Piping and instrument diagrams: Part 2 Causes and management of change
It is difficult to categorise or group the many reasons for routine or late changes to a P&ID. Some causes are listed here.
Bharat (Bob) Shah
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An unreasonable schedule. Contractor management will commit to unrealistic schedules to win a project. Sometimes, schedules are based on awarding the contract by a certain date, and then the award is delayed but the dated schedules remain unchanged. The engineers on the ground are stuck with that shorter schedule.
One of the most important items on the entire project schedule is the completion of the P&ID. The work of all engineering disciplines and their group’s deliverable schedules and staffing plan are based on this date. If P&IDs are delayed, job-hours are burned; if the delay is significant, personnel brought to the project must be de-staffed and the entire project schedule slips. Process engineering will need to provide justification for late changes.
P&ID development takes time. More people can be put to work on them, but this introduces the law of diminishing returns. Poor scheduling. Schedules for an engineering, procurement and construction (EPC) project will contain thousands of items. P&ID schedules are watched more closely than anything else because the rest of the project work depends on them. One problem is that for large projects, several hundred P&IDs will have conflicting schedules showing start dates, internal reviews, client reviews, hazard and operability (HAZOP) studies, approved for design (AFD) and approved for construction (AFC) issues, etc. All of these P&IDs cannot have the same schedule; they must be divided into several groups of units or systems and each must have separate and staggered schedules.
Identical schedules with different contractors. When a large project is divided into two or more teams executed by different contractors in different parts of the world, it is inevitable that the teams will end up with different completion dates. When one team finishes its work, the work of the other team may still be evolving. Late developments by one team can have a big impact on the other team, resulting in P&ID changes.
Too few engineers. Engineers can get overloaded handling too many systems and too many P&IDs. P&ID reviews with clients, HAZOP reviews, etc., occupy a large number of job hours. Without careful planning, adequate staff to carry out non-HAZOP engineering becomes an issue. Typically, staffing should allow for four P&IDs per day for client review and four P&IDs per day for HAZOP review.
Inadequate or inexperienced supervision. Without adequate supervision, work quality suffers. Systems, such as utilities and offsites, do not get the deserved attention and suffer the most. In fact, because these are the open-art technologies, everyone comes up with their own ideas.
If the supervisor does not have the experience of having worked before on such systems, design will suffer from deficiencies. Cases have been noted where neither the working engineer nor the supervisor had the correct experience to execute the work. Omissions and errors were found—later rather than sooner—and fixing them forced others to redo their work and, of course, led to schedule delay.
Inadequate definition of work. If the work scope is poorly defined, changes will continue to happen over an extended period of time. A well-defined and detailed process design basis and scope of work can reduce this risk. Once again, utilities and offsite units, which are open-art technologies, suffer from such needed attention. In some cases, the design basis is copied from a type of facility that may not directly apply to other facilities. An experienced engineer will recognise this and try to convince the owner to change it.
Project philosophies. In an ideal scenario, project philosophies are established at the beginning of front-end engineering design (FEED); in reality, project philosophies continue to evolve during FEED and often change during the EPC phase. Once again, various parties are involved in writing these philosophies and gaps, conflicts and omissions can persist among the philosophies and/or between them and other project documents. Like with the design basis, a philosophy may also be a direct copy from a facility that is completely different than the current project and therefore may not be completely suitable. Additionally, a new party from the owner’s side may be assigned to the project and rewrite a philosophy. Various project philosophies that affect equipment and P&ID work are listed here:
• Relief, flaring, venting and blowdown
• Process control
• Operation and maintenance
• Design margin
• Material selection and corrosion management
• Emergency shutdown
• Process isolation
• Line sizing
• Metering philosophy
• Commissioning, startup and handover
• Overpressure protection
• Drainage philosophy
• Safety philosophy
• Fire and explosion.
Gaps and conflicts. No matter the effort, gaps and conflicts will exist in various project documents. Project-defining and scoping documents include an environmental impact statement (environmental assessment statement), project design basis, process design basis, FEED or EPC scope of work, FEED or EPC contracts, and engineering scope of work, among others. For FEED, there may be preliminary PFDs; during EPC, there will be FEED PFDs and P&IDs that typically are the basis of project cost of +/– 10% accuracy.
It is important to remember that multiple parties have produced these documents and may not have consulted with each other or seen each other’s documents. As end of FEED approaches, significant changes will be implemented in some FEED drawings; however, not all FEED drawings can be updated in time. If such last-minute changes are not separately documented, conflicts will show up during EPC.
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