purchase_order_line_sequence/view/purchase_view.xml

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

        <!-- purchase order line tree -->
        <record id="purchase_order_line_sequence_tree" model="ir.ui.view">
            <field name="name">purchase.order.line.sequence.tree</field>
            <field name="model">purchase.order.line</field>
            <field name="inherit_id" ref="purchase.purchase_order_line_tree"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='order_id']" position="after">
                    <field name="sequence"/>
                </xpath>
            </field>
        </record>

        <!-- purchase order line tree showed in the purchase requisition form -->
        <record id="purchase_order_line_sequence_tree_tender" model="ir.ui.view">
            <field name="name">purchase.order.line.sequence.tree.tender</field>
            <field name="model">purchase.order.line</field>
            <field name="inherit_id" ref="purchase_requisition.purchase_order_line_tree_tender"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='name']" position="before">
                    <field name="sequence"/>
                </xpath>
            </field>
        </record>

        <!-- purchase order line form -->
        <record id="purchase_order_line_sequence_form" model="ir.ui.view">
            <field name="name">purchase.order.line.sequence.form</field>
            <field name="model">purchase.order.line</field>
            <field name="inherit_id" ref="purchase.purchase_order_line_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='name']" position="after">
                    <field name="sequence"/>
                </xpath>
            </field>
        </record>


        <!-- purchase order line form no create -->
        <record id="purchase_order_line_sequence_form2" model="ir.ui.view">
            <field name="name">purchase.order.line.sequence.form2</field>
            <field name="model">purchase.order.line</field>
            <field name="inherit_id" ref="purchase.purchase_order_line_form2"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='name']" position="after">
                    <field name="sequence"/>
                </xpath>
            </field>
        </record>

        <!-- purchase order line tree embeded in the purchase order -->
        <record id="purchase_order_sequence_form" model="ir.ui.view">
            <field name="name">purchase.order.sequence.form</field>
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.purchase_order_form"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='order_line']/tree//field[@name='product_id']" position="before">
                    <field name="sequence"/>
                </xpath>
                <xpath expr="//field[@name='order_line']" position="attributes">
                    <attribute name="context">{'order_line': order_line}</attribute>
                </xpath>
            </field>
        </record>

    </data>
</openerp>