There are four main design codes that are used on a regular basis for the design of vertical storage

tanks these are as follows:

• Good Engineering Practice

• BS EN 799 Part 5 : Carbon Steel Oil Storage Tanks

• BS 2654 : Manufacture of vertical steel welded non-refrigerated storage tanks

with butt welded shells for the petroleum industry.

• BS EN 14015 : Specification for the Design and Manufacture of site built vertical,

cylindrical, flat bottomed above ground, welded, steel tanks for the

storage of liquids at ambient temperature and above.

• API 650 : Weld Steel Tanks for Oil Storage

Below Wefco has summarised the main design limits and the NDT requirements of each of the above

common codes / practices.

Good Engineering Practice

This is not a national design code, but an interpretation of the requirements to build a simple

atmospheric vertical storage tank and such can vary greatly from fabricator to fabricator both in

interpretation of the requirements and the fabrication and welding quality.

Wefco’s “Good Engineering Practice” tanks are usually based on BS EN 14015 but with out any of

the NDT requirements of the code (lifting attachments would still be 100% MPI / DPI). Full design

calculations would not normally be carried out or made available to the client. The tanks would

generally be 5 or 6 mm thk depending of the tank dimensions and would normally be pneumatically

tested, with a hydro test being available at the clients requested.

BS EN 799 Part 5

This standard covers small rectangular tanks, vertical flat bottom dished top, vertical dished top and

dished bottom tanks and also horizontal tanks and are limited to 10 m max in height. These tanks

are sub-dived into types A to K, based on size and equivalent liquid head above the tank. These

Types are summarised in the text below taken directly from the code

Shell and head thickness varies for each type and size of tank and range from 4 mm to 10 mm for

shell and dished ends. The code covers the use of carbon steel materials only.

There are no requirements for any NDT to BS EN 799 Part 5, however Wefco would carry out 100%

MPI on the lifting attachments as a matter course. The tanks can be pneumatically tested and leak

tested using a soapy water solution, or hydro tested at the client’s request. Wefco’s preferred option

is an air test (which is the more cost effective option for the client), due the environmental issues of

using and deposing of the test water.

BS 2654

This code covers the design and fabrication of flat bottom cone top vertical storage tanks and has

been superseded by BS EN 14015.

There are three design sub-groups which are:-

1) Non-pressure tanks. Which are designed for an internal pressure of 7.5 mbarg and 2.5

mbarg vacuum.

2) Low pressure tanks. Low pressure tanks are design for an internal pressure of 20 mbarg

and 6 mbarg vacuum.

3) High Pressure tanks. These are deigned for an internal pressure of 56 mbarg and 6

mbarg vacuum.

BS 2654 covers the use of carbon steel only.

The NDT requirments included radiograpgy (see a the table below), MPI/ DPI and vacuum box

testing. A 100% MPI / DPI is required for the the shell nozzles

The code requires a hydro test with an air test to the roof space. Pneumatic testing of the tanks is

not covered in the code. Again it is still our preferance to air test and we do ask for an concension

depending on the tank contents.

BS EN 14015

This is the replacement for BS 2654 and covers a wider range of design conditions and also includes

wind loading and earthquake.

The code does however state it is for site built tanks but is widely used to cover the design and

fabrication of smaller shop built storage tanks in both carbon and stainless steel. The code covers

the use of flat bottom and cone roofs and does not allow the use of dished end.

The maximum design condition allowed for under the code is -20 mbarg to + 500 mbarg and is done

in four stages (see table below), with a design temperatures of between -40 to +300 deg C.

Therefore not all tanks built to this standard will take the maximum design pressures noted above.

There are requirements for NDT (visual, radiography, vacuum box testing and MPI/DPI) in BS EN

14015 these are cover by tables 29, 30 and 31 shown below.

The code requires a hydro test with a air test to the roof space. Pneumatic testing of the tank is not

covered in the code. Again it is still our preferance to air test and we do ask for an concension

depending on the tank contents.

API 650

API 650 is to put it simply the American version of BS EN 14015. Obviously there are differences in

allowable design pressures, minimum thickness, testing etc. It allows the the use of both carbon and

stainess steel, with the stainless having its own appendix (Appendix S)

The maximum allowable design pressure to API 650 is 172 mbarg (2.5 psig)

The are requirements for both radiography and MPI , see the table below

The code requires a hydro test with a air test to the roof space. Pneumatic testing of the tank is

covered in API650 but only in the absence of adequate quantity / quality of test water. Again it is still

our preferance to air test and we do ask for an concension depending on the tank contents.