How the European Standard was Hammered Out

When London’s Fire Inspector, Jamie Thompson, was asked to help write a European standard on underground tanks, he thought it might take a year or two. He explains why it took six.

The right question is not
“Why did standardization on underground tanks take so long?”
but
“How was it achieved at all?”

When I was first approached to help write a European standard on underground tanks, I was surprised when our committee was given three whole years to complete the job. That was in 1990. You may therefore appreciate my relief in January 1996—some six years after the first meeting—when the final draft was produced for public comment. This standard is expected to be adopted before the end of 1996. What on earth did we talk about for so long and what caused the problems?

European CEN and sensibility
To answer this question, I will need to give you a little background information. Each country has a certain amount of bureaucracy in running its own affairs. When the European Community was formed, it was soon evident that an additional (although necessary) level of bureaucracy had been added for us Europeans to concern ourselves about: CEN.   

CEN is the “Comite European de Normalisation,” or the European Committee for Standarisation. Headquartered in Brussels, Belgium, CEN’s main function is to produce, promote and disseminate European standards. The object of producing these standards is to allow free market access across the community (in fact, 32 nations) with no artificial barriers being placed in the way of manufacturers.

Eighteen nations are CEN members, and represented by their own standardization organizations. Another 14 nations, mainly from eastern Europe, are affiliated members of CEN (see Directory below). CEN is a busy organization, with some 2,700 full European standards produced by the middle of 1996. Today, there are still hundreds of standards being developed—many of which directly affect the petroleum industry.

How hard could it be?
One of these many standards is for underground steel gasoline tanks. You might think, as did I initially, “what possible problems could be encountered in getting a standard completed for a simple cylindrical object that is welded together?” Well, there are only four meetings a year, which are sometimes attended by more than one representative from a country. Another factor is the need to cope with different languages. Translations are necessary into the three official community languages of English, French and German.

In addition, practically each country had its own standards for underground tanks, and was keen to see its own views reflected in the new standard. Also, no two countries were alike in how they enforced their standards. Some in the north of Europe were very environmentally minded; others were more safety minded; and some had no enforcement at all.

Given these challenges, maybe the right question is not “Why did standardization on underground tanks take so long?” but “How was achieved at all?”

It is my observation that the progress of our work has been proportional to the time we spent together. As we got to know one another, we came to understand each other’s problems, fears and ambitions. That’s why it was almost as important to mix socially as to attend the official sessions. Only after we got to know one another as individuals was real progress made.   

Each of the four annual meetings is hosted by one of the countries taking part in the process. A typical meeting starts at 10 a.m. on the first day and lasts until 5:30 p.m., with a social function that evening. The following day, the meeting begins at 8:30 and ends early at 4 p.m., to give people enough time to fly home.

This tank is being coated with a polyethelene paint, which is up to 0.04 inches thick. The European standard specifies the type and thickness of the coating.

US vs. European tanks
Shape—One of the first items we covered in our meetings was the shape of the tanks. We agreed that the tanks would be cylindrical and have dished ends—mainly because they would be better able to withstand external pressure, but more practically because the vast majority of tank manufacturers in Europe already built their tanks that way. The U.S. tanks traditionally have flat ends.   

Double skin—A major turning point in developing the standard was the agreement to have double skin tanks for storing gasoline. This proved to be quite an improvement in standards for most countries since the majority of them still accepted single skin steel. Germany was a prime supporter of secondary contained tanks since they had been required in that country since 1968. Steel thickness—The steel is made to specific European norms, with the minimum thickness determined according to a table. This is another area where there will be vast differences between US and European tanks.

Tanks manufactured in Europe are made to three classes: A, B and C. The table on page 7, European Tank Classifications, shows how tanks are categorized. There are two main distinctions among the three classes: (1) the thickness of steel in the larger diameter tanks; and (2) the pressure that the tanks are subject to after they are manufactured.

Class A tanks are the most widely used in Europe in that they include the standard gasoline tank. Class B tanks are stronger than Class A tanks; and Class C tanks are identical to Class B tanks, except that they have the design type tested to a pressure in excess of 10 Bar (145 psi), making this design “explosion proof.”

According to the standard, each Class A tank, before leaving the factory, will be filled with water and hydraulically tested to .75 Bar (11.0 psi). The interstice will also be tested to 0.6 bar (8.8 psi) to ensure that the tank will operate successfully in the conditions in which it is installed.

Class B 3m (10 ft) diameter specifications will have a 9mm steel inner skin and 5mm outer skin. The tank will also be hydraulically tested before leaving the factory to 2 Bar (29.4 psi), and the interstice between the skins will be pressure tested to 0.6 Bar (8.8 psi).

Traditionally, the interstice will be filled with an environmentally friendly anti-freeze that resists corrosion. Alternatively, a pressure or vacuum leak detection system is used. These systems form the basis for a positive leak detection method. Tanks do not have the vapor or liquid detector often used in the interstice of double skin tanks in the U.S.

European Tank Classifications
Test pressure and nominal wall thickness for inner and outer skin of tanks, dished ends and compartment dished ends:

Separate compartments
It is quite common to have European tanks divided into separate compartments, but this is not so usual in the United States. Each European tank is required to have at least one manhole, with the only entry into the tank provided through it (or them). The manhole needs to be at least 600mm (24"). The number of bolts and bolt sizes is also universal throughout the standard; this makes it easier for the manufacturers. In addition, the standard lays down the methods of welding, and where in the tanks that these weld types are acceptable.

Several issues proved to be contentious. One concerned the surface preparation and coating of tanks. Germany used thick bitumen at least 5mm (G") thick, and France used polyurethane. I regret to admit that the UK at the time had probably the worst coating in Europe, but we were soon to benefit from our neighbors and their investment made in the modern coatings.

A matrix of coatings has now been established with surface preparation, minimum thickness and holiday testing of the coating. There seems to have been a preference in Europe for polyurethane coatings developed by the manufacturers and customers—with manufacturers now providing 30-year guarantees for their tanks.

The most contentious issue affecting the standard was Germany’s request to build explosion resistant tanks. In Germany, technical rules had long given this option to users who would then be free from placing flame arresters on tank vent pipes. Although the vast majority of participants felt that building explosion resistant tanks was unnecessary, we were all able to work together to develop a class of tanks to enable Germany to continue with this option. (Although in the telling of it, this process sounds simple, it did take many months of negotiation and not a few beers to reach agreement!)

Standard development
I think that the most remarkable part of this process was that manufacturers were building to the standard as it was developing. In the first 12 months of our discussions, industry leaders in the UK were calling for tanks to be built to the new specification—which was altering as the meetings progressed. This was also happening in other countries, and it demonstrated the need for the standard.

Almost in unison, the heads of major oil companies in Europe saw the benefit that this standard provided, and they are now purchasing one common gasoline tank for each European country—which, a few years ago, would have meant trying to satisfy at least 18 different standards!

Our committee has yet not tackled corrosion in the standard, other than by providing high standards for coatings. Despite some prodding from regulators, it appears the Industry is not yet ready to support the need for cathodic protection; however, I hope its time will come.

Standard review
CEN committees review standards periodically—after three years, if companies wish it, but always after five years. When produced, this standard will be a descriptive product standard—written using the good experience of many countries.

However, the ultimate objective of CEN standards is to produce performance standards. This means, in effect, that written criteria are established that a tank has to meet when it is buried underground. Then it is left to designers to build tanks and prove that they meet those performance requirements.

Discuss