Overview
Relief devices are a special class of equipment that protect other equipment from overpressure scenarios. AllAssets has two approaches to create a plan for inspection and maintenance activities; risk-based or reliability-based. This section explains how to develop risk-based plans using RBI models.
RBI models for relief devices determine the probability of failure on demand based on two damage mechanisms (corrosion and fouling) that can result in failure to open. The consequence of failure is determined by obtaining the worst consequence of failure from protected equipment which requires a special hierarchy.
Creating Hierarchy for Relief Devices
There are three parts to the relief device hierarchy; Relief Device Location, Physical Relief Device, and Protected Equipment.
- Relief Device Location represents the tag displayed on the P&ID such as PSV-1075. In AllAssets the Relief Device Location will be a hierarchy item type Location where “Relief Device Location” is true or checked. The parent of a Relief Device Location can be any Location within the hierarchy.
- Physical Relief Device represents the physical relief device. Customers use a variety of ways to identify the physical device such as the serial number, asset number assigned by the EAM/ERP system or generic name such as PSV-101. All of these naming conventions are possible in AllAssets. but we recommend a unique identifier such as serial number. Since some customers use a Location to represent physical equipment instead of an Asset, Physical Relief Device can be set up in AllAssets as either a hierarchy item type Location or Asset where “Physical Relief Device” is true or checked. The parent of the Physical Relief Device must be the associated Relief Device Location.
- Protected Equipment represents the equipment protected by the Relief Device Location from overpressure scenarios such as pressure vessels, exchangers and piping circuits.
Since Protected Equipment items already exist in AllAssets, you just need to establish a relationship between the Relief Device Location and the one or many Protected Equipment. This is done in the Manage Equipment Hierarchy application from the Relief Device Location by clicking the action button “Protected Equipment”. A new screen appears that displays a table of Protected Equipment. Click “+Add Equipment” to select an existing item that will be protected by this Relief Device Location. If an equipment item is protected by more than one relief device, then go to each Relief Device Location to establish the relationship. When changes occur, the list of protected equipment can be edited, and the system keeps track of equipment previously protected by each Relief Device Location.
The relationship between Relief Device Location and Protected Equipment is also shown on the Protected Equipment. Navigate to one of the Protected Equipment items to see the Protected By table that shows all Relief Device Locations currently related to this equipment item as well as the table Previously Protected By.
Linking Models for Relief Devices
There are three RBI models for relief devices; pressure relief valve, vacuum vent and rupture disk. The pressure relief valve RBI model has an option to include a rupture disk in the analysis when an equipment item is protected by both types of devices. The rupture disk model is only used when a rupture disk is the only device providing overpressure protection.
RBI models for relief devices are linked to Relief Device Locations.
Running Criticality for Relief Devices
Since the consequence of failure is obtained from one of the Protected Equipment there is a certain sequence that must be followed to run criticality for relief devices. Save a driving scenario for all Protected Equipment before running Criticality for the Relief Device Location. The relief device RBI model will retrieve the Protected Equipment ID and consequence of failure from the Protected Equipment with the worst consequence of failure. If more than one equipment item has the same worst consequence, then the first one found by the system will be retrieved.
Creating a Mitigation Plan for Relief Devices
Go to the Mitigations application to create a risk-based mitigation plan for the Relief Device Location in the same way as other equipment types.