orden_servicio/data/sequence_servicio.xml

<?xml version="1.0" encoding="utf-8"?>
<openerp>
    <data noupdate="1">

        <!-- Sequences for repair.workorder -->
        <record id="seq_type_servicio" model="ir.sequence.type">
            <field name="name">Orden de servicio</field>
            <field name="code">orden.servicio</field>
        </record>

        <record id="seq_servicio_order" model="ir.sequence">
            <field name="name">Orden de servicio</field>
            <field name="code">orden.servicio</field>
            <field name="prefix">SER</field>
            <field name="padding">3</field>
            <field name="company_id" eval="False"/>
        </record>

    </data>
</openerp>