Working with chemicals can pose a host of dangers. Those in the process industries must take every step possible to protect employees and others from hazardous conditions.
The U.S. Occupational Safety and Health Administration (OSHA) issues and enforces standards designed to increase worker safety, including for facilities that process chemicals. Other countries have similar programs, and the United Nations oversees the Globally Harmonized System for Hazard Communication in an effort to protect workers internationally. One mandated OSHA standard is the Process Safety Management (PSM) of Highly Hazardous Chemicals (standard, 29 CFR1910.119) to prevent the unwanted release of hazardous chemicals that could cause serious exposure.
The PSM program requires a systematic approach for evaluating process design, process technology, operations, maintenance and emergency preparedness plans. The program also mandates the implementation of an employee-training program.
A properly conducted PSM is a team effort in which the company and employees work together to develop the necessary expertise, experience, judgment and proactive initiative to implement the plan.
Since many of the hazardous chemicals covered under a PSM are in either a liquid or gaseous state, possessing a clear picture of all the elements in a piping system is a key point in determining the plan’s success.
The requirements of the PSM plan state that the employer provide written instructions detailing the methods in which they will design, operate and maintain the plant to minimize the inadvertent release of highly hazardous chemicals. This article describes how commercially available fluid piping software can be an integral tool in developing and implementing a successful PSM program.
Piping System Model
Piping software can create a piping system model that contains a wealth of information and detailed specifics about each element in the piping system. The information in the model is used by the software’s calculation engine to simulate the operation of the total system. The simulation calculates the flow rates and pressures showing the interaction of the tanks, vessels, pumps, components and controls. It provides a clear picture of how the process piping system operates under any expected condition.
To maximize the value of the piping system model as a simulation tool, the following features are included.
A piping schematic is the primary interface used by the piping system model. The piping schematic has the look and feel of a process flow diagram showing the major items in the system along with of the interconnecting pipelines (See Image 1). Each item on the schematic displays a unique plant equipment identifier, and a variety of symbol shapes are available to choose from, increasing the presentation value of the piping schematic.
Each item in the piping system contains thorough information that can be viewed from within the software such as pipe material, the number and types of valves and fittings in the pipelines, along with the process fluid and its properties. Tank information includes the dimensions, volume and capacity for a given level, along with the tank penetrations and their height.
Detailed information is available for equipment supplied by pump and control valve manufacturers. For example, the pump information includes the manufacturer’s make, model, test speed, impeller diameter, allowable operating flow rate, minimum allowable flow rate and net positive suction head (NPSH) requirements. This information is supplied in electronic form by the pump manufacturers and can be viewed by the program as a pump curve.
The simulation engine uses the detailed information to calculate the flow rate and pressures through the system and shows how each piece of equipment operates in the system. Comprehensive results show where each pump is running on its pump curve, along with the differential pressures across the control valves and its expected valve position.
The simulation engine can evaluate the operation of the total system under any expected operating condition. This is accomplished by creating various operating scenarios by opening and closing pipelines, turning pumps on or off, adjusting the set point for control valves, along with changing the level and pressure in tanks and vessels. The operating scenarios can be saved allowing the user to quickly review the results.
The models also contain hypertext links to electronic documents. By inserting links to electronic design documents either on the owner’s network, or to a website, the user has immediate access to design documents, drawings, specifications, codes, standards and operating procedures.
Links can be created to other mission critical programs such as maintenance management or document management software. The model can display the maintenance history for a specific pump by clicking on the pump symbol on the piping schematic. Immediate access to data from a variety of sources greatly increases the situational awareness of the system and its operation.
The fourth element of the model is the ability to provide a clear picture of what is happening in the process system. This clear picture includes a view of how the system operates, along with the ability to drill down in the system to see how each specific item is operating. The primary way of communicating system operation is through the piping schematic. Calculated results are displayed on the drawing next to the item. The use of color indicates when an item is not operating within a specified range. For example, if a pump is running outside the manufacturer’s recommended range of operation, the pump turns red on the piping schematic.
Further details are available by pointing to an item and viewing additional information in the fly-by viewer. When pointing to a pump, you can see the pump’s head, flow rate and NPSH available. If the equipment is running outside a manufacturer or user’s limit, that information is displayed as well. Results can be viewed in tabular form, allowing the user to monitor how like items behave.
Next, we’ll discuss how the piping system model can be used be as an integral part of the PSM of Highly Hazardous Chemicals plan for process piping systems.