Pipeline Intervention Data Sheets – A Closer Look

1. Introduction

There are various definitions of a data sheet and even more opinions on the contents of a datasheet.

This subject, however, has never translated well into the pipeline intervention arena because the dreaded datasheet seems to invoke a mixture of trepidation and downright disdain.

The goal of this article is to provide an insight into the various components contained in a datasheet to show the importance of some of these questions.  Our focus will be only on the services (hot tapping & linestop) and not the engineering data we collect when designing or manufacturing a hot tap or linestop fitting.

There are two broad categories for the datasheet information:

• Design parameters
• Operating conditions

Design parameters are used to design a permanent item, like a hot tap or linestop fitting, for use on a pipeline or piping system.

Operating conditions are essential to ensure equipment and ancillary items are rated to the conditions during any application, e.g., hot tap, linestop or in-service welding

What follows are the data points mostly found on a typically detailed data sheet with a brief explanation of why the information is considered important enough to collect by way of a data sheet.

Here is a summary of the specific data points your hot tap and linestop service provider will request from you at the time you are looking for either a quotation or to have them perform a service for you:

• Type of service required
• Parent pipe diameter
• Branch diameter
• Branch flange rating
• Pipe wall thickness
• Customer supplied valve details
• Pipe material
• Pipeline content
• Seamed, seamless or spiral pipe
• Probe details
• Flow rate
• Pipeline piggability
• Reason for pipeline isolation
• Horizontal or vertical application
• Bypass and size
• Distance above or below grade

We will take a look at each one of these data points and highlight why they are essential to your service provider.

2. Type of Service Required

The choice here is between a hot tap or linestop service that is required, but the topic of a future article will also look at in-service welding.

Hot tap services

• A hot tap usually utilizes a standard hot tap cutter with a smaller cutter OD than that of a linestop cutter
• A hot tap may have a few variations:
  • Perform a hot tap through a valve, which is then used to tie in or offtake.
  • Perform a hot tap and set a flow through plug with pig guide bars.
  • Perform a hot tap through a three-way tee fitted with a completion flange and plug. This option could require the setting of guide bars or simply a tie in to eliminate the use of a valve.

Linestop services

• A linestop service, by comparison, is a different application from a regular hot tap, with one commonality that it starts with a hot tap.
• The shell cutter used in this application is larger than that of a standard hot tap cutter to create an opening as close as possible to the pipe ID so that a pivoting plugging head can be inserted into the pipe to create a seal and isolate the pipeline section.
• Linestop applications have varying possibilities:
  • Single position linestop
    • Zero flow conditions.
    • Usually, this is done to change out a malfunctioning valve or another appurtenance where maintaining the flow is not a requirement
    • Not generally associated with any additional bypass
  • Double position linestop
    • Generally used with an additional bypass and here again, the two possible options include an external bypass, which requires two additional fittings, or the integral bypass, using the linestop housings as the source for the bypass connections.
    • Both have their place and have to be judged on their merit before a decision is made as to which option will be the most suitable.
• There are more variations, e.g., tandem linestop high temperature, high flow linestop, but the basis remains very similar, and the data collected simply becomes more critical.

3. Parent Pipe Diameter

Hot tap services

For starters, knowing this data point allows the service provider to select the correct tapping machine, cutter, and pilot drill length. The flatter the surface where a hot tap is planned, the higher the torque requirement is for the hot tap machine.

As an example, using a tapping machine type A to perform a 16” size on size hot tap may not be able to complete a 16” hot tap on a 36” pipe.

Hot tap into a storage tank or flat plate may require the use of a special cutter to address the torque requirement of the tapping equipment to effectively and safely execute this particular hot tap.

The flatter the surface at the planned hot tap location, the longer the pilot drill length to ensure sufficient u-wires will still engage in the coupon once the hot tap cut is complete.

Linestop services

On traditional linestop applications, the pipe diameter always equals the branch size, and that is known as a size-on-size fitting or linestop fitting. 

There are exceptions such as a folding linestop or a bag-stop application where a reduced branch outlet, smaller than the parent pipe or run pipe diameter, is possible to fit through the isolation equipment required to divert or stop the flow in the pipeline.

4. Branch Pipe Diameter and Length

Hot tap services

For hot tapping, it is pervasive to have reduced branch configurations  during the execution of a hot tap. There are many different variations on the reduced branch, such as:

• Regular hot tap through a permanent valve
• The setting of a flow-through plug with or without pig guide bars
• Hot tapping through a three-way tee fitted with a completion flange and plug

These aspects will be discussed in more detail later on in this article. This data point allows the service provider to select the correct tapping adaptor, cutter, and pilot drill.

Linestop services

As per the previous comment, we are assuming that all linestop branch runs are equal to the pipe run diameter, i.e., size-on-size.

5. Customer Supplied Valve Details

This is mostly applicable to hot tap tie-in. It is important to know the following information:

• Face to face measurement: This determines the selection of hot tap machine based on the stroke requirements. 
• Valve ID: The valve ID determines the maximum cutter size and when the service provider is required to set a flow through plug, the valve has to be a full port valve and it is important to confirm this measurement.

Together with the valve overall length, the stub length is also important as this will further add to the stroke requirements of the tapping machine.

6. Pipe Wall Thickness

Hot tap services

During the hot tap cutting process, cuttings or swarf is generated by both the shell cutter and the pilot drill.

The standard hot tap cutter has sufficient relief to complete the cut in the most common size pipe wall thickness.

If the service provider considers having two u-wires as sufficient to retain the coupon confidently, then the pipe wall thickness has to be checked against the distance available between the u-wires on the pilot drill, and possible resizing of a pilot drill should be considered if less than the desired two u-wires remains after the total tapping distance is reached.

Linestop services

For linestop applications, the same consideration will apply to the cutter and pilot design to effectively deal with the cuttings or swarf generated by the cutting activity.

The additional reason why this is an important data point when considering a linestop application is the fact that the linestop sealing element is sized according to the pipe ID, and the sealing element is ultimately the item that provides the seal in a linestop application

7. Pipe Material

The type of pipe material at the hot tap location determines the cutter and pilot bit selection. In most standard applications, the high-speed steel tips would be sufficient to meet most requirements.

Although not a common concern, performing a hot tap into a thick-walled stainless steel pipe should have the service provider consider possible work hardening and due consideration to cutter and pilot management during the job.

When we address in-service welding this becomes a critical parameter, but that is the subject for another article.

8. Pipeline Content

This data point allows the service provider to ensure compatibility with elastomers, machine packings, and internal machine parts. Knowing the content further allows us to determine the additional requirements of venting or draining and associated safety protocols.

In another section, the content will play a role when discussing the flow velocity, and then a very clear distinction has to be made.

If the application is in sour service, then this is certainly a data point that the service provider, fitting manufacturer, and pipeline owner has to be aware of to ensure the long term success of any project involving hot tapping or linestop applications.

This is also critical for in-service welding consideration, and a very in-depth article can be found at PRCI referenced PR-82680771-5: Development of criteria/guidelines for welding onto in-service chemical pipelines.

It is not always the chemical inside the pipeline that presents the most significant risk, but at times how a particular chemical will behave when introduced to another, seemingly innocent chemical or product; for instance, how oxygen will react to hydrocarbon (grease or oil) on a tapping machine or how liquid propylene will react when released from a pressurized pipeline.

9. Branch Flange Rating

This data point allows the service provider to ensure their adaptor, housing, or linestop valves will fit onto the branch through which the hot tap or linestop is to be performed.

10. Seamed, Seamless or Spiral Saw Pipe

Hot tap services

Pipeline owners and operators have strict requirements when performing a hot tap through the welded seam of a pipeline. In this instance, it is then advisable to relocate the position of the hot tap to an area where the welded pipe seam will not interfere with the hot tap. 

Another consideration is on a spirally welded pipe where the use of a coupon reinforcement or coupon support is highly advisable. 

The use of a coupon reinforcement device mitigates the risk of the completed coupon flattening inside the cutter, shearing the u-wires, and falling into the opened valve, causing unnecessary and, for the most part, preventable challenges.

Linestop services

Additionally, it is prudent to consider the sizing of a sealing element in a spiral pipe due to pipe ovality concerns.

Similarly, with seamed ERW pipe, the internal seam is potentially an area for concern when sizing a sealing element and the ability of the service provider to maintain a workable seal. Manufacturing defects are uncommon, but the service provider has to be forewarned about any possible issues.

There are times when the retrieved coupon can also assist in determining what awaits the linestop plugging head. In unusual cases, the service provider has had to make slight alterations to their plugging equipment to accommodate a very proud internal weld seam, and fortunately, the information about the weld seam was known, and mitigating measures were employed.

11. Angled Hot Tap

Angled hot taps require different procedures, cutters, pilots, and fittings. 

The fitting must include a guide to provide a flat surface to start the twist drill or pilot bit.

12. Probe Details

If the purpose of the hot tap is to insert a probe into the pipeline, the diameter of the probe must be known to select a cutter or twist bit of the proper size. 

13. Flow Rate

Hot tap services

The rule of thumb for the maximum flow rate when executing a hot tap is as follows:

• In liquid: 15 fps
• In gas: 30 fps

The reason why the flow rates are important is for coupon retention. A high flow rate could potentially cause the freed coupon to overcome it’s inertia and rotate, shearing the u-wires from the pilot drill.

Additional measures can be implemented for flowrates higher than the above, but this must be made known to the service provider and will entail other steps to ensure coupon retention.

Linestop services

For linestop services, flowrates are very critical data points when setting or retracting the plugging heads.

Maximum flowrates are as follows:

• Single position linestop – ZERO flow
• Double position linestop with bypass:
• Gas: 30 fps
• Liquid: 7.5 fps

There are requirements in each case where the bypass is independent or as part of the linestop housing or 3-way tee, but this information is required when the finer aspects of the project are being discussed.

14. Piggability of Pipeline

Hot tap services

If the line is and has to remain piggable, then the use of pig guide bars is a requirement.

These guide bars allow for the safe passage of any pig past the hot tap location without hanging up in the hot tap.

If a pipeline is not piggable, then the additional supply and installation of a flow-through plug with pig guide bars are not necessary.

Linestop services

To aid in the recovering of equipment upon completion of a linestop on a pipeline, a completion plug is required to be set in the linestop flange.

The difference between a piggable and an un-piggable pipeline is the addition of a scarfed nipple to the bottom of the completion plug and entails welding the retrieved coupon to the base of the scarfed nipple (with a little trimming required)

Once the plug is set, the coupon at the end of the scarfed nipple acts like a pig guide to ensure safe passage past the linestop location.

15. Reason for Pipe Isolation

This data point allows us to estimate the duration of the linestop equipment on the pipeline.

There are times when the linestop service provider may have recommendations on different execution methods to assist the pipeline owner and potentially shorten the project timeline.

16. Horizontal or Vertical Application

Hot tap services

A vertical application is always preferred, but when performing a horizontal application, the following factors should be considered:

• Due to the weight of a cutter and pilot drill together with an extended stroke requirement, the hot tap technician must pay careful attention when completing a hot tap to prevent having equipment stuck.
• Boring bar droop is a consideration when performing larger hot taps in the horizontal position.
• Setting a flow through plug in the horizontal position has similar challenges as with the weight of the cutter and pilot drill, causing the boring bar to droop.

Linestop services

A vertical application is always preferred, but when performing a horizontal application, the following factors should be considered:

• Setting a plugging head in the horizontal position does require a few additional measures to ensure the plugging head articulates perfectly in line with the pipeline, especially considering the weight of the articulating or pivoting plugging head.

17. Bypass and Size

During the isolation process, it may be necessary to maintain the flow in the pipeline, and for this to be achieved, a bypass is required.

The service provider should know that a bypass is required and then, too, the size and length of the bypass.

This information is required to ensure the service provider understands the full job scope requirement and that ultimately all the correct equipment is brought to the job site.

There are different types of bypass option:

• External, independent bypass
  • Two different fittings are installed outside the two linestop fittings, and these can be size-on-size or reduced branch fittings, depending on the flow requirements during the pipeline isolation.
• Bypass through either the linestop housing or three-way tee fitting bolted between the linestop fitting and housing.
  • This will save the use of two separate fittings, but there will be flow restrictions through the linestop housings.

18. Distance Above or Below Grade

Access and safety are the two factors the hot tap or linestop service provider will consider with this data point.

For below-grade applications, there will be excavation required, and with this activity, there is a slew of considerations to keep the personnel and equipment safe at all times. Here it is also an essential consideration whether or not the application is in the horizontal or vertical position because this will have a significant impact on the nature of the excavation.

Working at heights, in turn, has numerous factors to consider to ensure a safe and successful job execution. From fall arrestor harness to scaffold safety and hot tap location support, all are part of knowing what the job site will look like and how does the service provider ensure the safety of not only their personnel and equipment but too, the pipeline or plant where the work is being done.

19. Conclusion

The current status quo in the industry requires a considerable investment in time to simply get to a stage where the hot tap or linestop service provider will be willing to provide the pipeline operator with a quotation for their services.

There may be a fair compromise if certain assumptions are made based on the operating parameters of the equipment to be used, to limit the data points for quotation purposes and a more detailed data point collection before job execution, but this will be very dependent on the choice of the service provider.

It is an indisputable fact that these application data sheets are of critical importance to ensuring a successful job execution, and it is advisable to take the time to collect the correct data points.