Gas Pipeline Drying Methods

Achieving the ideal dryness for a subsea natural gas pipeline is a crucial step not only for commissioning of a pipeline, but also for is subsequent integrity management. Attaining the correct dryness level can help inhibit microbiologically influenced corrosion (MIC), hydrates and other issues.

Drying of a pipeline is usually completed in stages that involve one or more of the following techniques: pigging, methanol/glycol swabbing, air drying, vacuum drying and nitrogen packing.

Selection of methods for drying is often driven by economics and time restraints, without sufficient consideration given to operability and corrosion issues.

Shore Crossing Pipeline Cathodic Protection Design

The region in which a pipeline transitions from offshore to onshore is called a shore crossing. Often, this shore crossing zone is not very well-defined and there is much uncertainty in terms of scope and responsibilities between onshore and offshore design teams. This inconsistency can lead to issues when designing cathodic protection (CP) systems for near shore and shore crossing areas.

Introduction to Leak Testing

Leak testing, commonly confused with hydrostatic testing, is a means of verifying the quality of facility construction. Hydrostatic testing uses liquid media under pressure to test the structural integrity of weld joints and piping spools, while leak testing uses gas or service media, at or close to the maximum working pressure of the system, to serve as a final confirmation that the system is “leak tight” and ready for service. Leak testing simulates “live” conditions without actually using hydrocarbons, allowing flange connections to be checked for “tightness”.

Corrosion Testing: Methods, Results & Interpretation

It is often necessary to predict the performance of a specific material in a particular environment to determine the inherent corrosivity of the system. Such tests are often substantially different from those used for corrosion inhibitor qualification, particularly in the case of the corrosion testing of corrosion resistant alloys. Predicting corrosivity is especially important when designing subsea equipment, most of which is extremely challenging to repair or replace once it is installed. Corrosion testing is a widely used method of evaluating a material’s ability to withstand specific environmental conditions. 

Control Systems Part 3: Rules For Tuning Loops Prior to Startup

In this GATEKEEPER series, we introduced the Ultimate Gain Plot (Figure 1) and the variables dead time (DT), time constant (TC), and controller gain (Kp). These four aspects along with a basic understanding of the control loop to be tuned, are all that is required to develop preliminary tuning parameters. The examples in this GATEKEEPER demonstrate simple tuning rules. 

Control Systems Part 2: Introduction to System Dynamics - Tuning Controllers for Initial Startup

This is part two of the GATEKEEPER series on control systems tuning. To effectively tune a control loop, there needs to be an understanding about the dynamics of the system. The intention of this GATEKEEPER is not to provide a detailed review, but to provide an 80/20 solution.

Control Systems Part 1: Introduction to Control Systems & Controllers

Effectively tuned control loops provide for more efficient and safer operation. After process startup, there are various techniques available for tuning controllers ranging from trial and error methods to mathematically sophisticated programs. Few options are available for tuning loops prior to startup. Many control systems are started with the manufacturer’s default tuning parameters. This series of GATEKEEPERS will provide methods for using readily available process design data for determining effective tuning parameters before startup.

Slugging Management

Topsides separators are  designed to handle a relatively constant flow of liquid and gas, but  may also have an allowance for slugs. Under certain operating conditions (low flow rate, over-sized flowline ID and unfavorable flowline profile), gas and liquid are not evenly distributed throughout the flowline, but consist of large plugs of liquid followed by large gas pockets. This is called slug flow.

Paraffin Wax: Formation, Mitigation Methods & Remediation Techniques

Paraffin precipitation and deposition in flowlines and pipelines is an issue impacting the development of deepwater subsea hydrocarbon reservoirs. The buildup of paraffin deposits decreases the pipeline cross-sectional area, restricts operating capacities, and places additional strain on pumping equipment.

Bacteria Testing: Genetic Methods

The first line of defense against microbial proliferation is the measurement of actively growing microorganisms. The medical and food industry have used genetic methods as a means of testing for years to obtain results more efficiently and effectively than culture methods; however, this has not been the case with the oil industry.

NACE TM0194 is the current standard followed by the industry for measuring bacteria in the system. This standard uses the Most Probable Number (MPN) method to quantify the bacteria in the sample. Typically, only a small percentage of the actual bacteria population grows in culture media in a laboratory and the test only quantifies what can grow in the laboratory media instead of what is actually in the sample. Results are obtained 14 to 28 days after the samples are inoculated, a major disadvantage if there is a real problem in the system.

Pipeline Pigging Part 2: In-Line Inspection for Metal Loss

As mentioned in Part 1, pigs are devices that travel through the pipeline and can be used for cleaning or maintenance purposes (utility pigs) as well as for gathering information about the condition, features and integrity of a pipeline (intelligent pigs).

Intelligent pigs are designed to identify different features or abnormalities as they travel through the pipe. Figure 1 briefly lists the functionalities for which intelligent pigs are commonly used. API 1160 and NACE RP0102 provide guidelines for selecting the appropriate tool for a given purpose. In this paper, the most commonly used In-Line Inspection (ILI) techniques, methodology and limitations applicable to detecting metal loss and wall thickness measurements are presented.

Pipeline Pigging Part 1: Cleaning Pigs & Pigging Strategy

Build-up of deposits can create conditions for accelerated localized corrosion, which may be caused by under-deposit corrosion, localized acidic conditions and/or bacterial attack (microbiologically induced corrosion - MIC). This may result in sections of the pipeline needing repair or replacement before the end of their anticipated design life. Deposits will also impact throughput due to the reduction in the effective pipe diameter, which may require up to 140% increase in pressure in the line to maintain flow (Titratsoo 1).

This paper is the first part of a two part series and presents an overview of pig selection criteria for cleaning and maintenance of the pipelines, and covers high level guidance on establishing a progressive pigging strategy.