What is the common failure mecahnism for a Deaerator Tank, what is the recommended inspection method, and how often should they be inspected?

Answered by: Kevin Kissig

 

 

A Deaerator (DA) Tank is a pressure vessel found in boiler systems which removes gases (mainly oxygen) from condensate and make-up water.  They generally consist of a water storage section and a deaerating/heating section.  These tanks are typically made of welded carbon steel, and the residual stress of the welds coupled with the mechanical stress of operation makes them susceptible to weld cracking.  Left undetected, these weld cracks can lead to catastrophic failures.  In addition to the damage caused to the tank itself, catastrophic failures of a DA Tank often turn the tank into a projectile as steam and water are released from the failure resulting in additional destruction to facilities, equipment, and personnel.

 

Preventative measures are a good starting point when considering a maintenance program for DA Tanks.  When purchasing a DA Tank, while it is generally not required, insist that all welds be stress relieved (post-weld heat treatment) in order to reduce the residual weld stress that often leads to cracking.  All welds should be inspected for cracking by qualified technicians utilizing wet fluorescent magnetic particle inspection (WFMT) within five years of being placed in service, and then on a five-year cycle.  This will help ensure that any cracking caused by operating stress can be detected and repaired prior to a catastrophic failure.

 

While there are monetary and time costs associated with timely inspection and repair schedules, these costs are minimal when considering the costs associated with a single unscheduled repair resulting from a catastrophic failure.  It is very important that these thanks be properly maintained from both a reliability and safety consideration.  For more information, please refer to the National Board of Boiler and Pressure Vessel Inspectors at www.nationalboard.org











I am new to the NDE industry. How long does it typically take to become certified in each method?

Answered by: David Kissig

In order to properly answer this question, it is important to know the type of industry and country the work will be performed in.  A list of several certification programs are listed below to provide a short insight into the many programs available.

• SNT-TC-1A - The American Society of Nondestructive Testing (ASNT) - This set of guidelines, first published in 1966, is call the Recommended Practice No. SNT-TC-1A.  This document established the levels of qualifications based upon a combination of education, training, experience, and qualification examinations.
• CP-189 - The American Society of Nondestructive Testing (ASNT) - This standard was approved in 1989.  The intent was to produce a document that provided strict requirements rather than guidelines.  ASNT obtained ANSI (American National Standards Institute) accreditation to process this document and recognized ASNT CP-189 as a national standard thus becoming ANSI/ASNT CP-189.
• NAS-410 - The National Aerospace Standard - In the 1990's MIL-STD-410E was replaced by NAS-410 for aerospace and defense related military or government contracts.  The current revision (rev. 3) is considered technically equivalent to the European Standard EN4179.
• ISO 9712 - International Standard for Nondestructive Testing Personnel Qualification and Certification - ISO 9712 was published in 1992 as an international standard that would be recognized by participating nations.  This document is similar to SNT-TC-1A with an additional requirement that personnel be certified by a nationally recognized certification program and required more training than does SNT-TC-1A.
• CGSB-48.9712 - Natural Resources Canada (NRCan) - This certification program is utilized in Canada and is managed by a nation-wide independent NDT certification agency.  The purpose of this program is to provide an unbiased Canada-wide NDT certification of personnel.

As you can see, there are many different personnel qualification and certification programs currently in use around the world.  The ASNT SNT-TC-1A employer-based certification has been widely accepted throughout the United States and is the program First Quality Solutions uses.  It is this program that we will outline to provide our answer to your question.



SNT-TC-1A has been prepared to establish guidelines for the qualification and certification of NDT personnel whose specific jobs require appropriate knowledge of the technical principles underlying the nondestructive tests they perform, witness, monitor, or evaluate.  Two definitions that are important to this discussion are: Qualification and Certification.

• Qualification - Defined by ASNT as; Demonstrated skill, demonstrated knowledge, documented training, and documented experience required for personnel to properly perform the duties of a specific job.
• Certification - Written testimony of qualification.

Once the qualification requirements have been met, the employer then certifies the individual in the particular method.  Prior to certification of NDT personnel the employer shall establish a written practice for the control and administration of NDE personnel training, examination, and certification.  The length of time to become certified will vary based on the method and the requirements of training, experience and testing.  Another concern is whether a company will certify to level I and then to level II, or directly to level II.  The training hours remain the same for both approaches, however, the requirements for level I and level II are combined to certify directly to level II. 

The  recommended practice provides the required hours of experience and training for each method.  The requirements vary from 210 experience hours and 24 training hours to obtain visual inspection certification with a high school education to 1470 experience hours and 68 training hours for thermography. 

The question of how long does it take depends on many factors and needs to be addressed with one's employer, with the requirements of each industry, codes, and standards taken into account.  As you can see there are many variables to consider, but I hope this gives you a general idea of the commitment needed to become a part of this exciting and rewarding industry.  A more  specific answer can be provided by asking about a single NDT method, please email us if you would like more details.