Successive brownfield projects in GASCO plants utilized spare space on existing pipe racks to route new pipes. These pipe racks were originally designed as per erstwhile industry standards and environmental data, which have become obsolete over the years. In the absence of distinct guidelines, indiscriminate approaches were followed to confirm adequacy of these racks in order to reutilize them. Most of these approaches were irrational, had design flaws and raised serious concerns on the safety and integrity of the existing structure. This paper presents the full-fledged methods and procedures followed in GASCO for adequacy check and modifications of structures that assures high level of integrity of existing racks. Adequacy checks present diverse challenges such as unavailability of as-built documents, want of primary analysis model, revision of codes etc. GASCO has developed an exclusive design guideline for structural adequacy check and execution of modifications, as a consequence of few incidents of failure of old pipe racks. Based on ‘Available' and ‘Not Available' state of required data, the pipe rack is grouped into different categories and stepwise design procedure is outlined for each of the categories. Tips on usage of right codes, estimation of missing loads, elimination of design errors, essential design checks, etc., are supplied. Practical techniques for strengthening of structurally deficient existing members and foundations are elucidated with sketches. Development and implementation of common guideline encompassing all the design requirements for adequacy check and reinforcement of existing structures has resulted in unifying the approaches across GASCO plants thus ensuring a high level of safety and integrity of the existing pipe racks used in expansion projects.
Buildings that are manned and/or housing critical equipment are ideally conceived to be sited at safe distance away from potential explosion sources of the gas processing facilities. However it is not always possible to maintain the required stand-off distance due to several layout/operational constraints in brownfield projects and hence plant buildings are invariably subjected to the blast effects. The paper discusses challenges confronted and best practices followed in GASCO for blast protection of plant buildings. Quantitative Risk Assessment study forms the basis for blast considerations on the building, wherein potential Vapor Cloud Explosion scenarios are identified and blast overpressure are quantified in the form of contours on the plot. Buildings located within the blast contours and are manned/housing critical equipments are classified as blast-resistant to ensure safety to occupants and facilitate safe shutdown of process units during explosion. Building performance requirement defining acceptable level of damage is determined based on criticality of the facility/expected occupancy (control room, FAR, etc.). Structural system/material appropriate to blast intensity is chosen and a dynamic or equivalent static analysis is performed. Blast resistant design followed for buildings in GASCO plants incorporates a practical approach blending past experiences with best known practices in the industry. Building Blast Design Requirements (BDR) data sheet is introduced at early stages of the project and specific requirements such as blast load parameters, building configuration, structural system & foundation type, building response range and other special requirements are developed and firmed up before the commencement of detailed design. Single-storied regular shaped buildings with no windows or minimum windows with special features are preferred. Elevated ground floor is permitted in certain cases such as Substation to create cable vault. However this presents unique challenges in establishing blast pressure distribution due to lack of guidelines for such set-up, which is overcome by own novel solutions. For low blast loads, simplified static approach is adopted for structural analysis, while dynamic analysis with SDOF approach yields economical design for medium to high blast loads. In specific cases where SDOF idealization is inappropriate (as in multi storied building), a MDOF non-linear FE analysis is carried out. RC framed structure with reinforced masonry walls, or steel structure is adequate for low blast, while RC shear wall structure is found most effective to sustain moderate to high blast. The paper presents best practices and unique approach followed in GASCO for such design amid growing challenges of achieving high performance at low cost. These requirements are common for similar expansion projects and hence can be adopted across the industry.
Plant buildings that housing critical equipment and/or manned are generally sited at safe distances from potential explosion sources of process facilities or designed considering anticipated blast pressures during initial construction. However, addition of new process facilities during plant expansion generates new potential explosion sources, blast overpressure range of which exposes some existing facilities to new risk. This paper discusses the approaches followed to assess risks and mitigation measures employed to ensure safety of occupants and integrity of assets. Quantitative Risk Assessment forms the basis for blast considerations on buildings, wherein potential Vapor Cloud Explosion scenarios are identified, and blast overpressure are quantified in the form of contours on plot. Buildings located within blast contours are identified for blast-resistant design to ensure occupant's safety and facilitate safe shutdown of process units during explosion. Whenever Plant expansion is envisaged, a fresh QRA is carried out with potential explosion scenarios. For the explosion analysis, a detailed computer model of plant is generated to closely simulate the congested vulnerable sites and accurately predict blast overpressure, thus optimizing the impact on existing buildings. Based on outcome of the analysis, existing buildings requiring additional blast protection are recognized. In new set-up, process related buildings such as control rooms, OMS, IES etc. are located closer to process area and non-process buildings are sited away from process area. Buildings are designed to resist normal loads along with/or without estimated blast loads based on its location, occupancy and function. During plant expansions, due to space/operational constraints, some new process facilities get closer to the existing buildings. This imposes increased/additional blast load and causes risks to occupants, equipment and building integrity. Hence a comprehensive assessment needs to be carried out and mitigation measures explored. A study was done to assess the impact of such a scenario in one of the gas plants. The study found that some buildings which were originally designed for normal loads are now being subjected to certain intensity of blast loads. The criticality of the building was assessed considering the occupancy level and functional requirement of buildings. The inherent capability of buildings to withstand these additional loads were also evaluated. Based on the study outcome, different mitigation measures such as reducing occupancy, relocating critical items, retrofitting of structure, etc., were explored and feasible options recommended. Assessment of existing buildings for blast overpressure has gained importance in recent years due to steady expansion of old plants. The paper presents the approach followed in the study for such situations and effective measures that can be taken without compromising the safety of the personnel. These requirements are common for similar expansion projects and can be adopted across the industry.
Extending the life of aging assets is a demanding task, especially if they have been exposed to harsh marine environment. Jetty berthing structures commissioned in 1980s for exporting hydrocarbons in one of the gas processing plants were required to be operational beyond their design life to sustain business requirements. Rejuvenation of these critical assets was therefore embarked upon to safely and reliably extend their life by twenty more years. This paper discusses challenges confronted and structured approach followed in restoring the integrity and extending the service life of the aged structures. Special assessment strategy was devised to overcome tough challenges such as limited availability of existing drawings, non-existent original design documents, absence of loading & equipment data, thick marine growth enveloping the structural members, lack of underwater inspection history, etc. To ascertain the current condition of structures, a detailed inspection plan was developed. Close Visual Inspection of splash zone and under water regions of jetty structures viz., loading platform, breasting & mooring dolphins, utility platform, pipe / access trestles, etc., was performed to detect corrosion, fatigue cracks, damaged members, marine growth, etc. In areas of identified or suspected damage, Non-Destructive Testing viz., LRUT, PEC, FMD techniques were employed to detect potential defects. Structural models reflecting as-is condition were developed based on inspection findings and through rigorous structural analyses viz., In-Place, Push-Over, Fatigue and Seismic analysis, the fit-for-purpose fitness of structures was evaluated for life extension. Obstruction to visual examination of the structures due to excessive algae growth, inclement weather conditions to conduct surveys, limited berth availability, etc., presented further challenges that were successfully mitigated by unique inspection strategies. Inspection revealed localized corrosion of nearly 30% metal loss particularly in splash zone, while sub-sea segments exhibited a general metal loss of 10-15%. Wrapping system previously employed to mitigate corrosion had suffered damage. Structural members under water were found completely swamped with thick marine growth. Structural capacities of members, joints and pile foundations were evaluated as part of In-Place analysis. Push-Over analysis was performed to ascertain the available reserve strength (RSR) up to collapse limit under extreme storm condition. Through Fatigue analysis, fatigue life of joints due to cyclic loading from oscillating waves were checked for any integrity concerns. Based on the assessment results, various potential vulnerabilities in the structure were identified. Cost effective and fit-for-purpose corrective actions consisting of strengthening, modification and repair schemes were finalized. Modern techniques / devices to remove / prevent marine growth, and durable protective wrappings in highly corroded regions were implemented. With these considerations, integrity and reliability of the aged near-shore structures was assured for its extended lifespan. In today's challenging economic situation, the demonstration of fitness of ageing assets for prolongation of service life is gaining significant attention. In this regard, this paper presents various challenges faced, unique assessment strategy followed and cost effective remedial techniques adopted for life extension of aged critical near shore structures in order to assure their safety, integrity and reliability. The requirements are common for similar ageing assets and hence the implemented strategy and techniques can be adopted across the industry.
In Oil & Gas plants, steam is supplied to different process units such as turbines & reboilers through piping and is routed on pipe racks. The steam system is encountered with typical problems such as condensate accumulation, hammering, vibrations, condensate discharge, etc. These can cause serious damages to the piping and supporting systems. Such operational and design issues related to steam service can affect the integrity of Plant structures. This paper presents the improvements that are considered in steam lines and their supporting structures which assures high safety and integrity of the system. Steam traps are provided to filter out condensate and non-condensable gases without letting steam escape from steam pipes. Faulty working of steam traps causes accumulation of condensate resulting in hammering which induces heavy vibration and impulsive loads. The impact loads are not accounted in structure design as their magnitude can't be precisely computed due to its complexity and dynamic nature. These accidental loads can have destabilizing effects on the system such as failure of pipe supports, supporting structure, consequential damage of neighboring pipes etc. Conventional practice of open discharge of steam trap condensate on concrete substructure is another cause of concern. Comprehensive study of failure of piping & structural systems at different plants was undertaken to identify possible root causes and realize mitigation measures. To address the deficiencies identified and to further enhance safety, various improvement options were studied and optimal solutions to steam system design were finalized. Some of the improvements proposed included positive isolation / blinding of steam lines to avoid condensate build up, removal of abandoned steam lines, periodic condition monitoring of steam traps, installation of automatic Wireless Acoustic Monitoring system for steam traps, design prerequisites for cantilever supports, sampling and testing of supplied structural bolts as a part of QA/QC, routing of condensate drain discharge to plant drainage system. Suggested improvements and recommendations were implemented and no further issues were reported until this time.
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