The Mirage MHT/CHT range will work with either
pneumatic or hydraulic power, and comes supplied with a
toolkit, cutter holders to cover the machines range, a hose
connection and operating valves, and studs and nuts for
flange connection. Tooling comes available with optional
accessories such as line stop actuators, hot tap/line stop
cutters and pilot drills, flange adapters and valves over
various pressure ranges to cover the full operating range of
equipment.
Preparation and machine-operator
competency as fundamental components
Hot tapping machines are in essence simple mechanical
tools, but often work in an extremely dangerous
environment. Whilst each model and application has
different operating requirements and methods, a general
minimum standard applies.
Operators must be trained and conversant with the
specific hot tapping machine being used, and have the
ability to achieve the required dimensions with a full
understanding of the powered machine functions of the
device.
They must be able to identify the correct and incorrect
use of static or portable machines, and comply with all
local and internationally recognised techniques.
Understanding the specification of the machine
required is also vitally important, bringing a focus on
engineering and supply chain management far in advance
of the physical deployment of the asset.
A full record of the size of the pipes to be hot tapped
is needed, and must be verifiable – the data provided will
limit the choice of machines available.
An item that must not be overlooked when planning
a hot tap operation is the flowrate of the product in the
line. An excessive flowrate during a hot tap could mean
the loss of a coupon, resulting in a costly plant shutdown.
Pressure differential dangers
In some scenarios, a differential in pressure can be used
to the operator’s advantage – for example with sandwich-
type valves, used in many applications, the floating gate
used features a pressure differential across the gate that
activates the seal.
The elements used on the Mirage Machines Linestop
Plugging Heads are flared, when a differential in pressure
is produced across the head the flare is activated, thus
producing a good seal.
A pressure differential within a hot tap machine
assembly can also have a catastrophic effect.
For example, in a scenario where a 20 in. completion
plug is being set, the seal has just entered the neck of the
branch, product is accidentally vented above the plug
resulting in a pressure differential of 400 psi.
In this case, a 20 in. completion plug with a surface
area of 314 in.
2
at 400 lb/in.
2
, equates to a load of 56 t
being applied to the boring bar which in turn is transferred
to the gearbox – and in that scenario, the only way is up
for the product exerting that pressure.
Proactive maintenance reduces risk and
extends machine lifespan
Prolonged use of hot tapping machines results in a vital
requirement for scheduled maintenance to be recognised
and carried out – with failure to perform the works likely
to result in a loss of performance, potentially affect the
product’s safe operation and reduce its lifespan.
Maintenance has a number of key phases – after ten
hours of use, each machine must be thoroughly cleaned
and oiled, with components being checked and the boring
element extended for inspection.
To reduce the risk of corrosion, the pressure cylinder
should be flushed after 100 hours of use, this piece of
work taking around four hours to complete, and the
condition of the cylinder
evaluated before it is returned
to use. Technicians should
remove the drive gear, feed
gearboxes and pressure
retaining plate.
After 1000 hours of use, the
drive gearbox, grease bearings
and gear should be split, the
condition of seals checked and
replaced as necessary.
At the 5000 hour limit,
the entire machine must be
stripped and each component
inspected, including the
machine motor. ISO 32
hydraulic oil should be applied
to the motor to keep it good
working order. These works will
take in excess of eight hours, in
addition to repeating all actions
from the 1000 hours service.
Figure 3.
Used to make connections and branches to pipelines without shutdown.
74
World Pipelines
/
JUNE 2015
