ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Identity entails the creation of socio-cultural meanings and the symbolic means to express them. Some Sindhis describe their socio-cultural identities as the product of a 'strange amalgamation' process that symbolically mixes 'everything that is good'. 2 In scholarly terms, this process could be labelled and/or described as syncretism. 3 Despite a seemingly positive connotation, syncretism is not without its critics. At various moments in history, syncretism has negatively described a 'jumbled and confusing mixture of religions' and/or distinguished '"hybrid"-and thus "lesser"-religions from what is "pure" and "authentic".' 4 Accordingly, Carl Ernst and Tony Stewart caution against using the term. They describe how syncretism can result from violent domination: when one group conquers a different group, syncretism can 'describe the product of the large-scale imposition of one alien culture, religion, or body of practices over another that is already present.' 5 In such situations, the subjugated group often reconstructs its identities by borrowing symbols and meanings from those who dominate it. Syncretism can thus negatively imply that the borrowing group is 'dependent, lacking in creativity, and fundamentally incapable [2] of defining itself.' 6 Among the metaphors used to describe syncretism, Ernst and Stewart are particularly concerned about its 'alchemical model':

The more common alchemical model of syncretism, however, is that of the mixture, a colloidal suspension of two ultimately irreconcilable substances. The result is a temporary mixture that will invariably separate over time because the component parts are unalterable Ernst and Stewart argue that 'explanations that hinge on syncretism really serve only to concretize the initial religious or cultural categories presumed to be self-evident.' 8 By linking self-evident 'orientations that are normally disparate, if not disjunctive,' syncretism reaffirms differences of identity by implying an 'inappropriate' combination of 'intrinsically alien' socio-cultural symbols and meanings. 9

Considering Ernst and Stewart's critique, it is worth re-evaluating the idea that Sindhi identities are syncretic. Sindh can be described as a 'shatter zone' or a region 'through which large numbers of people passed either in military or peaceful invasion … socio-culturally the area[s] tend to be more of a mosaic than a relatively unitary kind of social structure.' 10 The historical creation of such a mosaic in Sindh entails people reworking and intertwining shards of symbolic meaning. As a process, it involves 'taking things apart' just as much as it does 'putting things together'. 11 By linking convergence with divergence, this process resists creating identities from 'irreconcilable substances'. 12 Instead, it utilizes multi-voiced symbols and meanings to generate new sociocultural 'solutions'. Comprehending these solutions analytically involves numerous 'side-long glances' toward different socio-cultural assemblages. 13 Such glances reveal how Sindhis create their identities not from the simple historical mixing of oppositions but a socio-cultural codeswitching process that transgresses boundaries by intertwining them. 14 Such 'intertwined' identities point towards meanings in [3] multiple socio-cultural assemblages and rarely 'speak', symbolically or otherwise, in singular voices and/or tones. Rather than simply conclude that Sindhi identity is syncretic, the region's intertwined socio-cultural character points toward seeing it as a zone in which people's lives are not constituted by a mixture of parts bound to naturally separate.

The Pre-Partition Politics of Sindh and Identity

Prior to Partition in 1947, Sindhis did not generally view the intertwining of identities as incoherent and/or disorderly. Free from negative connotations, these identities resisted 'vertical fallacies' that separated Muslims and non-Muslims into socio-culturally discrete columns based on Islam and Hinduism. 15 By not framing in-group solidarities and networks into discrete realms of religious belonging, such identities socio-culturally subverted clear-cut communal distinctions by failing to foreground differences between Hindus and Muslims as politically relevant. In other words, religious distinctions were not particularly important political categories of identification for people in Sindh as they did not translate into radically segregated faith experiences. This lack of segregation reaffirms the historical divergence in Sindh between political power and socio-cultural purism. Although Sindh's rulers before its annexation by the British in 1843 were Muslims, access to positions of power in the region was rarely pre-conditioned on exclusive membership in the area's majority Muslim population. The codes (i.e., 'principles for selecting variants from a range of possible choices') of power and purism in Sindh did not historically encapsulate each other. 16 The relationship between political power and socio-cultural purism began to shift in Sindh during the 1920s and the immunity that intertwined identities provided against communal politics weakened. Following the deaths of non-communal politicians like Ghulam Mohammad Bhurgri (1878-1924) and Seth Harchandrai Vishindas (1862-1928), as well as the communal riots of Larkana [4] (1927) and Sukkur (1930), the holding of political power in Sindh increasingly hinged on being part of its Muslim majority population. 17 This shift manifested itself in the political demand that the British give Sindh provincial autonomy from the Bombay Presidency. Stressing Sindh's distinctive character, Vishindas argued in 1913 that the region deserved autonomy because it possessed 'several geographical and ethnological characteristics of its own, which give her the hallmark of a self-contained, territorial unit.' 18 Vishindas, as well as Bhurgri, sought the backing of the secular Indian National Congress for Sindh's provincial autonomy. However, this unity of opinion between Muslim and non-Muslim politicians dissolved after communal riots in Larkana and Sukkur. Rather than becoming minorities in an autonomous province, Sindh's non-Muslims shifted their support for autonomy and advocated that the region remain part of the Bombay Presidency.

At the same time, Muslim politicians in Sindh campaigned to make autonomy an all-India issue and gained the support of the All-India Muslim League (AIML) in December 1925. United under the banner of the Sindh Azad Conference, they continued to put forward the argument that Sindh's socio-cultural uniqueness justified autonomy. Prominent politicians like Shahnawaz Bhutto and Ghulam Hussain Hidayatullah maintained that Sindh deserved autonomy because of the 'racial and linguistic differences between Sindh and those of the Bombay Presidency proper.' 19 But the most elaborate argument in favour of Sindh's unique character came from Muhammad Ayub Khuhro, a young landlord and politician who highlighted the region's continuity as a sociocultural and political unit from the Indus Valley period onwards. Although not explicitly referenced, Khuhro's pluralistic perspective pointed towards the importance of Sufism as well as 15 Barbara Metcalf, 'Too Little and Too Much: Reflections on Muslims in the History of India', Journal of Asian Studies 54.4 (1995): 959. In Sindh, such resistance did not always extend to socio-cultural distinctions outside of the communal domain (e.g., along vectors of caste, class and the urban/ rural divide). 16 Hill and Hill, 100. 17 Prior to this period, political power in Sindh depended largely on the ownership of land (David Cheesman, Landlord Power and Rural Indebtedness in Colonial Sind, 1865-1901 [London: Curzon/Routledge 1997]). 18 Seth Harchandrai Vishindas quoted in Alhaj Mian Ahmad Shafi, Haji Sir Abdoola Haroon: A Biography (Karachi: Begum Daulat Anwar Hidayatulla, 1942), 70. 19 Allen Keith Jones, Politics in Sind, 1907-1940: Muslim Shah Abdul Latif Bhittai (1689-1752) as a symbol of Sindh's intertwined religious inclusiveness. 20 Both Muslims and non-Muslims promoted and participated in Sufism but-by the 1930scommunal politics increasingly obstructed its inclusiveness. So much so that, when Sindh became [5] autonomous in 1936, it did so under the leadership of politicians who 'were, on occasion, openly hostile to the Hindus'. 21 Despite communal overtones, Sindh's provincial autonomy from Bombay did not initially tax the resilience of its intertwined identities. Following autonomy, Sindh's first Chief Minister, Ghulam Hussain Hidayatullah, called for unity:

What is most urgently needed above everything else is complete trust and confidence between various communities. We must refuse to believe that there is much deep-rooted hostility on the part of the majority towards the minorities, that the interests of the one can never be trusted in the hands of the other. If this attitude of distrust and suspicion is maintained, we might as well throw overboard all our schemes of nationalism. We call ourselves a nation and demand for ourselves the right of self-determination. But how can we possibly be one nation if we are so helplessly divided? 22 The first provincial governments in Sindh under Hidayatullah (1937-8), Allah Bux Soomro (1938-40/1941-2), and Mir Bandeh Ali Khan Talpur (1940-1) all included Muslim and non-Muslim politicians. By respecting the region's socio-cultural mosaic, these governments illustrated how power codes after autonomy were encapsulated more by class and landownership than those of purism. 23 Nonetheless, efforts to establish an inclusive politics in Sindh were challenged after autonomy: the landowner-dominated Sind United Party only ran Muslim candidates and it emerged as the largest winner in the 1937 provincial elections. The separation of political power and communal ideas concerning purism also received a severe jolt from the Manzilgah incident of 22 Ghulam Hussain Hidayatullah, 'The Task Before Us', Alwahid: Special Sind Azad Edition (1936): 6. 23 Having an exclusively Muslim identity was not a precondition for participating in any of these governments. Two government ministers under Mir Bandeh Ali Khan Talpur were non-Muslim Lohanas (i.e., Nichaldas Chotmal Vazirani and Rai Sahib Gokaldas Mewaldas) from different endogamous moieties. Hidayatullah's government also included non-Muslim ministers, like the bhaiband merchant Mukhi Gobindram Pritamdas (a leader of the Sindh Hindu Mahasabha) and the Amil Hemandas Rupchand Wadhwani. Additionally, Hidayatullah crossed the communal divide to support Bhojsingh Gurdinomal Pahalajani as Sindh's first Assembly Speaker in 1937. Allah Bux Soomro, while from an "indigenous" Sindhi family, was only able to form a government with support from Vazirani in 1938. Subsequently, Vazirani became Public Works Department, Public Health, and Medical Minister. Allah Bux Soomro's second government (1941-2) also had support from non-Muslims and included Mewaldas as Minister for Local Government and Agriculture. It is also relevant to note that Mir Bandeh Ali Khan Talpur's power base was largely ethnic rather than religious: he led an alliance of Baluch-Talpurs. The family and personal histories of some key politicians from this period were also not always so religiously lengthy: Ghulam Hussain Hidayatullah came from a family that converted to Islam and Shaikh Abdul Majid Sindhi, a minister in Mir Bandeh Ali Khan Talpur's government, converted to Islam in his youth (Bhavnani, xxxi).

1939. This incident, in combination with Partition in 1947, dealt a body-blow to Sindh's intertwined identities from which they never fully recovered.

The seeds of the Manzilgah incident can be found in the failure of the All-India Muslim League to establish a firm foothold in Sindh until the 1940s. While the AIML had individual members in Sindh [6] prior to the provincial elections of 1937, the party had no proper branch office. While political parties led by Sindhi Muslims had contacts with the AIML, they did not lead to the foundation of a provincial branch office. Establishing a foothold in Sindh was also stymied by disagreements among Sindhi politicians as well as those the AIML had with its local advocates. 24 The AIML's lack of structure resulted in the party failing to secure a single win in Sindh's 1937 provincial elections. 25 Despite its electoral failure in 1937, some Sindhi politicians continued to view AIML in a positive light. Abdullah Haroon (1872-1942), a prominent Karachi businessman and a member of the Central Legislative Assembly in Delhi, organized the Sindh Provincial Muslim League Conference in 1938. The AIML leader Muhammad Ali Jinnah attended this conference at which the Muslim League Assembly Party (MLAP) was formed. The MLAP's aim was to lay the foundation for the AIML's electoral success in Sindh by building and organizing a united political front for Muslim politicians. 26 Nonetheless, regional politicians who wanted to safeguard their influence and interests within Sindh were an important block within the MLAP. While some MLAP members (e.g., Haroon) prioritized the AIML's all-India agenda, others (e.g., Shaikh Abdul Majid Sindhi) used the organization as a vehicle to promote regional issues. Such divisions within the MLAP resulted in it frequently not consulting and/or coordinating with the AIML. One important example of this lack of consultation/coordination was the Manzilgah incident. The Manzilgah was a group of buildings in Sukkur, which some believed was a mosque complex. These buildings stood on the shore of the Indus River and across from the socio-culturally intertwined island shrine of Sadh Belo. 27 Fearing that prayers at the Manzilgah would impede access to Sadh Belo, locals protested against the possibility of the site becoming a mosque. Attempting to bring down the government of Allah Bux Soomro, the MLAP backed making the Manzilgah a mosque. It supported a civil disobedience protest that occupied the Manzilgah on 3 October [7] 1939. The use of force by the police to expel protesters resulted in communal riots that killed 15 Muslims and 19 Hindus. 28 These riots represented a particularly intense challenge to Sindh's intertwined identities. After the riots, this challenge was further intensified by the assassination, on 1 November 1939, of Bhagat Kanwar Ram, a 'Hindu' Sufi singer with followers 24 Jones, 160; Hamida Khuhro, 'Masjid Manzilgah, 1930-40: Test Case for Hindu-Muslim Relations in Sind', Modern Asian Studies 32.1 (1998): 50. For example, Shaikh Abdul Majid Sindhi's Sind Azad Party sought the AIML's endorsement but refused to identify itself as its branch. 25 This situation particularly stung the AIML since 32 out of 60 seats were reserved for Muslims and Sindh's population was 72 per cent Muslim. 26 Many politicians in Sindh had multiple party memberships. A major goal of the MLAP was to prevent politicians from shifting their alliances when favorable political winds shifted from one party to another party. 27 Swami Bankhandi Maharaj Udasi established this shrine in 1823. Swami Bankhandi Maharaj Udasi followed a religious sect that centered on the teachings of Sri Chand, the son of Guru Nanak (i.e., Sikhism's founder). Reflecting Sindh's intertwined identities, members of this sect also worshipped the panchayatana (i.e., Shiva, Vishnu, Durga, Ganesh, and Surya). Prior to the rise of the Akali or Gurdwara Reform Movement in the twentieth century, udasis were the key custodians of Sikh shrines and philosophy. 28 These riots were apparently started by jeering aimed to imply that protesters 'had gotten what they deserved' (Jones, 138). from across the communal divide. Hassaram Sunderdas Pamnani (a non-Muslim member of the Sindh Assembly from Sukkur) openly accused the Sufi Pir of Bharchundi of ordering Bhagat Kanwar Ram's death. Later, in July 1940, Hassaram Sunderdas Pamnani was also assassinated (purportedly at the direction of the Pir of Bharchundi).

By heightening communal tensions to new levels, the Manzilgah incident and its aftermath dealt a blow to Sindh's intertwined identities. 29 Although orchestrated independently from the AIML, this communal blow, in conjunction with the MLAP's generally successful creation of a united political front for Muslims, helped it expand its base in Sindh. This expansion led to the AIML forming a provincial government in 1942 under the leadership of Ghulam Hussain Hidayatullah. AIML's formation of a provincial government in 1942 illustrated how holding political power in Sindh after the Manzilgah incident increasingly depended on being part of the region's majority population. The elections of 1946 further reaffirmed this fact when the AIML won a landslide victory with 82.1 per cent of Sindh's rural Muslim vote and 98.8 per cent of its urban Muslim vote. 30 After these elections, power codes in Sindh were increasingly encapsulated by the socio-culturally purist codes of communalism. The region's historically intertwined identities hit an additional turning point with Partition in 1947. Migrations into and out of Sindh after Partition significantly modified its socio-cultural mosaic: many non-Muslims left while Urduspeaking migrants arrived from India. Rather than result in the further intertwining of identities, these migrations increasingly communalized them. As a result, the processes by which people created their identities in Sindh became less intertwined and more 'colloidal' after Partition. 31 [8]

Identity, History, and the Journal of the Sindh Historical Society

The Sindh Historical Society (SHS) published its journal from May 1934 to January 1948. The articles printed in the Journal of Sindh Historical Society (JSHS) were first presented and debated at meetings of the SHS. The society's participants primarily included the educated elite of Karachi, both European and South Asian. 32 Its founding President, Hotchand Mulchand Gurbaxani, reflected Sindh's intertwined identities: a non-Muslim professor of Persian who knew Arabic, he was well known for his annotated translation of the Sufi poetic compendium Shah Jo Risalo. In a newspaper article, 'Writing the History of Sindh', historian Mubarak Ali states that the SHS was the key that unlocked 'modern' methods for understanding Sindh's past:

The modern historiography of Sindh was introduced during the British rule when the Historical Society of Sindh [sic] was founded with the purpose of reconstructing the history of Sindh. The Society held regular meetings where the members presented research papers on different aspects of history, as well as published a historical journal which contained well-researched papers, thus contributing immensely to recording the history of Sindh. 33 29 Ibid. 145. 30 While the 1946 elections were a clear victory for the AIML, the results should be taken with a grain of salt since important candidates were excluded and/ or prevented from filing applications to run (e.g., G. M. Sayed). 31 Ernst and Stewart, 587. 32 The lists of SHS officers and members at the beginning of each edition of the Journal of the Sindh Historical Society reveals the socio-cultural spectrum of urban Sindh. It also explains why so few Muslims, who dominated the population of rural Sindh, contributed articles to the journal. 33 Mubarak Ali, 'Writing the History of Sindh', Dawn, November 23, 2014 <http://www.dawn.com/news/1145793> During the period in which the SHS met and published its journal, the socio-cultural and political ecologies of Sindh were increasingly communal. As products of their time, some articles published by the SHS had a communal tinge. However, these articles mostly swam against the emerging current of communalism by detailing Sindh's socio-cultural mosaic. Before and after the region's autonomy from the Bombay Presidency in 1936, the SHS published articles about this mosaic that supported Vishindas, Bhutto, Hidayatullah and others who argued that Sindh deserved greater political independence due to its distinct socio-cultural identity. Through the Manzilgah incident and Partition, the SHS published research [9] that reaffirmed Sindh's distinct character. However, symbolic of the region's increasingly colloidal rather than intertwined identities, the SHS disbanded in the wake of Partition and ceased publishing in January 1948. 34 With a sense of loss, the SHS dedicated the last edition of its journal to the memory of Gurbaxani (who died in January 1947). This loss was also represented by the last article published in the Journal of the Sindh Historical Society: it was about the Lohana, a group that fled Sindh after Partition and the formation of Pakistan. 35 This collection of articles from the Journal of the Sindh Historical Society concentrates on precolonial and colonial Sindh. It focuses on indigenous and British actors. It also showcases Sindh's broad socio-cultural spectrum. Scholarship on Pakistan frequently overlooks the subjects and people in this collection. In part, this oversight is due to such few libraries in Pakistan (and around the world) having copies of the Journal of the Sindh Historical Society. It is also explained by the fact that articles from the journal are not often reprinted in books. Beyond this collection, Mubarak Ali's Sindh Observed is the only book to reprint full articles from the Journal of the Sindh Historical Society. 36 None of the articles in this collection are in Ali's Sindh Observed, nor has anyone reprinted them in their entirety since the 1930s and 1940s. This collection is chronologically organized. Chapter 1 describes Sindh's Kalhora rulers and their eighteenth-century overthrow by the Talpurs. Chapter 2 addresses justice and its decentralization under the Talpurs. Chapter 3 focuses on two men, Gidumal (an aamil, or government administrator) and Naomul (a bhaiband or merchant) as well as their relationships with the Kalhoras and the Talpurs. Chapter 4 is about Mirza Khusro Beg, a Georgian and influential advisor to the Talpur rulers of Hyderabad. Chapter 5 tackles the British 'militarization' of Baluch tribes on Sindh's frontier during the late 1830s. Chapter 6 describes three less-known military clashes between the British and Sher Muhammad Talpur: the Battle of Hyderabad, the Battle of Pir Ari and the Battle of Shadadpur. Chapter 7 depicts, [10] from a first-hand indigenous perspective, diplomatic interactions between the British and the Talpurs. Chapters 8 and 9 address the private opinions and correspondences of John Jacob, a key figure in the British conquest and early rule of Sindh. Chapter 10 analyses Baluch poetry and history in Sindh. Chapter 11 socioculturally and historically examines Hyderabad's Amil community. Chapter 12 details four popular Sindhi folk legends. Chapter 13 compares the Sindh census reports of 1931 and 1941.

Individually, the articles reprinted as chapters in this collection reveal much about Sindh's past. Collectively, these articles not only deepen knowledge about Sindh but also the history of Pakistan and the diversity of its people. They represent, like most research published in the Journal of the Sindh Historical Society, 'forgotten' chapters in both Sindhi and Pakistani history. These chapters celebrate Pakistan's socio-cultural diversity as well as point toward how the histories of region and nation should be 'intertwined' rather than exclusive.

  Michel Boivin, Matthew A. Cook, Julien Levesque To cite this version: Michel Boivin, Matthew A. Cook, Julien Levesque. Introduction. Michel Boivin; Matthew A. Cook; Julien Levesque. Discovering Sindh's Past: Selections from the Journal of the Sindh Historical Society, 1934-1948, Oxford University Press, pp.1-14, 2017, 9780199407804. halshs-02464285 Introduction Michel Boivin, Matthew A. Cook, and Julien Levesque Means and meanings are inextricably intertwined. 1

  Identity and the Demand for Pakistan (Karachi and London: Oxford University Press, 2002), 16.

20

  Discourses that link identity in Sindh with Sufism were also fueled by Sindhi writers influenced by the Theosophical Society (Michel Boivin, 'The New Elite and the Issue of Sufism: A Journey from Vedanta to Theosophy in Colonial Sindh', in Muhammad Ali Shaikh, [ed.] Sindh Through the Centuries II: Proceedings of the 2 nd International Seminar [Karachi: SMI University Press, 2015], 215-31; Michel Boivin, Historical Dictionary of the Sufi Culture of Sindh in Pakistan and India [Karachi and London: Oxford University Press, 2015]). 21 Nandita Bhavnani, The Making of Exile: Sindhi Hindus and the Partition of India (Chennai: Tranquebar Press, 2014), xxxiii-xxxiv. Muslim politicians frequently blamed banias (i.e., Hindu moneylenders) for the woes of rural peasants in Sindh (David Cheesman, 'The Omnipresent Bania: Rural Moneylenders in Nineteenth-Century Sind', Modern Asian Studies 16.2 [1982]: 445-62).

This date is particularly meaningful due to the killing of about 200 Sikhs in Karachi during January 1948. These killings contributed to the exodus of upper caste non-Muslims from all over Sindh after Partition. Despite this exodus, many from the low castes (e.g., Kohlis, Bhils, and Meghwars) remained in Sindh.

T. S. Thadani, 'The Lohanas', Journal of the Sindh Historical Society 8.3 (1948): 166-70.

Mubarak Ali, (ed.) Sindh Observed: Selections from the Journal of the Sindh Historical Society (Lahore: Gautam Publishers, 1993).


François Grosjean

Rémy Mingant

J Kittel

L Ke

Carol Taravel-Condat

Vaufleury Maxime

Bruno Vuillemin

M Vaufleury

Corrosion and pH prediction in the annulus of flexible pipes under high pressure of CO2

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Flexible pipelines are widely used for the transport of fluids in oil and gas applications. They are composed of successive layers of steel and polymer materials. An example of a structure of a flexible pipeline is described in Figure 1. In the recent years, oil and gas production conditions evolved to higher temperature, higher pressure and greater acid gas contents, with a great incidence on materials selection. For the flexible pipelines used in offshore conditions, these conditions apply directly to materials from the bore, i.e. the carcass and the polymer pressure sheath. But there is also a great impact on the environment of the annulus, where high strength low alloy steels armour wires are used to withstand both the internal pressure and the weight of the riser. The selection and design of these steel armours need to consider possibilities of corrosion. Indeed, presence of water in the annulus is possible. Seawater can be found due to accidental rupture of the outer polymer sheath, or deliberate flooding for design purposes. Pure water may also be found, as a result of condensation of water vapour after permeation from the bore through the inner polymer sheath. Similarly, acid gases from the bore also permeate through the inner layer, and water with dissolved CO 2 and H 2 S can be found. The corrosive environment thus depends in the first place of permeation rates and equilibrium pressures of acid gases. These properties can be determined from experimental and modelling data, as described in [START_REF] Taravel-Condat | MOLDI TM : a fluid permeation model to calculate the annulus composition in flexible pipes: validation with medium scale tests, full scale tests and field cases[END_REF]. Corrosion in the annulus is also strongly influenced by the high confinement ratio (V/S) between the volume of electrolyte and the exposed surface of steel. Typical V/S ranges from 0.02 to 0.06 mL/cm², i.e. corresponding to a film of electrolyte of 10 to 100 µm at the steel surface. As already described in details, the corrosion conditions in the annular space are very specific [START_REF] Ropital | Eurocorr[END_REF][START_REF] Rubin | Corrosion rates of carbon steel in confined environments[END_REF][START_REF] Remita | A kinetic model for CO 2 corrosion in confined aqueous environments[END_REF]. In such conditions, the electrolyte pH no longer corresponds to the thermodynamic equilibrium with the acid gases partial pressures, but to a kinetic equilibrium involving iron dissolution and iron salts precipitation. The environment is highly supersaturated in ferrous ions, and the pH exceeds by far the natural pH at saturation [START_REF] Remita | A kinetic model for CO 2 corrosion in confined aqueous environments[END_REF]. Corrosion rates are thus greatly reduced compared to the ones that would be observed in water with similar partial pressures of acid gases and without confinement. Lots of experimental and modelling efforts are directed to predict the annulus pH, since it represents an important parameter for materials selection for the carbon steel armours. Until recently, most applications presented CO 2 equilibrium pressure in the annulus below or close to 1 bara. However, the development of high pressure fields with up to several hundred bars of CO 2 moved the upper limit of CO 2 content in the annular space to more than a few tens of bars [START_REF] Taravel-Condat | The use of flexible pipe for CO2 enhanced oil recovery applications[END_REF]. It became thus necessary to extend the range of available data on pH measurements in confined conditions to higher pressures. The goal of the present paper is firstly to describe the basis of the corrosion phenomena modeling and secondly to show pH measurements in confined conditions at CO 2 partial pressures from 1 bara to 45 bara CO 2 . Finally, comparisons between the experimental results and the predicted values from the model are presented.

pH in confined environments

Modeling aspects

Leaving aside the specificities of confined environment, corrosion in the annulus of a flexible pipe can be described by chemical equilibria and electrochemical equations that are commonly used in mechanistic models of CO 2 and H 2 S corrosion [START_REF] Nesic | An electrochemical model for prediction of corrosion of mild steel in aqueous carbon dioxide solutions[END_REF][START_REF] Nesic | CO 2 corrosion of carbon steel -from mechanistic to empirical modelling[END_REF][START_REF] Nesic | An open source mechanistic model for CO 2 / H 2 S corrosion of carbon steel[END_REF][START_REF] Nordsveen | A mechanistic model for carbon dioxide corrosion of mild steel in the presence of protective iron carbonate films -Part 1: Theory and verification[END_REF]. The governing reactions are acid gases dissolutions and dissociations, reduction of proton and/or other acid components, oxidation of iron, and iron salts precipitation.

In CO 2 environment, the global electrochemical reaction is:

2 2 3 3 2 Fe 2H CO Fe 2HCO H      (reaction 1)
This reaction produces alkalinity, thus a local increase of pH, or a global increase of bulk pH in stagnant conditions, and subsequently a decrease of corrosion rate. At the same time, 3 HCO  is also the precipitable anion. As soon as the solubility limit is reached, iron carbonate precipitates and the whole reaction can thus be written as:

2 3 3 2 Fe H CO FeCO H    (reaction 2)
At the equilibrium and if there is no renewal of the electrolyte, the solution is then buffered by FeCO 3 , with a stable saturated pH (pH sat ). Now let us consider the geometrical configuration of the annulus. The main parameter is the high degree of confinement, i.e. a large surface of exposed steel with a small volume of electrolyte. Considering the worst situation, one can also make the hypothesis that there is no limitation on acid gas dissolution, nor diffusion limitations in the thin electrolyte layer. Then, as soon as corrosion starts through reaction 1, and since it happens on a large steel surface and a small volume of electrolyte, H + ions are consumed while Fe 2+ and decrease of corrosion rate. For example, one can consider a system composed of pure water under 1 bar CO 2 at ambient temperature. Application of pH and water chemistry software shows that the initial in-situ pH is 3.9, while it reaches 5.3 at saturation in iron carbonate, corresponding to 78 ppm Fe 2+ . And with a confinement ratio of 1 mL/cm² and a reasonable initial corrosion rate of 0.5 mm/year, one easily determines that saturation is reached after less than a few hours, leading to start of precipitation. However, iron carbonate precipitation is a rather slow reaction, so that the precipitable products of the corrosion reaction Fe 2+ and 3 HCO  are allowed to accumulate above the solubility limit, all the more so as the confinement is important. Consequently, pH increases above its saturated value (super-saturated pH, pH ssat ). The corrosion subsequently decreases, until a kinetic equilibrium is reached where all new corrosion products immediately precipitate. This scheme also holds for H 2 S, with a global reaction written as:

22 Fe H S FeS H    (reaction 3)
and with an intermediate electrochemical reaction producing the precipitable ions (Fe 2+ and HS -) along with the buffer of the weak acid. However, the solubility of iron sulfides is much lower than that of FeCO 3 , and the kinetics of the precipitation reaction is also thought to be faster so that the super-saturation effect is expected to have a lower amplitude than in the case of CO 2 , provided that the corrosion rate is in the same range.

Based upon these principles, a kinetic model for CO 2 corrosion and pH prediction was developed, allowing to calculate the super-saturated pH and corrosion rate for various V/S and P CO2 [START_REF] Remita | A kinetic model for CO 2 corrosion in confined aqueous environments[END_REF][START_REF] Remita | Experimental and theoretical investigation of the uniform corrosion in the annulus of offshore flexible pipelines[END_REF][START_REF] Kittel | Corrosive environment in the annulus of flexible pipes: pH measurements in confined conditions and under high pressure[END_REF].

Compared to the model presented in 2013 [START_REF] Kittel | Corrosive environment in the annulus of flexible pipes: pH measurements in confined conditions and under high pressure[END_REF], improvements were made to describe the impact of precipitation on the metal surface. For instance for CO 2 , the evolution with time of the total amount of precipitated FeCO 3 is calculated ([FeCO 3 ]), and an empirical equation is then used to calculate the corresponding residual active metal surface (Surf) (Equation 1).

Surf (%) = 100 -α x [FeCO 3 ] (Equation 1)

In this equation, α is an empirical parameter, adjusted to experimental results. As a consequence, the active surface area decreases as iron precipitates, generating a slight decrease of pH. This model is now able to fully represent experimental pH transients. It is used in this paper to analyze experimental pH measurements in confined test cells, with P CO2 from 1 bar to 45 bar.

Experimental verification

Experimental devices allowing to measure pH in confined and pressurized environment were used (Figure 2). In these test cells, the pH electrode is surrounded by steel coupons, with a V/S ratio of 0.3 mL/cm². During the test, saturation of acid gases is ensured by a continuous bubbling in the solution, and gas flow rate is continuously monitored. Internal pressure is maintained by a pressure control valve, and is also monitored during all the test. A condenser placed before the pressure valve avoids liquid losses. The range of operating conditions covers 1 -100 bara total pressure, and 4 -100 °C. Gas mixtures containing N 2 , CO 2 and H 2 S can be used. The evolution of in-situ pH with time is illustrated on Figure 3 for different P CO2 from 1 bar to 45 bar. The initial rise of pH is associated with the production of alkalinity due to reaction [START_REF] Taravel-Condat | MOLDI TM : a fluid permeation model to calculate the annulus composition in flexible pipes: validation with medium scale tests, full scale tests and field cases[END_REF]. It corresponds to a parallel increase of Fe 2+ and HCO 3 -concentrations. After a few days, pH value reaches a maximum, and starts to decrease. At this stage, the system is governed by kinetic equilibrium between iron dissolution and iron carbonate precipitation. Since the precipitation of FeCO 3 is a slow reaction, this kinetic equilibrium corresponds to pH values far above thermodynamic saturation of the solution with iron carbonate. For instance, in a 35 g/L NaCl solution at 1 bar CO 2 , saturated pH calculated with Cormed2™ is 4.5, while the experimental value at the maximum is close to 5.8. Previous version of the model presented in 2013 [START_REF] Kittel | Corrosive environment in the annulus of flexible pipes: pH measurements in confined conditions and under high pressure[END_REF], was already able to predict the pH transient up to this maximum value. At that time, the model could not represent the long term pH evolution. It was mentioned however that the slow long term decrease of pH was associated with the build-up of iron carbonate layer at the metal surface, resulting in a decrease of active corroding surface, hence lowering the average corrosion rate. Qualitatively, it automatically induces a decrease of pH. In order to capture this effect, the model was then modified with a function relating the evolution of active surface with the total amount of precipitated iron carbonate (Equation 1). The model was calibrated and then verified with experimental data, using a database of more than 20 long term in situ pH experiments up to 45 bara CO 2 . In all cases, the deviation between the model and experimental results was less than 0.15 pH units.

As can be seen on Figure 3, the main experimental trends are correctly fitted, especially the long term stationary pH. It must be noted that this long term equilibrium pH ssat corresponds always to a high degree of super-saturation, with + 0.5 pH units above saturated values.

In addition, the model also allows to calculate the evolution of corrosion rates with time. For the experiments of Figure 3, long term corrosion rates below 10 µm/year are predicted, in excellent agreement with the feedback from long term field exposures. It is particularly remarkable that even with such low corrosion rates, the high level of confinement induces super-saturation effects, with equilibrium pH values exceeding the saturated pH by several tenths of units.

The current criteria for steel grade selection and design of flexible pipelines rely on similar long term experiments, i.e. pH ssat experimentally measured. This pH evaluation method still presents a reasonable safety factor, since the real average confinement ratio in flexible pipes is ten times lower than in our experiments, which should increase the long term super-saturated pH equilibrium. For some specific areas where the local confinement is lower, it is still in the same order as in our experimental devices, which thus represents a reasonable and safe envelope for real operating conditions in the annulus.

Conclusions and perspectives

The annulus of flexible pipelines is a complex corrosive environment. It depends on acid gases and water diffusion through polymer sheaths, kinetic equilibrium between corrosion of steel surfaces, iron salts precipitation and the subsequent alkalinisation of the electrolyte.

In situ pH is one of the main parameters traditionally used to evaluate the potential corrosivity of oil and gas environments. pH measurements were therefore performed in specific test cells with a confinement ratio of 0.3 mL/cm² between the volume of electrolyte and the exposed steel surface. Total pressure up to more than 100 bar is now experimentally accessible, with test gases containing pure CO 2 or CO 2 / H 2 S mix.

In this paper, pH transients in CO 2 environments at various pressure from 1 bar to 45 bar and at ambient temperature are presented. pH increases rapidly after immersion, then goes through a maximum after a few days, and finally decreases slowly until a plateau is reached after several weeks. The final pH values still exceed saturated pH by several tenths of pH units. This long term equilibrium is reached after more than three weeks in confined test cell, and therefore longer exposure periods must be adopted to determine relevant pH ssat for real service conditions. At room temperature, a minimum test duration of two months is often needed.

A predictive model, derived from the 2013 version, is now able to represent surface evolution associated with iron carbonate precipitation. pH evolution with time can be calculated. A good fit with experimental data is obtained for conditions up to 45 bara of CO 2 . The model also predicts final corrosion rates below 10 µm/year for the tests between 1 and 45 bar CO 2 and a confinement of 0.3 mL/cm².

Further work is ongoing to take into account the effects of H 2 S and temperature into the model.

Figure 1 :

 1 Figure 1: Example of a flexible pipe structure

Figure 2 :

 2 Experimental devices for pH measurements in confined environments at pressure up to 10 bara (a) and up to 100 bara (b)

Figure 3 :

 3 Figure 3: Long term evolution of pH measured in a confined test cell (V/S = 0.3 mL/cm²) with high strength steel wires exposed to 3.5 % NaCl solution at ambient temperature, under 1 to 45 bara CO 2 . Comparison with calculated pH transients with different models.

HCO  concentrations increase extremely fast, with subsequent rise of pH and