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