The Development and Use of 'smart' Gauge Pigs in Offshore Applications

Considerable time, effort and cost are used in recovering gauge pigs from the subsea to inspect guage plate conditions prior to beginning hydrotest operations. Vessels used for pigging have to disconnect, travel to the receiver and recover the gauge pig to deck for visual inspection.

The Copipe Arrival Condition Monitoring Equipment (ACME, also referred to as Smart Gauge plate; UK and international patents pending) provides a means of determining the condition of a pig-mounted gauge plate after a gauging run, without the need to retrieve the pig for examination. ACME operates by using electrical circuits bonded to the gauge plate to control the frequency of a signaling device. Gauge plate damage results in circuits being broken, which in turn causes a frequency change.

ACME offers significant project cost savings by reducing vessel movements and intervention requirements and providing a direct progression into hydrotesting if the gauge plate is acceptable (Fig. 1).

The ACME System

ACME is an add-on system for a standard gauging pig which enables the facility to remotely determine the condition of the gauge plate on the pig's arrival in the pig receiver. This avoids the necessity to recover a gauge pig to determine the condition of its gauge plate, thereby saving significant vessel and intervention costs when working at subsea levels.

ACME uses a standard aluminum petalled gauge plate with a simple instrumentation adaptation to sense the plate condition. Prior to setting up the plate, a Go/No Go criterion is agreed, based on the deflection of a bent peal relative to an undeflected petal (the usual condition for acceptance). Based upon this criterion, an electrical break sensor detects any deformation beyond the agreed criterion.

The gauge plate sensor provides two possible outputs:

• Short circuit-plate is within agreed GO condition;
• Open circuit-plate is in NO GO condition.

The output from the gauge plate sensor is used on a pig receipt in the receiver to switch the output of a pig-- mounted pinger between two conditions to announce plate condition (this can be frequency, pulse pattern,on/off, etc., depending upon the application and other systems in use). The ACME signal is detected at the receiver, and the gauge plate condition is broadcast from there, back to the launching end or another convenient location, using either the "Pig Home" system beacons, or a dedicated transmitter system.

Existing gauge plates may be easily adapted to operate with ACME. A typical plate arrangement is shown here:

An undamaged plate not only confirms acceptable bore, allowing the pig to be removed when more convenient, for example at tie-in stage, but also allows high-pressure receivers to be used to allow immediate hydrotesting without vessel relocation, receiver removal and pig recovery.

If damage does occur to the plate, when the Copipe impact logger is used, it is possible to determine where the plate became damaged, (which requires recovery of the pig). This can be used to rule out the possibility of damage at launch/receive (Fig. 3).

Development And Testing Program

A section of 16-inch pipe had been provided to Copipe as part of the preparatory phase for the Draugen commissioning project. This pipe was set up in Copipe's yard between two coiled tubing reels. One reel was used as an anchor and the winch on the second reel was used to pull pigs through the pipe sample (Fig. 4).

To provide a means of damaging the gauge pig, a threaded pin was fitted through the pipe wall at the midpoint of the pipe sample, in the 12 o'clock position. This pin was inserted such that 40 mm of protrusion was caused. This was sufficient to ensure that the gauge plate would be damaged, and is not the minimum damage that the system can detect (Fig. 5).

The pipe sample was cleaned by drawing a utility brush pig through it three times prior to the gauging trials. The pin was not fitted during this cleaning operation.

The ACME system utilizes a gauge plate that is modified by the addition of electrical sensors in a set of grooves machined into the rear face of the plate. The location of the grooves relative to the outer edge of the gauge plate determines the sensitivity of the plate. The plates used in the trials had been constructed to give a sensitivity matching the value being defined by the Draugen project.

Visually, the ACME plates are almost indistinguishable from standard plates: only the connector for the electrical connection, and the epoxy potting protection for the electrical sensors distinguish the plate. The pig used for the test was an IPP 16-inch gauging pig of specific design for Draugen (Fig. 6).

The epoxy filling used to protect the electrical components is extremely tough. Plates are hydrostatically tested to their maximum service pressure and water jetted to confirm the robustness of the plate.

The rectangular items around the waist of the pig are pickup magnets for collecting any metal objects from thepipeline, and are not a part of the ACME system (Fig. 7).

The signaling device used in the test was a dual-frequency acoustic pinger, set to operate in pulsed mode and to transmit according to the following convention:

Gauge plate intact ................30 KHZ

Gauge plate damaged ............21 KHz

A standard pinger receiver with manual tuning was used to detect the output from the pinger. In this mode of operation, the gauge plate may be considered as a switch, the function of which is to change over the pinger frequency.

The acoustic antenna of the pinger was arranged to protrude through the front bulkhead of the pig, and can be seen in Figure 8 with the hauling loop removed from the pig nose.

The test procedure was simply to insert the pig into the pipe, and then pull it through on the winch at approximately 0.5 meters per second, stopping it at the far end of the pipe, and listening to the output frequency of the pinger to determine plate condition. Two runs were carried out in this manner.

Outcome of Tests

Figure 9 shows the pig about to be inserted, and the peg can also be seen at the top of the pipe. On both test runs, one plate petal was bent back by approximately 15 mm.

Test One

In the first test, the pinger was heard at 30 KHz, despite the plate being obviously damaged. On recovery of the pig, the electrical connector to the plate was removed and the pinger continued to transmit at 30 KHz. The pig was dismantled. It was found that the nose connector to the pinger was dislodged by the assembly method used, and was shorting in its receptacle, thus causing the 30 KHz signal. A new plate was fitted and tested fully, and the pig returned to the test pipe.

Test Two

In the second test, the pinger was heard at 21 KHz after the pull through, confirming the successful function of the system.

Further Tests

The second successful test was repeated an additional six times. On each occasion, the system functioned perfectly.

The pig was also equipped with a Copipe impact logger, which is a small cylindrical instrument approximately 50 mm x 50 mm. This records any impact loading the pig experiences, and may be used to determine where gauge plate damage occurred. Both logs were identical.

The small events (approximately 10g) are the pig entering and leaving the pipe, and the much larger 20g event is the plate being damaged. In a test of this type, where speeds are low, this impact results from the release of elastic energy in the polyurethane of the pig as the pig rides off the obstruction.

The gauge plate damage was similar in both tests. The plate from test two is shown in Figure 10. The mark where the pin struck the plate can be clearly seen in this view. Of"= use

Since the development tests, ACME has been successfully used on a number of North Sea and international projects. Diameters, lengths and water depths have varied. Consistent success has created customer interest beyond expectation.

Sumber : Graves, Les; Yates, Tony. "The Development and Use of 'smart' Gauge Pigs in Offshore Applications:. 27 Januari 2014. http://search.proquest.com/docview/197470744?accountid=31562