Hydro testing: the real story

Understanding API 650 and API 653 Hydro Testing

First of two parts

Hydro testing and API 650

A common misunderstanding in the market is the purpose of Hydro Testing (also known as Hydrostatic testing) of new built API storage tanks. Many folks are of the belief that the hydro test on a new built API 650 tank is just a leak tight test while others believe that hydro testing is important to do for settlement measurement. Both are partially correct, but also demonstrate the inconstancy around a full understanding of what is involved when hydrostatic testing a new built tank. In our next article, we will cover the hydro testing requirements of existing tanks and/or those repaired under API 653 and recertification.

This article will discuss how hydro testing is not just simply water transfer and that, when done by experienced specialists, a hydrostatic test can be made to suit several types of tank(s) services, including testing of components and elements of a tank that are evaluated when hydro testing is performed completely and properly.

Without getting too involved in risk management guidelines in specific end users’ and owners specifications, or considering the exemptions or the waivers that are granted within the body of the API-650 Standard, the following are quite simply summarized “the main reasons for Hydro testing a new built tank”:

• Confirm that the tank is leak free and tight, nozzles, manways, shell seams, attachments etc.
• In the event a pontoon style floating roof is installed, confirm pontoons are leak free and manway access operational.
• Confirm weld integrity is suitable to withstand operational conditions
• Allow for confirmation of uniform settlement on the tank base.
• Perform full functional test of all working components of the tank accessories, such as: Check rolling roof stairways for full range of operation and self leveling functional test, floating roof drain range of operation, floating roof range of operation, floating roof seal may be elected to be installed and tested for range of operation, anti rotation devices etc.…

In summary, Hydro testing demonstrates a tanks fitness for service by providing an integrity test, minimizing the risk of catastrophic failure by using test conditions that replicates operational conditions using test medium (water) with a specific gravity greater than that designed for cargo. Therefore, this hydrostatic test subjects the tank to a harsher condition than the tank would see during normal operation. Additionally, other testing steps may also be added to a hydrostatic test situation for items such as, uplift test of anchor bolts and chairs as well when tanks are designed for elevated internal pressures (lower than those in a API- 620) or in situations where a tank is designed to operate in a seismic zone, tests for uplift can be confirmed.

As just mentioned above, in situations where a tank may be designed to operate at a small internal pressure, which is less than 2.5 PSI (above 2.5 PSI API-620 applies) or when the internal pressure does not exceed the weight of the roof plates and additional test is performed. In this designed for situation, this type of tank must be tested with water 51 mm or 2 inches above the top angle and a vacuum box test of all roof seams / welds is performed. Caution must be used when conducting the following test condition and strict operating test procedures must be followed. The code does allow test some pneumatic test procedures where design pressure exceeds the weight of the roof plates and additional pneumatic test of 1.25 times design pressure can be added. While there are many situations that may dictate this additional testing, this procedure is typically used on tanks having anchor bolts and chairs to test uplift as well avoid deflection of tank shell to bottom over pressurization and bottom deflection. It is not recommended that the cargo be used to hold the tank done as the shell to floor weld joint is still under stress which is not the preferential joint of failure should it occur.

Many tank terminal owners do take the hydro testing portion of the tank out of the contract and manage the test themselves, in some cases the testing may be left in the scope of the tank constructor, who may elect to perform the hydrostatic test portion themselves or subcontract this out to specialists such as NCS Fluid Handling Systems. These same tank constructors may subcontract the water supply, transfer portion of filling and draining the tank(s), however contrary to what some water supply or management companies may advertise this is not performing the hydrotest, casting another area of confusion around expertise and capability of performing a proper hydro test.

The team at NCS Fluid Handling Systems take the training and education of what a full Hydro test involves quite seriously and provides training sessions through various forums such as lunch and learns to any size team or group. We believe that through ongoing education at the customer level we can help those designing or evaluating testing requirements to understand the whole process, not just water management or transfer and, how by considering a few relatively simple requirements that do not add significant overall project expense, we can provide comfort that operational risk is minimized and asset integrity is maximized.