Welding

Well, while doing checking on drawing, there is one things that i keep on learning but keep on forgetting: that is welding. I'd stumbled upon the fillet weld and bevel joint during the checking. So basically you look into the figure on the left, you have a basic mental idea of the welding drawing practices.



Actually the tail is where reference like the welding or cutting processes, welding specification, procedures, or the supplementary information used in making the weld. So, if you ain't got any information that you would like to present, you can omit the tail. As for the weld side, you can put it beside the symbols of type of weld: below and above the reference line.

What is that things on oil platform?

What is the function of christmas tree? Well, it is used as a way to regulate the flow of hydrocarbon product form individual wells to the process equipment.

What is the function of vent stack? Well, again the gas vent stack is to discharge the process gas in order to depressurize.

So why do we need to burn the gas kinda wasting right? Well, well, well, because the gas requiring disposal is huge and it would be hazard if simply released into the atmosphere.

What about flare tower? Well, well, it provides a safe, remote location for the disposal by burning, or unwanted gaseous products produced during oil refinery process.

How about conductor? Well in a team of choir, the conductor direct while in the oil platform the conductor direct the well head against lateral movement.

What is the roles of piping?
Transportation basically. You can categorized the piping systems into 2:
1) Hydrocarbon process
2) Utility

Brief Process roles on oil platform

The main purpose of process in oil & gas platform is refine the crude oil to a quality suitable for transportation by sub sea pipeline or oil tanker. How do they do it? by removing associated gas and formation of water within a series of production separators.

The roles of instrument is about all the gadget that install in the platform to monitor the condition like temperature, pressure, viscosity, speed flow...etc like when you do medical check up all the small gadget that measure you body weight, temperature, blood pressure in order to give an idea of you health. Similarly with the instrument at the oil platform.

You have probably heard wellhead, and what the hell is well head? Well, well head is where we manipulates the pressure to 30 bar prior the oil enter into the production header or the well test separator. Now, another touch down for you.

When we call export oil as "Dead crude" if the processing was completed at atmospheric pressure while we call it "live crude" as oil processed at a pressure slightly higher than atmospheric pressure.

So in gas process, we try to produce gas that complies with (hydrocarbon & moisture) criteria specified for subsea pipeline. Why need to do that? Why not just send to refinery plant to do the process. Well, well they say love and money make the world goes around. In this case there are 3 reason that will cost money if you ignore it.

1. corrosion
2. hydrate formation
3. the build up of condensate liquid

So if you happened to be the process guy, you are responsible to water, natural gas liquid and gas impurities such as Hydrogen Sulfide (H2S) and Carbon Dioxide (CO2). And the process science use in the oil platform is very basic fluid dynamics to effect the separation of oil (or condensate), gas, water, and sand.

Surf Load (Part IV)

The steel jackets of offshore structures can usually be regards as hydro dynamically transparent. So in order to figure out the waves forces on the submerged member can therefore be calculated by Morrison's equation which express the wave force as the sum of an inertia force proportional to the particle acceleration and a non linear drag force proportional to the square of particle velocities.

F = CM * (r * 3.142 * D^2)/4*v + CD * (rD/2)*v*/v/

F = wave force per unit length on a circular cylinder (N)
r = water density (kg/m3)
D = member diameter including marine growth (m)
CD = drag coefficient
CM = inertia coefficient
v = water particle velocity normal to cylinder
/v/ = water particle acceleration normal to cylinder

According to API-RP2A:
CD> 0.6 - 1.2
CM > 1.3 - 2.0

Surf Load (Part III)

Wave caused by the moon gravitational is huge, you have been to yearly event even at the River mouth here Sarawak and China which i am aware of. The tides affect the waves and current loads indirectly: through the variation of the level of the sea surface.

So there are two reason that tides happened. Firstly, astronomical tides is caused by the gravitational pull of the moon and sun. Secondly, the storm surge that cause by the combined wind and atmospheric pressure during a storm.

In platform design, the effect of current superimposed on waves are taken into account by adding the corresponding fluid velocity vertically. If you look at the formula, the drag forces is depend on the square of the velocity and this addition can greatly increase the force on platform.

So, also like the slender structure like flare tower which may be wind sensitive, we also have slender structure below the sea that is wave sensitive. So the phenomena called vortex shedding that caused cyclic loading should be investigated if your structure happened to be slender. From my observation cyclic loading if like what i saw at the SMTC when the tall grass swing back and forth. The mystery is vortex shedding.

Surf Load (Part II)

In the sea, you will find it funny that large volumes bodies, is terms as hydrodynamics compact structures, how the shape of the body influence the wave field is by: diffraction and reflection. For reflection, it is easy to explained but for diffraction will be need more heavy mental lifting. Like me, you might ask why do they label big volumes bodies as compact because you reason like me hey man compact camera= small camera. No answer man. Just remember diffraction is the bending of wave when hit small obstacles.

So the forces on this bodies are to be calculated by using the diffraction theory.

How about the slender, hydrodynamic transparent structures that have no significant influence on the wave field. We can calculated the forces in a straight foward manner with Morison's equation. So we use morison equation when the D(member dia.)/L(wave length) < 0.2. This idea may be very abstract if you look into it for the first time.

Let talk about Morrion's equation in more detailed, you see the morison's equation expresses the wave force as teh sum of

1. an inertia force proportional to the particle acceleration
2. a non linear drag force proportional to the square of the particle velocity.
   

Surf Load

Yeah, taking about surf load should be interesting because it is about surf, beach and sun. However, if you are doing some designing for sea structure it is not more so fun.

Have you ever wonder how the wave is created by the natural. If you happened to be man made wave before you simply said cause but mechanized machine which you can't fathom. Well, the nature create wave by the wind, the gravitational pull from the moon and sun. Next, by the storm and atmospheric pressure differences, and by the tectonic movement that created the killer waves tsunami. But we human also can created waves by using our body, remember the time when you lost your direction or accidentally drank the waves caused by the wave of swimmer near you. So, when the big ship sail past, they also created massive wave.

Enough about introduction though bit poor and simple. How do we calculate the wave load that slam into the structure in the sea? Firstly, in terms of seastate, we idealize the wave surface profile and wave kinematics, sound like wind load by wave theory.

Secondly, computation of the wave forces off individual members and on the total structure from the fluid motion.

Almost similar concept to the wind load calculation. So, no sweat. Designed wave where a regular wave of given height and period is defined and forces due to this wave are calculated using high order wave theory (no idea bout the high order theory, but it give me the impression of complicated stuff). Like in the wind load case, you thought how come we take the wave load as the static load when you are at the seaside you can few the wave: some weak, some medium and some whack in to you hard. Boy, you are really curious. We consider the assume the structure static behaviour when the max wave period of 100 years is chosen and that dominant wave period is more than the design life span of the structure normally, 25 years.

Wind Load

In poetry, songs, and story we like to use wind as a metaphor. For instance, the hit movie, gone with the with. In engineering if you thought you can take wind as metaphor you will be in big trouble because wind is no small matter as a matter of fact.

The first important parameter about wind is the time interval over which wind speed is averaged. For averaging intervals less than 1 minute, wind speeds are classified as gusts. On the other hand, for averaging intervals of one minute or longer are called sustained wind speeds. So if you are doing designing for any structure on sea you can refer to API-RP2A

Vh/VH = (h/H)^1/n

Vh = wind velocity at height h
VH = wind velocity at reference height, typically 10m
1/n = 1/13- 1/7 depending on 2 factors: (i) distance from land
(ii) averaging time interval

Just for info: you will get 1/13 for gust or you get 1/8 for sustained winds in the open sea.
So you can load the figure in the wind profile and get the design wind speed, V. So with that basic information we can calculate the static wind force Fw. So if you have curious mind you might be wondering how come the wind is not constant but we take it as static, does not represent the reality. Well, if you have thought that way you are right on the bull's eye. You see only if your structure least horizontal dimension/height is > 5 we worry about the wind sensitive. So if that case happen, we need to take into consideration the dynamic effect of the wind and the cyclic wind loads due to vortex shedding .

So complicated huh? Luckily most of structure you will stumble in your life is not wind sensitive. So continue about the static force by the wind.

Fw = (1/2)rV^2CsA

r = wind density
V = wind velocity that you get from the wind profile
Cs = Shape coefficient Cs = 1.5 for beams
Cs = 0.5 for cyclindrical section
Cs = 1 total projected area of platform
A = Area (just intution telling me that)

So the guidance from the API is that we've got to consider 2 case of wind load:
one) mean 1 hr wind speed to combined with extreme waves and current
two) used extreme wind speed without waves.

If you managed to read all, congratulations. But make sure do you own reflections on it as our memory will trick us, huh, huh, already times. That they said time heal because you forget, haha.

What you got to do after you have done with the as-built?

You simply hand up the
1. as-built drawing (the product you want to give to client)
2. the drawing list (so that the client know the quantity)
3. Transmittal so that we have the proof the doc. already send.

So after you have check, the designer have check that check print will be stored as a documentation. While another copy without the what they call check print will be send to the kind. Kinda confused because all the jargon with are not so mental friendly.
Not an inspiriting post but if you messed up it will make your day uninspired though.

Soil Basic Instinction

Put it up front, the soil is defined and group together by their size and mutual interaction. This is the first time i come across this definition which is different form soil mechanics. SO, what we talk about mutual interaction, we talk about things like the friction and cohesion, water content and consolidation ratio.
There are 2 kinds of soil: granular soil and cohesive soil. Sand are (1mm-0.05mm) which give good permeability. On the other hand, silts is 0.05mm -0.02mm they are generally ober consolidated and exhibit some cohesion.
Clay is cohesive soil, if you are city boy and never touch a grain of soil, think of the clay you use to shape your hair. How does it feel like? Yeah their permeability is low meaning they absorb water and they stick together so you can shape your hair.

Marine Growth

Marine growth visually look like skin diseases on the jacket leg. Why do marine growth influence our structural analysis? Mainly because it become part of the structure, it directly increase the expose areas and volumes, but also the drag coefficient due to higher surface roughness. Besides that, it increase the gravity loads of structure.

Like the human demographic effect, tall people grew in Europe and shorty from Asia. The locations.

What do you know about tides? Like the G-shock surfman which can predict the sizes of wave and the phase of moon. From here, you can make a simple connection that tides are casued by the gravitional pull of the Moon and Sun. Besides the predictable monthly phenomenon, tides also can combined action of wind and barometer pressure differencee during storm.

When do we need to do fatigue analysis?

A lot of time we thought hey! which part of structure that i need to do fatigue analysis. Anyway, you simply need to analyze the structure that take cyclic loadings. so, there are 3 situations:
1) Wave (Jackets, flooding structures)
2) Wind (flare booms, Stair towers)
3) Structures under rotating equipment

Oil and Economics

Everything in life have limitations, so in oil and gas exploration and production. So if you plan to spend your money on oil exploration you will see does the venture production exceed the spending. In short, profitable. So you need to consider the CAPEX (Capital expenditure), tax, royalty, and OPEX (Operational Expenditure). So, what kind of activities that requires capital expenditure, huh? First of all, project management and design. Then, material and equipment procurement. Besides, that it is fabrication. The fourth, transportation and installation. Finally, hook up and commissioning. And what does hook up and commisioning means?

Talk about the wind? Do you know what is gust? it is the wind averaging intervals that less than 1 minute. Like sex that last one minute is quickie though it is considered sex also. Most of the time when we do analysis on wind impact on any structure we assume the load is static, unless your structure is lanky and sensitive to wind. height/horizontal > 5.

Wave loading on an offshore structures is usually the most important of all environmental loadings.

Another engineeng word of the day that you should have a feel is appurtenaces. Appurtenaces is conprised of risers, J tubes, caissons, conductors, boat fenders, etc.

About Jack(et) and Topsides

Jacket act as 2 function. The first one provide the leg to the topside and keeping it stable above the pounding of waves. Secondly, they support laterally and protect the 26-30in well conductors and the pipeline rise.
If you look at the jacket, you can see the different shoes that they used. The first one, the piling it done through the jacket leg, and the hammer pounding is done above the water level. One the other hand, the piling around the skirt which surround the jacket's legs. So in this case, the hammer is pound under the water. Well, how deep we need to put the piling then? Depend on the sea and the soil, could be as deep as 120m.
Well, topsides would be human body if oil platform is human being. Think about the size of human baby is limited by the opening of pelvis, and the limiting capacity of crane vessels and the load out capacity at the yards that limit the sizes of topsides. You will probably stumble upon this words MSF (Module Support Frame).

Probability and chance

Life is sometime funny, out of sudden i believe in luck and chance. You see in these two days i have take on different experience out of two years. Funny, huh?

From my new understanding, why do we need to go to site? First of all, because these case is special. Usually when they contractor after finishing their work on the structure will put some red line on the drawings. On these case all the red line drawing is like a corpse that is rotten already and can't be found. In that case, site visit will be conducted and the three project that is involved will be our road map, compass for the journey for as-built. In short, we are going to incorporate the 3 project into master drawings. Basically, we need to go out there to check whether the reality is similar to the project drawings.

So what is the different between project drawings and key drawings? Get that answer later. Basically, these are new language that i have learned: A-, B: is for fabrication yard as built. C:

So my role is to check whether the drilling rig barge going to the platform. the structure modification that is made on the platform is reflected in the drawings. Put it this way when the rig barge come in for drilling, i do not know how exactly it work, but anyway the structural modification is done on the platform. Basically, high pressure, biggest producer, big asset don't messed with it.

Lastly,

(1) The first stage: IFR - Issue for Comment

Basic Drawings A C
B

Key Drawings A Z
B

(2) 2nd and last stages: ASB

The Birth of Structural Blog

Today is the birth of my structural blog, my 2 years journey in the structural field. I decided that this is the way i can share my experience and thought on structural engineering. My aim is to build a blog that even those without any engineering background can grapes the concept of engineering or those who are practicing can get some insight, ideas, and knowledge from this blog. Why engineering become a tough subject? Because language, all those technical jargon. All the mathematical formula is used to predict only, in the end it is the insight and experience that matter.