Modeling an Uncertain Permit and a Cure Period in a Pipeline Tie-In
A 620-activity pipeline tie-in schedule includes 'Obtain rail-crossing permit.' No committed approval date exists; the rail authority states only 'within 60 days.' The scheduler modeled it as a start-to-start relationship with a 60-day lag from 'Submit permit application' and added a start-no-earlier-than constraint. Field work uses a 7-day calendar; engineering uses a 5-day calendar. The hydrotest follows weld completion and requires 48 hours of cure, modeled as a lag on the weld-to-hydrotest finish-to-start relationship. The schedule shows hydrotest with 12 days of total float and no successor driving project completion. The baseline is due in three weeks.
1. Evaluate how the permit is modeled. What would you change?
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The model is not wrong in intent but is wrong as a control. A 60-day start-to-start lag treats a best-case regulatory statement as a fixed duration, is not progressable, and conceals slippage - if the authority takes 90 days, the schedule will not show it until the constraint is violated. Replace the lag with a discrete activity, 'Rail authority review and approval,' with a duration supported by historical submittals or the authority's published service standard; link 'Submit application' to it finish-to-start. If the contract or permit truly fixes an approval date, keep a start-no-earlier-than constraint on the approval activity, document it in the schedule basis, and use it to protect the contractual milestone - not as a substitute for logic. Add a risk buffer or a separate contingency activity if the approval is a major uncertainty.
2. How should the 48-hour cure and the calendar mismatch be handled?
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Model the 48-hour cure as an activity of two days on a 24-hour, 7-day calendar, or as a lag with an assigned 24-hour calendar. Prefer an activity: it can be statused, inspected, and audited, and a lag with the wrong calendar silently converts 48 hours into four working days. Calendar mismatch matters because total float computed on a 5-day engineering calendar and a 7-day field calendar is not directly comparable; a '12-day' float may be 8 working days in one chain. Normalize float reporting to calendar days, or align calendars where activities interact, and record the rule in the schedule basis. Check that the hydrotest activity's calendar matches field work.
3. What schedule quality checks should be run before baseline?
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Before baseline, run a logic check for open ends (activities without predecessors or successors), negative or excessive lags, hard constraints, and unrealistic durations. Verify calendar assignments on every activity and on lags. Trace the longest path to the completion milestone to confirm it is continuous and sensible. Check that the permit and cure activities are represented correctly and appear on the driving path if they truly drive. Confirm resource and cost loading if required, and validate that all contractual milestones are represented. Review the schedule basis memorandum, and have the superintendent walk the driving path. A baseline with a 60-day lag and a start-no-earlier-than constraint should be flagged before approval, not after the first update.