Suggestion for plan API 51 with heating?

[mbmechanical]

Somebody have experience in plan 51 with heating ?

The media is crude oil grade API 8-12, and where the pump is running we only have electrical power (480 v).

The main problem is the start time, the crude is too sticky and the face broken.

What are your experience in this kind of situation or what do you think about to use oil iso 22 and to heat the veseel of the plan 51.

 

[ecotech]

manuelboada,

You are working with a very heavy crude oil, what kind of pumps are you using?

I don´t believe that you will find the solution to your problem heating the pot of the API 51 plan, this is a dead-ended blanket plan with a minimum incidence over the temperature of the product that is contained into the seal chamber. It is not recomended to use plan API 51 for working with dirty or thermal sensitive products.

Due to the high viscosity of your crude oil at ambient temperature the seal faces must be maintained around 100ºC, this is accomplished by jacketing the gland face and flowing another hot fluid (glicol or hot oil) through the jacket, as you can appreciate you need to focus in the crude oil contained in the seal chamber and not in the other one that is in the pot of the plan API 51.

Taking in consideration your comment that you only have an electrical source on place, another altervative could be to use an insulation blanket and heat tracing on the exterior of the stuffing box for keeping the crude in the stuffing box hot.

What are you located? There are a very few places with crude in the conditions that you are mentioning.

Ecotech

 

[flexibox]

Manuelboada,
What face materials are you using and what is the operating temperature? Sounds like you have carbon? If you are using a single seal,the seal type should be external spring design (keep the springs removed from the product ) Use Silicon Carbide Vs Tungsten Carbide faces. try to use narrow faces as there is less area on the faces to shear. Using Plan 51 heated will help but leakage from primary seal will collect in vessel. Use ISO grade 10 oil keep a low viscosity. How will you be sealing the buffer fluid? Lip seal or mechanical seal? Lip seals are not reliable. Do you have steam available? If so then consider API plan 02 & 62 LP Steam. This plan is for Single seals.

Option 2 is a dual pressurized seal with API Plan 53B. This depends on your budget but should be a solution to the problem. You may find that the best seal design may not fit the pump. Again beware of the possibility of hang up in the seal design. Keep the springs away from the product and ensure the sliding diameter is also kept clean for the dynamic Oring to slide on.

Ecoteh mentioned heat tracing but because the seal area is small and the faces are away from the heat source I found this to be uneffective. You need the heat at the faces and his suggestion of a heating jacket in the gland plate is good providing you have a heating medium available. In either case single seal arrangements will benifit with a steam quench to assist in keeping the seal area warm and wash away seal leakage to prevent hang up on the atmospheric side of the seal.

I did some work in Indonesia on Crude Oil using a single seal and no heating was available because it was a remote area. It was a single external spring with Silicon Vs Tungsten (narrow face) Viton Orings 316 S/S wetted parts and it worked perhaps you can just change the face materials and solve your problem!

You should describe your seal and materials used together with operating parameters and piping plans and what seal life you are currently achieving and what do you want to achieve?

I guess Crude oils are not all same either!

 

[longeron]

If the viscosity of the crude oil is too high there are a couple of ways to approach the problem.


Heat- Steam jacket the seal chamber. If you do not have steam available perhaps you could electric heat trace the seal chamber and or pump.

Single seal with heat- I'm working with an End-User who is happy with a Plan 32 of Boiler Feed Water. The BFW is injected into the seal chamber to displace the crude so the seal only sees the BFW. A steam quench, Plan 62 is also used.

Utilize a dual seal- pressurized or unpressurized.

When I think of a Plan 51 I think of a grease or other fluid between two seals. A dual pressurized seal (the Plan 53 mentioned above) would provide a barrier fluid at a higher pressure than the seal chamber to lubricate the seal faces. You'll need a way to pressurize the barrier system. Plan 53A utilizes a Nitrogen header. 53B, as mentioned above, uses an accumulator that you charge every so often. This could be a good choice for an area with limited utilities. Another choice would be to use a specific kind of dual unpressurized seal. There is a seal that is related to dry gas seals called Upstream Pumping, or Active Lift. This kind of seal has faces desgined to "pump" an unpressurized fluid across the faces into the processs. This would provide the same benifit as the dual pressurized seal without the support system.

What is interesting is that one of the last End-Users I worked with had problems with a dual unpressurized seal utilizing a Plan 52 seal with too much heat generation between both sets of seal faces. Quite the opposite problem.

 

[flexibox]

Longeron

It seems a waste of energy to inject BFW into a crude Oil pump, I have never heard of such a piping plan on a crude oil service! (that's not to say nobody has done it in desperation) It also seems a waste to include steam if you inject BFW Plan 32. In this case you may create other problems like vapourization. You would have to look at the VP and ensure you have a Delta T across the face. Adding heat to it (Plan 62 LP steam quench) you add the risk of vapourizing the BFW fluid film.

Your suggestion of the Upstream Pumping seal is a great suggestion. This seal works well however you will have to choose the correct primary seal arrangement to prevent hang up unless you flush the pump each time it is sat idle without product. When the pump stops product may solidify under the dynamic Oring causing hang up leading to seal failure. Also need to select a suitable buffer fluid.

 

[mbmechanical]

Thanks for yours replies,

Ecotech. - the location is in the south of Venezuela, extra heavy crude oil.

the actual materials are SIC&SIC, the pump is a screws pump type and also other reason for a failures very frequently is because the pump not work continuously and the procces of start up don´t help us. Beside the oil well is in a remote area where we can not checking continuously.

I´ll to evaluate all your comments and share with eveybody the final desing.

best regards

 

[ecotech]

Manuel Boada,

As I was thinking you are in the Orinoco belt, where a lot of the pump stations are so far to the operation centers and for that reason must be fitted with the best qualtity mechanical seals (designs, materials and support plans), bearing protectors, couplings etc. The objective is to get the higher MTBF as possible from a pump that need to run with very low maintenance.

I asked about the type of pumps because we had some experiences with tiwn screw pumps that use mechanical seals with isolated springs and hard faces as Flexibox recomended but the MTBF was allways less than 12.000 hr.

Pls. consider to give me a call, 0414.524.74.26

Ecotech

 

[longeron]

Flexibox,

I was suprised to see the Plan 32/62 as well. But if they are happy with it- go with the flow. Besides, it all comes out in the Desalter, right?

In my experience the best choice for a crude oil application is a single spring elastomer bellows seal with Ni-Resist vs. Tungsten Carbide with a Plan 11/62.

I'll put sometihng on the EAA site with an idea I just had.

 

[ecotech]

Longeron,

API plan 11/62 is a good selection for crude oil in general terms, obviously it will depend of the particular characteristics of the crude.

As I mentioned isolated springs is a good option, pls. give more details about the reason for using single bellow spring. Also the face combination that you are mentioning Ni Resist vs. Tungsten Carbide is not usual, any special reason for crude applications?

Ecotech

 

[longeron]

2 relatively hard faces first of all. The rest is conjecture on my part- Ni-Reist lapps in such a way that there are void pockets on the face that can hold oil very much like these new fangled laser surface treatments and impregnated SiC.

 

[pumpsandseals]

We dealed with this problem in the past in twin screw pumps on bitumen and found a good solution by using 2 metal bellow seals in a back to back configuration. the bellows are enforced with internal drive lugs to have a better resistance to the high friction during the cold start-up.Between the seals we are circulating heated oil at 150c dgr. After start-up we will stop the heating of the oil and switch over to a cooler to reduce the temperature around the seal faces of the secondary seal faces ( friction heat) . The materials are Tungesten/Tungsten/graphite/AISI 316

 

[ciddik]

Dear mbmech

i agree with flexibox, to use dual seal but then u have to go for jacketed type of gland to maintain the temperature above 100 deg C. or else the inboard spring loaded face will hang up



siddik