value of the goodwill due to productivity challenges within the business.

Identifiable intangible assets consisted of the following:



	December 31, 2018							December 31, 2017
In millions	Gross		Accumulated amortization			Net		Gross		Accumulated amortization			Net
Customer relationships	$	13.4	$	(3.8	)	$	9.6	$	13.4	$	(2.9	)	$	10.5
Technology and trading related	7.9		(2.9		)	5.0		8.6		(3.0		)	5.6
	$	21.3	$	(6.7	)	$	14.6	$	22.0	$	(5.9	)	$	16.1

Identifiable intangible asset amortization expense in 2018, 2017 and 2016 was $1.2 million, $1.3 million and $1.1 million, respectively.

In 2017, we recorded, within restructuring charges, an impairment charge of $0.5 million in the Gas Cylinders segment for technology and trading related intangibles following the announcement to exit our Luxfer HEI business.

Intangible asset amortization expense over the next five years is expected to be approximately $1.2 million in 2019, $1.1 million in 2020, $1.1 million in 2021, $1.1 million in 2022 and $1.1 million in 2023.