Offshore Rigs Diesel Engine NOX Emission

The diesel engine combustion process mainly produces NO (approximately 60–90%) and little NO2in the combustion chamber. They are considered a mixture called NOX but only NO2 is relevant for air hygiene as a pollutant input. Diesel engines systematically produce NO2 from NO in catalytic converters. deNOx systems use it to oxidize and efficiently reduce soot particulates.

In air, NO oxidizes to NO2, a gas that irritates mucous membranes and is caustic when combined with moisture (acid rain). It increases asthma sufferers’ physical stress, especially when they exert themselves physically. NO2 has a ‘‘fertilizing’’ effect on plants, i.e. it promotes growth.

According to authority, a limit concentration of NO2 of 40mg/m2 will be in force in the EU in 2010.

Achieving the aforementioned limits will necessitate considerable efforts in all sectors, i.e. not only in the transportation but also the major offshore industry and shipping businesses will be required to reduce NOX emission worldwide.

The IMO (International Maritime Organization) imposed limits on NOX emissions for marine diesel engines

with power outputs >130 kW as of January 1, 2000. It plans to later adapt the limits determined from the test cycles dependent on use (main propulsion or auxiliary engine) and the mode of operation (constant speed or propeller drive) specified.

In 1999, EPA adopted regulations requiring new marine diesel engines to comply with emission standards

beginning in 2004 (tier 1) and 2007 (tier 2). 

In May 2008, EPA published new rules aimed at dramatically reducing air pollution from marine diesel engines.

↓ particulate matter (PM) emissions by 90%

↓ nitrogen oxide (NOx) emissions by 80 %

 

Tier 1 and Tier 2 emission standards currently applicable to new marine diesel engines

Tier 1 limits NOx emissions only, and applies to model years 2004 and later

Tier 2 limits NOx, CO, and PM, and applies to model years 2007 and later

Tier 3 “near term” emission standards for “existing” engines for most towboats, Tier 3 standards become effective in 2016

Tier 4 “long term” emission standards for “newly-built” engines mandates high-catalytic after-treatment application of high efficiency after technology for most of our towboats, Tier 4 standards may become effective in 2016

Growing opportunities for dual-fuel and gas-diesel engines in land and marine power markets have stimulated designs from leading medium speed and low speed enginebuilders. Development is driven by the increasing availability of gaseous fuels, the much lower level of noxious exhaust emissions associated with such fuels, reduced maintenance and longer intervals between overhauls for power plant.

A healthy market is targeted from floating oil production vessels and storage units, rigs, shuttle tankers, offshore support vessels and LNG carriers.

Valuable breakthroughs in mainstream markets have been made since 2000 with the specification of LNG-burning engines for propelling a small Norwegian double-ended ferry (Mitsubishi high speed engines), offshore supply vessels and a 75 000 cu.m. LNG carrier (Wärtsilä medium speed engines).

Natural gas is well established as a major contributor to the world’s energy needs. It is derived from the raw gas from onshore and offshore fields as the dry, light fraction and mainly comprises methane and some ethane. It is available directly at the gas field itself, in pipeline systems, condensed into liquid as LNG or compressed as CNG. Operation on natural gas results in very low emissions thanks to the clean-burning properties of the fuel and its low content of pollutants. Methane, the main constituent, is the most efficient hydrocarbon fuel in terms of energy content per amount of carbon.  Wärtsilä’s dual-fuel (DF) four-stroke engines can be run in either gas mode or liquid-fuelled diesel mode. In gas mode the engines work according to the lean-burn Otto principle, with a lean premixed air-gas mixture in the combustion chamber. (Lean burn means the mixture of air and gas in the cylinder has more air than is needed for complete combustion, reducing peak temperatures). Less NOx is produced and efficiency increases during leaner combustion because of the higher compression ratio and optimized injection timing. A lean mixture is also necessary to avoid knocking (selfignition).

Marine engine designers in recent years have had to address the challenge of tightening controls on noxious exhaust gas emissions imposed by regional, national and international authorities responding to concern over atmospheric pollution.

Exhaust gas emissions from marine diesel engines largely comprise nitrogen, oxygen, carbon dioxide and water vapour, with smaller quantities of carbon monoxide, oxides of sulphur and nitrogen, partially reacted and non-combusted hydrocarbons and particulate material. Nitrogen oxides (NOx)—generated thermally from nitrogen and oxygen at high combustion temperatures in the cylinder—are of special concern since they are believed to be carcinogenic and contribute to photochemical smog formation over cities and acid rain (and hence excess acidification of the soil). Internal combustion engines primarily generate nitrogen oxide but less than 10 per cent of that oxidizes to nitrogen dioxide the moment it escapes as exhaust gas.

Sulphur oxides (SOx)—produced by oxidation of the sulphur in the fuel—have an unpleasant odour, irritate the mucus membrane and are a major source of acid rain (reacting with water to form sulphurous acid). Acid deposition is a trans-boundary pollution problem: once emitted, SOx can be carried over hundreds of miles in the atmosphere before being deposited in lakes and streams, reducing their alkalinity.

Sulphur deposition can also lead to increased sulphate levels in soils, fostering the formation of insoluble aluminium phosphates which can cause a phosphorous deficiency. Groundwater acidification has been observed in many areas of Europe; this can lead to corrosion of drinking water supply systems and health hazards due to dissolved metals in those systems. Forest soils can also become contaminated with higher than normal levels of toxic metals, and historic buildings and monuments damaged.

Particulate matter (PM) is a complex mixture of inorganic and organic compounds resulting from incomplete combustion, partly unburned lube oil, thermal splitting of HC from the fuel and lube oil, ash in the fuel and lube oil, sulphates and water. More than half of the total particulate mass is soot (inorganic carbonaceous particles), whose visible evidence is smoke. Soot particles (unburned elemental carbon) are not themselves toxic but they can cause the build-up of aqueous hydrocarbons, and some of them are believed to be carcinogens. Particulates constitute no more than around 0.003 per cent of the engine exhaust gases.

Noxious emissions amount to 0.25-0.4 per cent by volume of the exhaust gas, depending on the amount of sulphur in the fuel and its lower heat value, and the engine type, speed and efficiency.

De-NOx technology options are summarized as follows:

The primary NOx reduction measures can be categorised as follows:

-Water addition: either by direct injection into the cylinder or by emulsified fuel.

- Altered fuel injection: retarded injection; rate-modulated injection; and a NOx-optimized fuel spray pattern.

- Combustion air treatment: Miller supercharging; turbocooling; intake air humidification; exhaust gas recirculation; and selective non-catalytic reduction. (Miller supercharging and turbocooling are covered in the Pressure Charging chapter.)

- Change of engine process: compression ratio; and boost pressure.

The basic aim of most of these measures is to lower the maximum temperature in the cylinder since this result is inherently combined with a lower NOx emission.

MARPOLAnnex VI choong

Below courtesy of CATERPILLAR USA


Below courtesy of Watsila
Watsila IMO Tier III



Below courtesy of Watsila
Watsila Emission AAA

More on Drilling Jack-up and some installations on board

The first step in the jack-up rig design is the definition of its configuration. This is based on operational and economic requirements and past design experience. Decisions made at this stage have a significant impact on the behaviour of the structure. The geometry of the configuration developed should have the necessary capacity to accommodate needed equipment, preload tanks and quarters. Preliminary estimates of weights should be made and a naval architect should assess the configuration for the “afloat” mode of the jack-up rig. A configuration for the legs should be developed. The system for connecting the legs to the hull so as to achieve efficient moment transfer should be chosen. A classification society should also be chosen [American Bureau of Shipping, 2001; Det Norske Veritas-Rules for Classification of Mobile Offshore Units]. A preliminary assessment should then be made to ensure that the chosen configuration complies with the requirements of the chosen classification society. After this, the basic design can be developed. The efforts of the structural engineer are important from this stage on. Hull scantlings are the individual elements that makeup the structure.

Due to the numerous complexities associated with jack-ups, it should be remembered that a structural analysis would be based on a number of simplifying assumptions and approximations. Though software is available to execute a non-linear dynamic analysis, the designer may opt for a simple static analysis using wave forces generated from a hydrodynamic analysis applying a linear wave theory (Such as the Stoke’s Fifth Order Potential Wave Theory) to a hydrodynamic model generated for this purpose.

The following steps should serve as a general guideline for the analysis of a jack-up platform:-

Define the environment including water depth, wind speed, wave (type, height, period) and current velocity and its variation with depth. This can be a location specific environment (North Sea, Persian Gulf) or a world wide criteria. The worldwide criterion is a reference benchmark that does not necessarily reflect any particular location. Some of the storm parameters (100 knot wind) are defined per code or classification authority or refer to API.

The results of these environments are then used as reference for the actual unit location. With the exception of very heavy loads (such as cantilever, transom and hold-down reactions, heliport support members, etc.), this may be accomplished by summing all the equipment weight on a deck, a proportion of the variable load on that deck and dead load and distributing this load uniformly over the entire deck. This may be done for all decks. Loads from the drill floor may be applied as concentrated forces at appropriate locations. Usually, the weight is assumed to be balanced equally among the three legs. This is normally achieved by moving the liquids among the various tanks to reach a balanced condition.

Generate a hydrodynamic model of the jack-up platform. This may be a simple model consisting of three “stick” elements that have the same hydrodynamic properties as the trussed leg. The ideal source of the drag values of the unit would generally be determined via wind tunnel models. This takes into account the actual geometry of the unit and the effects of shielding. Usually the product of these studies is a single drag value for the legs and hull. The main problem with this source of parameters is cost and time.

Generate a Global Structural Model: a typical finite element analysis model of a jack-up platform structure and usually the length of leg that should be used in the modelling for a given water depth. For a jack-up platform whose legs have independent spud can foundations, the legs are usually assumed to be pinned at a depth of about 10 ft below the mudline. For a mat supported jack-up, the structure of the mat may be modelled using plate elements and the legs could be fixed to this structure. Per the ABS Rules [American Bureau of Shipping, 20011, the minimum crest clearance to be provided is 4 ft (1.2 m) above the crest of maximum wave or 10% of the combined height of the storm tide plus the astronomical tide and height of the maximum wave crest above the mean low water level, whichever is less between the underside of the unit in the elevated position and the crest of the design wave.

Spud Cans

This is the most common type of jack-up platform foundation in use. Spud cans typically consist of a conically shaped bottom face. The purpose of a spud can is to transfer the jack-up leg loads into the seabed below. The structure of the spud-can should thus have the capacity to resist the resulting shear and bending stresses exerted on it by the leg and the foundation soils. To determine the maximum force on a spud can during the design phase, the total weight of the upper hull during the worst design storm condition and its center of gravity is first established. This weight is then distributed over all the legs of the jack-up platform. From the applied environmental forces, the overturning moment is determined next. The direction of this overturning moment should be so as to cause the maximum compressive force on one leg. An appropriate load factor should then be applied to this force. The area of contact between the spud can and the soil should be sufficient for the weakest chosen soil condition to support this force.

Other criteria that are applied to design the structural strength of the spud can are:

Assume that the entire reaction acts as a concentrated load on the tip of the spud can.

Assume that the entire reaction acts on a circle centred on the tip of the spud can, whose radius is (i) %, (ii) %, (iii) 3/4 and (iv) 1 times the equivalent radius of the can.

The lower plating should be designed for the resulting distributed loads. Spud cans are usually designed to be flooded during operation. To facilitate access to the inside of the can, during the floating condition of the jack-up platform, vents may be provided to a certain height above the top of the can. The upper plating should be designed for a hydrostatic head corresponding to the height of this vent in case the can is not flooded.

Legs

Trussed legs are the most common type on modern jack-up rigs, the other type being cylindrical legs. Legs are subjected to the following forces:

(1) Elevated condition:
(a) Compression forces due to gravity loads on the hull.
(b) Compression forces due to the reactive couple caused by overturning moments on the jack-up.
(c) Bending moments at the hull due to the horizontal displacement of the hull and the moment connection between the leg and the hull.
(d) Horizontal forces on the leg due to wave, current and wind action.
(e) Bending moments due to P-A effect on the leg.
(f) High local stresses due to force transfer and from the pinions. “rack chocks, hull upper and lower guides”.
(2) Afloat condition:(a) Gravity loads on the leg.
(b) Wind force.
(c) Inertia forces due to vessel motions.
(d) Restraining reactions from guide units or other locking devices in the hull that create high moments in the leg.
(e) Fatigue causing cyclic stresses in the lower bays of the legs due to the constant pitch and roll motions of the floating vessel.

Electrical Installation Concept on a MODU rig

One of the earliest tasks for the electrical engineer who is designing a power system is to estimate the normal operating rig power plant load. He is also interested in knowing how much additional margin he should include in the final design. There are no ‘hard and fast’ rules for estimating loads, and various basic questions need to be answered at the beginning of a project, for example,

• Is the rig power a new plant?

• How long will the offshore rig power system to exist e.g. 10, 20, 30 years?

• Is the old rig power being extended?

• Does the owner have a particular philosophy regarding the ‘sparing’ of equipment?

• Are there any operational or maintenance difficulties to be considered?

• Is the power factor important with regard to importing power from an external source?

• If a generator suddenly shuts down, will this cause a major interruption to the rig operation?

• Are there any problems with high fault levels?

 

The electrical engineer will need to roughly draft a key single-line diagram and a set of subsidiary single-line diagrams. The key single-line diagram should show the sources of power e.g. generators, utility intakes, the main switchboard and the interconnections to the subsidiary or secondary switchboards. It should also show important equipment such as power transformers, busbars, busbar section circuit breakers, incoming and interconnecting circuit breakers, large items of equipment such as high voltage induction motors, series reactors for fault current limitation, and connections to old or existing equipment if these are relevant and the main earthing arrangements. The key single-line diagram should show at least, the various voltage levels, system frequency, power or volt-ampere capacity of main items such as generators, motors and transformers, switchboard fault current levels, the vector group for each power transformer and the identification names and unique ‘tag’ numbers of the main equipment.

 

Vital loads are normally fed from a switchboard that has one or more dedicated generators and one or more incoming feeders from an upstream switchboard. The generators provide power during the emergency when the main source of power fails. Hence these generators are usually called ‘emergency’ generators and are driven by diesel engines. They are designed to automatically start, run-up and be closed onto the switchboard whenever a loss of voltage at the busbars of the switchboard is detected.

 

Vital AC loads, example below

Emergency lighting
Emergency generator auxiliaries
Helicopter pad lighting
Control room supplies
Vital LV pumps 

 

Essential AC loads, example below

 

Diesel fuel transfer pumps 

Diesel fire pump auxiliaries

Main pump auxiliaries

Main compressor auxiliaries

Main generator auxiliaries

Electric fire pumps

Living quarters
Air compressor
General service water pumps
Fresh water pumps
Equipment room HVAC supplies
Life boat davits
Anti-condensation heaters in panels and switchboards
Security lighting supplies
Control room supplies
UPS supplies
Radio supplies
Computer supplies
Battery chargers for engine starting systems
Instrumentation supplies

Vital DC Loads, example below 

Public address system

Plant alarm systems
System shutdown system
Telemetry systems
Emergency radio supplies
Fire and gas detection system
Navigation aids

Hence each switchboard will usually have an amount of all three of these categories. Call these C for continuous duty, I for intermittent duty and S for the standby duty. Let the total amount of each at a particular switchboard j be Cjsum, Ijsum and Sjsum. Each of these totals will consist of the active power and the corresponding reactive power.

In order to estimate the total consumption for the particular switchboard it is necessary to assign a diversity factor to each total amount. Let these factors be Dcj for Csumj , Dij for Isumj and Dsj for Ssumj . Offshore rig companies that use this approach have different values for their diversity factors, largely based upon experience gained over many years of designing plants. Different types of plants

may warrant different diversity factors.

Electrical Installation Concept on MODU_ Choong
The info  presented in the slides are samples only and may not represent the total correctness of what is being installed subjected to the specifications of the contract scope.    

 

Comparison of US and IEC Nomenclature, eg. below

While there are many similarities and even direct interchangeabilities between U.S. and IEC recognized standards, specific applications must be considered.

Motors may be acceptable under all standards but not necessarily certified under all standards.

The IEC "flame-proof" motor is essentially the same as the U.S. "explosion-proof" motor. Each design withstands an internal explosion of a (specified) gas or vapor and prevents ignition of the specified gas or vapor that may surround the motor. However, construction standards are not identical. The U.S. standard is generally more stringent and acceptability can be based on approval of local authorities.

The U.S. totally enclosed "purged and pressurized," or "inert gas filled," motors are manufactured to similar standards as those of IEC pressurized motors. Each operates by first purging the motor enclosure of any flammable vapor and then preventing entry of the surrounding (potentially explosive

or corrosive) atmosphere into the motor enclosure by maintaining a positive gas pressure within the enclosure.

IEC Type 'e' (Increased Safety) motors are nonsparking motors with additional features that provide further protection against the possibilities of excess temperature and/or occurrence of arcs or sparks.

NEMA and IEEE standards and testing are more comprehensive than the IEC standards. In general, motors designed to NEMA/IEEE standards should be suitable for application under IEC standards from a rating, performance, and testing viewpoint.

 

 

 

Rig Stability during tow or transit

Offshore rig stability is a complicated aspect of naval architecture which has existed in some form or another for past years. Historically, offshore rig stability adopted some of the ship stability calculations and for ships, it relied on rule-of-thumb calculations, often tied to a specific system of measurement. Some of these very old equations continue to be used in naval architecture books today, however the advent of the floaters including rig and ship, model basin allows much more complex analysis.

Stability standards for both ships and offshore rigs ( jackup, semi-submersibles ) are based on a two-tier approach:

• intact stability requirements, designed to ensure that the unit will withstand all expected environmental conditions when in its normal operating or survival condition, and while it remains
undamaged and watertight;

• damaged stability requirements, designed to ensure that the unit will not capsize in foreseeable environmental conditions, after undergoing a limited amount of damage or flooding, and will be capable of returning to the upright condition.

Two alternative approaches are normally adopted when defining damage: damage to any one compartment at any draught, or waterline damage, including breaching of internal watertight divisions between compartments. Both approaches have their strengths and weaknesses. An offshore unit designed to meet the any one compartment standard cannot necessarily be guaranteed to meet the waterline damaged standard, and vice versa.

NMD adopted a three-tier approach. The first two tiers were the established intact and damaged stability philosophies, and the third was a requirement that the unit should withstand loss of buoyancy from either the whole or a major part of one column, but without any requirement to return to the upright position. The objective in this case was to allow the crew time to evacuate the unit. This requirement was expressed in terms of providing a maximum angle of heel after a large loss of righting moment, and a minimum level of reserve buoyancy above the damaged waterline. The concept of providing some level of reserve buoyancy, beyond that necessary to meet basic code requirements, has since been widely accepted.

This information is intended to provide an adequate level of stability during routine operations of floating Installations. The aim is to take account of the most probable damage cases, in particular low energy collisions with supply vessels during loading, towing and anchor handling. Consideration should be given to carrying out an inclining test on the first unit of a design, when as near to completion as possible, to determine accurately the lightship weight and position of centre of gravity. The test will need to be conducted in accordance with an approved procedure.

For successive units of a design which are identical with regard to hull form and arrangement (with the exception of minor changes in machinery or outfit) detailed weight calculations showing only the differences of weight and centres of gravity may be acceptable. However, the calculated changes in weight and position of centre of gravity should be small, and the accuracy of the calculations confirmed by a deadweight survey.

 
 
 
Vessel Stability_1
 
 
 


Stability_Jackup
 

Ship_Stability.pdf

Offshore Rig Power - Diesel engines

What is a diesel run engine gen-set and how does it differ to the industrial engine on which most are based? The following basically explain many of the terms applicable to diesel gen-set design, development, operating and ownership by the rig operator.

MARINE DIESEL ENGINE denotes the engines used either as the propulsive prime mover of a ship or generating electrical power to the consumers onboard the offshore rig or semi-submersible. The consumers not only provide to the drilling equipment but also services to the hotel onboard, fire and safety systems, etc. The term may be extended to include the propulsion of engines that are used for shipboard auxiliary services such as the generation of electric power.

IOPU – Independent Operating Power Unit. These are multi speed non vehicle power units. The are normally sold with radiator, cooling group and fan, and typically share ratings from their off highway derivatives. Typical applications include pumps and compressors.

Operating Speed – Gen-sets are normally governed to fixed speed running. 1500 rpm to produce 50Hz electrical supply for European market and 1800 rpm to produce 60 Hz for US market. 60Hz supply can be achieved at 1200Hz with some alternator sets– this is uncommon.

kWe – Kilowatts electrical is a measure of electrical power produced by a gen-set. 60Hz generator sets are usually marketed in terms of kWe.

kVa – Kilovolt amps is a measure of electrical power produced by a genset. 50Hz gen-sets are usually marketed in terms of kVa. As gensets produce an alternating current P=VI doesn’t hold true. Voltage and current follow sinusoidal wave forms with a phase shift due to the reactance (generated by inductance & capacitance) of the load on the alternator, and hence a power factor is used. Industry assumes a 100% resistive load for which a 0.8 power factor is used. This relates kWe to kVa by the following:     kWe = kVa x 0.8

Fuel Coolers – Gen-sets are normally fitted into a frame, which holds a small fuel or “day tank” for limited time running. If the gen-set operates in elevated ambient temperatures, or the engine has a high fuel spill ratio, the temperature of the fuel will often be controlled by a small fuel cooler (air-to-fuel) mounted on the cooling group. The cooler prevents rises in “day tank” temperatures preventing fuel injector damage.

Alternator Efficiency (ha) – The alternator on the gen-set converts the mechanical energy delivered by the engine into electrical energy, and has an associated efficiency. Typically alternators have an efficiency of 0.95 (95%).

kWm – Gen-sets are marketed in terms of the electrical power which they produce. However engine manufacturers are more interested in the mechanical power which their engine needs to deliver to the alternator to provide the quoted electrical power. This includes fan powers and alternator efficiency:

kWe = (kWm –Fp) x ha or kWe = kWm x 0.90 x 0.95 (<10L engine)

kWe = (kWm –Fp) x ha or kWe = kWm x 0.95 x 0.95 (>10L engine)

Emissions- Genset emissions are complicated and specific to the country in which they operate. Generally requirements are less demanding than other off highway equipment, but are often driven by marketing rather than legislative needs. Legislative limits are complicated, determined by introduction date, engine powers and power rating.

Ambient/Altitude Clearance - Gen-sets are operated in global environments, with extreme ambient and altitude operating environments. Running at higher ambient temperatures adds additional loads on the cooling system, and at elevated altitudes the inlet system struggles to deliver sufficient air for combustion with the lower air density/pressure. Gen-sets are expected to run at altitudes up to 4000m and ambient temperatures of 55 ⁰C, which may require derate. Clearance is defined as the margin on the altitude/ambient performance limiting parameters (such as coolant and exhaust temperature) when tested at standard operating conditions (sea level 25 ⁰C). From the Ambient/Altitude clearance, curves are developed to assist application engineers in sizing appropriate derates for extreme operating conditions.

Governing – Gen-sets are fixed speed applications with governors developed to maintain the desired running speed within careful limits. This is particularly important as electrical equipment powered by the genset may be damaged by supply outside of the normal 50/60Hz limits. Gen-set governing is detailed by ISO 8528.

Load Acceptance – Gen-sets are often used for standby/emergency power, where they will be expected to start-up, run up to running speed and then accept a large % of maximum electrical load. Load acceptance is measured in terms of a % frequency dip and a recovery time, and are defined by ISO 8528-5 and NFPA 99/110. Additional requirements are customer driven demanding typically 80% of the prime rating within 10 seconds of start-up, within ISO 8528-5 limits. Engine load acceptance has been demonstrated as a linear function of trapped mass.

Power Rating - Gen-sets are sold at three main power ratings determined by their application. Power ratings are defined by ISO 8528-1.

An important parameter for a marine diesel engine is the rating figure,usually stated as bhp or kW per cylinder at a given rev/min. Although engine makers talk of continuous service rating (csr) and maximum continuous rating (mcr), as well as overload ratings, the rating which concerns a ship or rig owner most is the maximum output guaranteed by the engine maker at which the engine will operate continuously day in and day out. It is most important that an engine be sold for operation at its true maximum rating and that a correctly sized engine be installed in the ship or rig; an under-rated main engine, or more particularly an auxiliary, will inevitably be operated at its limits most of the time.

Rig or ship owners usually require that the engines be capable of maintaining the desired service while fully loaded, when developing not more than 80 per cent (or some other percentage) of their rated brake horsepower. Such stipulation may leave the full-rated power undefined and therefore does not necessarily ensure a satisfactory moderate continuous rating, hence the appearance of continuous service rating and maximum continuous rating. The former is the moderate in-service figure, the latter is the enginebuilder’s set point of mean pressures and revolutions which the engines can carry continuously.  Normally a ship or semi rig ( with thrusters)  will run sea trials to meet the contract speed or thruster load (at a sufficient margin above the required service speed) and the continuous service rating should be applied when the vessel is in service.

DERATING

An option available to reduce the specific fuel consumption of diesel engines is derated or so-called ‘economy’ ratings. This means operation of an engine at its normal maximum cylinder pressure for the design continuous service rating, but at lower mean effective pressure and shaft speed. By altering the fuel injection timing to adjust the mean pressure/ maximum pressure relationship the result is a worthwhile saving in fuel consumption. Example, the horsepower required for a particular speed by a given ship or semi rig with thrusters is calculated by the naval architect and, once the chosen engine is coupled to a fixed pitch propeller ( in this case of ship propulsion ) , the relationship between engine horsepower, propeller revolutions and ship speed is set according to the fixed propeller curve. A move from one point on the curve to another is simply a matter of giving more or less fuel to the engine.

Diesel Power Choong1

A major boost to engine output and reductions in size and weight resulted from the adoption of turbochargers. Pressure charging by various methods was applied by most enginebuilders in the 1920s and 1930s to ensure an adequate scavenge air supply: crankshaftdriven reciprocating air pumps, side-mounted pumps driven by levers off the crossheads, attached Roots-type blowers or independently driven pumps and blowers.

The first turbocharged marine engines were 10-cylinder Vulcan- MAN four-stroke single-acting models in the twin-screw Preussen and Hansestadt Danzig, commissioned in 1927. Turbocharging under a constant pressure system by Brown Boveri turboblowers increased the output of these 540 mm bore/600 mm stroke engines from 1250 kW at 240 rev/min to 1765 kW continuously at 275 rev/min, with a maximum of 2960 kW at 317 rev/min. Büchi turbocharging was keenly exploited by large four-stroke engine designers, and in 1929 some 79 engines totalling 162 000 kW were in service or contracted with the system.

The turbocharger comprises a gas turbine driven by the engine exhaust gases mounted on the same spindle as a blower, with the power generated in the turbine equal to that required by the compressor.

There are a number of advantages of pressure charging by means of an exhaust gas turboblower system:

- A substantial increase in engine power output for any stated size and piston speed, or conversely a substantial reduction in engine dimensions and weight for any stated horsepower.

- An appreciable reduction in the specific fuel consumption rate at all engine loads.  A reduction in initial engine cost.

- Increased reliability and reduced maintenance costs, resulting from less exacting conditions in the cylinders.

- Cleaner emissions (see section below).

- Enhanced engine operating flexibility.

Larger two-stroke engines may be equipped with up to four turbochargers, each serving between three and five cylinders.


Compared with four-stroke engines, the application of pressure charging to two-stroke engines is more complicated because, until a certain level of speed and power is reached, the turboblower is not selfsupporting.  Two-stroke engine turbocharging is achieved by two distinct methods, respectively termed the ‘constant pressure’ and ‘pulse’ systems. It is the constant pressure system that is now used by all low speed two-stroke engines. For constant pressure operation, all cylinders exhaust into a common receiver which tends to dampen-out all the gas pulses to maintain an almost constant pressure. The advantage of this system is that it eliminates complicated multiple exhaust pipe arrangements and leads to higher turbine efficiencies and hence lower specific fuel consumptions. An additional advantage is that the lack of restriction, within reasonable limits, on exhaust pipe length permits greater flexibility in positioning the turboblower relative to the engine.
The main disadvantage of the constant pressure system is the poor performance at part load conditions and, owing to the relatively large exhaust manifold, the system is insensitive to changes in engine operating conditions. The resultant delay in turboblower acceleration, or deceleration, results in poor combustion during transition periods.

Diesel Engine Turbocharging

Some more insights of a Semi-sub Drilling Rig

The company has secured a US$300 plus million to build a repeat semisubmersible drilling rig for Brazilian drilling contractor group Queiroz Galvão Óleo e Gás (QGOG) and to be named "Alpha Star". The first one built earlier was named Gold Star ( see below rig data taken from QGOG website ). An innovative design, the DSSTM 38 semisubmersible drilling rig is designed to meet the operational requirements in the deepwater “Golden Triangle” region, comprising Brazil, Africa and the Gulf of Mexico.

The rig is rated to drill to depths of 30,000 feet below mud line in just over 9,000 feet water depth. It is 103.5 metres in overall length, with a main deck size of 69.5 metres by 69.5 metres. Its operational displacement is approximately 38,000 tonnes. The rig has accommodation facilities to house a crew of up to 130 men. It has both vertical and horizontal riser storage. The eight 3000kW Azimuthing thrusters configuration are designed to keep the vessel in position. All configurations comply with the  Dynamic Positioned System (DPS-2) requirements.

 Photo


Alpha Star


Gold star



Source : Straits Times, QGOG website.

Jackup Terminologies and Types

In early 1955 ( before I was born in '59 and I started to work only in 1980, see my blog article on pressure vessel design ), the first 3-legged jack-up appeared on the offshore scene. The rig was the R.G. LeTourneau jack-up, the Scorpion, for Zapata Offshore Company. The Scorpion, an independent leg jack-up, used a rack and pinion elevating system on a truss framed leg. The rig worked very successfully for several years but was lost during a move in the Gulf of Mexico. The Scorpion was closely followed by The Offshore Company Rig No. 54. For Rig No. 54, however, a hydraulic jacking system on a trussed leg was used. These jack-ups were followed by Gus II, a mat supported unit using a hydraulic jacking system, which was built by Bethlehem Steel Corporation.

Those early breed of jack-ups were primarily designed to operate in the U.S. Gulf of Mexico area in water depths up to 200 feet. Wave heights in the range of 20 to 30 feet with winds up to 75 mph were considered as design criteria for these units. In most cases, in the event of a pending hurricane, the rigs were withdrawn to sheltered areas. Jack-ups can be either self-propelled, propulsion assisted, or nonpropelled. The majority of jack-up rigs are non-propelled. The self-propelled unit, although very flexible, requires a specially trained crew of operators as well as a better trained rig drilling team.

Jack-ups have been built with as many as 14 legs and as few as 3 legs. As the water depth increases and the environmental criteria become more severe, we find that to use more than 4 legs is not only expensive but impractical. The prime forces on a jack-up are generated from the waves and currents, hence, the less exposure to the waves and currents the fewer the forces being developed on the unit. From this standpoint the optimum jack-up is the monopod or single leg unit.

Problems other than wave forces, however, must be overcome with the monopod type unit. But in areas such as the North Sea with very rough' seas there is a need for the monopod jack-up.

When evaluating which type of jack-up to use, it is usually some of the criterias to consider :

1. Water depth and environmental criteria.

2. Type and density of sea bed.

3. Drilling depth requirement, environmental conditions.

4. Necessity to move or stop during hurricane or storm season.

5. Capability to operate with minimum support.

6. How often it is necessary to move.

7. Time lost preparing to move.

8. Operational and towing limitations of the unit.

The independent leg unit depends on a platform (spud can) at the base of each leg for support. These spud cans are either circular, square, or polygonal, and are usually small. Nowadays, spudcan bottom comes with tips for better holding on ground. The larger spud can being used to date is about 56 feet wide. Spud cans are subjected to bearing pressures of around 5,000 to 6,000 pounds per square foot, although in the North Sea this can be as much as 10,000 psf. Allowable bearing pressures must be known before a jack-up can be put on location.

Jackup Slides Ckw


Le Thourneau rigs have been the majorities in the Gulf of Mexico and most of them operating in the region are coming to thirty years or more in operating life. Some have gone through many upgrades, eg, increasing the cantilever outreach and hook load increase.

Le thourneau jackup

Continuing leadership from within - a myth?

We are always hearing how promoting from within to continue the helm from it's predecessor is better than seeking qualified and expertise from outside the organisation. It may be suggested that the long-term health of a company should be measured by whether or not it has produced and developed homegrown or in-house talent similar to developing or improving it's core business or competency. Some would argue that anybody  could buy or hire talent; only real leaders develop from it experience. It may hold truth or partially true but while it is important to build a “concrete foundation” for the successor, the truth is that, depending on the company and it's situation, it can be just as important and a need to bring in expertise from outside.

Managers or leaders may not be all “born” in the organisation; they all have to come from somewhere or develop their talent from within or from outside. And suggesting that companies are better off when every or even most executives “grow up” there is not only wholly untrue but may at times end up with wrong judgement. As with all things in business, there is no one-size-fits-all answer; it depends on the corporate needs of the company and what is it's long term strategic goal and it's core business. And more often than not, it’s not a question of either-or, but a question of balance and right choice.

Some big organisation that are famous for promoting from within - IBM, Caterpillar, and 3M, for example - however have all brought in outsiders when they needed to. After realizing that its “home-grown mentality” was hurting the company, company like Caterpillar began bringing in executive outsiders from Ford according to a Wall Street Journal story.  Also for 3M, it has hired outsiders for its last two CEOs. And we all know that bringing in former RJR Nabisco and American Express executive Lou Gerstner saved IBM.

In fact, most of America’s biggest and most respected companies - Microsoft, Apple, Google, Cisco, and Microsoft, among them - regularly hire executives from outside the company. Before joining Apple, COO and heir apparent Tim Cook was a vice president with Compaq and, before that, he spent 12 years at IBM. Ironic, considering Apple’s ancient feud with Big Blue. And Google CEO Eric Schmidt hails from Bell Labs, Zilog, Xerox, Sun, and Novell.

There could be no correlation between executives being promoted from within and the health or success of a company. As for the reason why that’s the case, it mostly comes down to this. There are indeed advantages for promoting from within, i.e. knowing the company and how it operates, growing up with the company culture, etc. But those same advantages can also be liabilities, since myopia and lack of perspective is probably the number one reason why executives and companies might have fallen into the red. The cloning effect of leadership from within may not bring new ideas or "out-of-the-box" concepts from external. Businessess have to generate new ideas to face up with competitions and myopic business acumen will kill the company in no time with short-sighted ideas within.

But what is a “leader” anyway? What does a “leader” do?
Who is better, a leader or manager ??

Some may consider the “leader” of the team as the person who formulate a working team and then got out in front of it to give direction and provide the vision for an action plan. The concept of a “leader” means that credit for what the team does goes to the leader but not the team. However the real fact is that you might see it in the lower level where leaders bloviate about leadership and try to inspire people, when in fact they’re usually just making everyone under them want to puke. What Drucker said — and most tend to agree — is that the business world doesn’t really need strong leader but better off with capable managers — people who can actually manage a team of staff especially working under tremendous work stress.  Being a great manager means being in service to the team. It means giving the team credit and making everyone else successful but himself.

Leadership and management may not go hand-in-hand or inter-related. While it could be true that there are different skill-sets, there are some intimately relationship. The truth is that good management skills make better leaders and the converse is also true. We could argue that great management requires excellent leadership skills. MBAs make better managers. You learn a lot getting an MBA - especially from a top notch school - if you aspire to be in senior management. There might be no credible evidence that it will make you or anyone else a better manager. That’s largely because management is more "art than science" as some management gurus would say. If you’re capable, you’ll become a manager but it takes a lot more than that to become a successful manager. Certain qualities and processes work better for certain people in certain organizations and industries, but that’s a far cry from a general blueprint for management success. Every so often you may about whether you should or shouldn’t get an MBA in engineering or technical field. There is no fix answer to such and it all depends on individual's aspiration and end of the day, there is zero loss should you decide to embark or spend S$50K-S$100K on an part-time or full time MBA degree. The knowledge you gain is worth every cent you had to spend.

So, as we go forward, let’s value the real managers ( so-call leader ), who actually do the hard work of making other people productive with high spirit.

Very likely scenario for most successful corporations is that they will continue to either selectively promote from within as well as taking the step to hire from outside the same time. They should do whatever they need to do to ensure the company has the necessary talent scouted and bring into the workplace new experience it required at that point in its evolution. There is simply no broad argument for choosing the leader or managers from within will be one sure success formula for any organisation. 

Drilling Contractor expectations & Equipment onboard

Common Specificatlona in Drilling Contract to an offshore drilling operator, usually a day rate for a jackup is around US$100K region and may be higher if the rig is working in north sea where the rig design is of higher specification :-

1) Depth in feet

2) Commencement date

3) Formations to be penetrated

4) Hole size

5) Casing sizes to designated depths

6) Drilling mud properties

7) Logging program

8) Cementing program

9) Type of testing

10) Well completion program

11) Size, weight and grade of drill collars

12) Hole deviation restrictions

A) More emphasis should be placed on the rate of hole angle change than on the maximum hole angle.

Types of Drilling Contracts

1) Turnkey Drilling Contract

A) It requires the Operator to pay a stipulated amount to the Drilling Contractor upon meeting contract specifications.

B) The Drilling Contractor:

-provides all of the labor.

-furnishes most of the material (contract specific).

-controls the entire drilling operation independent of any supervision by the Operator.

C) Provisions Common to Most Turnkey Contracts

-Location of well

-Commencement date

-Adequate location

-Conductor pipe, should be arranged for and set by the Drilling Contractor

-Contract depth, given as depth to which the Drilling Contractor should drill

-Hole sizes, includes the surface hole

-Price

1. includes these items usually fumished by the DrillingContractor

-Bits

-Water

-Fuel, ration, etc

-Surface pipe, and Intermediate pipe if required, clearly defined size, weight and grade

- API or non-API

- 3rd party testing equipment, logging unit, etc

-new, or if used, tested to (# ) psi

-cement (with additives)

-cement services

-maximum number of hours to wait before nippling-up (i.e. - set slips, cut off casing, etc.) operations are started

-Mud and chemicals

a. according to a mud program included in the contract

b. Specify who owns the mud at contract depth.

-Log type and Service Company

-All mobilization charges

a. move in

b. rigup

c. rigdown

d. move out

-Drilling the rat hole and mouse hole

-Cost of well control insurance

a. certificate

b) Straight hole specifications (e.g.)

-Unit to hole deviation per 500 feet, usually 3 degrees or less ?

- How frequently the DrillingContractor should survey the hole deviation

A. at least every 1000 feet ??

~ Clearly define when Daywork begins and ends (e.g.).

Daywork begins when:

A. a readable log is furnished to the Operator.

B. drilling reaches a certain depth.

C. drilling reaches a certain zone by cuttings, etc..

D. special operations such as drill stem testing and coring are done.

2. Daywork ends when:

A. blow-out preventers (BOPs) are nippled-down.

B. the tanks are cleaned.

C. the drill pipe is laid down.

A clearly defined deadline as to when payment is due :

1. This is normally handled through an escrow account at a bank that both the Operator and the drillingContractor agree to use.

A. a three-way agreement with the bank

2. The total Turnkey cost is held in an interest-bearing account.

A. The Operator receives the interest money.

3. All parties concerned sign a letter which spells out:

- the release of the contents of the account.

- other provisions of the terms of the agreement.

The Drilling Contractor is usually required to furnish evidence that all third-party bills are paid in full.

Below slides showing some of the machinery equipment inside the drilling rig  ( p/s : move your mouse to the photo, to see the title of each photo ) 

The rig crew has to carry out their maintenance of machineries,etc and there will be periodic or yearly classification renewal inspections required onboard, eg. testing of safety, fire fighting equipment, lifting appliances, padeyes,etc and renewal of classification certificate will be given.

Class of the rig will be suspended and the Certificate of Classification will become invalid in any of the following circumstances:

i) if recommendations issued by the classification surveyor are not carried out by their due dates and no extension has been granted,

ii) if Continuous Survey items which are due or overdue at the time of Annual Survey are not completed and no extension has been granted,

iii) if the other surveys required for maintenance of class, other than Annual, Intermediate or Special Surveys, are not carried out by the due date and no Rule allowed extension has been granted, or

iv) if any damage, failure, deterioration, or repair has not been completed as recommended.

Class is automatically suspended and the Certificate of Classification is invalid in any of the following circumstances:

i) if the Annual Survey is not completed by the date which is three (3) months after the due date,

ii) if the Intermediate Survey is not completed by the date which is three (3) months after the due date of the third Annual Survey of the five (5) year periodic survey cycle, or

iii) if the Special Survey is not completed by the due date, unless the vessel is under attendance for completion prior to resuming trading. Under exceptional circumstances, consideration may be given for an extension of the Special Survey, provided the vessel is attended and the attending Surveyor so recommends; such an extension shall not exceed three (3) months. More information may be referred to the rule book of any of the classification society or clarification with the society surveyor, if need to.