design, construction and test of corrosion
TRANSCRIPT
Design, Construction and Test of Corrosion
Amir-Reza Oskui
Corrosion
• Corrosion is the gradual degradation and destruction of materials,• usually metal
• Corrosion is caused by water and oxygen in the environment, it is accelerated by multiple factors• Salts in solution
• Acids
• temperature
• Presence of less reactive metal
• Working history of metal
Tribocorrosion
• Tribo-corrosion is the general term for any corrosion process enhanced by flowing fluids
• Tribo corrosion is both a physical process and an electrochemical process• where both mechanisms act in synergy
• It occurs when a metal object is under the influence of a moving fluid and the metal or the oxide are removed by the action of fluid
• . Even metals that normally form protective layers of oxide are at risk as the oxide will be continually removed rather than form a protective layer.
Corrosion
• Corrosion is a major issue in all forms of heavy industry.
• In the oil pipeline industry in America alone, companies spent 9 billion dollars on corrosion prevention, inspection and maintenance on 750,000 km of pipelines,• or roughly $9 per meter.
• The National Gird comprises of a route length of over 7,200 kilometres
• The corrosion-related cost of operation and maintenance makes up 80% of this cost
• Corrosion occurs because crude oil and natural gases contain small but significant amounts of impurities, such as water, salts, sulphides and particulates.
Natural Gas and Pipelines
• Pipeline are used to cheaply transport liquids very large distances in large quantities
• Almost half of UK mains are still made of cast iron.
• The expansion of non-conventional gas means Transmission networks will have to deal acidic gas that they were not designed to handle
• Even the Polyethylene pipes are nearing the end of their working lives in some places.
Pipelines and new corrosion issues
• Sour hydrocarbon: Oil that contains Sulphuric Acid, potentially releases H2S
• Acidic hydrocarbons : Contains Sulphuric acid, Carbonic Acid (CO2) and Naphthenic Acid
• Asphaltenes and diluted bitumen: Oil that is very viscous and requires heat and pressure to move it along.
• Sand and particulates in oil, even within the distribution network, the gas velocity is limited to 20m/s due to gas dust and vapour.
Corrosion Simulation
• Not feasible to constantly monitor all pipeline network
• Corrosion rates are found experimentally, and used to predict where damage will occur• Also used for design, extra thickness is added to parts where corrosion will
occur
• A sample of the metal, a corrosion coupon, is then placed in the simulated environment for a set amount of time. The corrosion coupon is them removed from the environment and the corrosive effects are measured.
Impingement rig
• Sprays a solid jet of oil upon a sample of metal.
• The fluid impinges upon the metal coupon at an angle or perpendicular to it.
• The oil velocity can be varied
• The oil can be pure oil, or have a mixture of oil and water• The water can be a salt solution• The oil can contain solids
suspended
Design
• The test rig was based on pre-existing impingement rig designs
• An oil-water mixture was to be pumped through a nozzle and impinge upon a test probe or corrosion
• The experiment has to be built materials and equipment that was found and salvaged within the aero lab
Viewing box
• Perspex was used due to its chemical resistance, hardness and transparency. • 2 sheets of one cm thick Perspex were
acquired from old spare parts of a wind tunnel.
• Sides of the box were held together by screws
• Edges were sealed with silicone, the silicone layer was covered by resin to prevent chemical damage to the silicone
• Box is reinforced by a frame
Pump
• A pump at the back of the aero lab was resourced.
• Pump was very old, it needed a lot of electrical parts replaced• Several weeks were wasted waiting for orders for parts to be fulfilled
• Piping was set up to pump oil though the nozzle and onto the jet
Nozzle
• Once the pump was working, it was possible to calculate the flow rate of the pump
• The flow rate was used to calculate the size needed of the nozzle orifice to get a speed consistent with literature requirments• . Using a standards ASTM G-73, a speed of 60m/s was needed
Oil
• For the base oil, the commercially available hydraulic oil Hydrol VH 32 was used
• The oil was chosen as it was cheap and has a good tolerance of heat and pressure.
• The experiment started with pure oil to provide a control, and to examine the effects of the fluid impinging on its own
Corrosive additives
• A solution was made to simulate ground water within a typical sour crude oil reservoir
• A compositional analysis was provided by Dr Akanji
• A the salts were dissolved in a 25% v/v solution of Sulphuric acid
• Salts include NaCl, CaSO3.H2O, KCL, NaHCO3
• 10g of Poly anionic Cellulose was added as an emulsifier
Corrosion Coupon
• these are of a predetermined shape, and a carefully measured weight and thickness and are made from the material being tested• The coupons are cleaned with a solvent and sandpaper to remove all dirt and
oxide• The starting mass is measured and pictures taken under a microscope• The coupon is then placed in the test rig for 200 hours• The coupon is re-cleaned and the final mass taken. Pictures of the coupon
under the microscope are retaken and compared, Vickers hardness tests are also done
• For the is experiment, the coupon was cut to 100mm by 150mm out of 5mm cold-rolled mild steel.
• The coupons material can be changed or coatings used in later experiments
Testing
• Two experiments were ran• The first was a control with pure oil and no water or acid
• The second had oil with 2% acid and a salt fraction in emulsion
• The first test ran for 200 hours,
• The second test only ran for 2 hours before the pump failed
• Experiment ran perfectly otherwise
Results
• The first coupon showed no damage, it had no mass loss to one hundredth of a gram
• The second coupon was only in the rig for a couple hours, it was thought that under such a short time, there would be very little mass change, and it would not give an accurate average.
Microscopy pictures
Coupon 1 at x10, note the Vickers hardness indent Coupon 1 at x10 after test,
Coupon 2 before the Test x10Coupon 2 after the test at x10 note the Vickers hardness test
Coupon 2 after the test at bare area X200
Coupon 2 after test at heavily rusted area x200
Future work
• The rig itself held up to the oil very well
• The pump can be replaced and the experiments continued• The pump, piping and nozzle are all designed to be replaceable.
• The tests were mere a proof of concept, a working impingement rig has a lot of potential for further research