Frequently Asked Questions (FAQ)

Here are some of the most common questions:

If you don’t see the question you’d like answered below, please use the contact form on our Contact Us page and let us know what your question is.  We want to keep this FAQ as comprehensive and current as possible.

Do you fabricate the sand traps you sell?  Click to visit Dura-Strong's web site

Our sand trap vessels are fabricated by our code fabrication company, Dura-Strong Fabrication, LLC. Dura-Strong is an ASME code shop that holds a Section VIII, Div. 1 “U” code stamp as well as National Board “R” and “NB” stampsClick for ASME Certificate.  When the sand trap vessels are finished and fully certified by the AIS, Mountain Equipment mounts them on a platform (skid or trailer), hydro-tests, paints and then puts them through final QC.

Do the sand traps operate vertically?

10000 psi cyclone sand separator in vertical operational orientationYes they do.  In pictures they frequently appear horizontal but they always operate vertically.  However, when they are stored or moved, they are usually horizontal. That’s why the skids are “L” skids, so they can be easily placed in either orientation.

When in vertical operation, the built-in ladder makes it easy to access the top (outlet) connection and inlet connection when rigging up or down.

What are the max flow rates of your sand separators?

Flow rates are highly variable and can be influenced by many factors including sand separator type, operating pressure, amount of entrained fluids, amount of entrained sand, sand type and size, slugs, entrained asphaltenes and/or paraffin.

The max flow rates shown are based on Computational Fluid Design (CFD) methodology and provided for general guidance only. They are not a guarantee of performance. Flow rates can, and will, vary. That said, here are the computed max flow rates per 24-hour day for our standard cyclonic  models:

  • 20″ x 8′ x 5800 psi cyclonic: 5500 BBL/D and 25 MMSCFD gas
  • 24″ x 8′ x 10,000 psi cyclonic: 6000 BBL/D and 30 MMSCFD gas

Where are the inlet and outlets?

Click on the picture to see the connection type and size.  This applies to both the 5800 and 10,000 psi models of our cyclonic sand separators:

Does the well need to be shut in to dump sand?

No, using native pressure, sand can be blown down easily.  Blow down is usually controlled by a gate valve, plug valve, or a variable choke. A choke gives the best level of control and typically doesn’t wash easily, especially when a choke with a tungsten-carbide stem and seat is used.

How often does sand need to be dumped?

Sand is blown down every few minutes depending how much sand the well is producing.  Typically a newly fracked well requires a blow down every 15 or 20 minutes, but the frequency drops quickly as sand is removed. We have heard of wells making so much sand the first day that a blow down is required every 5 minutes. The actual sand blow down is very quick, often taking only seconds.

A really well-adjusted variable choke can sometimes be left barely cracked open to allow for a continuous outflow of sand, at least during the first few days. Cracking a choke for continuous sand flow is a technique that requires supervision and close monitoring.

How much sand is removed by your cyclonic sand separators?

Because our cyclonic sand separators feature solid stainless internals they are extremely efficient at removing sand. The smooth finish provided by stainless steel aids the centrifugal and centripetal forces that make a cyclonic sand separator work. Up to 100% of 100 mesh sand is removed from the flow in both gas and liquid flows. Under sluggy or waxy conditions, or at very low operating pressure in extreme gas volume situations (less than 100 psi), separation removal efficiency will drop.

How long do these sand traps last?

DuraStrong Fabrication uses thick, durable stainless steel for its cyclonic internals which ensures the longest possible life and excellent sand capture. Sand capture is aided by the ultra-smooth surface that stainless steel provides. Lifetime will vary based on usage, proppant type, mesh size, sand cut, flow rate, flow type, and average operating pressure.  As a general rule of thumb figure 3-5 years lifetime for heavy use, 6-7 years for medium usage, and 8+ years for light / reservoir use.

Which Authorized Inspection Service do you use?

Dura-Strong Fabrication uses Hartford Steam & Boiler (HSB) as their Authorized Inspection Service (AIS). HSB is the oldest and most respected pressure vessel inspection agency.  Once vessels have been inspected and approved the resulting U1A Data Form for that pressure vessel is submitted to the National Board of Boiler and Pressure Vessel Inspectors for review and registration.

What is the difference between a coded and non-coded vessel?

Dura-Strong coded ID plate example

Coded means the vessel has been built according to ASME standards since its inception.  The design and the materials used meet code, as do the welding and fabrication techniques.  It also means the vessel has been inspected by an Authorized Inspector (AI) from an approved AIS.  Coding adds significant cost but ensures that the pressure vessel has been designed, built, tested, and inspected to meet the very demanding ASME criteria.  A coded vessel must display a Manufacturer’s ID plate and should show the year the vessel was fabricated, the MAWP, the manufacturer’s name, the minimum and maximum operating temperature, the vessel serial number, and the appropriate stamps.

Non-code means that the vessel was designed and built to whatever specification the manufacturer deemed appropriate.  In most (but not all) cases, the manufacturer will follow accepted design and manufacturing criteria and will hydro-test the pressure vessel to at least 1.3 times its maximum design pressure.  Companies that hire flow back, well testing, and related services may not allow the use of non-code pressure vessels on their well sites due to safety concerns.

Can non-code pressure vessels be coded?

Nope. And if someone tells you they can, hold onto your wallet!  An ASME coded vessel must start, from the very first moment, as an ASME vessel.  Through the entire fabrication process ASME guidelines must be followed and recorded.  Upon final successful inspection by the AI, the U1A Data Form is generated and acts as the vessel’s birth certificate, fully describing the vessel and its pedigree.

Where can I get an ASME coded vessel’s U1A data form?

U1A Data Form example
U1A example

The easiest way is to ask the manufacturer or dealer for a copy.  If that option isn’t available, you can request it (for a fee) from the National Board of Boiler and Pressure Vessel Inspectors.  You can either order that online or call them at 614-888-2463.  They are located in Ohio.  You’ll need the following vessel information:

  • Original Manufacturer’s Name (req’d)
  • National Board Number (req’d)
  • Manufacturer’s Serial Number
  • Year Built

Remember, there is a cost for each U1A you order from the National Board.

What is the difference between a cyclonic and gravity sand trap?

10K psi cyclonic sand trap animated flowA cyclonic sand trap uses a combination of centrifugal and centripetal force to remove sand and solids from the well stream while a gravity type sand separator uses slowed flow speed combined with gravity to remove particulates. Cyclonic sand separators are primarily designed for high-volume liquid flows like those encountered during flow back operations.  They are very efficient at removing solids, often exceeding 98%.  Gravity type sand separators are “Jack Of All Trades” sand separators.  They are very rugged and will handle flows that are unknown and / or highly unpredictable.  They cannot handle the high fluid and gas volumes that cyclonic sand traps can, but they’re reliable workhorses for a wide range of flow conditions.  Gravity sand separators are often used on low volume flow back jobs (< 1500 BBL/Day), gas wells, sluggy wells, wells making paraffin and/or asphaltenes, and production wells for removing residual reservoir and injected proppants.

What are the internal diameters of the sand separators?

ID is extremely important for the efficient removal of sand. The 5800 cyclonic sand separators has an ID of 14 inches.  The cyclonic  10,000 psi sand separators has an ID of 14.5 inches.

How much sand will a cyclonic sand trap hold before it must be purged?

32 gallons is the maximum amount of sand the 5800 psi cyclonic sand separator can hold. The 10,000 psi sand trap can hold a maximum of 35 gallons due to its slightly larger ID. Sand can be purged at any time, with less than the max amount of sand; you don’t have to wait until the max amount is reached. Typically, sand is purged frequently, especially when the well first starts flowing and for several days (and up to 2 weeks) thereafter. Frequent purging prevents the sand dump from being clogged by wax, asphaltenes, or compaction.

Can sand traps be mounted on trailers?

Trailer mounted gravity sand separatorYes, both cyclonic and gravity type sand separators can be mounted on trailers with lift / lower hydraulics.  Talk with us when you call about your specific portability needs.

Can downcomers be added to a sand trap?Trailer mounted sand trap with downcomers

Yes, downcomers can be added to both skidded and trailer mounted sand cans. There is an extra cost for the cushion-tees and heavy duty pipe. Ask your sales-person for a quote.

How easy is it to service your sand separators?

After each job, clean the sand trap by flushing it with air or clean water. There is a drain on the bottom of a gravity sand trap when it is vertical, designed specially for this purpose. The sand dump is used as a drain when cleaning a cyclonic sand trap.  Also, be sure to check the 1502 connections for any sand washing or damage to the gaskets inside the 1502 hammer unions. Replace if needed. On a long-term basis (at least once a year), re-certify the safety relief valve and do an ultrasound test (UT) on the vessel.

 Do you have a drawing that shows suggested Ultrasound Test points?

Click to enlarge
Yes, just click on the map picture on the right and a full sized UT map will be shown that can be printed (press Ctrl+P).  This map works well for our gravity and cyclonic sand separators.  It may not be suitable for other manufacturer’s sand traps.

Are your sand traps NACE?

Yes, all our 5800 psi and 10,000 psi sand traps follow NACE specifications and are built using welding procedures and components that conform to NACE MR-0175/ISO 15156-2:2003(E) and are heat treated for at least three hours above 1100 degrees Fahrenheit (593.33 degrees C) for stress relief.  “NACE” was an acronym for the National Association of Corrosion Engineers but is now used more as a brand name.

What is Post Weld Heat Treating (PWHT) and why do sand traps need it?

Post weld heat treating, which is also called stress relief, is a procedure done to relieve micro-stresses in the welded areas of the vessel allowing them to relax and close.  By doing this, carbon steel becomes less permeable to hydrogen.  Hydrogen is the typical culprit that causes steel to become brittle over time.  Hydrogen is a molecular component of oil (hence the term “hydrocarbons”) but when locked up in a carbon molecule it isn’t much of a problem. However, when hydrogen is encountered in a form like hydrogen sulfide (H2S) that allows it to bind , it can be an issue.  High pressure sand trap vessels typically have thick shells and heads and so must undergo post weld heat treating by code. Look for a “PWHT” stamp on the vessel’s ID plate to see if the vessel has been heat treated.

Where is the Post Weld Heat Treating (PWHT) done?

Post weld heat treat oven
Our custom-built heat treating oven.

Post weld heat treating is done on-site in our custom designed heat treating oven.  Up to four sand separators can be heat treated at the same time. We use five thermocouples to measure and record the ambient and vessel temperatures during the entire heating and cool-down process.  This ensures accurate and complete data for each vessel as well as the overall oven internal temperature.

Do you ship overseas?

Yes, we can ship sand separators internationally in most cases.  The customer is responsible for all related shipping and customs charges.

Can you ship via Air Freight overseas?

Yes, we’ve done this several times.  It can be expensive as a single skidded 5800 psi sand trap weighs 7,300 pounds (3,312 Kg) or more. A 10K psi sand trap weighs almost twice that. The customer is responsible for all related shipping and customs charges.

FAQ Updated 10-24-2021