Tài liệu PIPELINE PIGGING TECHNOLOGY- P11 ppt

Cable-operated and self-contained ultrasonic pigsCABLE-OPERATED AND SELF-CONTAINED ULTRASONIC PIGS IN ORDER to establish the integrity of ageing pipelines, intelligent pigging has become

Pipeline Pigging Technology

Pigging for pipeline integrity analysis

Pipeline Pigging Technology

CONCLUSIONS

m technology, as used in the D/S tool, is state-of-the-art for giving the

operator conclusive data about the physical condition and changes of

posi-tion in a pipeline system

1 DOT: DOT Form 7000-1, 01/06/1990

2 DOT: DOT ORRSPAF 7100.1, /F7100.2.

3 D.J Jones, G.S.Kramer, D.N.Gideon and R J.Eiber An analysis ofreportable

incidents/or natural gas transmission and gathering lines, 1970 through

June, 1984

4 DJ Jones andRJ.fiber An analysis ofreportableinciden tsfor natural gas

transmission and gathering lines, June 1984 through 1987.

Cable-operated and self-contained ultrasonic pigs

CABLE-OPERATED AND SELF-CONTAINED ULTRASONIC PIGS

IN ORDER to establish the integrity of ageing pipelines, intelligent pigging

has become of increasing interest For several decades, pigs> using magnetic

stray flux were the only tools available for this purpose on the market The

need for more accurate tools was an incentive to develop ultrasonic systems

to measure metal loss

This paper provides an overview of special ultrasonic pigging systems and

methods Conventional cable-operated ultrasonic field-proven tools for

dis-tances up to 2000m are described, as well as those using long glass-fibre cables

up to 6000m in length

Such tools can be propelled either by reversible wheel-driven crawlers, or

by differential pressure, as applied for self-contained intelligent pig

propul-sion Self-contained liquid-propelled intelligent pigs are used for on-stream

inspection of pipelines; a field-tested system (RPIT) to inspect riser pipes is

also described

INTRODUCTION

Long-distance pipelines are often equipped with launch and receive traps

to operate cleaning pigs; most of these traps are long enough also to handle

intelligent pigs Propulsion of such is by the pumped liquid

Short pipelines, most of the time, are not provided with traps; if such lines

are on land, and local excavation is possible, spot checks may be sufficient to

ensure their integrity

For short offshore pipelines, which are often weight-coated with concrete

and buried, inspection from the outside is impractical, and is prohibited by

the costs involved In this case, inspection from the inside seems more

practical; this also can provide information over the full length, and not just

as spot checks A typical example is the off-loading line illustrated in Fig.l

Fig.l Layout of the off-loading line and PIT.

These lines are used to connect tankers at some distance from the shore

to an onshore terminal, and are often found at shallow locations or where

extreme tide conditions exist Lengths up to several kilometres are common

Only very few of these off-loading lines have launch and receive traps for

cleaning pigs; such traps are far too short to accommodate intelligent pigs

Moreover, at the offshore end of the off-loading line, there often is a

manifold of reduced diameter, to which the flexible hoses are connected As

a consequence, any inspection vehicle would have to enter from the land and

reverse at the manifold Most intelligent pigs, however, are not reversible, due

to the design of their propulsion cups, and in any case, two-way pumping

facilities do not exist at off-loading line locations

Usually the pumps of the ship are the only pumps available for off-loading

lines, although for loading lines there are of course pumps on the land In that

case, reverse pumping could be considered but, as explained above, most

intelligent pigs are not reversible

A few other considerations directed the solution ultimately chosen by

RTD At the time, in the early 1980s, when the first need to inspect an

off-loading line arose, even the best existing intelligent flux pigs (ultrasonic pigs

did not exist then) were not quantitative enough to justify their offshore

application [ 1 ] Also prohibitive was the fact that flux pigs require a

relatively-high minimum speed to operate properly This relatively-high speed in itself creates a

high risk when the pig, with its large mass, has to be stopped before entering

and damaging the manifold The approximate location of the pig could only

be indicated by the amount of liquid pumped, which is far too inaccurate

Pipeline Pigging Technology

Cable-operated and self-contained ultrasonic pigs

Last but not least, the risk of an intelligent pig getting stuck in an off-loading

line was considered too great These lines are often old, sometimes with mitre

bends, dents or other unknown obstructions or features To imagine an

obstacle without a rescue line in what is often a "life line" for a plant or refinery

was alone reason enough for operators not to apply intelligent pigs to

off-loading lines

It is for all the above-mentioned reasons that RTD worked on a solution,

and decided to construct cable-operated ultrasonic pigs In our solution, as

Fig.l shows, we use a motor-driven crawler This self-propelled unit makes

the operation independent of pumping facilities

The umbilical for transmission of signals to and from the inspection

crawler is reinforced for rescue purposes An array of ultrasonic probes is

mounted at the front end of the inspection tool

To deploy the tool, the pipeline has to be opened for several metres to

attach a simple open launch tray; apart from power supply and hoisting

equipment, no other facilities are needed On-line presentation of results and

full control over speed and direction makes the pipeline inspection tool (PIT)

very attractive to pipeline owners

To date, eight successful world-wide applications have proved the viability

of this concept

THE ULTRASONIC STAND-OFF METHOD

The most suitable method of quantifying internal and external corrosion

is the stand-off technique as illustrated in Fig 2 A circular array of transducers

is located at some distance from the inner pipe wall, and the liquid in the pipe,

usually oil or water, acts as the essential acoustic couplant In this way both

the distance from the transducer to the pipe wall as well as the pipe wall

thickness can be measured These readings can be undertaken

simultane-ously, and with an accuracy of far better than 1mm

To obtain a fine grid of data, a small axial sampling interval of a few

millimetres is usually applied, while for circumferential coverage, a large

number of transducers are used; the size of the corrosion pits that can be

detected and quantified will depend on the type and number of transducers

employed

Not only is the stand-off technique as shown in Fig.2 well-suited for the

measurement of internal corrosion (i.e profile), but the array of transducers

is several centimetres away from the pipe, making the tool less vulnerable to

damage This allows'a relatively-simple form of transducer suspension

Fig.2 Ultrasonic stand-off method

ULTRASONIC PIPELINE INSPECTION TOOLS

Cable-operated inspection tools

1 The RTD PIT 2000

To inspect almost-straight off-loading pipelines of restricted length, the

cable-controlled pipeline inspection tool (PIT) was introduced Fig.l shows

an overview of the application and the tool itself in more detail At present

with the PIT, a length of up to 2000m of pipeline can be inspected to detect,

locate and quantify depth of internal and external corrosion, and measure the

remaining wall thickness in corroded areas The stand-off method is applied

as illustrated in Fig.2 The PIT applies 24 ultrasonic transducers (see Fig.3),

which can either be distributed freely around the circumference, or densely

staggered, on any sector of a pipe (see Fig.4)

Results are instantly presented, as well as being tape recorded for later

retrieval and analysis The tool is launched and operated from an open pipe

Pipeline Piggina Technology

Cable-operated and self-contained ultrasonic pigs

Fig.3 Probes distributed around the pig circumference.

end; all the electronics are installed in a container at the shore, equipped as

a control room, from where the direction and speed of the PIT can be

controlled As the PIT is wheel driven, it does not disturb the internal pipe

condition The tool requires oil or (sea) water in the pipeline

Fig.5 shows the single-body PIT which can negotiate 3D bends for

diameters over 30in; the cable on the reel is shown in the background Fig.6

shows the newest PIT, designed to be suitable for pipelines of 20-in diameter

and over In the background the associated equipment is shown; at the left is

the multi-channel (32) ultrasonic instrument, magnetic tape recorder

(be-low), and the paper-chart recorder and control box are at the top right hand

side To allow passage of 3D bends or mitres, the PIT consists of three

articulated units connected by universal joints; its flexibility is shown in Fig.7

The tools available are suitable for inspection of pipelines with diameters

from 20-48in Until now, they have been successfully applied in North

America, Europe and the Far East for diameters between 26 and 42in To

inspect off-loading pipelines with lengths over 2000m, the tool can be

deployed from both ends; this was done in Italy, where one section of the

pipeline was inspected from the landfall as illustrated in Fig.8, with the second

Pipeline Pigging Technology

Fig.4 Probes staggered to provide full-sector coverage.

section being inspected from the sea as shown in Figs 9 and 10 In all cases,

detachable spoolpieces or launch traps were used to deploy the PIT

2 The RTD PIT 6000

In order to inspect long off-loading pipelines in one run, preferably from

the shore, the PIT 6000 has been designed and is under construction Basically

it uses the same design and construction as the PIT 2000, although as it is

almost impossible to increase the length of the 2000-m long conventional

cable, it was decided to replace all the copper signal wires in the "galvanic"

cable by glass-fibre technology Experiments have shown that signal

transmis-sion for distances over 15,000m is feasible

For signal transmission, the new cable consist of only a few glass fibres, and

is reinforced with aramide fibres to provide a tensile strength of 5000kg The

cable, including a low-friction outer coating, has less than half the diameter

Cable-operated and self-contained ultrasonic pigs

Fig.5 Single-body 30-in PIT with cable reeL Fig.6 20-in PIT and electronic equipment.

Pipeline Pigging Technology

Fig.7 The bend-passing capacity of the 20-in PIT

Fig.8 30-in PIT launch trap at the landfall at Taranto, Italy Note

the cable in the background

Fig.9 Subsea FIT deployment.

Cable-operated and self-contained ultrasonic pigs

Pipeline Pigging Technology

Fig 10 PIT prior to lowering into the subsea manifold at Taranto.

of the conventional cable, and the same reel as used for the 2000-m

conven-tional cable can store the 6000-m optical cable The reel will be equipped with

optical rotary joints for uninterrupted rotation

The PIT 6000, to be completed in the second half of 1991, will be suitable

for inspecting pipelines from l6in diameter The tool will be capable of

passing both 3D and mitred bends, and the number of ultrasonic probes has

been increased to 32, in order to provide more circumferential coverage

Once the PIT 6000 has been introduced, expensive offshore deployment will

no longer be necessary for pipelines with lengths up to 6000m

Cable-operated and self-contained ultrasonic pigs

3 Stripper PIT testing

For relatively-large pipe diameters (at present I6in), wheel-driven

inspec-tion tools such as the various PlTs described are attractive; this technology

cannot be used for small diameters

To propel such tools with cables over long distances, up to 6000m, as well

as through bends, high pulling forces are required which cannot be generated

by small crawlers Therefore, the stripper technique has been developed, as

illustrated in Fig.l 1 The measuring module consists of the ultrasonic

trans-ducers and multiplexer, and thus can be quite small, and standard

compo-nents allow the construction of a transducer module suitable for a 6-in pipe

diameter, which can also pass 10-D bends A study has shown that with some

additional design effort, a 4-in unit can also be built

The transducer module is, as for self-contained pigs, propelled by

differen-tial pressure over its propulsion discs To retrieve the tool, the pressure

difference has to be reversed For proper sealing of the cable at the launch/

retrieve end of the pipe, a special closure head has to be installed in which a

feed-through (e.g stripper) has been provided This stripper contains an

air-pressure controlled flexible seal to provide the proper balance between

sealing and cable friction This technique was successfully applied in a 10-in

Fig 11 The ultrasonic tool using the stripper concept.

Pipeline Pigging Technology

Fig 12 The stripper technique being used in the 10-in test loop.

pipeline as shown in Fig 12 The system proved its capabilities over the full

length of the pipe (400m) and several 3D bends (up to 360°)

We assume that the current cable length (2000m) is the only range limit for

this technique when applied in an almost-straight pipeline Probably the

combination of bends and cable length sets the practical limits, and this has

to be investigated further An 8-in tool (see Fig 13) has recently been

completed for a job in 1991 Fig 14 shows this tool, including the motor-driven

winch

Self-contained ultrasonic tools

4 The RTD RPIT

In order to inspect an oil riser on-stream, RTD and Shell mutually decided

to build a fluid-propelled ultrasonic pig using the stand-off method, as shown

in Fig 2; Fig 15 shows the schematic lay-out of the consequent riser-pipe

inspection tool (RPIT) which was built to the following design specifications:

Cable-operated and self-contained ultrasonic pigs

Fig 13 8-inch stripper FIT with 2,000m of cable on a

motor-controlled recL Fig 14 8-in stripper PIT with 2,000m of cable on a motor-

controlled reeL

Pipeline Pigging Technology

overall length of 16-in tool: 2.45m maximum

weight: less than 200kg

maximum measuring speed: 4m/sec

pressure: 150bar

temperature: 5-60°C

measuring range: 300m (without data reduction)

travelling distance: 100km

wall thickness range: up to 40mm

accuracy of remaining wall

thickness measurement: ± 1 mmcorrosion detection: internal and external

circumferential coverage: 40%

axial measurement interval: 2.5mm

The tool is also capable of passing 3D 90° bends, full-bore T-joints and

valves; 10% symmetric and 15% asymmetric diameter reductions can also be

negotiated TTie system has been designed to provide a field report of results

within 1 hour of retrieval of the tool

In addition, the RPIT is bi-directional; propulsion disc design provides

by-pass of fluid if this is necessary in the unlikely event that the tool becomes

stuck

The RPIT can be started by pressure, time, distance or bench-marker, or

any combination of these options For a delayed start, it travels in a safe and

dormant, energy-saving mode to the section of interest in order either to

measure internal or external corrosion, or both simultaneously

The on-board memory stores all the data collected After retrieval of the

tool, a powerful portable desk-top computer is used to process the data;

Fig 16 shows an example of the results obtained In practice, colours are

applied to enhance and identify thickness ranges Results can also be

pre-sented in numerical, statistical or graphic modes for further data analysis The

16-in RPIT as shown in Fig 17 has been extensively tested and validated[2] in

Shell's 16-in test loop

5 RPIT field tests

The 16-in and 20-in RPIT have been used twice offshore[3] The first

application was a wire-line field test: pending a field test of the 20-in tool, the

opportunity was given to test the 16-in RPIT in open J-tubes on the Dunlin

Alpha platform, located in the northern North Sea New flowlines were to be

pulled through the J-tubes, which were installed several years ago High forces

were anticipated on the J-tubes during the flowline pulling operation, and

therefore a thorough integrity check of the tubes was required