Pressure test witnessing beyond a graduate's competence
You are a graduate engineer with 22 months' experience on a water supply project. The resident engineer is on leave. The contractor has completed a 450 mm diameter ductile iron rising main and asks you to witness the hydrostatic pressure test. The specification requires 1.5 times the working pressure of 1.0 MPa for one hour, with make-up water measured. The contractor's test gauge has a range of 0–4 MPa and a calibration certificate that expired three months ago; the contractor says the gauge was 'checked against a master' last week but has no record. The test section is 800 m long and passes within 5 m of a school boundary; the contractor proposes to test at 09:00 with children present. A pressure relief valve is fitted at the low end but the high point has no vent. The contractor's supervisor asks you to sign the test sheet after the test so the works can be handed over.
1. Identify the technical and safety issues and decide whether you would witness the test as proposed.
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Technical and safety issues. The gauge calibration is expired, and there is no record of the 'check against a master'; a verbal assurance is not acceptable for a test that will be used for handover. The test pressure should be 1.5 × 1.0 MPa = 1.5 MPa. A 0–4 MPa gauge is within a reasonable range (the test is at 37.5% of full scale), but it must be calibrated and preferably duplicated. The high point has no vent: air can be trapped, causing erratic pressure, slow pressure loss and a stored-energy hazard if a fitting fails. The test section is 800 m long and passes within 5 m of a school; testing with children present is not acceptable without a risk assessment, exclusion zone, notification and control of access. Thrust restraints and anchors must be checked for the test pressure, and the pressure relief valve must be set and tested. I would not witness the test as proposed. I would tell the contractor what must change and inform the resident engineer.
2. What conditions must be met before you would witness the test, and what records should be produced?
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Conditions before witnessing. The contractor must provide: valid calibration certificates for the test gauge and a second gauge; a test procedure including filling, soaking, venting at the high point, pressurisation in stages, hold period and make-up water measurement; confirmation that thrust blocks, restraints and anchors are designed for 1.5 MPa; a pressure relief valve set at a safe limit; a risk assessment and exclusion zone; and notification and agreement with the school, with testing outside school hours or during holidays. The line should be filled slowly, vented at the high point, and allowed to stabilise. During the test, record pressure, make-up water, temperature and time; inspect for leakage at joints and anchors. I would witness only what I am competent to witness and record. The test sheet should be signed by the contractor's competent person and the resident engineer or a delegated chartered engineer, not by me as a graduate acting beyond my competence.
3. How should you handle the request to sign the test sheet, and what would you record in your logbook?
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Professional judgement. My 22 months' experience does not make me the authority to accept the test on behalf of the client. I can witness and record under supervision, but I should not sign the handover test sheet as if I were the resident engineer. I would contact the resident engineer or another delegated engineer, explain the non-compliances, and ask for instructions. If the contractor pressures me to sign, I would decline and put the reason in writing. In my logbook I would record the date, the plant and test section, the calibration status, the safety issues, the advice I gave and the response. This is also a training opportunity: I would ask the resident engineer to brief me on the specification and acceptance criteria before the next test. The key professional point is to recognise the limit of my competence and to escalate rather than sign to keep the programme moving.