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.

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Introduction to Leak Testing

Leak testing is ideally performed onshore, although construction activities (i.e. delay in construction, offshore hookup spools, etc.) have a tendency to push testing offshore. Offshore leak testing can have a substantial impact on project schedule and planning. The equipment needed for testing requires valuable deck space, additional personnel to perform testing and the suspension of nearby work during testing due to the pressurization of equipment. For higher pressure systems, more limitations are introduced. Restrictions on simultaneous operations are widened, inducing a delay in the project schedule. Therefore, it is important to maximize leak testing activities onshore as much as practically possible.

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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.

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Commissioning Lessons Learned—Methanol Systems

Deepwater oil and gas facilities are designed, constructed and commissioned by multiple teams with multiple objectives. Consequently, design disconnects and lack of foresight become apparent during the commissioning and startup phase.

Recent commissioning and startup experiences on an FPSO have provided many valuable lessons regarding such issues. This GATEKEEPER explores how a foreknowledge of design flaws and common discussion would have prevented significant problems seen during the final commissioning and processes startup.

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Control of Flow Rates at Startup

Either by nature, or by training, engineers are conservative. That is generally a good thing, but we sometimes go too far. For example, chokes and control valves are often oversized even for normal operation, and are sometimes far too large to provide adequate control of low flow rates at initial startup. Startup planning should include an assessment of the operability of chokes and control valves.

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A More Effective HAZOP Process

The typical HAZOP defines nodes based on equipment items; often one equipment item per node. The GATE HAZOP Process features stream-based nodes. A stream is followed from its inception to its logical conclusion. This is especially useful when considering FLOW deviations, because a FLOW disruption in any part of the stream affects all parts of the stream. These stream based nodes are much larger than typical equipment-based nodes and hence overcome the tendency of HAZOPs to create tunnel vision.

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Keys to a Successful Initial Startup

Deepwater oil and gas facilities are designed, constructed and commissioned by multiple teams with multiple objectives. Effectively managing those interfaces is important in every phase of the project and critically important at Initial Startup. The Initial Startup is the moment of truth where everything from subsurface to topsides becomes a single entity and has to work together. Design disconnects will become apparent. Also, the Initial Startup phase is transient in nature, which presents significant challenges. Careful planning will minimize many of the risks that may arise. This article provides a set of suggestions for planning the startup of a deepwater oil and gas facility in an effective and efficient manner to ensure a smooth transition from Final Commissioning to Initial Startup and Operations exists.

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