TIPS for Above and Below Ground GRP Pipe Installation

I compiled a collection of tips on pipe installation that I believe would be helpful for you. The installation of GRP pipes above and below ground can be tricky. But if you follow these tips, you can have a smoother installation.

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Laying GRP pipes above the ground

In the design stage, you define the distance between the supports, the type of supports, the anchorage, and the fixing points. In general, pipes should be supported by concrete cradles surrounding the pipes over an arc of 150° with a layer of rubber in between. This should be at least 4 mm thick.

During the laying operations, it is necessary to take all possible precautions to avoid damaging the product. In particular, you should keep in mind the following steps:

• tightening of the fixed points (clamps) should be carried out with the pipe at the temperature that is expected during the working conditions. The design values should be meticulously respected.
• bolts of flanges should be tightened at the specified loads;
• elbows should be anchored when it is foreseen that the pipe will undergo torsion stresses;
• fittings not made of FRP, such as valves, steel flanges, and the like, should be supported individually;
• battery limits made of different materials, such as connections to equipment or pipelines, should not transfer additional stresses to the FRP pipeline;
• all tee connections should be supported in order to avoid interactive stresses between the mainline and the branch lines.

You have to keep in mind, that these are general tips and do not cover all of the problems associated with the laying of pipes above ground. Therefore, during the design stage, you should analyze the stress for each individual case and select the most suitable support system. When pipes are installed in contact with the flammable products, all metal parts should be earthed to prevent the build-up of electrostatic charges leading to sparks.

Laying GRP pipes below ground

The underground pipes are laid on a bed of sand or screened material, compacted to the level anticipated in the design. Then, you carry out the backfilling process at the sides and above the pipe in layers of 20-30 cm. You use the same material as for the bed.

You should apply the first layer of the backfill with great care since it provides firm support under the pipe. Each layer must be compacted with the methods and systems adapted to the nature of the material employed. Take care to avoid any damage to the pipe during this operation. It is beneficial to increase the vertical diameter of the pipeline during the laying operations by 1% – 3%. This way you compensate for the reduction of the vertical diameter, which occurs during the pipeline operation.

Like with the above-ground installation, it is not possible to provide full instructions for the below-ground laying operations. Each installation has different requirements, but the following recommendations can be very useful.

Recommendations for below-ground pipe installation

• the trench walls should be dug as vertically as possible;
• any contact between the pipe and large stones or rocks should be avoided;
• in the case of the installations below the water table, continuous drainage should be provided in the trench until the backfilling has been carried out;
• crossing areas, subjected to heavy external loads (permanent or mobile), must be very carefully analyzed to establish if special steps have to be taken, e.g. different stiffness to fit the situation, increased burial depth, use of sheet metal or a reinforced concrete cover;
• in soils with a low modulus of reaction, such as clayey soil, or grounds with a high content of organic substances, the width of the trench should be increased and pipes should be surrounded with the compacted and selected backfilling material;
• the behavior of the underground pipes is greatly affected by the surrounding soil. When carrying out the laying operations, it is, therefore, essential to comply with the requirements of the design.

An engineer designing underground pipelines should take great care in examining the soil parameters. In case they have any doubts, they should assume the worst possible conditions.

Do you have any questions or concerns about your pipe installation?

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Welcome to Hardhatengineer.com. I am Varun Patel. In this video, you will learn about the most common questions regarding piping that you may face during the interview.

1. What is the insulation gasket kit and where do you use it?
2. What is the insulation joint?
3. What is the minimum distance to be maintained between two welds in a pipe?
4. What are the different types of insulation used in piping?
5. What is the difference between GRE and GRP Pipe?
6. What is the difference between the post-heating of weld and PWHT?

So please watch this video till the end. And don’t forget to subscribe to my channel because that way you will get regular updates on a new video. You can subscribe right now by just clicking the subscribe button on your screen. So let’s start with the first question.

What is the insulation gasket kit and where do you use it?

The insulation gasket kit is a specially designed gasket package that use to prevent galvanic corrosion of flange face in a piping system when the material of connecting flanges is different.

Here, in the image, you can see the complete kit of insulation gasket. Basically, it prevents direct metal-to-metal contact between two different flange materials.

What is the insulation joint?

The insulation joint is used to break the current flow of an underground pipeline that is equipped with cathodic protection. To protect the underground pipeline from corrosion, cathodic protection is used. An external current is supplied to the pipeline.

However, if this current flow continues when the line goes above-ground, it will damage the paint that was applied to protect the above-ground pipeline. To avoid this situation, an insulation joint is used.

Hebei KNT Product Page

It is designed in such a way that it will break the flow of current. Here in the image, you can see the configuration of the insulation joint.

What is the minimum distance to be maintained between two welds in a pipe?

No, American code and standard mandate the minimum distance between two welds in a pipeline. But most company specifications will give you a minimum distance to maintain between two nearby welds. This is to avoid the overlapping of heat-affected zones.

The thumb rule is that the minimum distance between adjacent butt welds is 1D. If not, it is never closer than 1-1/2″. This is supposed to prevent the overlap of heat-affected zones. You can see what I am trying to explain in the image.

Here, A and B are two weld joints. The minimum distance between these two joints should be the one-time diameter of the pipe. So, if your pipe is 4” NPS, the distance should be 4”. If this is not possible, it should not be less than 1½”.

The minimum spacing of circumferential welds between centerlines shall not be less than four times the pipe wall thickness or 25 mm, whichever is greater. Here, you can see the example.

If you have branch welding on a pipe, then the distance between two adjacent branches or nearest girth weld should be four times the pipe wall thickness or 25 mm, whichever is greater. Please note that these are thumb rules and vary from company to company.

What are the different types of insulation used in piping?

You know that two types of insulations are used in the plant for the conservation of heat. First is cold insulation with a cryogenic system that prevents heating of the system and hot insulation that is used to protect against heat loss to maintain the temperature of the system.

Commonly used hot insulation materials are:

• Mineral wool
• Glass wool
• Calcium Silicate
• Ceramic Fibre
• Foam Glass

Commonly used Cold insulation materials are:

• Expanded Polystyrene (EPS) Thermocole
• Polyurethane Foam (PUF)
• Polyisocyanurate Foam (PIR)
• Foam Glass

What is the difference between GRE and GRP Pipe?

• GRP is Glassfibre reinforced plastic. GRE is Glassfibre reinforced epoxy.
• GRE/GRP pipes are used in seawater and sewage transport applications. These pipes offer excellent corrosion resistance property over all other types of pipes.
• The main difference between GRE and GRP is the resin used for bonding the glass fiber. GRP pipe used Isophthalic Resin, whereas GRE pipe used Epoxy Resin.
• GRE pipes are also used for industrial applications, as they can withstand higher temperatures than GRP pipes. GRE pipes are used in the offshore platform and water treatment plant to handle salty water.

What is the difference between the post-heating of weld and PWHT?

You can easily answer this question if you know what post-heating and PWHT are.

In post-heating, you raise the temperature of the weld joint to a predetermined temperature range (usually 250° C to 350° C) for a minimum period (usually 3 hours) before the weld cools down to room temperature. Post heating is performed immediately before the weld gets cold when welding is completed or terminated any time in between.

Post-heating is also known as Dehydrogenation as it removes entrapped hydrogen from the weld. Post-heating is done to avoid delayed cracking in the weld.

PWHT, known as post-weld heat treatment,, is performed on the completed weld to relieve the stress from the weld joint. This will soften the heat-affected zone and reduce the hardness of the weld.

Now you can answer the difference between post-heating and PWHT. Post-heating is used to avoid delayed cracking, and PWHT is used to relieve the stress from the joint.

This is the end of the video and also the end of the Piping Interview Question series. I hope you have enjoyed the videos in the series. Please do share and like these videos with your friends. Don’t forget to visit my website, hardhatengineer.com, to learn more about piping. See you soon — goodbye, take care.

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