Figure 1 - uploaded by Wenda Wang
Content may be subject to copyright.
Pigging operation for wax removal (Ref: http://www.software.slb.com/store/_layouts/SLB/Pages/ProductDetailPage.aspx? pidAWAX-M1).
Source publication
Pigging is widely used in pipelines for wax removal. However, pigging operation relies heavily on “rule-of-thumb.” Because of its complexity and lack of methods, the wax removal mechanism is still poorly understood. This work aims to reveal the nature of the wax breaking process and thus promote understanding of wax removal physics. A unique experi...
Contexts in source publication
Context 1
... as thermal insulation, use of microbial products, and a combination of the above (Al-Yaari 2011; Kang et al. 2014;Mokhatab and Towler 2009;Aiyejina et al. 2011). While prevention of wax deposition is preferable from the outset, it is not always practical. In comparison to other methods, mechanical pigging on a planned frequency, as described in Fig. 1, has been the most popular approach for wax removal in pipelines (Davidson 2002;Tiratsoo 2013). In addition, a similar scrapers and/or cutting operation to pigging operation is used extensively to remove wax deposits from well tubing because it can be economical and result in minimal formation damage (Al-Yaari 2011). It is important to ...
Context 2
... Hence, after the initial breaking of the wax, increase in the wax removal force become very small and it can be considered to remain constant in this pre-plug phase (Phase 2) ( Wang and Sarica, 2001). Hence, the wax breaking force can be determined by averaging the wax removal forces experienced during the pre-plug phase (Phase 2) as shown in Fig. 10. Fig. 10 gives the wax breaking force determination principle. The result demonstrated the breaking force of wax deposits formed with 50 wt.% mixing ratio at 10 °C experimental temperature and at 2-mm wax thickness against cup pig (85HA) is 56.8 N. It was observed to be one third of the maximum wax removal force during pigging process. This ...
Context 3
... this paper, the effects of wax thickness, mixing ratio, pipe wall temperature, pig shape and aggres- siveness on wax breaking force were investigated in detail by using the mixtures of crude oil and field wax deposit. Fig. 11 shows the results from a cup pig for different wax thicknesses. The wax sample was prepared with 50 wt.% wax deposit and 50 wt.% crude oil. The pig being used has two cups with hardness of 80HA. It can be seen from Fig. 11 that the wax breaking force increases with the increase in wax thickness. In other words, the thicker the wax was, ...
Context 4
... aggres- siveness on wax breaking force were investigated in detail by using the mixtures of crude oil and field wax deposit. Fig. 11 shows the results from a cup pig for different wax thicknesses. The wax sample was prepared with 50 wt.% wax deposit and 50 wt.% crude oil. The pig being used has two cups with hardness of 80HA. It can be seen from Fig. 11 that the wax breaking force increases with the increase in wax thickness. In other words, the thicker the wax was, the more force was needed to break up the wax. This conclusion confirmed the findings by Wang and Sarica (2001). ...
Context 5
... samples being used in this study have different hardnesses with different mixing ratios between wax deposit and crude oil. Also, their WAT and wax content are different. The higher the mixing ratio of wax deposit, the higher WAT and wax content were. Fig. 6 has validated this point. Fig. 12 presents the results from a disc pig (90HA) for 4-mm wax thickness. The results revealed that the wax breaking force increases with the increase in mixing ratio of wax deposit at different experimental temperatures of 10, 20, and 30°C. It can be further concluded that the harder the wax was, the more wax breaking force was required to ...
Context 6
... conclusion is also identical with the experimental results obtained by Sarica (2001, 2008). Note that only limited data is presented in Fig.12 due to experiment failures for some cases. ...
Context 7
... effect of pipe wall temperature on wax breaking force was investigated for the first time. A cup pig with hardness of 90HA was used to remove the wax with thickness of 6 mm. Fig. 13 shows that the wax breaking force decreases with the increase in pipe wall temperature. This effect is more significant at higher mixing ratio. The rheological property of wax deposit at different temperatures may have significant influence on wax hardness. Fig. 14 shows a comparison of the wax removal performance between the cup and ...
Context 8
... A cup pig with hardness of 90HA was used to remove the wax with thickness of 6 mm. Fig. 13 shows that the wax breaking force decreases with the increase in pipe wall temperature. This effect is more significant at higher mixing ratio. The rheological property of wax deposit at different temperatures may have significant influence on wax hardness. Fig. 14 shows a comparison of the wax removal performance between the cup and disc pigs at same experimental conditions. It can be seen from Fig. 14 that the wax breaking force is bigger for disc pig than cup pig at the same experimental conditions. This may be the reason why disc pig is more efficient for wax removal than cup pig. This also ...
Context 9
... increase in pipe wall temperature. This effect is more significant at higher mixing ratio. The rheological property of wax deposit at different temperatures may have significant influence on wax hardness. Fig. 14 shows a comparison of the wax removal performance between the cup and disc pigs at same experimental conditions. It can be seen from Fig. 14 that the wax breaking force is bigger for disc pig than cup pig at the same experimental conditions. This may be the reason why disc pig is more efficient for wax removal than cup pig. This also implies that the wax removal performance can be promoted by optimizing the pig ...
Context 10
... wax removal performance of different pig aggressivenesses was also studied for the first time. Fig. 15 shows that different scraper (cup/disc) hardnesses have different wax removal performances. As shown in Fig. 15, cup and disc pigs have different wax breaking performances. For the experimental condition as presented in Fig. 15, the wax breaking force of cup pig increased first and then decreased when the cup strength is enhanced. In ...
Context 11
... wax removal performance of different pig aggressivenesses was also studied for the first time. Fig. 15 shows that different scraper (cup/disc) hardnesses have different wax removal performances. As shown in Fig. 15, cup and disc pigs have different wax breaking performances. For the experimental condition as presented in Fig. 15, the wax breaking force of cup pig increased first and then decreased when the cup strength is enhanced. In contrast, the effect of disc hardness on wax breaking force is difficult to evaluate due to missing data for 85HA ...
Context 12
... wax removal performance of different pig aggressivenesses was also studied for the first time. Fig. 15 shows that different scraper (cup/disc) hardnesses have different wax removal performances. As shown in Fig. 15, cup and disc pigs have different wax breaking performances. For the experimental condition as presented in Fig. 15, the wax breaking force of cup pig increased first and then decreased when the cup strength is enhanced. In contrast, the effect of disc hardness on wax breaking force is difficult to evaluate due to missing data for 85HA case. ...
Context 13
... the wax yield stress measured by the rheometer. The wax failure stress can be obtained by dividing the wax breaking force with the cross sectional area of the wax deposit (Galta 2014). A linear relationship between wax failure stress and yield stress is obtained with good accuracy by fitting the experimental data for a cup pig (85HA), as shown in Fig. 16. Hence, it is found that the linear fitting can be expanded to the entire experimental matrix, as depicted by Fig. 17. Fig. 17 reveals that the linear relationship is different for different pig designs. Moreover, it is also found that there is an overwhelming effect between the wax failure stress and yield stress, where the wax ...
Context 14
... with the cross sectional area of the wax deposit (Galta 2014). A linear relationship between wax failure stress and yield stress is obtained with good accuracy by fitting the experimental data for a cup pig (85HA), as shown in Fig. 16. Hence, it is found that the linear fitting can be expanded to the entire experimental matrix, as depicted by Fig. 17. Fig. 17 reveals that the linear relationship is different for different pig designs. Moreover, it is also found that there is an overwhelming effect between the wax failure stress and yield stress, where the wax failure stress exceeds the yield stress of the same wax deposit during the wax removal process. This effect is more obvious for ...
Similar publications
Purpose
The wax deposition in oil wells and pipelines is very viciously negative to the petroleum extraction and crude oil transportation, and it even causes severe blockage accident. This study aims to describe cleaning experiments performed on wax deposition of different deposition layer and experimental conditions to investigate the removal and...
Wax deposition makes up one of the main problems in the petroleum industry. Different types of techniques and treatments have been used to inhibit wax deposition. In this work, crude oils from Malaysian oil fields and Sudanese oil field are studied to determine their wax formation tendency for flow assurance purposes. In addition, effect of CO2 inj...
In this study, the cloud and pour point of the Nigerian Niger Delta Crude oil were determined so as to ascertain the temperature at which wax crystallizes and precipitates during crude transportation. Four (4) crude samples were collected and analysed in the laboratory and the results showed that each of the samples had varying cloud points; Sample...
The oil and gas industry is exposed to fow assurance issues such as wax deposition and scale precipitation. The sector has been tackling this issue using the chemical method while extensive research is being conducted to fnd an efective solution. The conventional method is costly and not eco-friendly. This paper focuses on using Jatropha curcas see...
To explore the influence of different wax components and the shear effect exerted by the pump and pipe wall in the process of crude oil pipeline transportation on the microbehavior of wax aggregation in crude oil at low temperatures, molecular dynamics models of binary and multivariate systems of crude oil with different wax components are establis...
Citations
... Given the current state of pig development, wax removal by pigs is inadequate, and the mechanism for wax removal remains to be elucidated. Wang et al. [11] conducted experiments on wax removal using various models of non-super-diameter polyurethane pigs. Their findings are pivotal in determining the optimal dewaxing frequency and assessing associated risks with pig usage. ...
The initial running speed of the pig during gas–liquid two-phase pipeline pigging can significantly influence the velocities of both gas and liquid phases within the pipeline. However, due to the complexity and limited understanding of these velocity variations, developing an effective operational plan for pigging becomes challenging. To enhance pigging efficiency and effectively seal the pig, it is crucial to monitor the velocity variations in the gas–liquid phase within the pipeline. In this study, an experimental platform was established to facilitate precise observation of these variations. Particle image velocimetry (PIV) technology was employed for a comprehensive understanding of gas–liquid two-phase velocities during pig operation in the pipeline. The experimental results demonstrated that increasing both the velocity and the initial liquid level height of the pig resulted in a corresponding augmentation of velocity fluctuation range. Specifically, at a holdup rate of 30%, there was a 10% reduction in the maximum liquid-phase velocity, while at a holdup rate of 25%, this reduction amounted to 16% compared to the pigging velocity.
... Predictive models can also be used for design considerations and wax deposition remediation schedules [7]. Wax deposits are usually periodically removed by mechanical pigging and chemical remediation [5,8]. These techniques add more production and operational costs [2,7]. ...
Oil wax deposition is becoming a major problem during oil production, transportation, and refining. Deposition mitigation by chemical additives, like polymer and surfactants, are commonly used in the oil industry. Because there is no clarity in wax inhibition mechanisms of the additive with crude type and conditions, chemical wax inhibitors are still used in a trial-and-error manner in the oil fields, which is an expensive and inefficient methodology. Understanding the wax inhibition mechanism is important for the design of new inhibitors. This review aims to give an overview of the understanding and development of nanoparticle technology, surfactants, polymer, and their combination in the inhibition of wax deposition. The review looks into lab and pilot plant experiments reported from 2000 to 2022, with more focus on the fundamentals of nanohybridization approaches in wax deposition control, testing methodologies (i.e., thermal, rheological, and morphological analysis), inhibition performance assessment, and mechanisms. The review begins with an overview of bibliometric analysis to shed light on the emerging areas in that field and explore and analyze the large volumes of scientific data reported in this field. The performance parameters used for assessing the wax inhibitors in the laboratory are also summarized and addressed. Finally, the challenges and future remarks of the reported chemical inhibitors are reported in this paper. This review provides insights into the integration of nanomaterials into the existing technologies to overcome the existing challenges.
... № 2(38) ISSN 1993-9868 print ISSN 2415-3109 online дуже великою, наприклад, рівною густині рідини, тоді зміна швидкості поршнів практично відсутня [9]. В [10] розроблено і змонтовано унікальну експериментальну установку для досліджень фізичного процесу видалення парафіну із внутрішньої стінки горизонтального трубопроводу внутрішнім діаметром 50 мм, довжиною 600 мм. Встановлено, що під час видалення парафіну манжетами поршня напруження його руйнування перевищує границю плинності парафінового відкладення, а залежність між цими величинами є лінійною. ...
Розглянуто проблемні питання, які виникають під час очищення систем збору газу газових родовищ очисними поршнями. Наведено вимоги, яким повинен відповідати матеріал поршнів призначених для очищення внутрішньої порожнини шлейфів свердловин від рідинних забруднень. Обґрунтовано доцільність поршні для очищення складних трубопровідних систем виготовляти із гіперпружних матеріалів. Виготовлено циліндричні очисні поршні з гіперпружних матеріалів із різними фізико-механічними характеристиками (пінополіуретан різної щільності, пінополіуретан покритий уретаном, саморуйнівна пружно-полімерна композиція, силіконовий герметик, силіконовий компаунд).Розроблено і змонтовано лабораторні експериментальні установки із скляних труб і відводів для оцінювання ефективності очищення поршнями із гіперпружних матеріалів горизонтальних і понижених ділянок трубопроводів, дослідження динаміки руху поршнів. Запропоновано технічне рішення з зміни аверсного напряму руху поршня на реверсний після проходження поршнем усього експериментального трубопроводу. Експериментально досліджено динаміку руху поршнів із гіперпружних матеріалів трубопроводами, визначено чинники які впливають на ефективність очищення. Встановлено при якій швидкості руху поршнів ефективність очищення горизонтальних прямолінійних ділянок трубопроводу є максимальною. Описано сили, які діють на поршень під час початку його руху трубопроводом, руху із сталою швидкістю, тимчасової зупинки в місці застрягання. Розглянуто основні чинники, які чинять вплив на силу тертя між поршнем і внутрішньою стінкою трубопроводу. Встановлено можливі місця і причини тимчасової зупинки поршнів із гіперпружних матеріалів у трубопроводах та негативні наслідки до яких це може призвести. Експериментально виявлено, що через усі досліджувані поршні із гіперпружних матеріалів відбувається перетікання повітря, яке подається у запоршневий простір. Таке перетікання сприяло підвищенню якості очищення трубопроводу. Надано рекомендації щодо сфери застосування поршнів із різних гіперпружних матеріалів.
... Mechanical methods involve brushing or scraping the interior of the pipe with a pig (Schaefer 1991;Wang et al. 2015;Huang et al. 2017). The operation of wax removal with a pig is called pigging. ...
Wax and hydrates deposition is a major concern for hydrocarbon transport in pipelines, production tubing, and other pipes in cold environments. Traditionally, chemical, mechanical, and thermal methods are used to mitigate the deposition at the expense of production interruption, complex maintenance, costs, and environmental hazards, and many of these methods are not feasible in deep water environments.
This paper studies the potential of nanopaint-aided electromagnetic pigging. This process has potentially low production impact, simple maintenance, low energy cost, and no chemical expense or hazards. The electromagnetic pig contains an induction coil that emits an alternating magnetic field. The alternating magnetic field induces heat in the nanopaint coating (i.e., coating with embedded paramagnetic nanoparticles) on the pipeline's inner wall and in the pipeline wall itself. The heat then melts and peels off the wax and hydrates adhering to the pipeline, allowing the hydrocarbon to carry them away. Without loss of generality, we focus on wax remediation in this paper.
We analyze the heating effectiveness and efficiency of electromagnetic pigging. The heating effectiveness is measured by the maximum pigging speed that allows deposit removal. The heating efficiency is measured by the ratio of the heat received by the wax over the total emitted electromagnetic energy, which we define as the pig induction factor.
An axisymmetric transient model is built to study the heat transfer without considering phase change. Based on our numerical model, we compare the pig induction factor for different coil designs, different hydrocarbon flow rates, and different pig traveling speeds. We re-evaluate the maximum pig speed defined by the static pig model from our previous work and found the electromagnetic pigging system is much more effective than previously estimated, while we confirm that a solenoid with larger radius allows higher pig speed. We find that faster pig speed generally improves the efficiency but decreases effectiveness and that shorter solenoids with larger radius have higher efficiency. The hydrocarbon flow rate does not impact the heating process if the wax is thicker than the threshold wax thickness. Based on the simulation results, the field application is discussed.
... Pigging is by far the most often utilized wax reduction method, particularly in offshore subsea systems (Wang et al., Huang et al., Liu et al., 2015;Wei, 2015), in which the wax is retrieved physically by washing the streamline. Pigging must all be prohibited regularly to avoid significant quantities of wax from accumulating. ...
Due to low-temperature circumstances, precipitation and paraffin wax deposition in manufacturing pipes and transportation tubes from offshore to onshore are significant challenges in the oil and gas sector. It may cause a reduction in output, a shutdown, pipeline blockage, and increased fluid viscosity. The most often used method for resolving this problem is to inject a wax inhibitor into the channel. Most current studies about paraffin wax are disseminated in literary works or exist as tacit knowledge in professional crania. This review research aims to exchange information and fulfil the deficits caused by providing a complete overview of the chemistry of paraffin wax precipitation and accumulation and causes, processes, and detection. It also discusses the overall impacts of paraffin wax deposition, how to deal with it, and several cleaning options. It also includes a conclusion and beneficial tips.
... Pedersen and Rønningsen [20] tested 12 different commercial pour-point depressants and concluded that viscosity reduction in crude oils with wax was the highest within the temperature range of 10 to 25ᵒC. Wei [21] provided a review of several newly developed wax-crystal modifiers such as ethylene-vinyl acetate, polyethylenepoly (ethylene-propylene), poly (ethylene-butene), and poly (maleic anhydride amide co-a-olefin), and determined that the performance of wax-crystal modifiers was a strong function of their ability to cocrystalize with wax. Therefore, in addition to the structure of the wax-crystal modifier, its composition is also significant. ...
... Therefore, in addition to the structure of the wax-crystal modifier, its composition is also significant. The efficiency of wax-crystal modifiers is increased by using them with solvents [21]. ...
The world demand for energy has led oil companies to expand their operations in the cold environments such as the offshore deep-water for more reservoirs. During hydrocarbon production, oil companies are challenged with the problem of wax deposition from the crude oil building up on the pipe wall. The precipitated solid phase of wax, creating pressure abnormalities and causing an artificial blockage leading to a reduction or interruption in the production. It leads to increases in operational and remedial costs while suppressing oil production. This research outlines the important methods that used to reduce or mitigate wax deposition in the hydrocarbon production systems around the world, such as the chemical, mechanical, thermal methods, or a combination between them, microbial treatment, cold flow, cold-oil recirculation method, choke cooling method, the wax eater method, magnetic-fluid conditioning method, Eco-wave TM treatment, ultrasonic wave treatment, bacterial treatment, and spiral flow method. Many researchers have been used various different types of chemical inhibitors, such as polyethylene, ethylene/vinyl acetate copolymers, copolymer esters, polyacrylate polymer, ester/vinyl acetate copolymers, olefin/ ester copolymers, polymethacrylates, alkyl phenol resins, xylene and toluene. The reduction in wax deposition was 100% after using the influence of bending spiral flow with polyacrylate polymer at a concentration of 1000 ppm and 2000 ppm at different time and flow rates, and the ambient temperature was 33°C. The reduction in wax deposition was 100% after using the effect of bending the spiral flow with the inhibitor at a concentration of 500 ppm at flow rate 4.8 L/min, and the reduction in wax deposition was 94% at the same concentration and flow rate 2.7 L/min. Despite of all the previous mitigation methods, many oil companies still suffer from wax deposition problems and are still looking for a good solution to solve this issue.
... There are thermal, chemical, and mechanical ways among different methods of ARPD removing from well (Huang, 2016; Wang, 2015). The simple-to-apply method is mechanical, but there is a risk of jamming rods and equipment failure when the process of paraffin deposition is quite intensive. ...
One of the main oil production complications is that asphaltene-resin-paraffin deposits (ARPD) are formed during production wells' operation. This is an urgent problem in the oil and gas industry, especially in the fields of the Ural-Volga region (Russia). This study aimed to develop a technological solution for the effective thermal treatment of deposits based on the wells' thermal state calculation during a sucker rod pump operation. In practice, the thermal effect on ARPD is carried out by flushing-out with a hot agent (water, oil). Traditionally, flushes are carried out through the casing annulus. However, this method is ineffective due to large heat losses and the impossibility of heating the inner part of the tubing in a sufficient way, where ARPD is deposited. Dynamic modeling of the process was performed in the ANSYS Fluent software product. The heat problem was solved on the basis of the Navier-Stokes Reynolds-averaged heat and mass transfer equation. It was noted that the temperature of the injected agent (hot oil or water) affects the temperature of the tubing's inner wall to a lesser extent than the coolant flow rate. It has been established that it is impossible to reach the melting point of wax at the submersible pump level. The flow rate of the coolant affects this parameter more intensively. When flushing with hot oil 120°C with a flow rate of 300 m3 /day, the temperature above the pump will be equal to the wax melting temperature. Calculations indicate that it is most advisable to use oil heated to 120°C as a coolant for flushing wells than water with a 90°C temperature. The implementation of the methods proposed can be used on any well equipped with a sucker rod pump.
... Mechanical methods involve brushing or scraping the interior of the pipe with a pipeline inspection gauge, or 'pig' for short, and the process itself is called 'pigging' (Huang et al., 2017;Schaefer, 1991;Wang et al., 2015). Pigging usually interferes with hydrocarbon transport in pipelines, and the tool can be easily stuck in the pipe. ...
Precipitation and deposition of paraffin wax and hydrates is a major concern for hydrocarbon transport in pipelines, tiebacks, and other production tubing in cold environments. Traditionally, chemical, mechanical, and thermal methods are used to mitigate the deposition at the expense of production interruption, complex maintenance, costs, and environmental hazards.
This paper studies the potential of nanopaint-aided electromagnetic pigging. This process has potentially low production impact, simple maintenance, low energy cost, and no chemical expense or hazards. The electromagnetic pig contains an induction coil that emits an alternating magnetic field. The alternating magnetic field induces heat in the nanopaint coating (i.e. coating with embedded paramagnetic nanoparticles) on the pipeline's inner wall and in the pipeline wall itself. The heat then melts and peels off the wax and hydrates adhering to the pipeline, allowing the hydrocarbon to carry them away.
We analyze the heating effectiveness and efficiency of electromagnetic pigging. The heating effectiveness is measured by the maximum pigging speed that allows deposit removal. The heating efficiency is measured by the ratio of the heat received by the wax over the total emitted electromagnetic energy, which we define as the pig induction factor.
Based on our numerical model, we compare the pig induction factor for different coil designs, different hydrocarbon flow rates, and different pig traveling speeds. We find that slower pig speed generally improves the pigging performance, that shorter solenoids with larger radius have higher efficiency, and that the oil flow does not considerably affect the process. We re-evaluate the maximum pig speed defined by the static pig model and confirm that a solenoid with larger radius allows higher pig speed.
We investigate the potential of a novel, low-maintenance electromagnetic pigging method that poses minimal interruption to production. This investigation is a basis for a new technology that stems from initial experimental investigation done by our collaborators. We here provide parameters for pig design and pigging protocol optimization, and will put them in practice in our future lab experiments.
... Both the wax deposit thickness and strength are fundamental for the pigging operation. [23,24] Therefore, the structural characteristics of wax deposits after the addition of PWIs need to be carefully investigated. ...
Polyethylene vinyl acetate (EVA) has been widely investigated and employed as polymeric wax inhibitor (PWI). In this paper, the wax deposition characteristics of synthetic oils with different concentrations of EVA PWI were investigated. The obtained surface and bottom wax deposits were analyzed through differential scanning calorimeter (DSC), polarizing microscope, Fourier transform-infrared spectroscopy (FT-IR) and high-temperature gas chromatography (HTGC). It is found that the EVA PWI could obviously decrease the wax deposition rate and accelerate the aging of wax deposits. Adding the EVA PWI can trigger a novel heterogeneous wax deposit structure, in which the wax appearance temperature and wax content increases continuously from the bottom to the surface layer. Compared to the bottom wax deposit, the surface wax deposit has higher concentrations of both EVA and high carbon number wax molecules (Cn > C25). The formation mechanism of the novel heterogeneous wax deposit structure was explained from two aspects. Firstly, the wax crystal morphology of surface layer is significantly changed from needlelike to diamond-like due to higher temperature and the accumulation of EVA and high carbon number wax molecules in the surface wax deposit, therefore, higher solid wax content is needed for the building of a continuous three-dimensional network structure to resist shearing of pipe flow. Secondly, the lower temperature and larger aspect ratio of wax crystals in the bottom wax deposit are adverse for the diffusion of wax molecules into the bottom wax deposit, thus the aging rate of bottom wax deposit is lower than that of surface layer.
... Wax deposition is a significant flow assurance challenge for waxy crude oil production and transportation. When the pipe wall temperature falls below the wax appearance temperature (WAT), the dissolved wax molecules precipitate out from the oil and form wax deposits on the pipe wall [1][2][3][4]. Concomitant problems include the decreased crosssectional area and transportation capacity, and the increased pressure drop and pumping cost. In offshore productions, this holds particularly true due to low seawater temperatures [5,6]. ...
... Incorporating wax removal efficiency and pig geometry, Hovden et al. [37] established a wax breaking force model containing several empirical parameters. Wang et al. [1,38] found that the wax failure stress of wax layer always exceeds its yield stress. Based on this, a pigging model for predicting the wax breaking force was established. ...
... Particularly, the casted and removed wax in each pigging run was carefully weighed to determine the wax removal efficiency. More detailed information about the pigging facility and the test procedure is given elsewhere [1,38,39]. ...
