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API Plan 62 1
- Thread starter sinbj1
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1
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Wet steam is bad for a Plan 62 just as a general rule. The main concern is if you have wet steam injected into the seal, you will usually vaporize the residual water right at the seal faces (due to the face generated heat). This 'explosion', so to speak, at the interface will usually pop the faces open and in general cause premature face damage and ultimately leakage will ensue.
The best recipe for a steam quench: hot, dry, and not too much. One way you can ensure you get a nice hot / dry steam supply to the mechanical seal is to wrap the quench tubing around the suction or discharge flange prior to injection into the seal cavity. This creates a mini super-heat coil that should help ensure the steam is dry before it can cause damage at the faces. You also do not want a whole lot of steam injected into the gland since you may leave yourself open to bearing damage due to excessive condensate leakage out of the back of the seal and into the bearing housing (thus condensing in the oil). 1 - 3 psi is best, but for a visual a simple 'wisp' out of the back of the gland is what you want. You can also use a small diameter orifice upstream of the seal (.062") to achieve the flow you desire.
One other point to note: make sure you have a good floating or segmented throttle bushing in the seal design to restrict the steam flow to atmosphere. I have have come across seal installs with steam quenches that have a fixed throttle bushing in the gland. This is not optimum as the excessive clearance on the fixed bushing will lend itself to more steam usage and also cool the low pressure side of the seal. This is couterproductive to what you are trying to achieve with the steam quench to begin with. You want this area warm to keep solids from forming in the first place. If you are specifying API 682 requirements for your seal design, then the bushing type should be segmented as a default.
The best recipe for a steam quench: hot, dry, and not too much. One way you can ensure you get a nice hot / dry steam supply to the mechanical seal is to wrap the quench tubing around the suction or discharge flange prior to injection into the seal cavity. This creates a mini super-heat coil that should help ensure the steam is dry before it can cause damage at the faces. You also do not want a whole lot of steam injected into the gland since you may leave yourself open to bearing damage due to excessive condensate leakage out of the back of the seal and into the bearing housing (thus condensing in the oil). 1 - 3 psi is best, but for a visual a simple 'wisp' out of the back of the gland is what you want. You can also use a small diameter orifice upstream of the seal (.062") to achieve the flow you desire.
One other point to note: make sure you have a good floating or segmented throttle bushing in the seal design to restrict the steam flow to atmosphere. I have have come across seal installs with steam quenches that have a fixed throttle bushing in the gland. This is not optimum as the excessive clearance on the fixed bushing will lend itself to more steam usage and also cool the low pressure side of the seal. This is couterproductive to what you are trying to achieve with the steam quench to begin with. You want this area warm to keep solids from forming in the first place. If you are specifying API 682 requirements for your seal design, then the bushing type should be segmented as a default.
BK19702 covered most everything.
The only other point to make about wet steam, or pump start-up is to line the seam up early. I usually tell operators to get the steam to the seal a half hour before operating the pump. That way any condensate that has built up in the steam line to the seal is blown long before the hot product is in the pump. Imagine water flashing inside the seal- not ideal. Slugs of water on hot seal faces could cause thermal shock. Water expanding quickly inside the seal could damage the seal.
The half hour is long enough that the operators leave it alone for a while, I don't really expect that anyone will watch a clock.
The only other point to make about wet steam, or pump start-up is to line the seam up early. I usually tell operators to get the steam to the seal a half hour before operating the pump. That way any condensate that has built up in the steam line to the seal is blown long before the hot product is in the pump. Imagine water flashing inside the seal- not ideal. Slugs of water on hot seal faces could cause thermal shock. Water expanding quickly inside the seal could damage the seal.
The half hour is long enough that the operators leave it alone for a while, I don't really expect that anyone will watch a clock.
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