Personnel-Protection Surface Temperature on a Walkway Steam Line
A 6 in, 450°F steam line crosses an operator walkway at 6 ft 8 in above the floor. The line has 2 in mineral wool with aluminum jacket. A contact-temperature survey finds 128°F on the flat jacket, 146°F at a seam, and 151°F on a flange cover. The plant criterion is 140°F maximum for surfaces that can be touched for 5 seconds, based on ASTM C1055. The area is marked but not barricaded; operators sometimes reach over the line to open a valve. The insulation was installed two years ago and shows no staining, but the seam bands are loose and one flange cover is uninsulated. Maintenance wants to place Do Not Touch signs rather than modify insulation because the line is scheduled for replacement in six months. Production will continue through the replacement.
1. Determine which locations fail the personnel-protection criterion and whether signs are an acceptable substitute for insulation or guarding.
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The flat jacket at 128°F passes the 140°F criterion, but the seam at 146°F and the flange cover at 151°F fail. Signs alone are not an acceptable substitute for an engineering control on an accessible walkway, especially where operators reach over the line. The correct approach is to repair the loose bands, reinsulate the seam, and install an insulated flange cover or guard so all touchable surfaces are below 140°F. Until then, barricade the area and use signs as an interim measure, not the final fix.
2. Recommend a repair that addresses the hot seams and flange while the line remains in service.
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Re-tension or replace the seam bands and add insulation at the seam if the gap is open. For the flange, install a removable flange cover with at least 2 in of mineral wool or a preformed insert and a stainless jacket; seal it so moisture cannot enter. If the flange must remain accessible, use a guard that keeps the surface below 140°F. After repair, measure the seam and flange with a contact thermometer at several points. Do not rely on the flat jacket reading.
3. How would you verify the repair without relying on a single spot measurement?
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Use a grid of contact measurements on each touchable surface, including seams, flanges, valves, and supports, not just one spot. Measure at steady operating temperature and record ambient conditions. Use an IR camera to find the worst spots, then confirm with a contact probe. Acceptance is that the highest touchable surface is at or below 140°F for the 5-second criterion. Document the readings and retain them until the line is replaced.