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

        <record id="purchase_order_form" model="ir.ui.view">
            <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='name']" position="after">
                    <field name="prodlot_id"/>
                </xpath>
            </field>
        </record>

        <record id="purchase_order_line_form" model="ir.ui.view">
            <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='product_id']" position="after">
                    <field name="prodlot_id"/>
                </xpath>
            </field>
        </record>

    </data>
</openerp>

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

        <record id="purchase_order_form" model="ir.ui.view">
            <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='name']" position="after">
                    <field name="prodlot_id"/>
                </xpath>
            </field>
        </record>

        <record id="purchase_order_line_form" model="ir.ui.view">
            <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='product_id']" position="after">
                    <field name="prodlot_id"/>
                </xpath>
            </field>
        </record>

        <record id="view_purchase_order_filter" model="ir.ui.view">
            <field name="model">purchase.order</field>
            <field name="inherit_id" ref="purchase.view_purchase_order_filter"/>
            <field name="arch" type="xml">
                <xpath expr="//field[@name='partner_id']" position="after">
                    <field name="order_line" string="Serial Number" filter_domain="[('order_line.prodlot_id.name','ilike',self)]"/>
                </xpath>
            </field>
        </record>

    </data>
</openerp>

Add a search field on Serial Number of Purchase Order Lines in Purchase Order view
[IMP] Add a search field on Serial Number of Purchase Order Lines in Purchase Order view
