Design Code for Horizontal Storage Tanks

I thought you wanted to eliminate anonymous posters.

What are they, then?

Nice illustration.

If you can't beat 'em............................................ use 'em and toss 'em aside.

What you have pointed to, Wagas, is the classic hole in the western system of codes and standards relating to atmospheric storage tanks.

Some items to remember:

- Horizontal axis, dished end tanks are ALWAYS more expensive than flat bottomed, vertical tanks for low pressure liquid storage. You should have a good reason to be selecting this type of tank..... " my boss said to do it this way" is not a good reason.

- Flat bottomed tanks are limited to 2.5 psig design pressure under API-650 and ASME VIII tank rules are for storage at 15 psig and above.

- Horizontal tanks (sometimes called bullets) are economically supported on two saddles and must resist the bending stresses generated by this type of support as well as the concentrated stresses at the horn of the supporting saddle .

Based on this, the answer to your question is that low pressure horizontal tanks are commonly designed to the rules of ASME VIII with a minimum pressure of 14 psig. No code stamp or certification is required.

The tank cost will, of course, also be controlled by your selection of diameter, length and accessories.

Why must your tank be horizontal ?

In the United States, UL-142 'These requirements cover steel primary, secondary and diked type atmospheric storage tanks intended for noncorrosive, stable flammable and combustible liquids that have a specific gravity not exceeding 1.0 in aboveground applications.' is often used for stationary tanks. DOT requirements would cover portable tanks. Don't know about your location.

21.4.2 Design Standards for Storage Tanks.

21.4.2.1 Design Standards for Atmospheric Tanks.

21.4.2.1.1*

Atmospheric tanks shall be designed and constructed in accordance with recognized engineering standards. Atmospheric tanks that meet any of the following standards shall be deemed as meeting the requirements of 21.4.2.1:

1. API Specification 12B, Bolted Tanks for Storage of Production Liquids
2. API Specification 12D, Field Welded Tanks for Storage of Production Liquids
3. API Specification 12F, Shop Welded Tanks for Storage of Production Liquids
4. API Standard 650, Welded Steel Tanks for Oil Storage
5. UL 58, Standard for Steel Underground Tanks for Flammable and Combustible Liquids
6. ANSI/UL 80, Standard for Steel Tanks for Oil-Burner Fuels and Other Combustible Liquids
7. ANSI/UL 142, Standard for Steel Aboveground Tanks for Flammable and Combustible Liquids

1. UL 1316, Standard for Glass-Fiber Reinforced Plastic Underground Storage Tanks for Petroleum Products, Alcohols, and Alcohol-Gasoline Mixtures

1. ANSI/UL 1746, Standard for External Corrosion Protection Systems for Steel Underground Storage Tanks
2. UL 2080, Standard for Fire Resistant Tanks for Flammable and Combustible Liquids
3. ANSI/UL 2085, Standard for Protected Aboveground Tanks for Flammable and Combustible Liquids

"Recognized engineering standards" for the design and erection of tanks used for the storage of liquids have evolved from over 100 years of experience. No single standard is universally applicable because of the wide variety of liquids and their properties. In addition, latitude in the choice of construction materials is permitted where circumstances warrant. The standards listed in 21.4.2.1.1, 21.4.2.2.1, and 21.4.2.3.1 cover those tanks that are designed with a suitable factor of safety to ensure that the contents of the tanks are safely contained under normal operating conditions. Emergency conditions, such as exposure to fire, require special details of construction or special protection. Such requirements are dealt with later in this chapter.

The wording of 21.4.2.1.1 is broad enough to allow flexibility in tank design and installation methods. The authority having jurisdiction may allow departures from recognized standards where special needs or unusual situations warrant, as long as equivalent performance is ensured. This enhanced flexibility has proven to be beneficial for aboveground tanks as well as underground tanks, as environmental protection receives more attention. Witness the many factory-built "new technology" tanks being produced today, such as concrete-encased tanks, now recognized by addition of the reference to ANSI/UL 2085, Standard for Safety for Protected Aboveground Tanks for Flammable and Combustible Liquids, and the several types of secondary containment-type tanks now included under the listing criteria of UL 58, Standard for Steel Underground Tanks for Flammable and Combustible Liquids, and ANSI/UL 142, Standard for Steel Aboveground Tanks for Flammable and Combustible Liquids.

The allowance for bolted tanks for storage of oil in producing areas, as given in 21.4.2.1.1(1), recognizes the fact that the tanks are usually small and can be easily relocated. An oil well normally has a relatively short life; consequently, the need for tanks at a particular site might be temporary. A bolted tank is easily dismantled and moved to a new location. Although such tanks are vulnerable to fire damage from a ground fire because of damage to the gaskets, the advantages outweigh the shortcomings. At main gathering stations and pipeline terminals, more substantial tanks would be required.

21.4.2.1.4

Horizontal cylindrical and rectangular tanks built according to any of the standards specified in 21.4.2.1.1 shall be permitted to operate at pressures from atmospheric to a gauge pressure of 1.0 psi (6.9 kPa) and shall be limited to a gauge pressure of 2.5 psi (17 kPa) under emergency venting conditions.

FAQ

What is meant by the term emergency venting conditions in 21.4.2.1.4?

Tanks constructed to ANSI/UL 142, Standard for Steel Aboveground Tanks for Flammable and Combustible Liquids,specifications are shop-built and leak-tested prior to shipment as completely assembled units. Although horizontal tanks are pressure-tested to 5 psig to 7 psig (34.4 kPa to 48.2 kPa), they are limited to service at a 1 psig (6.9 kPa) maximum internal operating pressure and to 2.5 psig (17.2 kPa) under emergency venting conditions. These restrictions recognize that failure of a horizontal tank is invariably accompanied by release of the tank contents. Vertical tanks are required to be tested only to a pressure that exceeds 1.5 psig (10.3 kPa); however, they are also subject to liquid release upon failure, so the same service restrictions apply. There is an exception: Vertical tanks built to UL 142 specifications and labeled "built to weak shell-to-roof joint design" are not expected to fail in such a manner as to release the contents. It is assumed that the weak seam will fail upon overpressure and only vapors will be released.

The term emergency venting conditions is not defined in Chapter 3. It is meant to describe a situation where a tank is fully exposed to flame, resulting in heating and boiling of its contents. Normal venting is based solely on liquid addition or withdrawal and atmospheric temperature and pressure changes. (See 21.4.3.) Because consequences of fire exposure can have a substantial effect on the allowable spacing and location of tanks as set forth in Section 22.4, this subject must be dealt with before commenting on specific requirements. Section 22.7 addresses the venting capabilities necessary if the tank is exposed to a fire.

Flames contacting aboveground tanks can heat the contained liquid, causing it to boil and can also damage tank supports and the unwet portion of the tank shell. Boiling effects can be mitigated by design (see 22.7.2) or by additional relief valves (see 22.7.3). Supports for elevated tanks can be constructed of fire-resistive materials, as covered in 22.5.2, or insulated to delay failure. Flame contact on the unwet portion of the shell of a tank can heat that portion of the shell to the point that it loses much of its structural strength. For a vertical tank, this heating can result in distortion at the top of the shell, but tank collapse and spill of contents is not likely. Heating the top of the shell of a horizontal tank, however, is likely to result in structural failure with release of contents.

For a pressure tank, the result of heating the unwet portion of the shell can be serious. Such tanks usually store liquids having boiling points below atmospheric temperature, and therefore their relief valves are set to maintain the resulting higher pressure. When heated sufficiently, the shell loses strength and the resulting tear is likely to spread below the liquid level. This tear can extend completely around a horizontal tank so as to sever the head, release the contents, and cause the pieces to rocket. The possibility of this type of failure is accounted for in Table 22.4.1.3. This phenomenon is known as a "BLEVE" (boiling liquid-expanding vapor explosion) and is defined as catastrophic failure of a container into two or more major pieces at a moment in time when the contained liquid is at a temperature well above its boiling point at normal atmospheric pressure. The classic cases of BLEVEs have involved tank cars of liquefied petroleum gases, but the phenomenon is applicable to liquids as well.

Whose standard is that?

The posting above refers to Section 21.4.2 - part of NFPA 30 ( This tank fire protection standard covers inflammable and combustable liquids)

But, we know nothing about the OP's liquid to be stored or the SG of that liquid.... This is because it is his first assignment in tank design.

The UL standards are only acceptable for hydrocarbon storage, to 50,000 gallons, with a liquid SG maximum of 1.0. They are prescriptive standards, not design standards

Use of ASME section VIII (no code stamp) will cover ALL TANK SIZES, ALL LIQUID SGs and provides complete, conservative and competent designs....... like it has for the past 75 years !

Again, what are you storing and why must the tanks be horizontal ?

I think you can open https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CB0QFjAA&url=https%3A%2F%2Fwww.aij.or.jp%2Fjpn%2Fdatabox%2F2011%2Fstoragetanks2010edition.pdf&ei=Mm1qVNDqNIeUuATIuoCADg&usg=AFQjCNFAQmNKESORjziwyEK-lUyMncQQ6w&sig2=JxU7d-0kAOtXwTNcQ2dtXg&bvm=bv.79908130,d.c2E. Just for your referrence. Thx.