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Time limits on pre-loading wiper darts
11 April 2009
At a recent DWOP we facilitated, the topical recommendation to pre-load cement wiper plus/darts came up.

This can be the subsea release wiper plugs run below casing hangers and/or liner wiper darts in cement heads.

We know there are potential issues with storing these pre-M/U assemblies due to the fact that the dart may distort.

Please can you share with us your standard practices within your own companies, along with any experiences (bad or good, plus precautions you have taken.


Dave Taylor
12 answer(s)
Drilling Specialist/Well Engineer/Training Consultant
Kingdom Drilling
Total Posts: 361
Join Date: 10/01/05
All below is in regards to subsea cement heads.

Plugs would be pre made with casing hanger, seal assembly running tool etc. Balls and darts pre-loaded into cement head. I would not consider doing such a task on the critical path unless it could simply not be done offline.

The key issue is that taking 1-2hr critical path rig time is a 50,000-$100,000 operating loss/waste to the operator. So we plan, prepare and organise to prevent and mitigate any latent cause and effect failure of such systems. Note: Where I would suspect as many of the noted problems resulted from systems loaded just before the job. The latent cause of failures etc being nothing to do when the plugs etc loaded.

e.g. If a plug cannot stand changes in surface temperature on deck etc. Why would one then want to run it into a wellbore where temperature change will indeed result far more?

1. Do you store vertically or horizontally ?
Both ways dependent on what way the rig prefers to pick the complete top drive cement stand up .i.e. off the deck or from the derrick

2. Do you place time limits on this ?
Not really. Norm is when convenient to best accommodate this taks off the critical path.

3. Do you use an 'special' tools and techniques to address the above ..
Some subsea cement heads need a more formalised set of rig/wellhead/cementing tools and equipment guidelines. Get the supervisors together and prepare a job plan and risk assessment before job commences. Some subsea head require a lot of force to load the darts and can only be done horixontally or with a home made tool i.e. have to be driven in. Other are much easier to load (simply by hand)

4. What failures, if any, have you experienced with pre-loaded items ?
I cannot recollect a failure of release or how it can be associated to pre-loaded items.

The advantage of doing anything before hand is that it is safer, more efficient and effective. Far less stress is placed on everyone to do the right things and get it right first time.

You wait until the job, then you have a problem, this for me is then biggest problem, loss and risk that results in my view.

When things go wrong it generally is because of 'other' latent causes and effects where, how, why, what and not when.

How is placing an added task on the critical path an evolvement of drilling process improvement or a safer handling option. Where let's do it at the drill floor solves nothing apart from adding more handling process, time and cost to the client.

Subsea Engineer
Total Posts: 2
Join Date: 23/06/05

We load all of our SSR I and SSR II cement plug assemblies onshore and in the horizontal position. Baker (BJ Completions) pre install drill pipe pups and X Overs etc onto our running tools and pre load the cement plug assy into casing hangers and wellhead assemblies. As a rule of thumb we try to load the SSR plug assemblies into the hangers no sooner than 1 week prior to use with 2 weeks being the maximum. When the plugs are loaded into a casing hanger there tends to be very little side loading onto the fins of the plug as the swivel assy when made up to the Casing hanger running tool is rigid enough to prevent damage. However when using a slim hole wellhead assy 18¾" x 13â…œ" there is the possibilty of the SSR plug fins flattening as the weight of the drill pipe pup (to locate the Plug into the 13â…œ" casing) is being supported by the cement plug assy. In this case we rotate our pre installed wellhead assys on a weekly basis to try and prevent a flat spot on the plug fins.     
Regarding cement head darts we load both the SSR I type dart assembly and SSR II system foam darts into the cement head offshore as the drilling supervisors like to witness this operation. In the past 1½ years we have installed 12 production wellheads both standard and slim hole with no issues associated with SSR I & SSR II cement plug sets and dart assemblies.

Hope this is of some help.
Subsea Manager
Applied Drilling Technology International
Total Posts: 2
Join Date: 11/02/10
Dave, We have pre-installed wiper plugs in casing hanger assemblies (saves significant time in having to do it offshore on critical path)for many years in our North Sea operations, without any issues. We alway try and carry out the pre-installation around two to three days before going offshore, and they are always shipped horizontally. We always have one of our subsea engineers witness the assebly and make up, to ensure thaey have actually been installed. Don't really have any experience of "warmer climate" operations.
Technical Sales Specialist, Cementing Products & Liner Systems
Total Posts: 7
Join Date: 07/08/12
SSR Plug sets are routinely pre loaded onshore without any issues. Loading in the horizontal is also a common practice but some manufacturers plug sets may be more at risk when doing this due to the design of the releasing mechanism. Pre loading darts is a different matter as some distortion may well take place if stored in certain conditions for extended periods of time. Most Company men would prefer to see the darts being loaded just prior to the job. Suppliers should have proceedures for pre loading plug sets for review.
Sales Engineer
Downhole Products
Total Posts: 2
Join Date: 30/11/11

I concur Paul's comment as this is not a direct issue with the darts. The issue came when the darts have to be installed over period of time in squeezed manner hence distorting the fins. This could end up with fluid bypassing and displacement volume issue.
The best solution is try and get the exact Cement Head (CH) for correct Drill Pipe (DP) size hence maintaining the effective ID. This will then minimize the distortion on the fins.
Previously i was involved with similar campaign for deepwater here in Malaysia. We had several issue on the displacement volume not being tally with theoretical volume and sometime way off. Few of the recommendation on the best practice will be:
  • Comp rep / TPI will witness the installation with dated document
  • pre-installed darts shouldnt be left for more than 5 days
  • as per Elmen's comment - have a backup loose dart on the rig and should the operation delay, the darts will need to be replace.
Never heard of any issue with storage position.

Shouldnt be any issue with pre-installed SSR Plugs. But care should be taken and installation period should not be more 4 weeks especially on the hot climate area and storage within open yard - rubber limitation.

Hope this helps.
Total Posts: 89
Join Date: 10/04/08
You may remember I previously posted lengthy information on drill pipe dart storage in cement heads, and to summarise briefly, the problem is not the dart, not rubber, etc, but it is the design of the cement heads that squeeze and distort the dart fins. You should challenge the vendors that supply both darts and the cement heads and press them to explain why this problem has not been solved by them, their own equipment is not compatible! There is one cement head that I know of that does not suffer this problem at all, and it is supplied by Blackhawk Specialty Tools. I would tell your vendors to supply this head until they fix their own.

I had never heard of a similar problem with SSR plugs pre-installed, but this should be relatively simply to solve, the launching system should be modified to be properly centralised inside the casing, directly above the SSR plugs, either with a strong spring-bow type centraliser, or solid slightly under-gauge stabiliser blades. If you cannot do this, then build a special centralising device that is pushed up the bottom of the pup joint and temporarily holds the bottom of the plug central, that is removed before use, either way you can prevent fins from being squashed mechanically. It pains me to hear the industry is still suffering these frustrating failures when a modest amount of concerted design engineering effort and workshop testing could highly likely eliminate them forever.
Senior Rig Inspector
Total Posts: 26
Join Date: 20/05/09
My experience over many years 'physically' installing the plugs in casing hangers. It is NOT advisable to attempt installation in a horizontal position. It is NOT advisable to install 'in town'. You have NO idea if the plug is actually there. The company rep 'SHOULD' witness the installation on the rig. Rigs that DO NOT have a hole in the deck (or an ideal (overhang) that can be used, you should use the alternate (or main)rotary table to install the plugs vertically. Then lay out horizontally or stack vertically in the derrick or an appropriate storage area. BUT it must always be understood that the storage time MUST be limited. Ideally, the installation should ONLY be done when it is SURE that the equipment IS going to be used. I have experienced many times over the years, when a section of hole has been 'omitted' due to operations. You DO NOT want equipment sent to storage for lengthy periods, even if it can be used on the 'next' well. Especially if stored in a horizontal position in the tropics, where temperatures are extreme at times.
Drilling Engineer
Total Posts: 14
Join Date: 01/09/12
We do preload darts or plugs but we also send loose ones to the rig. If operation delays more than a week then requirement is to re-load the loose items and discard pre-loaded ones. I have not observed any particular storing position, mainly concentrating on the time limit.
Managing Director (
Relentless Pursuit Of Perfection Ltd.
Total Posts: 409
Join Date: 10/01/05
Hi folks

It's been a while since I started this discussion (about pre-loading wiper plugs).

At a recent DWOP (my company's 250th Workshop!!), we were discussing the practice of pre-installing SSR wiper plugs inside subsea casing hanger running tools.

The client uses the cunning stunt of constructing a mousehole in their yard and pre-loading the items there, vertically, to minimise the potential for any damage during installation.

However, it is a warm climate and also the items are then likely to be stored horizontally.

At the DWOP, we discussed the potential for 'sag' (when stored horizontally) causing localised flat-spots on the wiper plugs, increasing the likelihood of by-passing/leakage when used.

Please, can members provide an update on your current practices for storing pre-loaded assemblies.

Things like:
  1. Do you store vertically or horizontally ?
  2. Do you place time limits on this ?
  3. Do you use an 'special' tools and techniques to address the above ..
  4. What failures, if any, have you experienced with pre-loaded items ?
Many thanks


Total Posts: 89
Join Date: 10/04/08
This has been a difficulty encountered by many over the years, drill pipe wiper darts for subsea cementing plug systems or for liner wiper plug systems being pre-loaded into cement heads ahead of the job. The main cause of the difficulty is the fact that when cement heads for launching darts needed to be compatible with top drive systems the inner diameter of the cement heads got small to meet the strength requirements of the drill pipe and top drive as the head was sandwiched between the two, before this time, some 15 years or more ago most darts sat in a cement head that was not a tight fit for the dart and did not cause the rubber dart fins to crimp and perhaps take a temporary set in the crimped shape such that is by-passed when pumped on instead of being displaced from the cement head. A good example of this would be looking back at the BJ Hughes subsea dart launching head of the pre-80's when the dart sat in a relatively loose chamber and the fins did not get distorted in anyway and the dart was released and dropped into the flow below the pump-in inlet on the side. I worked with BJ using this cement head for 10 years and never experienced a dart not leaving the head properly. However when I moved into liners in the 90's this was not the case and several cement heads used then and still in use now crimped the fins in their static position and then by-passed when released instead of being positively displaced from the head. This obviously caused all sorts of practical problems once the cement was in the pipe and the cement head was above the rig floor. Quite recently this has been acknowledged a genuine issue with the industry and cement head suppliers and a few have adopted a new design of head that holds the darts inside the head in a cassette which does not adversely crimp the fins of the darts or squash foam or rubber balls, but when released from the cassette the ball or dart is allowed to gravitate into the lower part of the cement head below the pump-in sub but still above the dart indicator sub and then the pumping causes the device to be pumped into the flow below activating the indicator and then into the drill pipe below. These heads have also been equipped with remotely operated devices to prevent the need for any many riding once the head is in the derrick. The dart release indictor is a strong flashing light then blicks for a preset time each time a device goes through it. One head that we have researched to use with our liner systems is so impressive that we have arranged to launch it into the North Sea. It will be compatible with most if not all dart and balls required from all the various vendors and in some circumstances will be a better cement head to use than the one supplied by that vendor, partly due to the remote operation but also do to the design and the way that balls and darts are released from the head. These heads are currently being used in the GOM deepwater and are rapidly replacing the other versions. Anyone particularly interested in this area should contact me directly and I can send you the relevant technical information. These heads will be available in the North Sea in 2009. I am available for more questions and to provide more information on these devices at [email protected] It does seem strange that this area has not been properly addressed by other vendors in the past however I believe this new design of cement head will assist dramatically.
Managing Director
Rubberatkins Ltd
Total Posts: 5
Join Date: 01/12/08
This problem has been brought to Rubberatkins attention over the last couple of months. Clients have been particularly worried about the effect of leaving darts loaded at temperature.

We are currently developing elastomer dart compounds that will only take a minimum set when left in launch position.

If anyone would like an update of our progress on completion of the development of the new dart compounds, please drop me an email and I will make sure you are included in the results.

Best Regards

Nick Atkins
Rubberatkins Ltd
email: [email protected]
Drilling Supervisor
Total Posts: 5
Join Date: 22/06/05
Nexen has recently suffered 2 failures involving Drillpipe Wiper Darts not latching (or reaching) liner wiper darts. Darts were pre-loaded +/- 7 to 10 days before the jobs started in fairly cold conditions.

Current recommendation is NOT to pre-load Drillpipe Wiper Darts for liner jobs (especially 7”).

We have seen no failures with conventional sub-sea launch systems where the casing cement plugs are quite often loaded a considerable time before the cement job takes place (note DP darts always loaded offshore).


Ian Frizell
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