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Holiday Internal Detection Pig2014-12-30

IP.com Disclosure Number: IPCOM000239823D
Publication Date: 2014-Dec-03
Document File: 3 page(s) / 191K

Publishing Venue

The IP.com Prior Art Database

Abstract

Pipelines are internally coated to reduce corrosion, improve integrity, and extend life. Coating application may be done in the shop with girth welds coated during installation, or coating may be applied in-situ through a series of liquid slugs and pig scrapers to achieve an even coating through the line. However, the final coating may have holidays (defects) in areas such as adjacent to welds, bends, tees, wyes, etc. Additionally, the coating could disbond locally due to improper cleaning, residual debris, or a variety of other issues. In order to maintain pipeline integrity, it is important to know the condition of the coating, primarily the location and distribution of holidays prior to commissioning. Currently there is no technology to provide this data for installed pipelines. Therefore, the proposed invention is outlined to detect pipeline internal coating holidays. Several iterations of this invention are proposed in order to scale up the technology and provide fit for purpose applications. Additionally, the inventions can be combined with coating repair technology to repair any detected holiday. Although the language of this invention is referenced to pipelines, the technology is also applicable to downhole tubular applications as well.

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Problem: 

Pipelines are internally coated to reduce corrosion, improve integrity, and extend life.  Coating application may be done in the shop with girth welds coated during installation, or coating may be applied in-situ through a series of liquid slugs and pig scrapers to achieve an even coating through the line.  However, the final coating may have holidays (defects) in areas such as adjacent to welds, bends, tees, wyes, etc.  Additionally, the coating could disbond locally due to improper cleaning, residual debris, or a variety of other issues.  In order to maintain pipeline integrity, it is important to know the condition of the coating, primarily the location and distribution of holidays prior to commissioning.  Currently there is no technology to provide this data for installed pipelines.

Holiday Internal Detection Pig

For shop-applied coatings in tanks or other easily accessible surfaces, a hand held instrument (Holiday Detector) is used to create an electric field between a conductive probe, such as a wet sponge and the pipe.  Dielectric breakdown across the coating film between the probe and the pipe will result in a short, which is an indication of a coating holiday.  Such an instrument is commonly used for tank and vessel linings to verify coating quality prior to putting into service.  Similar instruments use other probes – wire or carbon brushes or wire coils – and may apply variable voltages based on the coating thickness, and are used for detecting holidays in thick films such as external pipeline coatings.  There are industry standards for the use and interpretation of results from holiday detectors.

The proposed invention is based on the same principles as the existing holiday detection instrument.  Several iterations of this invention are proposed in order to scale up the technology and provide fit for purpose applications.  Although the language of this invention is referenced to pipelines, the technology is also applicable to downhole tubular applications as well. 

The first iteration is a single sensor, tethered pig.  A foam pig can be used to maintain contact with the pipe wall.  The tether will provide electrical contact with the Power Supply and Ohmmeter.  The ohmmeter and power supply will also be attached to the base pipe such any electrical short between the pig and the pipe will register in the ohmmeter.  The foam pipe can be fitted with an internal GPS unit and XYZ sensor in order to correlate indications to position along the pipeline.  In this case, the entire pig will act as a sensor.  This will provide instant indication of any holiday locations. 

Figure 1 – Single sensor Pipeline In-Line Coating Holiday Inspection

The simple holiday detector devices currently utilized provide only a yes/no indication of a defect – when the resistance pathway drops to below the alarm level, the indicator activates.  It is easily possible to get continuous readings of resistance so that the proxim...