Get orders shipping items details in WooCommerce 3

How can I get the order shipping method id.?

For example 'flate_rate'.

Since WooCommerce 3 it is now complicated as everything has changed.

I have tried it with $order->get_data() in a foreach loop but the data is protected.

If you want to get the Order Items Shipping data, you need first to get them in a foreach loop (for 'shipping' item type) and to use WC_Order_Item_Shipping methods to access data

$order_id = 528; // For example

// An instance of 
$order = wc_get_order($order_id);

// Iterating through order shipping items
foreach( $order->get_items( 'shipping' ) as $item_id => $item ){
    $order_item_name             = $item->get_name();
    $order_item_type             = $item->get_type();
    $shipping_method_title       = $item->get_method_title();
    $shipping_method_id          = $item->get_method_id(); // The method ID
    $shipping_method_instance_id = $item->get_instance_id(); // The instance ID
    $shipping_method_total       = $item->get_total();
    $shipping_method_total_tax   = $item->get_total_tax();
    $shipping_method_taxes       = $item->get_taxes();
}

You can also get an array of this (unprotected and accessible) data using the WC_Data method get_data() inside this foreach loop:

$order_id = 528; // For example

// An instance of 
$order = wc_get_order($order_id);

// Iterating through order shipping items
foreach( $order->get_items( 'shipping' ) as $item_id => $item ){
    // Get the data in an unprotected array
    $item_data = $item->get_data();

    $shipping_data_id           = $item_data['id'];
    $shipping_data_order_id     = $item_data['order_id'];
    $shipping_data_name         = $item_data['name'];
    $shipping_data_method_title = $item_data['method_title'];
    $shipping_data_method_id    = $item_data['method_id'];
    $shipping_data_instance_id  = $item_data['instance_id'];
    $shipping_data_total        = $item_data['total'];
    $shipping_data_total_tax    = $item_data['total_tax'];
    $shipping_data_taxes        = $item_data['taxes'];
}

To finish you can use the following WC_Abstract_Order methods related to "Shipping data", like in this examples:

// Get an instance of the WC_Order object
$order = wc_get_order(522);

// Return an array of shipping costs within this order.
$order->get_shipping_methods(); // same thing than $order->get_items('shipping')

// Conditional function based on the Order shipping method 
if( $order->has_shipping_method('flat_rate') ) { 

    // Output formatted shipping method title.
    echo '<p>Shipping method name: '. $order->get_shipping_method()) .'</p>';