Design Considerations for the Use of Ultrasonic Phased Array Probes in Weld Inspection

Ultrasonic testing of metal welds has been in use for many years. Scanning methods using both contact and immersion methods are often used at the time of manufacture and also during periodic in-service inspection programs. But because of a variety of component configurations and potential flaw geometries it is often necessary to perform several inspections, each with a different probe configuration to assure adequate defect delegability. It is possible that a properly designed phased array probe can perform several different inspections without changing hardware thereby reducing inspection times. This presentation reviews the design and operation of ultrasonic phased array transducers and the necessary features to achieve the desired performance. Situations in which these probes have already been implemented effectively are also discussed.

Rational Modeling of Ultimate Pipe Strength Under Bending and External Pressure

The capacity of pipelines to resist collapse or local buckling under a combination of external pressure and bending moment is a major aspect of offshore pipeline design. The importance of this loading combination increases as oil and gas projects in ultra deep-water, beyond 2,000-m water depths, are becoming reality. The industry is now accepting, and codes are explicitly incorporating, limit state design concepts such as the distinction between load controlled and displacement controlled conditions. Thus, deep-water pipeline installation and limit state design procedures are increasing the need to understand fundamental principles of offshore pipeline performance. Design codes, such as API 1111 (1999) or DNV (1996, 2000), present equations that quantify pipeline capacities under combined loading in offshore pipelines. However, these equations are based on empirical data fitting, with or without reliability considerations. Palmer (1994) pointed out that “it is surprising to discover that theoretical prediction [of tubular members under combined loading] has lagged behind empirical prediction, and that many of the formula have no real theoretical backup beyond dimensional analysis.” This paper addresses the ultimate strength of pipelines under combined bending and external pressure, especially for diameter-to-thickness ratios, D/t, less than 40, which are typically used for deep water applications. The model is original and has a rational basis. It includes considerations of ovalization, anisotropy (such as those caused by the UOE pipe fabrication process), load controlled, and displaced controlled conditions. First, plastic analysis is reviewed, then pipe local buckling under pure bending is analyzed and used to develop the strength model. Load controlled and displacement controlled conditions are a natural consequence of the formulation, as well as cross section ovalization. Secondly, external pressure effects are addressed. Model predictions compare very favorably to experimental collapse test results.

Leak Detection Systems for Short Pipelines

This paper describes procedures developed by PETROBRAS Research & Development Center to assess a software-based leak detection system (LDS) for short pipelines. These so-called “Low Complexity Pipelines” are short pipeline segments with single-phase liquid flow. Detection solutions offered by service companies are frequently designed for large pipeline networks, with batches and multiple injections and deliveries. Such solutions are sometimes impractical for short pipelines, due to high cost, long tuning procedures, complex instrumentation and substantial computing requirements. The approach outlined here is a corporate approach that optimizes a LDS for shorter lines. The two most popular implemented techniques are the Compensated Volume Balance (CVB), and the Real Time Transient Model (RTTM). The first approach is less accurate, reliable and robust when compared to the second. However, it can be cheaper, simpler, faster to install and very effective, being marginally behind the second one, and very cost-efective. This paper describes a procedure to determine whether one can use a CVB in a short pipeline.

Pipeline Compressor Redesign With the Consideration of Both Noise and Performance

A complete effort to redesign the aerodynamic characteristics of a single-stage pipeline compressor is presented. The components addressed are the impeller, diffuser region, and the volute. The innovation of this effort stems from the simultaneous inclusion of both the noise and aerodynamic performance as primary design parameters. The final detailed flange-to-flange analysis of the new components clearly shows that the operating range is extended and the tonal noise driven by the impeller is reduced. This is accomplished without sacrificing the existing high efficiency of the baseline machine. The body of the design effort uses both Computational Fluid Dynamics (CFD) and vibro-acoustics technology. The predictions are anchored by using the flange-to-flange analysis of the original design and its experimental performance data. By calculating delta corrections and assuming that these deltas are approximately the same for the new design, the expected performance is extrapolated.

Freezing Technique Applied to an Offshore Pipeline at Campos Basin in Brazil

This paper describes an offshore pipeline freezing technique that was used to isolate a gas pipeline to effect repairs and to and perform associated tests. The freezing technique was used after evaluation and land testing and was successful in returning the pipeline to production much sooner that the other compared conventional methods. This technique reduced the amount of water used in the gas pipeline and enabled the repairs to be pressure tested prior to returning the pipeline to service.

Using Genetic Algorithm and Simplex Method to Stabilize an Oil Treatment Plant Inlet Flow

This paper presents a hybrid approach, composed of a genetic algorithm and a linear programming method, to achieve an efficient pipeline network operation. The pipeline network optimization consists of the determination of pump scheduling over a short-term horizon, usually one or more days ahead. The resulting mathematical problem has a dynamic and combinatorial characteristic, in which a sub-optimal solution was obtained through these two mathematical tools in a short computational time. The approach was applied in a Pipeline Network to a study case based on the Patagonia Argentina, which is comprised of 16 tanks and linked pumps, with 66 kilometers of pipelines, that transport the production of more than 100 wells to a pre-processing plant. The goal was to obtain a constant input flow rate at the plant respecting physical and chemical processes requirements.

Theoretical and Experimental Study of Stress Corrosion Cracking of Pipeline Steel in Near Neutral pH Environment

Stress corrosion cracking (SCC) is a complex phenomenon that involves various interacting physical and chemical processes. There is a combination of determinism and stochasticity that results in SCC colony evolution. A statistical model that generates a random field of corrosion pits and crack initiation at randomly selected pits is proposed in this work. A thermodynamic model of individual SC crack growth has been recently developed within the framework of the Crack Layer theory. Mathematical realization of the SC crack growth model is presented in the form of relations between the crack growth, hydrogen diffusion and corrosion rates on one hand and corresponding thermodynamic forces on the other. Experimental program for determination of the kinetic coefficients employed in crack growth equations is briefly reported. Finally, application of the individual crack growth law to random configuration of multiple cracks results in a simulation of SCC colony evolution, including a stage of the large-scale crack interaction. The solution of the crack interaction problem via FRANC2D Finite Element Methods results in a computer simulation of multi-crack cluster formation within the colony.

Pipe Supports and Skid Platforms: An Overlooked Noise Problem

When an energy industry facility must meet environmental noise regulations, the primary noise sources are the drivers (such as engines and motors), driven tools (such as compressors and pumps), air moving devices, and turbulent flow in valves and piping. The primary sound transmission path is the airborne radiation of noise, which is controlled by enclosures, lagging and silencers. The opportunity for sound energy to be transmitted through structural vibration and reradiated at another location is largely overlooked in typical acoustic impact analyses. Pipe support and skid structures often have large flat panels which are very efficient radiators of noise energy, where the sound energy generated by compressors can be emitted into the environment at some distance from the actual energy source. How a pipe is mounted on its supports, and the design of those supports, can have a significant effect on the noise emissions from its support structures.

Thermodynamic Assessment of Hybrid PSOFC/GT Systems for Mechanical/Electric Power Generation

Hybrid PSOFC/GT cycles consisting of pressurized solid oxide fuel cells integrated into gas turbine cycles are emerging as a major new power generation concept. These hybrid cycles can potentially offer thermal efficiencies exceeding 70% along with significant reductions in greenhouse gas and NOX emissions. This paper considers the PSOFC/GT cycle in terms of electrical and mechanical power generation with particular focus on gas pipeline companies interested in diversifying their assets into distributed electric generation or lowering pollutant emissions while more efficiently transporting natural gas. By replacing the conventional GT combustion chamber with an internally reformed PSOFC, electrical power is generated as a by-product while hot gases exiting the fuel cell are diverted into the gas turbine for mechanical power. A simple one-dimensional thermodynamic model of a generic PSOFC/GT cycle has shown that overall thermal efficiencies of 65% are attainable, whilst almost tripling the specific work (i.e. energy per unit mass of air). The main finding of this paper is that the amount of electric power generated ranges from 60–80% of the total power available depending on factors such as the system pressure ratio and degree of supplementary firing before the gas turbine. Ultimately, the best cycle should be based on the “balance of plant”, which considers factors such as life cycle cost analysis, business and market focus, and environmental emission issues.

Technical and Engineering Challenges Faced in Design of the Gelugor Mainline, Penang, Malaysia

PETRONAS Gas Berhad (PGB), a listed partly-owned subsidiary of PETRONAS is undertaking the Peninsular Gas Utilization Project - Stage III (PGU III). The PGU III Sector 2 & 3 project extends from Lumut, Perak to Pauh, Perlis on the West Coast of Peninsular Malaysia, with two laterals, the Gurun Lateral and the Penang Lateral. The Penang Lateral is further divided into the Prai Lateral, Gelugor Mainline and the Gelugor Tenaga National Berhad (TNB) Meter Station project individually. This paper will focus its’ discussion on the technical and engineering challenges faced in the design of the Gelugor Mainline Project. The Gelugor Mainline consist of about 7 km NPS 24 gas pipeline which runs from TNB Prai Power Plant of the mainline to TNB Gelugor Power Plant on the Penang Island. The pipeline is planned to operate at high pressure. The pipeline route traverses complex terrain with varied seabed lithology with depth up to 16m. The pipeline will cross active shipping lane, zones of live electrical cables, extensive system of submarine pipeline, mudbank and areas susceptible to mass gravity flows. There is also an area subjected to future development with an expected 170 kN/m2 distributed load with 3 m covers required which is an expressway and Light Rapid Transportation (LRT) system, the proposed development of a “Vision City” is also a few meters away from the pipeline. The pipeline also passes by an environmentally sensitive area that includes the rearing of caged fishing activities. It is essential for the project team to determine and investigate the variable risks to the pipeline in order to take appropriate evasive and mitigating action in design. This required comprehensive survey activities in the busy shipping straits. The paper will explore and detail out its’ study starting from the description of the design concept to the varied environmental challenges. This paper aims to describe the route selection process, the pipeline design process and outline some of the specialist techniques employed in the design construction of the Gelugor Mainline, Penang, Malaysia. In nearly every major project a drive for cost and risk reduction results in a number of new ideas with varying degree of impact. Hence, the following areas will be elaborated and presented in greater details: • Pipeline Design. • Pipe-lay vessel. • Pipeline installation methodology.