can a big pipe be designed using pressure vessel code in ASME?

regards,

sam

An intriguing question... The metal that forms bith the pipe or the pressure vessel does not know about codes....

So from a viewpoint of will it work or not I would say sure... froma code stand point it depends on the piping code. Some codes say do things my way or no other way some provide acknowledgment of other methods.

Yes a good question, and another way of looking at it, is when does a pipe become a pressure vessel and vice versa? A very experienced mechanical engineer asked me this once and I could not find the answer in any code that I looked at. I have seen a few smaller "pressure vessels" that are entirely made from standard piping components, and that could easily be designed/constructed by a piping code. One criteria where piping becomes outside the scope of say the B31.3 code is when the D/T ratio exceeds 100 per Table D300.
A particular example where this boundary is uncertain/undefined is for onshore slugcatchers, between an offshore pipeline and an onshore processing plant. In theory, 3 codes could be used, pipeline, vessel and piping, and all 3 have conflicting requirements in respect of allowable design stress, materials, welding requirements, etc. Also none of these codes specifically address the combination of large diameter pipe and fittings in the configuration of a slugcatcher. What was used for the basis of design and hence construction of a very large local slugcatcher, was the most stringent requirements of all 3 codes without incurring "unnecessarily high cost penalties". For this particular slugcatcher, for economy reasons the piping material and wall thickness were to satisfy the pressure vessel code. Smaller piping within the slugcatcher was in accordance with B31.3. So above question is very much open to interpretation and ultimately the owners decision.
Regards

On the first rain in the season, once my daughter came out in the school compound to get caught by school principal; when asked,she replied - rules are made by teachers to be broken by students a few times.

In B31.3:2004 clause 300.1.1(c) Fig 300.1.1 piping/equipment code judisdictions are described. For cost/schedule constraints in meeting the real but stringent code requirement, as mike wrote above, sometimes we, too, break the rules like the children in school to use the more lenient code alternative!

regards,

sam

Yes ... and no.

As was pointed out, the steel, welds, fittings, external loads (sagging, bending, heat stress, corrosion, and thermal/mechanical/earthquake shock) don't care what you used to design something. They will be present regards of what you or I do or assume.

The stress either will be present, and absorbed harmlessly within the metal (no corrosion, no bending, no swelling or rupture), or it will deform or break the metal at some point.

Pipe tends to be a more robust code by nature, because it is used many thousand times more often by many thousands more (sometimes less qualified/less well-trained) workers under more difficult field conditions than the "pristine" workshop and sheltered area of high-pressure tanks and vessels. Pipe metal also takes into account the lower strength of those metals, and the relatively few "wall thickness" choices in a single size pipe. You might find 15 or 20 thicknesses and webs for a single WF shape in a given size, but only 3 pipe walls are commonly used. So pipes will more often be "overstrength" than "exactly" designed to a given pressure. For vessel, the designer can choose a thickness to the exact 1/32" (to the exact millimeter or finer (plate gage) thickness) he or she wants to pick to allow for a predicted corrosion allowance and stress level. More often, she'll pick some standard size, but lots of other thickness are available (at higher price.) So the head and walls will be tightly spec'ed, but the thousands of feet of pipe wall thickness in a plant won't change over a wide range of diameters and internal pressures.

Support intervals, hangers, etc depend on that weight of pipe. So intermediate stress (cyclic loads from hammer and thermal expansions and vibration) vary all over the place on the same piece of metal.

The fundemental requirement is that the metal you chose be able to withstand all design conditions you predict and all accident conditions you are required to meet. Further, you must be able to justify the spec you referenced, the metal (spec & thickness) you chose, the loads you expected, and the limitations of those loads place on that metal choice when you face a dead employee, his spouse, your customer, the insurance commission, and the state registration board.

A lawyer might be able to argue points of law up the Supreme Court. If the metal breaks, it doesn't matter what the "law" is interpreted to be.

Piping Codes differ from vessel codes in several important ways.

1. As Robert Cook has suggested, they are more "robust," intended for use by many different groups of people rather than just engineers with a highly developed specialty such as the typical BPVC user.

2. Piping Codes deal with systems that are frequently restrained by other, more costly equipment. Thus the Piping Codes have to account for the self-limiting thermal stresses and other things that vessels and tank design engineers don't have to worry about.

3. Piping systems often have to cope with cyclic loadings. It's far easier to cause a full-range temperature cycle on a spool of pipe than on a pressure vessel, for example. Piping systems also react differently to wind and seismic loads than pressure vessels or tanks do, with cyclical bending stresses predominating. Pressure Vessel Codes tend to be more concerned with local stresses. So the Piping Codes are more reflective of the considerations of fatigue loads than the BPVC.

So, I would say that it's a mistake to design something that can surely be considered to be "pipe" without using the design rules and load cases required by the appropriate Piping Code. But as Mike Kowal explained, sometimes it's hard to tell what's pipe and what's a vessel. If you are operating in this gray area, it's a real good idea to discuss things with the owner before proceeding.

It's questions like these that make (or break) engineers! That key phrase that was used endlessly throughout my college courses comes to mind: "Engineering Judgement".

Can you treat a pipe as a pressure vessel? Absolutely. But does it make sense to do so? That is something that must be determined on a case by case basis.