Unless otherwise specified, valves and flanges on cold services insulation should be installed

• A. After insulation is complete
• B. During jacket application
• C. After mastic cap is installed
• D. Before mastic cap is installed

Answer: (D)

In cold service insulation, fittings like valves and flanges must be included before applying the final protective layer because you want a clean, continuous insulation envelope around the joint and ready access for future maintenance. The mastic cap serves as the final seal at the ends, protecting against moisture and minimizing heat transfer. If you wait to install the valve or flange until after the cap is in place, you’d typically need to cut or remove part of the cap to fit the fitting, which can damage the cap, create moisture paths, and disrupt the seal around the joint. Installing the fittings first allows the insulation and jacket to be built up properly around them, with the mastic cap applied afterward to seal the end and preserve integrity.