An Unapproved Clamp, a Lost History, and a Permanent Repair Plan

What is wrong. A mechanical clamp is a temporary repair, and a temporary repair is acceptable only when it is authorized, engineered, examined and time-limited. Here nobody approved it, no cause was established, no NDE was done on the surrounding wall, and the work order says 'complete' - so the record actively misleads the next person who reads it.

What must happen now:

• Notify the owner-user and engineering. Until reviewed, the clamp is an unapproved repair on a Class 1 flammable line, not a completed work item.
• Establish the cause. A pinhole at 6 o'clock on a naphtha line is usually internal corrosion from water bottoms, which means it is a symptom of a broader condition, and the clamp is currently covering the thinnest point on the line.
• Examine the wall: UT on a 360 degree grid around and adjacent to the clamp, plus the neighbouring low points and the upstream and downstream runs. If any reading is at or below t_min, the line comes out of service for repair or rerate.
• Document: date, location, fluid and operating conditions, the defect and its cause, clamp type and material, NDE results, approvals and signatures, the stated temporary service life, and a scheduled permanent repair date. A clamp that has sat for 14 months with no permanent repair date is itself a finding and a program gap, not just an operator error.
• The clamp may remain only as a documented, time-limited measure with the permanent repair scheduled. It is not a permanent repair and cannot be recorded as one.

Four readings taken the same day are one survey, not a history. They establish present thickness and nothing else. You cannot compute a corrosion rate from them.

• Use the survey as a new baseline and say so explicitly in the record: dated, with the method, instrument, coverage and CML locations. The four values (0.210-0.218 in.) are tightly grouped, which argues against a localized outlier, but four CMLs on a line in service since 1985 is not adequate coverage. Add TMLs at elbows, the low point, supports, downstream of any injection, and at deadlegs.
• Do not amortize the loss over 39 years. 0.237 to about 0.213 in. across 39 years works out to roughly 0.0006 in./yr, which is meaningless if the loss is recent or localized and dangerously optimistic if it is not. Assume an unknown rate.
• Set a short interval until the second survey produces a real rate - typically a year or less. The class maximum is irrelevant here because it will be far longer than the data supports.
• Mine other sources for evidence: maintenance work orders (the clamp leak is one), leak history, turnaround reports, isometrics, vendor and construction records, operator knowledge of water slugs or upsets. Any leak history is direct evidence of active corrosion and should drive the interval more than any calculation.
• Document the state. Record 'baseline established [date]; rate unknown; conservative rate assumed for planning; interval set at X months' and have it approved as a temporary basis rather than presented as a rating.
• Missing history is a reason to inspect more, not less, particularly on a Class 1 line. Consider weld NDE and a hydrotest if nothing in the file gives confidence in the original construction.

Replacing 12 ft with Sch 80 is a repair. It restores the line and does not change design conditions. 'Thicker is better' is not a substitute for thought, though: it needs a design check that the heavier spool does not create a problem (deadweight, flexibility, support spacing), and it must be recorded as an as-built change so the next inspector does not read 0.237 in. as the nominal wall in that span. If the heavier wall is being used to justify a higher MAWP, it has become a rerate and needs the full rerating basis and approval - those are different documents.

Adding the 1 in. drain is an alteration. It is a new connection with design implications: branch reinforcement, thermal and flexibility effects, a new deadleg and a new local water-draw point, and possibly a change to the venting/draining philosophy. It requires an engineering design to B31.3, inspector approval, and, if any design condition changes, a rerating calculation and record. The drain also becomes a new inspection location in its own right.

Records required for both:

• repair and alteration scope with the supporting design calculations;
• WPS/PQRs and welder identification;
• NDE reports, including radiography of the closure weld if a hydrotest is waived - and the waiver itself, with its basis and the approver, documented;
• the pressure test record, or the documented technical basis for the alternative;
• PWHT records if the material and thickness require it;
• as-built isometrics and line list updates showing the Sch 80 span and the new drain;
• an update to the inspection plan and CML list adding the drain and the replaced span.

The inspector signs off on the record before the line returns to service; the documentation goes into the permanent file for the line, not into a work order that will be closed and forgotten.