Sunday, February 5, 2012

Are there any software to help select seal-type, seal-MOC, API-Plan, etc.


Response by Mr. DominicDempsey (DD) -
Most major seal manufacturers will have some form of bespoke selection software. However, the reliability of the software is extremely variable because there are so many factors that one must take into account in order to produce a "good" seal selection. A few basic rules exist but by far the most useful tool is the experience of the application engineer making the selection.

Further by SLA -
I am glad at your mention that "...A few basic rules exist...". I guess, it would be a good idea to make a reference list of those few basic rules at least. Can you please volunteer ? I hope very much that interaction at this group may make the list more and more comprehensive. May I very earnestly request you to please set the ball rolling !

Further response by DD -
... the first step is to look at the industry, i.e. API / CPI / W&I, in conjunction with the machine type, pump, vessel, compressor.... this will determine the initial seal type... my way of selection is to begin with the most basic selection for a particular industry (I am going to use JC seal types for an example since this is who pays my mortgage but other manufacturers seals could be used in this example if preferred)... so if this were an API 682 application my first thoughts would be toward a 1648-2 seal (Type A, Arrangement 1)... I would then look through the application data / customer specifications and try to find reasons not to select this design... sounds strange but it is a good starting point... there can be many reasons to omit the design, i.e. customer prefers bellows seals, CAT. 1 will suit the pump better, pressure is too high (Engineered Special perhaps), speed is too high (sprung stator design), temperature is too high (Type C design required), solids in the flow (might want to protect the springs)... all of which would preclude the Type A design... if I can find no reason not to select the default offering then that is what is selected... I hope this is making sense...

Materials is then the next factor... and again can preclude a design because some seals are not available in all materials...

In terms of seal face combination, PV factors are worth considering although most applications are well inside the default material combination limits and as such are only really applicable in high pressure/high speed combination applications...

Inverting the seal (sprung stator) is used on applications where the face periphery speed is >25m/sec...

Be careful with some specifications with regard to temperature capability of elastomers because there are a few that require a 25 C buffer...

In applications where the true vapour pressure is >5 Bar(a) be careful with the selection of a liquid tandem (dual unpressurised - Plan 52) because there have been issues in the past due to vapour locking of the system... see SHELL specifications...

Plan 53A can be problematic above 10 Bar(g) due to N2 soak into the barrier fluid... again, it's not an exact science but something one needs to consider... hence the reason that SHELL use 53B by default...

There are lots of rules of thumb... too many to list... and new ones come about because we've all been "bitten" as the saying goes...

I hope this gets the conversation going and I look forward to other points of view on this... we should be aiming to learn something new everyday...

SLA - Dominic ! That's fantastic ! And I appreciate the closing "..I hope this gets the conversation going..." I am feeling tempted to convert this into an algorithm. Dialogue-boxes should allow better word-processing features, I guess.

Here is an invite ... would anyone volunteer an algorithm ?
Posted by at

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)