Pipe Schedule

Two pipes the same diameter may have different schedules, which means they have a different wall thickness. So somebody specifying a pipe for a high pressure application will select a bigger number which represents a bigger schedule (wall thickness).

When maintenance work on an active pipeline is needed a hot tapping machine can be used. This could be to repair a section of pipeline, or when a new branch needs to be added. The benefit of a hot tapping machine is that the work can be carried out without major disruption to the flow of product through the pipeline.

Pipe Schedule

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On occasions where subsea pipe connectors are to be used for attaching a new pipe run, it may be necessary to remove seam welds from the pipe to ensure a good fit. This operation is carried out using a portable milling rail attached to the pipe with a chain clamp.

In March 1927 the American Standards Association authorized a committee to standardize the dimensions of wrought steel and wrought iron pipe and tubing. At that time only a small selection of wall thicknesses were in use: standard weight (STD), extra-strong (XS), and double extra-strong (XXS), based on the iron pipe size (IPS) system of the day. However these three sizes did not fit all applications. Also, in 1939, it was hoped that the designations of STD, XS, and XXS would be phased out by schedule numbers, however those original terms are still in common use today (although sometimes referred to as standard, extra-heavy (XH), and double extra-heavy (XXH), respectively). Since the original schedules were created, there have been many revisions and additions to the tables of pipe sizes based on industry use and on standards from API, ASTM, and others.[3]

Stainless steel pipes, which were coming into more common use in the mid 20th century, permitted the use of thinner pipe walls with much less risk of failure due to corrosion. By 1949 thinner schedules 5S and 10S, which were based on the pressure requirements modified to the nearest BWG number, had been created, and other "S" sizes followed later. Due to their thin walls, the smaller "S" sizes can not be threaded together according to ASME code,[4] but must be fusion welded, brazed, roll grooved, or joined with press fittings.

Based on the NPS and schedule of a pipe,[5] the pipe outside diameter (OD) and wall thickness can be obtained from reference tables such as those below, which are based on ASME standards B36.10M and B36.19M. For example, NPS 14 Sch 40 has an OD of 14 inches (360 mm) and a wall thickness of 0.437 inches (11.1 mm). However, the NPS and OD values are not always equal, which can create confusion.

For a given NPS, the OD stays fixed and the wall thickness increases with schedule. For a given schedule, the OD increases with NPS while the wall thickness stays constant or increases. Using equations and rules in ASME B31.3 Process Piping, it can be shown that pressure rating decreases with increasing NPS and constant schedule.[a]

When a pipe is welded or bent the most common method to inspect blockages, misalignment, ovality, and weld bead dimensional conformity is to pass a round ball through the pipe coil or circuit. If the inner pipe dimension is to be measured then the weld bead should be subtracted, if welding is applicable. Typically, the clearance tolerance for the ball must not exceed 1 millimetre (0.039 in). Allowable ovality of any pipe is measured on the inside dimension of the pipe, normally 5% to 10% ovality can be accepted. If no other test is conducted to verify ovality, or blockages, this test must be seen as a standard requirement. A flow test can not be used in lieu of a blockage or ball test. See pipe dimensional table, Specification ASME B36.10M or B36.19M for pipe dimensions per schedule.

Stainless steel pipe is most often available in standard weight sizes (noted by the S designation; for example, NPS Sch 10S). However stainless steel pipe can also be available in other schedules.

Let's not forget the OH3 curves. The old curves used to be ".1" ".18", ".24", & ".30" for the 1500 square foot design areas (understanding that this isn't a hydraulic question but Ordinary Hazard had a third option for a time).

My question is what changed to bring you in to perform work? If the owner was being questioned by the AHJ as to system capability (with no modifications ongoing), then I would write up your findings stating the system does not work per current standards (design area & density + current water supply).

If you have a calc plate or system as builts, then the allowable design criteria should be available and the capabilities/limitations of the system need to be maintained (unless your AHJ has outright struck the IFC/NFPA references to use of pipe schedule systems). Without the original system design, the safest non-calculation method would be the approach you mentioned of the lowest OH design available. Luckily, the LH & OH pipe schedules are well defined and not an issue to prove intent.

Beyond that, to evaluate the system would require current NFPA guidance and, as you stated, the system does not work as currently configured.

Hey Dan, good questions. The occupant of the space is changing and the new occupant intends on storing a different commodity in a different configuration than the previous occupant. The AHJ typically makes us verify the existing system is adequate for a new occupant when they pull a building permit with new rack plans.

The building owner is the 3rd owner of the building since 1973 so there are no as-builts or hydraulic placards. The pipe schedule of the existing system is a textbook OH pipe schedule. It sounds like OH1 would be the safest storage capability to communicate to the building owner since the system does not work hydraulically.

I fully agree with Mike's comments.

Working for an insurance company for more than 25 years, I would definitely require an upgrade of the sprinkler system.

With the information you provided, if this is a correct understanding from my side:

- you have a pipe schedule system for OH

- when you do calculations, you can not achieve the demand for OH (in that case, your system is actually not an OH, but something weaker... maybe LH ?)

- the new owner want to install racks... and you know that in rack storage you may find in the future very different adverse conditions than what they ware approved (with your system, you will limit both the commodity classification and the height of storage... but everybody knows that if more plastic need to be stored, it will be stored, and if you can store higher, you will store higher...).

I would call this a scary situation...

In you case (again, as an insurer's point of view), the question is "will you be confident that a fire in the new configuration will be controlled". So far, I am not convinced. And the AHJ would probably be not convinced either.

NFPA 13, 2016 section 11.2.2.3 allows pipe schedule methods for additions or modifications to existing pipe schedule systems. If the water supply requirements of Table 11.2.2.1 are met, why would the system need to be modified if the maximum storage is kept to the OH1 storage limitations. NFPA 13, 2016 doesn't provide any guidance on upgrading existing pipe schedule system based on hydraulic calculations except for Extra Hazard occupancies. I hear what you're saying from an insurance perspective, but that sounds like an opinion above and beyond the standards of NFPA 13, 2016 since there is nothing that recommends doing that. The hydraulic calculations were for the owner, but doing calculations doesn't change the fact that pipe schedule systems are allowed. My understanding is that most pipe schedule systems don't work hydraulically. If the intent is to upgrade a system every time someone decides to try a hydraulic calculation (knowing that it probably won't work), why would NFPA 13, 2016 11.2.2.3 allow the pipe schedule method to be permitted?

I would have to agree with Franck as well on this. The question is how many pipe scheduled systems have not had any changes on what is being stored, how its being stored, the height, etc... it comes down to who has asked for this "analysis" and why. Also remember that an ordinary hazard occupancy is not the same as a storage occupancy using ordinary hazard density and area for protection. There are some nuances there that you should be very careful of making from Chapter 11 to Chapter 13, or vice versa. Like 11.2.2.1 water supply requirements mention light or ordinary hazard occupancies, they don't mention storage occupancies protected by ordinary hazard design requirements. Little bit of a rabbit hole there. Now that you have proof that the system doesn't work hydraulically (even if you didn't do an analysis of storage type, height, arrangement, etc..) you are in a precarious position.

The clarity and smooth interior walls of the Clear Schedule 40 PVC pipe make the pipe ideal for medical and hospital use, food and beverage processing, laboratory applications, chemical processing, electroplating and other applications that require visual monitoring and non-contaminating processes.

PVC schedule 80 pipe is for pressure applications and has a thicker wall than schedule 40 pipe. It is highly durable, is easy to install, and has better sound-deadening qualities than PVC and ABS foam core pipes. Installation requires the use of primer and solvent cement.

vegashunter - I ...am going to run schedule 80 plastic.BOY am I glad the wife isn't home. She would not have been proud of the yelling screaming fit I just had when I read that. This has been discussed almost as much as 2+2 tractors over the last few years, so let me put this in plain simple language you can understand:

It doesn't matter if it is Schedule 80, heated, unheated, it just does not matter. The only safe way to use it is put it inside a piece of steel pipe. You think that is dumb? Think how you will feel if that plastic pipe explodes and frags some innocent bystander. 2351a5e196