Appendix 1—Brief Introduction to the Performance of BoronizingPump Barrels
(China Invention Patent Number:ZL 2013 1 0166047.0)
1. Overviewof Previous Pump Barrel Processing Methods
Barrels are the most important parts of oil-well pumps, which are heavilyused in oil fields. Barrels normally account for about 60% of the total pump cost[1]. Barrels must be heat treated to improve innerhole surface hardness, wear resistance and corrosion resistance. The main heattreatment methods used in the past are the following:
1.1 Carbonitriding
Carbonitriding is a mature technology, which is widely used now. In orderto increase the depth of the infiltrated layer, the barrels is usually 20steel, and heated at over 900℃. After carburizing, quenching is needed, whichresults in large deformation. So the next step is heavy honing. The problem ofthis process is that when the temperature is lower than 880℃, thecontent of nitrogen is ideal with a certain anti-corrosion effect, but the wholelayer is thin and difficult to meet the use requirements; while when thetemperature is above 900℃, the whole layer is thicker, but the content ofnitrogen is little and the corrosion resistance is poor.
1.2 Hard ChromePlating
Plating hard chromium on the inner hole surface of pump barrels can meetthe requirements of corrosion resistance, wear resistance and hardness. However,chrome plating process should be reduced or avoided due to its seriousenvironmental pollution. In addition, the inner hole surface should be alkaliwashed for oil removal and acid washed for activation before chrome plating.But the inner hole is too long and narrow to be washed thoroughly, which willreduce the bond strength between the coating and the substrate. During oilpumping, the inner hole surface will be peeled off due to sand abrasion and squeezingbetween the plunger and the barrel, which may even stuck the pump. Moreover, thechrome coating is easy to be corroded by H2S and acid washing residuein the oil well.
1.3 Electrolessplating
Electroless plating is also known as nickel-phosphorus composite plating. Itsadvantages and disadvantages are similar to that of chrome plating, with bettercorrosion resistance and acid resistance. However, the coating of electrolessplating, which is only about 0.04mm, is easy to be scratched during oilpumping, and it is difficult to increase the coating thickness.
1.4 Nitriding
A qualified nitriding layer has outstanding hardness, corrosion resistanceand wear resistance. The ideal nitriding material should be 38CrMoAlA, which isvery expensive. The parts need to be heated in a furnace for 2 to 3 days, oreven longer, which highly increases the cost. Moreover, a difficult problem isthat the ammonia gas is decomposing all the time while flowing through the longand narrow hole of the barrel, so the decomposition rate of ammonia gas at theentrance side is far different from that of the exit side, and the nitridelayer is very uneven. Therefore nitriding is more suitable and mature for outersurface or short holes, while it’s difficult to control the product quality forlong and narrow inner holes.
1.5 Laser–quenching
This method is to apply a laser device into the barrel. When the laserdevice moves along the barrel axis and project laser perpendicularly onto theinner hole surface of the barrel, the barrel revolves around its axis, so thelaser projection point moves helically in the inner hole surface. As the laserbeams is very concentrated with an extremely high temperature, the laser projectionpoint is heated up instantly to nearly melting point. Then after the laser projectionpoint moves forward, the heated point is cooled down rapidly, as metal is agood conductor of heat, so that the point is quenched. It’s easy to find out thatthe method doesn’t change the material of the surface, so it can’t improve the corrosionresistance. In addition, the hardened zone made by laser–quenching is helical,but not the overall inner surface, so after a period of corrosion and sandwear, the unhardened zone of the inner surface will pit helically, which willincrease the loss of the pump and reduce the pump efficiency.
2. Brief introduction of pump barrel boridingTechnology
The technology is pump barrel boriding ,with solid penetrant , without anydischarge of waste water or gas, it’s environmentally friendly. The surfacemicrostructure of the pump barrel after boronizing is FeB and Fe2B,it‘s prominent corrosion resistance and wear resistance, especially resistanceto abrasive wear is most better than other pump barrel’s surface.As far as metal boronizing is concerned, it hasmore than half a century's history.Everyone knows that the surface corrosion resistance and wear resistance ofboriding is excellent, but it is not easy to use the technology in the pump barrelwhich is long and slender pipe and extremely high dimensional accuracy.Before and after 1986, many large enterprises andinstitutions of higher learning have cooperative research (the inventor wasalso involved), want to develop a boronizing pump barrel, but failed because ofmany difficult questions. These difficult questions as below:
1) Firstly, boronizingat more than 900℃ can produce ideal infiltrated layer, but pump barrel deformation is large (innerdiameter tolerance>0.05mm). As pump barrels can’t be honed after boronizing,many parts are scrapped due to out of tolerance,causingthe rate offinished products is very low. While boronizing at less than 880℃ can reducethe barrel deformation, but the infiltrated layer is very unsatisfactory as it’sthin and discontinuous.
2) Secondly, if quenchingis not applied after boronizing, the substrate will be too soft to bear thesqueezing by sand between the pump barrel and the plunger, so the infiltratedlayer will be easily chipped or peeled off; while if quenching is applied afterboronizing, the barrel deformation will be too large.
After 1986, nearly 30 years, the inventor has beencontinuing to explore inthis field , constantly adjust the agent formula and process equipment and technologicalmethod, finally achieved success, and won the national invention patentin inSeptember 2015 , the patent number is: ZL201310166057.0.
The innovation of the invention mainly has thefollowing five aspects:
First, the suitable penetrant formula is researchedand tested, and an ideal infiltrationlayer can be obtained at 880.
Second, after comparing the experiment, the propertemperature control curve is determined.
Third, after test comparison, determine theappropriate infiltration pressure, and design the corresponding pressurecontrol device.
Fourth, the design of a dedicated well furnace andspreader, to achieve the above requirements, to ensure that after theinfiltration pump barrel almost no deformation.
Fifth, the proper cooling method and deviceis studied，to ensure that base hardness of the pump burrel is up to standard and thatit doesn't deform after cooling.
3.The Performance ofBoronizing Pump Barrels
3.1MetallographicStructure of Infiltrated Layer
The infiltration layer mainly consists of FeB andFe2B, but single-phase Fe2B layer is also available. Single-phaseFe2B layer is less fragile with high hardness. The three potassiumreagent (K4Fe(CN)6 10g + K4Fe(CN)8·3H2O1g + KOH 30g + H2O 100g) can be applied to distinguish between thesetwo phases: after etching with the reagent, FeB is dark brown and Fe2Bis yellowish-brown. Figure 1 shows single-phase Fe2B layer, with Fe2Bwedged into the substrate. Figure 12 shows dual-phase layer, with FeB as theouter layer and Fe2B as the inner layer. FeB is wedged into Fe2Blayer, and Fe2B is wedged into the substrate.
3.2 Performance of the Infiltration Layer[3]
1) Hardness
Microhardness of FeB is 1800~2200HV, and microhardnessof Fe2B is 1200~1800HV. As the carbon content in steel increases,the relative content and hardness of FeB in dual-phase layer can be reduced.Refer to the following table:
2) Wear Resistance
workpieces with FeB and Fe2B on thesurface have better wear resistance than quenched, nitride or chrome plated workpieces.Figure 3 shows the weight loss in the friction of muddy pump sleeve model and rubberplunger. The abradant is clay solution with quartz sand.
3) Corrosion Resistance
After boronizing, the corrosion resistance of the workpiecesin sulfuric acid, hydrochloric acid, phosphoric acid, various alkali and saltsolutions is improved significantly, but it is not resistant to nitric acid.
4) High TemperatureOxidation Resistance
The infiltrated layer oxidation weight increase islittle when heated to 800℃ for 40 hours in the air.
5) Red hardness
FeB and Fe2B can maintain high hardnessat 900℃[4].
4 Surface Hardness Comparison of Common PumpBarrels
5.Standard for Infiltrated Layer Inspection inthis Invention
The infiltrated layer in this invention is originated in domesticinitiative, so there is no national standard for its inspection. To controllayer thickness and hardness, provide basis for manufacturing and inspection,as well as make sure the product meet the specification and customerrequirements, company standard is made based on GB/T 18607-2008 standard.
The following table is the company’s inspection standard for metallographicstructure, thickness and hardness of the pump barrels infiltrated layer in thisinvention:
Notes:
The basis and related instructions of the above companystandard are as below:
1) Theoretical basis:
The company standard can meet the requirements of hardened layer thickness& hardness, and Base core hardness on pump barrels inner surface in Table69 of GB/T 18607-2008 standard. Take chrome plating on steel as an example, (thehardness and corrosion resistance of boronizing layer in this invention are muchhigher than that of carbonitriding layer, the corrosion resistance is close to thatof chromium coating, and the hardness is higher than that of chromium coating),the detailed comparison is in the following table:
2) Technical Feasibility:
According to the pump barrel boroninzing process of our company, aboverequirements can be fully guaranteed. If layer thickness is to be increased, theheating temperature and the holding time must be increased accordingly, which wouldlead to decarburization of the substrate, and decrease the overall performanceof the pump barrel.
3) Field Test Results:
In recent years,our company‘s boronizing pump barrels have used in many oil fields.Thousands of barrels are purchased by other oil-well pump manufacturers eachyear, and some of their products equipped with our barrels have been soldaboard. The feedback has always been positive. Pump barrels treated in thisprocess and qualified by our company’s inspection standard have been proved inpractice to have excellent corrosion resistance, wear resistance and other performances.
4) In order to accurately detect the hardness andthickness of the infiltrated layer, it is necessary to use the micro hardnesstester. The test force is 0.1Kg or 1.0N, and the test block must be mountedbefore grinding and polishing. Refer to JB/T 7709-2007 and GB 9790-88 fordetailed test methods.
References
[1] Shen Dicheng, AiWancheng et aL, Sucker Rod Pumping Equipment and Technology: Oil-well pump.First Edition, Petroleum Industry Press, pp. 214, Jul., 1994
[2] Zhu Yuanpu, HouZengshou et aL, Heat Treatment Handbook. Second Edition,
[3] Zhu Yuanpu, HouZengshou et aL, Heat Treatment Handbook. Second Edition,
[4] Lei Tingquan, FuJiaqi, 300 Kinds of Heat Treatment process. Second Edition,
