Expansion / Debottlenecking of Industrial or Oil & Gas plants is a common phenomenon and many a times such expansion has to be located within limited plot boundaries posing multiple challenges in locating the equipment and design & execution of supporting civil structures. In some cases, finalized supporting civil structures are not feasible to implement due to additional challenges such as additional underground utilities not identified in as-built survey that may arise during execution stage affecting project schedule. Generally, such unique design challenges are not encountered in Greenfield project development. This paper presents the typical constraints encountered in expansion projects, key parameters required to finalize the innovative solutions and measures / methods adopted to overcome the constraints in most effective and economical way in one of the major brownfield project without affecting safe functioning of existing plant. Vibration transmissibility to structures / equipment from new equipment or old equipment vice versa, physical constraints in supporting / routing new piping, underground utilities present in the plot are some of the major challenges faced during detail engineering. Enhancing existing supporting structures for new codal requirements (e.g. revised seismic definition) and enhanced design life to support additional loads of new project in addition to existing ones are some of the additional challenge faced during engineering and construction of the brown field projects Key parameters to be studied / considered while arriving optimal civil engineering solutions to challenges encountered, dynamic properties of new or existing equipment, foot print and founding details of existing foundations, underground utilities present in the plot / boundaries, presence of ground water table, execution feasibility of proposed new civil structures under plant operating conditions thereby avoiding plant or unit shutdowns etc. The solution arrived may have to be revised based on additional challenges that may unfold during execution stage. Fit for purpose supporting structure configurations, out of box structural designs, usage of unique material etc., are some of the methods adopted in arriving safe and economically sound design to overcome the constraints. Brownfield expansion in constrained plots of existing plants is a common phenomenon in all industries. Fit-for-purpose solution needs to be arrived considering constraints applicable to that equipment / plot while maintaining Plant safety and integrity. Similar approaches may be adopted to mitigate challenges in brownfield expansion of other plants to arrive at cost-effective & safe solutions.

Some processes in the oil/gas plant generate wastewater that contain acids/alkalis with pH varying from 1 to 14. Stringent environmental norms require wastewater to be neutralized prior to disposal, which is normally carried out inside the concrete neutralization pits. These concrete pits tend to deteriorate in long-term as concrete and steel components have prolonged exposure to aggressive environment. This paper presents investigations undertaken to ascertain the main causes of concrete deterioration and efficient repair method adopted by GASCO for achieving improved service life and optimizing maintenance cost. Though pits are designed for a service life of 30years, defects such as cracking and spalling of concrete, peeling of coating, corrosion of reinforcement and embedded steel are commonly observed within the first 5 years of construction. Study of existing design and construction specifications were carried out followed by visual inspection and investigative tests such as chemical analysis, NDT tests and petrographic analysis of concrete to identify the sources of deterioration. After identification of the root cause, repair options were evaluated and remedial measures were recommended. These tests revealed significant concentration of H2SO4 & NaOH in the wastewater and sulphate content in concrete. Improper selection of coating material led to peeling/delamination, resulting in acid attack on concrete and subsequent corrosion of reinforcement. In general, even concrete comprising of sulphate resistant cement cannot provide complete resistance to sulphuric acid, without additional acid resistant coating. Sulphuric acid is highly corrosive and reacts with calcium compounds in concrete, to produce soluble calcium sulphate (CaSO4) and water (H2O) resulting in concrete disintegration. The corrosion of reinforcement leading to an increase in volume of reinforcement and causing cracking/spalling of concrete is the consequence that can jeopardize the structure integrity. Remedial measures involve the use of micro concrete with silica to repair the damaged surfaces and a protective coating of dense epoxies with silica fill. Use of silica in concrete fills the pores and decreases permeability. Epoxy coating has excellent bond, low shrinkage and moisture resistant properties and it prevents buildup of stresses that can cause delamination. Recommendations for improved service life include proper selection and optimizing embedded items in aggressive environment, proper selection of cement, water cement ratio, curing, and suitable coating. In addition, it is also recommended to use mechanical mixers to achieve a homogeneous and neutral liquid within the pit. Chemical attack on concrete structures is an important issue in wastewater treatment units. Early detection of deterioration with the application of sound remedial techniques and materials based on comprehensive investigations ensures integrity of the structure besides reducing repair costs and plant outages. This issue is common for process plants and the explored measures can be applied across the industry.

LPG storage facility in a GASCO plant is 35 years old and contains two propane tanks and two pentane tanks each of 60m diameter and 24m height surrounded by massive conical earth embankments. Cryogenic storage temperature (-45°C) of the products freeze the soil below tanks causing frost heave, a phenomenon of soil expansion due to capillary intake of ground water in freezing zone to form ice. To avoid potential risk of frost heave causing additional loads on tank bottom slab, original design provides heating systems at bottom and sides. Its partial failure and inaccessibility through embankments led to serious concerns on tanks safety/ integrity. This paper discusses several investigative studies performed on progressive heating element failures, subsoil frost heave prospects and mitigation measures to assure the integrity of tanks during its residual service life. Tank heating system consists of heating tapes in 1" GI conduits concealed in embankment/concrete base. In each tank, 64 Nos. of conduits exist at 900mm c/c; about 17% of them failed and 45% are in blocked conduits, but functioning. Aged inoperative tapes could not be replaced due to corroded conduits, snapping and access problems. Based on the status of heaters failure/ performance & their current duty-cycle, soil/ ground water temperature below tanks, thermal analysis was conducted and appropriate "duty-cycle" implemented - to avoid the failure risk of 300mm thick tank bottom slab which was not designed for frost heave load. Frost heave is caused by Frost susceptible soil, Water presence and Freezing temperature; role of each forms the basis for studies. Soil samples collected from 5 Nos. 30m deep boreholes were tested and confirmed for frost-vulnerability. Permanent piezometers installed in boreholes upto 4m below tank base continuously monitor ground water level and temperature. Borescope/videoprobe investigation provided heating tapes and conduits condition. Based on gathered information, comprehensive simulation for different heater failure scenarios were performed using ground-freezing analysis models. Results of the study showed that by adjusting the heater duty-cycles to maintain cut in/out temperatures at +5/+10°C (41% duty-cycle), soil shall not freeze until 6 adjacent heater fail; while in reality there are only 2 adjacent heaters failures. It was also inferred that with 100% duty-cycle, upto 10 adjacent heaters can fail before freezing begins. Continuous maintenance activities namely de-choking/ nitrogen purging of conduits, monitoring soil conditions and implementation of recommendations from sound engineering analyses resulted in maintaining safety and integrity of ageing storage tanks. The multi-perspective studies about frost heave effect on cryogenic tanks in the wake of progressive failure of heating elements are exclusive in nature. The findings and mitigation measures will provide ample guidance and knowledge to the industry in managing and operating similar ageing storage facilities in a safe manner.

Many GASCO pipelines cross major highways in Abu Dhabi through concrete culverts (lengths varying from 50 to 125m). Some culverts are in severely deteriorated condition and required immediate replacement. Collapse of culvert(s) may lead to failure of the pipeline resulting in Loss of Containment, environmental degradation and potential risks to personnel/neighbourhoods. This paper presents a techno-economical solution as an alternate to the repair/replacement option for safeguarding the integrity of the pipelines. GASCO identified four severely deteriorated concrete culverts which are protecting 6nos vital oil/gas pipelines, for major repair/replacement. Performing the repair/replacement of these culverts pose challenges due to access restraints, traffic obstructions/diversions, massive civil works, risk of working in the live gas pipeline vicinity etc., with huge overall estimated cost and more than two years execution time. GASCO studied/explored different options including the repair/replacement of existing culverts and ended up with selecting the option of flooding the culverts with a self-compacting mixture of sand and water using specialized pumps which can satisfy/meet the technical, commercial aspects and extend the remnant life. Detailed study was carried out to verify the various technical aspects and evaluate the methodology, with data collection of existing pipe sizes, pipeline wall thicknesses from pipe condition inspection reports, vehicle loads, vibration measurements due to vehicle movements at pipe depths and desktop evaluation of data. The existing pipelines wall thicknesses were checked for Barlow stress (Hoop stress), Circumferential Stress, Longitudinal Stress, Radial Stress and Fatigue check for Girth & Longitudinal Welds considering the overburden loads of earth/sand fill, vehicle cyclic load and internal pressure/temperature and found adequate. Methods of construction and different materials for filling were explored. In some culverts, there was not adequate headroom for people/ equipment access. The method of pumping sand (using special pumps) and compaction of each sand layer by water flooding was found to be the most suitable option in terms of technology, local equipment availability/easy mobilization, locally available filling material, reduced risk of working in the vicinity of live gas pipes, etc. The solution was successfully implemented for the four culverts (each 60m long) across the busy Abu Dhabi – Al Ain highway at Mussafah, in Sep-2015, within 2 months duration and resulted in a huge cost saving of AED 38millions. The followed approach is a long term solution that can be executed by the in-house resources of maintenance team with some support from local contractors (for pumping facilities, etc.) and it also eliminates the future maintenance cost. This solution is first of its kind that was implemented among ADNOC group companies and can be shared with/ adopted by other companies having similar facilities to benefit from the cost optimization & other advantages.

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.