Submerged Installations the Real Challenge
Posted: 04/15/2010 12:00:00 AM EDT | 0
Nirmalendu Bandyopadhyay an offshore asset integrity consultant from India, speaks exclusively to Oil and Gas IQ on the benefits, disadvantages and the untapped opportunities in the of the offshore asset integrity in Asia.
He has worked in various responsible positions with international Organizations during the last 47 years in India, Africa, the Middle East, Gulf and Asia Pacific. His expertise include handling of major EPCM projects from FEED stage to project delivery involving multidisciplinary Engineering functions in multicultural environment.
What are some of the challenges for selection of the most effective coatings for maximum protection?
Offshore structures and other installations are classified under three zones namely the atmospheric zone above water level, submerged zones under the water and soil zone under the sea bed.
Each zone has to withstand variety of environmental conditions and loadings. The most aggressive impact is from corrosion, resulting from sea water in which they stand from construction to end of service life. The primary cause of corrosion is salinity of the sea water and surrounding air.
This varies from location to location across the globe and even at a particular location the salinity undergoes rapid changes causing ever changing corrosion conditions. The other factors that cause degradation of protective coatings in the atmospheric zone are from strong wind carrying particles that cause abrasion. Those in the submerged zone suffer impact from sea waves and currents, growth of algae and bacterial slimes and in the soil zone, due to soil friction during installation. Discharge of chemical fluids and effluents from operation also adds to the aggressiveness of the environment causing damage to coatings.
There are no fixed or universal parameters regarding these factors on which the protective coatings can be designed. Each facility will have its own design parameters and as told earlier, even these parameters keep changing periodically. While installations above water can be inspected and maintained, there is severe problem in submerged and parts buried below the sea bed. Though coatings on parts of the installations under water and sea bed are designed with some initial loss of coatings but these damages are also not uniform over the parts in these zones.
These are some challenges that a planner has to face and try to overcome to the maximum possible extent, by collecting relevant environmental data from the sites.
What are some of the difficulties faced in effective budgeting for repair or replacement expenditure?
All offshore installations are far from onshore facilities and therefore, have inbuilt logistical difficulties. For day to day operations it is possible to plan for transportation of routine consumables to the production platforms or Floaters through offshore supply vessels and by helicopters for extremely emergency conditions.
Thus logistic planning and budgeting for these items is possible. The same also applies for production related plants and machinery which have planned maintenance and capital replacement programs. But the real problem arises for offshore structures, pipelines, underwater manifolds, production well heads, marine risers etc whose performance is difficult to predict but they form indispensable link in the production chain. Budgeting for their capital repair and maintenance is difficult.
Therefore they are designed to ensure fail proof performance throughout their service lives with little or no maintenance and capital replacement programs. But it is risky to assume that there shall be no failures. In offshore operations, lot of heavy transportation around the production set up becomes necessary and possibility of accidental damage cannot be ruled out. The occurrence of such eventuality will throw the entire operation into doldrums and may cause extreme damage to installations and human lives. Therefore, budgeting for such repair and maintenance needs to be done on ad hoc basis locking up finance which may or may not be required. Even these provisions have to be made in the annual capital and revenue budgets over the entire period of the field service life.
Could you please elaborate on the benefits and disadvantages of computerized maintenance management systems that ensure sound structural health?
CMMS is the most effective tool at the hands of the planners and operatives to ensure sound health of the assets. Every production related items like pumps, compressors, piping, valves, vessels, fans, motors etc are mostly OEM items and have guaranteed service lives and have routine and major overhaul and capital replacement manuals. These are included in the CMMS software and are constantly reviewed and updated after every action at site. Thus at a glance it is possible to review whether the recommendations of the OEM have been carried out and it is also possible to create data bases to keep control on cost by entering relevant data from site activities in respect of labour, consumables, idle time, reasons for idling and major slippages if any. These data bases are essential to ensure that the plants operate as planned without any major breakdown or interruptions.
The same logic can be applied to offshore structures in respect of routine maintenance programs and these may be included in the revenue budgets. But unlike OEM of production plants and machinery who supply maintenance and capital replacement program manuals, the structural vendors do not provide such manuals. It is up to the plant maintenance departments who have to prepare such maintenance programs. As told earlier that all parts of structures do not suffer identical damages and therefore needs to be done on ad hoc basis. Some critical structures may require annual painting and repair whereas some non critical parts may be painted every two or three years to economize on cost. Thus it is a disadvantage to try to include these activities under CMMS. Their inclusion only complicates the operation. Regular on site inspection and recommended NDT to assess the extent of damage and take appropriate actions, will be the only viable program.
What are some of the untapped opportunities that companies are facing when it comes to offshore asset life extension?
It is the normal practice to design all offshore assets to last till the full production life of the fields where they are deployed. As rate of deterioration in soundness and operability is high in marine environment due to high rate of corrosion, adequate attention must be paid to appropriate maintenance and capital replacement programs.
Often, the production service life of a field can be extended beyond plateau production phase and the period of decline is extended by various EOR methods. Thus it becomes imperative to ensure that the assets also get extended operating life till the abandonment phase.
A producing field may have a number of well heads each with its own production set up which are either connected to undersea manifold centre or connected directly to the manifold on the platforms or floaters .All wells do not produce at the same rate or do not have identical production life. Thus the overall plateau of a field may not apply to the plateau of individual well. Some well my stop producing earlier or may change the product mix abruptly requiring premature shut down and abandonment. Normally such abandoned well head set up including sub sea pipelines and risers are left in place till the entire field ceases production and enters into abandonment phase. One great opportunity is to try and salvage the set up from those wells which need earlier abandonment and reuse them at another producing well head set up and saves on capital replacement expenditures. There is no need to leave it in place till full abandonment. Since this work will need to be done when the other facilities are operating, extreme careful planning and execution must be carried out to prevent accidents.
Is there any scope of reuse of offshore assets from one field to another after abandonment?
Yes. But that will depend on the physical and operating conditions of the assets salvaged from abandoned field. While this is definitely possible for operating plants like pumps, compressors, fans, motors etc, it is applicable also for fixed offshore structures like platforms, pipelines, risers etc provided they are properly salvaged, preserved and repaired and strength assessed before deployment in another location. The normal practice is to scrap these items after abandonment. Structures salvaged in healthy conditions from one deepwater location can be redeployed in shallower locations with proper modifications and strengthening. This calls for design standardization of these structures to the extent possible.
Can composite materials be used in offshore structures and if so what are the advantages?
Yes. Composite materials can be used in secondary and non critical parts of offshore structures. These days structural steel strengthened by carbon fibres are being used extensively in many onshore heavy structures like bridges, viaducts , pylons etc The advantages are lighter weights, more flexural strengths, more resistance to corrosion etc. While offshore platform jackets need to be of high strength structural steel circular sections of at least 350 MPa yield strength, the structures used in top sides can be economized by using these carbon fibre steel sections. There are other steels like CORTEN®, which are self protected against corrosion and when these are used, the cost of maintenance gets reduced. Use of Aluminium alloys in ladders, handrails, balustrades etc also reduces the dead weights and stands better against corrosion.
How important is redundancy in the Asset Integrity chain. Is there any means to reduce the redundancy?
Redundancy in operating plants and machinery is absolutely necessary to ensure fail safe operation. Since production is a 24 x 7 operation, there must be redundancy with automatic switch over in case of failure of equipment. In offshore structures or static elements, redundancy can be reduced through proper NDT and follow up maintenance/replacement actions. Continuous assessment of remaining strength of a structure helps in determining the serviceability of the same. When these data are properly recorded and analyzed periodically, structural redundancy can be reduced drastically and in turn saves lot of expenditures.
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