Practical Process Engineering

26- All steam condensate piping including trap discharge to the header shall be sized for two-phase; i.e., they should be sufficiently large to handle the condensate and any flashed steam. 27- Inverted bucket type traps shall be acceptable where there is no danger of condensate freezing. Such applications shall be subject to Company’s approval. 28- In severe climate if requested by Company, steam traps on process Units should be protected by enclosing them in cabinets of steel or other suitable materials. Each cabinet should contain at least six traps and allow easy access for maintenance. 29- When minimum ambients are below -12°C, strong consideration should be given for electric heat tracing of traps on steam tracing systems. 30- Line from heat exchanger to steam trap or control valve: The pressure drop in this line shall be smaller than 11.3 kPa/100 m (0.1 kg/cm2/100 m) and shall be checked that no condensate may vaporize therein. 31- Line from steam trap or control valve to following vessel: a)Steam condensate return lines must be sized to avoid excessive pressure loss. Part of the hot condensate flashes into steam when it is discharged into the condensate return system. b) In this case, the flow velocity "V" must be limited to 1524 m/min to prevent erosion. c) The flow velocity shall be calculated by the following equation:

17- Insulation is an enemy to a good steam trap maintenance program and should not be used. To avoid problems, it is recommended that pipe insulation start approximately 300 mm. upstream and downstream from the trap. Insulating steam traps makes them difficult to check and maintain because once insulated, a steam trap may never be accessed unless it is clearly affecting process operation. Additionally, the performance of a steam trap can be affected by insulation, thermostatic traps, for example, tend to be sluggish when insulated and bucket traps can lose their prime (that is fail open). For traps in winterizing and heat conservation services the items listed below shall be strictly followed: 18- Condensate collecting piping for grouped tracer traps shall be such as to avoid excessive back pressure on traps and trap discharge lines and should be based on the lowest expected steam supply pressure. Minimum size of condensate collecting piping for grouped tracer traps shall normally be as follows: - 1 to 2 traps DN20 (¾" NPS) - 3 to 5 traps DN25 (1" NPS) - 6 to 15 traps DN40 (1½" NPS) 19-Each tracer shall have its own steam supply valve and steam trap. 20-For heat conservation service, each trap shall have a block valve upstream and downstream of trap. Traps will have an integral strainer and plugged drain. In winterization service no blocks will be required at steam traps. Drains will be valved. 21-Steam trap shall be impulse tilting disc type with DN15 (½") or DN20 (¾") threaded ends with integral strainers and blow off valves with removable internals. Body shall be forged steel, seat and disc shall be stainless steel or stellite. Traps shall be preferably installed with the flow down. If the trap is in a horizontal run, it shall be installed on its side to prevent freezing. 22- The condensate discharge from the tracers shall be carried out through one steam trap for each individual tracer. The steam trap may service two tracers only if they are tracing the same pipe in parallel for the same length and follow the same route. The steam trap may collect the discharge of more tracers in the particular cases of pumps and instrument tracing provided the tracers are completely self-draining with no pockets. 23- Valves and piping at trap shall be same size as the trap size. 24- Piping from the trap discharge to the header shall normally be DN15 (½") minimum piping. Condensate recovery shall be 100%, however in exceptional approved cases where it is not practicable to recover, discharge piping shall be short, without elbows and discharged into sewage or into a properly designed soakaway sump. 25- Instrument steam tracers shall be supplied only from independent main headers which will not supply steam to any other facility.

#Steam_Trap_Installation The following notes come from standard IPS-E-PR-845 & 420 15-Metallic gaskets shall be used for steam pressure above 20 bar. 16-there are applications where a steam trap can not be installed lower, such as buried tanks, drop-in (submerged) heating coils, or rotating drum dryers. In these instances, special consideration should be given to providing tank coils with a lift fitting and utilizing steam traps with control orifices to vent flashed condensate. A lift fitting is a loop into which condensate drains, a syphon tube is then placed down into it to syphon out the condensate. Control orifices are orifices in steam traps to vent flash vapor by providing continuous drainage (that is, the trap never shuts tightly). See below photo.

4- Trap should be accessible to operators, inspectors and maintenance team crew. 5- It is advised to install traps somewhere close to the condensate source (steam header, heat exchanger, etc.). But, if the condensate source is elevated, you'd better install the trap at an elevated location but a ladder should be installed or install the trap somewhere close to the ground and insulate the whole inlet pipe to reduce heat loss. 6- Regardless of the trap type, piping size and trap location, the whole piping system MUST be insulated to protect people and reduce heat loss to ambient air. 7- Traps can be installed both horizontally and vertically (not all of they) in case of limited space. 8- It is advised by many references to install traps every 100- 150 ft (30~50 m) to remove condensate at right time and location and doesn't allow the condensate accumulation. High velocity steam carries the accumulated condensate and causes water hammering that may damage and errode the equipment or injure the personnel. 9-Traps are installed upstream of all modulating valves (control/ manual) and any type of valve that has intermittent operation or kept closed for a long period. 10-Traps are installed at the bottom of all vertical lines. 11- Inlet line toward the trap inlet Must have a smooth slope. 12-some traps have bypass and some doesn't have? What is the criteria? There are two type of plant start-up; SUPERVISED and AUTOMATIC. In supervised mode, operators use bypass valve to drain cold condensate during start-up and steam header pressurizing. After header is warmed up enough, the baypass is closed and the condensate load is transfered to the trap. Such operation is suitable for large continuous plants like refineries or petrochemical plants with infrequent start-up. But, for small installations or header/equipment with intermittent operation, trap doesn't need bypass line and it controls the condensate load automatically. So, warm-up process should be slow and carefully controlled for autaomatic start-up. 13- Check valves are installed after steam traps to protect them against reversed flow and water hammering. It is installed at least one meter away for blasting steam traps. Thermodynamic, balanced bellows or inverted bucket traps blast the condensate and flash steam to outlet pipe so that check valve should be installed a little away from this blasting discharge. 14- If a trap is designed for horizontal mounting, do not rearrange the piping to install it vertically and this is right as well for vertically designed traps not to installed horizontally. So, make sure you consider all details regarding space and hydraulics before placing the order. However, some traps can be designed for vertical and horrizontal mounting. Mechanical traps like different type of float traps (free float and float with lever) or bucket traps are manufactured in both models. So, make sure you mention the orientation while purchacing these traps. In case of vertical installation, trap takes advantage of the condensate geavity as well as pressure force, but horizontally installed traps relay only on pressure force. Thermodynamic disk trap operation is independent of the orientation. But, the orrifice side should be installed toward the outlet and it should be head up in case of horrizontal installation. Fixed area orrifce can install in both orientation. Variable size orrifice should be installed so that the larger diameter is located at outlet. Pinch steam traps can be installed in both orientation and also they can be flipped up/down or left/right if they have same size inlet/outlet. (To be continued)

Flash steam (left) and live steam(right)

1-Strainer MUST be installed upstream of a steam trap, regardless of its mechanism. It can be a separated strainer or a built-in one. It removes the dirts and increases trap life time. It has to have a blow down valve to get cleaned. Traps are installed not only to remove condensate, but also to remove air and other non-condesables from the steam pipings. Some of them have better air removing capability like float and thermostatic. If a trap does not discharge these gases due to any reasons, they block the trap. Strainer blow down should be used to vent the gases and deperessurize the line. 2- Design pressure and temperature are different from operating conditions and the trap should be designed to sustain the highest possible pressure and temperature. Let's take an example. Steam flows through an exchanger to warm a cold liquid. steam is saturated at 40 psig pressure. The corressponding temperature in steam table is about 142 C. These are operating conditions. How to know the design conditions? The easiest way is to take a look at the P&ID drawing to see how much is the PSV set point for the steam header. This pressure is the highest possible for this application and corresponding temperature should be read from the steam table. Suppose the steam header PSV pops at 75 psig. So the design conditions are as below: P= 75 psig T=160 C Theses pressure and tempreture are used to determine pressure rating for the whole condensate drainage system. 3- Inlet piping MUST have the minimum possible length and number of bends to keep the pressure drop as los as possible. Do not reduce the trap inlet pipe size . If the outlet process pipe in above example was sized for 2", it should be 2" from the exchanger outlet through trap inlet connection. However, The outlet pipe MUST be sized to have at least the same diameter as the inlet. Why? As a matter of fact, condensate is flashed and some flash steam leaves the trap. I post a photo later to see the difference between live steam and flash steam. Anyway, the steam occupies larger volume comparing with liquid condensate and it makes a back pressure downstream of the trap. So, enlarge the outlet pipe to kill this excess pressure. The same rule governs sizing of all control valves that are installed on steam/ condensate lines.

#Steam_Trap_Installation Although there are sevaral type of steam traps, their operation can be catagorized in one of the below groups: 1- Mechanical/Density steam traps. They work based on the difference between condensate and steam density. *Flaot and Thermostatic *Free float *Inverted bucket *Open bucket 2- Thermostatic They open/close according to condensate temperature. *Ballanced bellows *Bimetalic *Liquid expansion 3- Thermodynamic/ Velocity steam trap They open/close based on velocity change *Constant size orrifice *Variable size orrifice: Venturi steam trap and pinch steam trap Here I only focus on steam trap piping, installation and orientation. However, a few details of their operation will be posted.

PTQ's 2018 Catalysis special

Process Heating Magazine, March 2018

Chemical Engineering Magazine, March 2018

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