The following are brief detailed analysis of the activities expected to be executed during an Internal Corrosion Monitoring, Chemical Inhibition and Cathodic Protection These processes involves in checking of underground pipeline and metallic structures from corrosion.
5.1 LABORATORY ANALYSIS SERVICES
Sampling systems are an invaluable component to corrosion control systems implemented in a variety of industries. Sampling aids in the detection and measurement of key reactants or products in a corrosion process, such as corroded metal ions and oxygen. Sampling also allows the measurement of the pH level and the concentration of inhibitors present in the system.
Sampling can be used in any environment to measure general corrosion, and the effects of corrosion control measures can normally be quickly detected. The aim of inhibitor Injection is to form a stable adherent film on the internal surface of a pipeline or vessel, which acts as a barrier to aggressive products in the flow line.
The function of the inhibitor can be to slow down the anodic or cathodic reaction, or to generate a film which increases the electrolytic resistance of the circuit. The liquid inhibitor can be added either as a batch or a continuous injection.
Oil production systems handle crude oil mixed with water that can contain salts and dissolved gases (e.g. C02 and H2S), which are corrosive. The concentration of dissolved gases can be very high and the pH correspondingly low, creating a very corrosive environment.
To minimize this situation, sampling to accurately verify the corrosive environment present, and injecting effective inhibitors, can prove to be an efficient preventive maintenance method.
Our injection/sampling system offers the advantage of easy, accurate sampling, and efficient distribution of inhibition agents, thus preventing corrosion, fouling, or scaling.
A connection is made to the valve on the access fitting,
The sampling tubes are then mounted either projecting into the line or flush with the pipe wall.
The sampled liquid are then safely directed to an appropriate container, reducing the risk of hazardous contact and potential spills.
Hence once samples are collected from the field, the following parameters are analysed in our laboratory:
Hydrogen sulphide (H2S)
Water Chemistry Analysis
Soluble Iron (SI)
Total Iron (TI)
5.2 INTERNAL CORROSION CONTROL SERVICES
ENVITE have a wide range of injection systems designed for discharge rates varying from 0.1 to 50 US gal/hr (0.38 to 190 lit/hr), with discharge pressures up to 6,000Psi (41.4 MPa). For low injection rates (less than 2 gal/hr / 9 lit/hr), drip methods using either an open tube or quill in order to disperse the chemical are available. The ENVITE injection system is suitable for: algaecides, bactericides, chemicals, corrosion inhibitors, defoamers, deionizers, emulsifiers, emulsion breakers, glycol, methanol, ordorizers, oxygen scavengers, product additives, scale inhibitor and wax inhibitors.
Fig: Access Fitting with Flanged-Tee & Injection Quill
When calculating the dimensions of the injection equipment to be used, fluid dynamics must be taken into account. The type of flow that exists in pipes is described by the Reynold’s calculation. The higher the Reynold’s number the more turbulent the flow.
Where p = density of the fluid,
v = velocity of the fluid,
d = diameter of the pipe or tube, and
µ = viscosity of the fluid.
The transition from laminar to turbulent flow occurs between Re = 2,000 and Re = 13,000, depending on the smoothness of the entry conditions. In practice most flow is turbulent.
The following information is needed to design an optimum injection system:
. Pipe/vessel diameter (also vessel length if applicable)
. Access fitting type
. Line pressure
. Fluid viscosity
. Fluid density
. Mass or volumetric flow rate
. Working temperature
. Anticipated injection pressure
. Mass or volumetric flow rate
5.3 CHEMICAL INHIBITION SERVICES
ENVITE as a company can make available the following production chemical need for inhibition at all times as may be required by the client:
|2||UCARCIDE 50||DRUMS||GLUTERALDEHYDE BIOCIDE|
|4||LAMOX SC||DRUMS||OXYGEN SCAVENGERS|
|7||TRIETHLENE GLYCOL (TEG)||DRUMS||GLYCOL|
|14||DOWTHERM||DRUMS||HEAT TRANSFER FLUID|
5.4 CATHODIC PROTECTION SERVICES
Cathodic Protection may be defined as a technique to reduce corrosion of a metal surface by passing sufficient cathodic current to it to cause its anodic dissolution rate to become negligible. Stated in simple terms it is the use of direct current electricity from an external source to oppose the discharge of corrosion, current from anodic areas of a metallic structure immersed in a conducting medium, or electrolyte, such as soils and water.
When a Cathodic protection system is properly installed, all portions of the protected structure collect current form the surrounding electrolyte, and the entire exposed surface becomes a single corroding area – hence the name “Cathodic Protection”.
In fact, Cathodic Protection is applicable only to control corrosion resulting from the flow of measurable direct currents from one portion of a structure (the anodic area) through an electrolyte to another portion of the structure (the cathodic area). This is electrochemical in nature, and the anodic area, where current is discharged to the electrolyte, corrodes. Conversely, the cathodic areas collects the current an does not corrode, i.e. Cathodically Protected.
Basically, electrochemical corrosion currents can be reserved by the proper application of cathodic protection, which makes the entire structure cathodic, overriding the naturally occurring anodic structure areas with direct current impressed on the structure from an external, more powerful anode.
Those not fully conversant with it treat cathodic Protection as a somewhat mysterious term. Apparently, many feel that Cathodic Protection is a complicated procedure. In actuality, the basic idea of Cathodic Protection is very simple. Any complications involved arise during the application of this basic idea
Cathodic protection does not necessary eliminate corrosion. It does, however, transfer corrosion from the structure under protection and concentrates it at another known location where the current discharging anode or anodes can be designed for long life and easy replacement.
This phenomenon is of value only to the surface of the metal exposed to the same electrolyte as the anode, e.g. application to the exterior bottom of a salt water tank has no effect on the internal corrosion, and the internal corrosion has no effect on the external bottom of a salt water tank.
A plot of the potential profile against pipeline distance or test point would be made. This will help to show areas of potential shift which may be caused by any or a combination of the following:- Coating holidays, insulation failure, interference problems, stray current effect and groundbed influence.