3.1 Occasional variation of pressure and temperature SR-12688 - ASME B31.3 allows for the piping to be exposed to temperature and pressure over the design in periods as defined in ASME B31.3 § 302.2.4. The use of this paragraph is encouraged where significant cost and weight savings can be achieved. To ensure safe and consistent practice and to document the use for the operational phase, the use of this paragraph shall be documented and approved in deviation system; DISP. The content of the deviation request shall be as specified in 3.1.4. The two Norwegian Notified Bodies DnV and TIS have accepted the use of this paragraph under PED.SR-12749 - Sound power level from the pressure reduction source (typically a valve or orifice) is calculated according to equation (a). In some cases the pressure drop in a branch junction may be large enough to contribute as source and should then be added with any other source.The acceptance level can be increased by 5 dB if the source is a PSV (Pressure Safety Valve) or a pressure relieving device that operates 12 hours cumulatively or less during the entire life time of the plant under the condition that design improvements are applied. Design improvements are required downstream the PSV as described in section 7.4 for a distance corresponding to the calculated sound power above the acceptance level in equation (e) and the calculated attenuation along the pipe in equation (b).SR-12756 - For valves that will be in use for much shorter time than 12 hours or for a one off event during the entire life time additional increase of the acceptance levels can be evaluated, but this requires company acceptance.SR-12757 - If the source is a valve designed for maximum 110 dBA SPL at an outside distance of 1 m from the valve, then the pipe inside noise power level is regarded as being too small to create acoustic fatigue and further calculations is thus not required. SPL = Sound pressure level (dBA)If a block valve is installed for the purpose of blocking the flare system for maintenance purpose, it should be installed upstream of the reducer. This is the more cost effective and thus the preferred solution. See TR3003 for location of the orifice/block valve, heat trace and slope requirements, and location of the temperature spec break. Nominal size and pressure rating of the block valve shall be the same as the upstream piping. There shall be no change in flow direction (elbows or tees) between orifice and reducer. In figure 3 an actuated BDV is shown, but it will also apply for a manual operated valve.10.1.2 Wall thickness upstream a reducer SR-12817 - Reference is made to the figure above. The thickness t F may be relatively large, ref Section 7 (“Acoustic fatigue in piping systems”). The thickness t of a small bore pipe including the flange, shall be specified with a thickness that results in a fairly robust transition piece from the smaller to the larger piping.10.3 Nitrogen purging SR-12821 - Connections for purging with nitrogen shall be provided for gas freeing at each item of process equipment. Reference is made to TR2325 Piping Detail Standard for details.