demo, Sql Server - rextester

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--Sql Server 2014 Express Edition
--Batches are separated by 'go'

IF OBJECT_ID('dbo.trackhist', 'U') IS NOT NULL DROP TABLE dbo.trackhist;

CREATE TABLE trackhist (userid varchar(55), customer int, event_name varchar(55), event_timestamp datetime);
INSERT INTO trackhist (userid, customer, event_name, event_timestamp)
VALUES
    ('k8227', 1125, 'access',     '2017-03-27 08:53:31'),
    ('k8227', 1125, 'order tab',  '2017-03-27 08:55:31'),
    ('k8227', 1125, 'access',     '2017-03-27 08:55:59'),
    ('k8227', 2990, 'access',     '2017-03-27 09:03:20'),
    ('k8227', 2990, 'order tab',  '2017-03-27 09:03:22'),
    ('k8227', 2990, 'order tab',  '2017-03-27 09:03:30'),
    ('k8227', 2881, 'access',     '2017-03-27 09:04:02'),
    ('k8227', 1125, 'access',     '2017-03-27 15:11:09'),
    ('k8227', 1125, 'order tab',  '2017-03-27 15:11:19'),
    ('k8227', 1125, 'select tab', '2017-03-27 15:13:33');

select userid, customer, event_name, event_timestamp,
       row_number() over (partition by userid, customer, grp
                          order by event_timestamp) as steps
from
(
    select t.*,
           (row_number() over (order by event_timestamp) -
            row_number() over (partition by userid, customer order by event_timestamp)
           ) as grp
    from trackhist t
) t
order by userid, event_timestamp;

View schema
Execution time: 0 sec, rows selected: 10, rows affected: 10, absolute service time: 0,16 sec