INTERNAL CORROSION

Prepared by: Dil NawazCourse: Cathodic Protection (level one)

AREA COVERED

Internal corrosionCausesInternal Corrosion Control TechniquesMonitoring Techniques

WHAT IS INTERNAL CORROSION ?

Internal corrosion can damage whole internal metallic structure of tanks and pipes. in oil and gas field 48 % pipelines failure are caused by internal corrosion and maximum rate of it occurs at 6 o’clock position

Internal corroded metallic structure of pipe

6

3

12

9

6’o clock position

CUASES

• Natural phenomenon • Fluid Corrosivity• Flow Velocity• Deposit Accumulation• Water Accumulation• Salt water • H2S (acid gas with iron sulfide the by-product) • CO2 (Major cause of produced gas corrosion) • O2 • Bacteria (by products, acid produced) • Other Impurities In Product

Internal Corrosion Control Techniques

Internal corrosion can be controlled by

1) Using corrosion inhibitors2) Proper monitoring techniques

Internal corrosion can be controlled by corrosion inhibitors. It is chemical Compound that when added to liquid or gas , decreases the corrosion rate.

The Effectiveness of a corrosion inhibitor depends on• Fluid composition• Quantity of water • Flow regime

Corrosion Inhibitors

Classification Of Corrosion Inhibitors

Corrosion inhibitor is classified into two major types

1) Oil soluble corrosion inhibitor ( for HSD)2) Water soluble corrosion inhibitor ( for crude)

Oil soluble corrosion inhibitor (for HSD)

Oil soluble inhibitor are used in many oil and gas fields. It has high solubility with oil and mostly added with high speed diesel products. DCL-6A corrosion inhibitor is achieving zero leak status in the pipeline. it is approved by US military specification

Water Soluble Corrosion Inhibitor (For Crude)

This type of corrosion inhibitor is used with crude product to protect the Internal metallic structure from corrosive crude. Crude oil has many harmful impurities that causes very fast rate of corrosion.

Mechanism Of Corrosion Inhibitor

A common mechanism for inhibiting corrosion involves formation of a coating often a passivation layer , which prevent access of the corrosive substance to the metal.

The nature of corrosive agent depends on

1) The material being protected.2) On the corrosive agents to be neutralized.

Inhibitor Deployment

TankInhibitor Injected area

Pipeline

How Corrosion Inhibitor Acts As a Barrier

Monitoring Techniques

Internal corrosion monitoring techniques includes

• Residual Analysis• Corrosion Coupons• Electrical Probes• Non Destructive Techniques•In-Line Inspection

Residual Analysis

To make sure the effectiveness of corrosion inhibitors residual analysis are common method, in which water sample re collected from all the crude storage tanks at pumping station .

Corrosion inhibitor residual analysis for any system are established based on corrosion rate achieved.

Residual analysis tested once in 5 year, or it depends on previous result.If previous result was not as such aspect then it is tested within 2 or 3 years.

Corrosion Coupons

Corrosion coupons are a simple yet effective tool for providing a quantitative estimation of corrosion rates occurring in an operating system. They also provide a visual indication of the type of corrosion which may be occurring in the monitored system.

Corrosion Coupons

•Corrosion coupon is a piece of metal of predetermined shape, size and surface area.•It is a metal of similar chemical composition to the process equipment.•It has a uniform reproducible surface finish.•It has a distinguishing serial number.•It is exposed to the same corrosive medium as the process facilities.•It is exposed for a fixed period of time.•It gives visual indication of the type of corrosion.•It indicates the rate of corrosion

1)The coupons have been cleaned and accurately weighed prior to shipping .

2)The coupons must be used in vertical direction at 6’o clock position

Corrosion Coupon Installation Points

3) Be sure the numbered corrosion coupons are recorded according to position and system for proper correlation. The dates of installation and removal from the system are critical.

4) Test periods are generally 90 days. Coupons may be observed at 30 days intervals for reference and signs of corrosive conditions. In observing the coupons, do not disturb the surface by scraping or removing material.

5) The corrosion products should be scraped off with a dry plastic utensil into a bio-sample bottle containing system water. the coupon can then be dried and returned to the lab for analysis along with the bio-sample bottle.

Electrical Probes

Electrical corrosion probes include devices that can detect the rate of corrosion in a variety of environments.

Corrosion probes are used in deep core oil and gas drilling. This corrosion-detecting devices are used to monitor the amount of internal corrosion in oil tanks, platform pipes, and deep core or subsea pipes.

Corrosion Probe Assembly

NACE Standard SPO 775

• Coupon size, metal composition, surface condition, andcoupon holders may vary according to the test system designor the user’s requirements.

• Coupons are often installed in pairs for simultaneousremoval and average mass-loss determination.

• This standard outlines procedures for preparing, installing, and analyzing metallic corrosion coupons.

Coupons may be used alone but they should be used inconjunction with other monitoring methods such as testnipples, hydrogen probes, galvanic probes, polarizationinstruments, resistance-type corrosion monitors, chemicalanalysis of process streams and nondestructive metalthickness measurements, caliper surveys, and corrosionfailure records.

Processing of Corrosion Coupons As NACE SPO 775

• Choose a method of coupon preparation that does not alter the metallurgical properties of the metal. Grinding operations must be controlled to avoid high surface temperatures that could change the microstructure of the coupon.

• Exposure to an environment capable of cracking the alloy used for the coupon or holder.

• Etch or stamp a permanent serial number on the coupon. It is possible for a coupon or holder to undergo SCC.

Non Destructive Techniques

NDT testing plays most important role for internal metallic structure through this techniques even we can detect very small defects and flaws.

Non Destructive testing consist of different testing methods

1) Radiography Testing (R.T)2) Ultrasonic's Testing (U.T)3) Fluorescent Penetration Inspection (F.P.I)4) Magnetic Particle Inspection (M.P.I)

Radiography Testing (R.T)

The radiography is the most commonly used non destructivetesting method for pipeline inspection .its principle is that asource of radiation is directed toward the inspected object. Asheet of radiography is placed behind the object. the setupusually takes a few minutes the exposure 1-10 minutes and filmprocessing about 10 minutes.

Ultrasonic’s Testing (U.T)

Ultrasonic is used as an NDT-method to evaluate the integrity of the automatic welded pipelines girth weld. The principle is to employ high frequency acoustic waves to probe the inspected sample. As the acoustic wave penetrates the sample , the wave is attenuated and/or reflected by any change in the density in the material. By observing the returned signal many of the characteristic of the material can be determined.

This setup takes less than an hour or depending on the size of the sample.

Fluorescent Penetration Inspection (F.P.I)

This method is suitable for the detection of cracking and porosity in welded joints. the principle is that the surface of the sample is coated a penetrant in which a fluorescent dye is dissolved or suspended. the penetrant pulled into surface defects by capillary action.

Less than one hour is usually required as an inspection time

This method is cheaper than R.T and U.T but can only detect external defects.

FPI Testing Procedure

Preclean partPreclean part

Apply penetrant

Prerins Spray

Apply developer powder

Inspect under U.v light

Magnetic Particle Inspection (M.P.I)

Magnetic particle method can be used for identification of surface or near –surface defects. The principle is that the sample is magnetized by dusting magnetic particle over it. A surface defect will form a magnetic anomly , attracting and holding magnetic particles and thus giving a visual indication of the defect.

The sample must be ferromagnetic and the evaluation time is typically few minutes.

Magnetic Particle Inspection Of Pipe

In-Line Inspection

Today pipeline inspection through the use of in-line inspection tool is a standard procedure. These inspection tools collect highly precise data regarding the geometry of flaws and defects in the pipe wall. The final goal of the operator being an understanding of the state of integrity for a given pipeline.

In-Line Inspection Methods

The main in-line inspection methods at present include:

•Magnetic Inspection•Transverse Field Inspection•Ultrrasonic Inspection•Ultrasonic crack Detection•Magnetic Flux Leakage•Geometric Inspection Tools•Pigging

Pig

Pig is used for the integrity of pipelines. Pipeline pigs are the device that are inserted into and travel throughout the length of a Pipeline driven by a product flow.

Today pigs are used during all phases in the life of a pipeline for many different reasons.

Types Of Pigs

•Foam Pig•Gauge Pig•Cleaning Pig With Disc•Cleaning Pig With Magnet•Caliper Pig (For Geometry of Pipeline)•Intelligent Pig

Cleaning Pig With Magnets

Cleaning Pig With Brushes

Cleaning Pig With Disc

Foam Pig

Function Of Pigging

•Cleaning out the deposits and debris•Gauging the internal bore•Location of obstruction•Liquids removal•Gas removal•Pipe geometry measurement•Internal inspection•Improving flow efficiency

Geometry/Caliper Pig

Geometry/caliper pig is a configuration pig designed to record conditions, such as dent, wrinkles, ovality, bend radius and angle and occasionally indication of significant internal by making measurements of the inside surface of the pipe.

Crack Detection Pig

Crack detection tools are specially designed to detect feature such as ultrasonic inspection tools stress corrosion cracking or fatigue cracks instead of transmitting sound waves perpendicular to the pipe wall pulses are transmitted at45 degree circumferentially through the pipe wall, which enable fine cracks to be defected.

Crack Detection Pig

Intelligent Tool With Ultrasonic Technology

On entering the pipe wall, there is an echo and another as the pulse reflects off the back wall. The taken for these echoes to return provide a virtually-direct reading of the wall thickness.

Intelligent Tool With Ultrasonic Technology

Magnetic Flux Leakage (MFL)

The MFL tools use magnets to induce a flux into the pipe wall. Sensor are mounted between the “poles” to detect any leakage which may occur due to thinning, or “metal loss”.

Magnetic Flux Leakage

Purpose Of In-Line Inspection

•Asses the health of pipeline. •Develop the data base of pipeline features.•Monitoring defects.•Asses corrosion growth rate.•Develop strategy for rehabilitation work.•Develop fitness for purpose assessment of defects.•Future inspection needs.•Safety assessment of the puipeline for current operation.

THANK YOUFOR

PAYING YOUR ATTENTION