oca-technical/odoo-bringout-oca-maintenance-maintenance_purchase/maintenance_purchase/views/maintenance_equipment.xml

<?xml version="1.0" encoding="utf-8" ?>
<!-- Copyright 2022 CreuBlanca
     License AGPL-3.0 or later (https://www.gnu.org/licenses/agpl). -->
<odoo>
    <record id="hr_equipment_view_form" model="ir.ui.view">
        <field name="name">equipment.form</field>
        <field name="model">maintenance.equipment</field>
        <field name="inherit_id" ref="maintenance.hr_equipment_view_form" />
        <field name="arch" type="xml">
            <xpath expr="//field[@name='serial_no']" position="after">
                <field name="purchase_id" />
            </xpath>
        </field>
    </record>

</odoo>