≡ Menu

Introduction to ASME IX

By Carlos F Molina

One of the content areas that worked out best for me during my exam three years ago was welding. In the time I presented the exam, the number of questions was different from nowadays. From a total of 16 questions about welding, I got 15 right (nowadays they ask only 8). It helped me a lot knowing about welding.

The body of knowledge gives a broad guide of what will appear in the exam related to welding. It says the following:

The inspector should have the knowledge and skills required to review a Procedure Qualification Record and a Welding Procedure Specification or to answer questions requiring the same level of knowledge and skill. Questions covering the specific rules of Section IX will be limited in complexity and scope to the SMAW and SAW welding processes.
1. Questions will be based on:
a) No more than one process
b) Filler metals limited to one
c) Essential, non-essential, variables only will be covered
d) Number, type, and results of mechanical tests
e) Base metals limited to P1
f) Additional essential variables required by API-650 or API-653
2. The following are specifically excluded:
a) Dissimilar base metal joints
b) Supplemental powdered filler metals and consumable inserts
c) Special weld processes such as corrosion-resistant weld metal overlay, hard-facing overlay, and dissimilar
metal welds with buttering
d) Charpy impact requirements and supplementary essential variables
e) Any PQR and WPS included on the examination will not include heat treatment requirements.

As you can see, some of the questions are based on ASME IX. With this in mind, I decide to put on some articles on successfully reading and reviewing a WPS and a WPQ. Let´s check an introduction.


ASME IX “Welding, Brazing, and Fusing Qualifications. Qualification Standard for Welding, Brazing, and Fusing Procedures; Welders; Brazers; and Welding, Brazing, and Fusing Operators” is a part of the ASME Boiler and Pressure Vessel Code, that regulates the design and construction of boilers and pressure vessels. API 650 trusts ASME IX for weler procedure and welder performance qualifications

Some important definitions found in QW-200

WPS: A Welding Procedure Specification (WPS) is a formal written document describing welding procedures, which provides direction to the welder or welding operators for making sound and quality production welds as per the code requirements
PQR: The Procedure Qualification Record is a Record containing information about the tests conducted over the welds made to a WPS, the variables used during welding of the test coupon, and the succesfull qualification of that WPS.
WPQ: A Welder Performance Qualification is a document recording the ability of a welder to deposit welds in the manner described in the WPS.

All of the three documents contain a set of variables to control. Variables that may be used in a welding procedure test are divided into 3 categories.

Essential Variables Are variables that have a significant effect on the mechanical properties of a joint. They must not be changed except within the limits specified by this code. e.g. Material thickness range, Material Group, welding proccess, etc. The PQR shall contain all essential variables.
Non-Essential Variables Are variables that have no significant affect on mechanical properties. They can be changed without re qualification of the PQR.
Supplementary Variables Are variables that have an affect on the impact properties of a joint. They are classed as Non-Essential if impact testing is not required. This kind of variables won´t show up in the exam.

All variables listed as essential and non-essential should be addressed on the WPS,  while all listed as essential should be addressed in the PQR. Supplementary essential variables should be addressed in both documents when required (See QW-200 of ASME IX). If any of the variables do not apply to the particular application then they should be specified as not applicable. The welding organization can have its own formats for these documents, as long as they meet the aforementioned requirements.

Understanding of the information that should a WPS and a PQR contain is critical. Several WPS can be written on the basis of the successful qualification of the initial preliminary WPS. There is no limit on the number of production WPSs that can be generated from a PQR. And as for the other way around, several PQR can be “summed up” to support a broad WPS, just making sure that the ranges of the variables in the PQRs are the same for the WPS generated.


ASME IX is divided in 4 parts
PART QG, General requirements
PART QW, Welding
PART QB, brazing
PART QF, plastic fusing

We will concentrate in Part QW, which in turn is divided in 5 articles.
• Article I – Welding general requirements
Article II – Welding procedure qualifications
• Article III – Welding performance qualifications
• Article IV – Welding data
• Article V – Standard welding procedure specifications (SWPS)

In ASME IX, as much as 20 different welding proccesses are mentioned when it has to do with procedure qualification. Essential, non-essential and suplementary variables for welding proccesses can be found in tables QW-252 to QW-269.1 of ASME IX. But remember “Questions covering the specific rules of Section IX will be limited in complexity and scope to the SMAW and SAW welding processes“. Which are the essential variables needed for these 2 proccesses? We can find them in QW-253 and QW-254

The nonmandtory appendix B of ASME IX illustrates the diferent formats for welding procedure specifications, Procedure Qualification records and Welder Performance Qualifications, for the SMAW, SAW, GMAW and GTAW proccesses, and the basis for other welding processes may follow the general format as applicable. You should take a look at them.

In the exam, it is required from the candidate to proficciently review a WPS and its supporting PQR that will be given to him. That´s why it is a good idea to be familiar with the appendix B formats.


As we said before, a PQR can be the basis of several WPSs and viceversa. The code only asks for the essential variables to be recorded on a PQR. But just complying with the standard in this case may not be enough to make Welding Procedures of consistent quality. The fact is that a preliminary WPS can be made (although not mandatory), a test set up for this preliminary WPS where all variables should be recorded (essential, non-essential and supplementary), and a PQR containing all of that variables created. After the weld is accepted by testing, now you can stablish a WPS and make it into your procedures. With this recommendations, I created a simple flowchart to understand the proccess.

wps pqr asme ix

Well that´s all for now. Next article will have some questions and more info on qualification of procedures and welders.


I have to give a sincere congratulation to the people that recently passed the exam. Two of my readers have passeb by to tell. Congratulations and keep up the good work.

NOTE: This article took information from wikipedia and gowelding

By Carlos Molina

Pitting is almost a common denominator of all types of localized corrosion. In fact, pitting in tanks can be a consequence of CUI (Corosion under Insulation), MIC (Microbiologically induced corrosion), Soil corrosion, Sour water corrosion, etc, all damage mechanisms mentioned in the BOK for the API 653 exam.

Having this in mind, how can we evaluate shell pitting in tanks? Please keep reading, as the explanation in the API 653 is very short.

[click to continue…]

{ 1 comment }

By Carlos Molina.

Any time that a tank construction project is about to begin, there is this critical part of the trade that is welder´s qualification. Strict control of welders and their qualifications, as the welding procedure specifications, is needed to ensure traceability of your welded joints, for integrity purposes. This webpage usually speaks about the API 653 examination, but today we are talking a little about welders qualifications based on ASME IX. (I assume my readers to know something about welding)

According to the API 653 standard.

Welding procedure specifications (WPSs) and welders and welding operators shall be qualified in
accordance with Section IX of the ASME Code, the additional requirements of API 650, and this standard. Welding procedures for ladder and platform assemblies, handrails, stairways, and other miscellaneous assemblies, but not their attachments to the tank, shall comply with either AWS D1.1, AWS D1.6, or Section IX of the ASME Code, including the use of SWPSs.

We will concentrate in the integrity of the tank; it is, the welds made in shell, bottom and roof.


The objective of welders tests. While WPSs are qualified to check if they can make a good joint, welders are qualified to check if they have the skills to make a sound weld, and there are certain variables that should be controlled during the test. In a tank, they need to be able to deposit weld in the flat, horizontal and vertical positions at least. The overhead position

How to know if the welder is good. There are two options regarding the use of a WPS during a welder´s test. Or you describe the WPS to him or he reads it by itself. I usually prefer that they read the WPS themselves, to check if they can do it. However, sometimes you will need to describe the procedure to them, in order to acommodate as many approved WPSs to the test being made. As you know, with one test you can approve the welder for several WPSs. As a way of avoid wasting time, welder’s qualification tests may only be taken by welders who have received appropriate previous training (both practical and theoretical) and who have had sufficient opportunity to practise the craft.

How identify welders for testing and production welds? There are many ways to do this, but we usually ask the welders to give us the first letter of his name, then the first letter of his surname and the last 2 digits of his I.D. number. This way, is very unlikely that 2 welders would share the same identification for the project. Besides, it is very difficult that a welder would forget this data when asked about his identification again.


How to set the plates? In a tank, the majority of welds will be Flat. Horizontal or Vertical. To qualify these positions, set 3 plates together with their bevels already made as in the picture below. The welders will set up the plates themselves. The first joint will be welded in the 2G test position and the second one rotated 90° and welded in the 3G test position. Once the welder finishes one position he can continue to the other position. Testing in 2G and 3G test positions will qualify a welder to practically all of the positions of welds according to ASME IX QW-461.2, except fillet welds in the overhead position (in an angle between 125 and 235 in the picture in QW-461.2)


If you wish your welders to be qualified for overhead fillet welds, make sure to test them using 4G or 3G and 4G.

Number of tests. For a given welding proccess, welders can take only one test. Test retakes will only be done if granted by the contractor. As a general rule,

What to look for. The root pass shall be with no holes or disuniformities. The final pass should show no disuniformities. No welder shall make any repair. As a general rule, they can use the angular grinder whatever much they want according to the WPS, but only if it is part of the normal welding process, not for repairs. It is a good practice not to qualify only with visual inspection, but with volumetric NDE as weld, so you will have something written to back up your visual testing, and avoid any bad feelings between you and the welder. Use a flashlight after any root pass to check if light passes trough it. A welder shall be regarded as having passed the test provided that the imperfections fall within the limits of ASME VIII.

What will you need. Carry a ruler, a flashlight, a voltiamperimetric  clamp that can handle AC and DC, a cronowatch, weld gauges and a calculator to estimate welder´s speed

What if you are a welder? Well. Practice a lot the days before a test, if you can by your own, or get some time in a local union training center so you won´t flunk.

Thank you so much for your time. I hope you fid this post useful

I want to receive more APIEXAM articles

* indicates required



By Carlos F Molina


What we are going to do is to dissect the diagram in FIG. 4.1 of API653 until we truly understand it. and there will be no way we fail any of the questions related to this in the exam. First of all we are going to see the following diagram.


Look at the vertical sections drawn in the picture. Remember that hoop stresses (stresses that are tangential to the shell of the tank) are higher in vertical planes than in horizontal planes. [click to continue…]

{ 1 comment }

Vacuum testing in tanks

By Carlos Molina.

I am writing this post because of this video that a good friend  sent to me about vacuum box testing, that I want to show you. Besides, I will give you instructions for the construction of your own flat vacuum box, but first a little background.


[click to continue…]


By Carlos Molina

Last time we saw the basics of shell calculations for reconstructed tanks. Today we will make some practice exercises on determining thicknesses for reconstructed tanks

The book of knowledge says this about reconstructed tanks:

The inspector should be able to determine the minimum thickness of the shell of a reconstructed tank. The inspector should be able to:

c) Calculate “td”, design shell thickness (API-650,, for tanks of 200 foot diameter and smaller)

d) Calculate “tt”, hydrostatic test shell thickness (API-650,


We have seen an advance to this issue in the article we had on calculating joint efficiencies, but we will have a further look to the formulas that appear there. [click to continue…]


By Carlos Molina.

Today we will have a glimpse on reconstructed tanks, as needed to pass the api653 exam. This is the first post of a 2 article series.

First of all, let´s see the definition of a reconstructed tank according to API 653


Any work necessary to reassemble a tank that has been dismantled and relocated to a new site. In short, a reconstructed tank is a tank that has been dismantled and its pieces used together to make a new tank. But this should be made carefully.


I have a confession to make: I have never seen one reconstructed tank in my professional exercise. Maybe one of my readers will give us more tips about it. At this stage, I seriously doubt that I would ever know one reconstructed tank, given that the subject of brittle fracture has prevented a lot of owners from using old tanks for new ones. [click to continue…]


By Carlos Molina

Hi. This is a short post, written to teach you how to calculate the number of points for settlement measurement around a tank. If you want to become a certified API 653 inspector, this is what the body of knowledge for the 2015 API 653 certification exam asks from you

The inspector should be able to calculate the number of survey points for determining tank settlement.

At least one question on this matter will show up in the exam. And it is such an easy thing…. [click to continue…]


By Carlos Molina

In terms of risk, catastrophic storage tank failure stands as one of the most costly events that can ever happen. It happens with no warning. It can have huge consequences of everything related to your plant: living beings, property, compliance, stakeholders, processes and finances. It is not something you would want for your facility.

Catastrophic tank failure is usually a consequence of brittle fracture, which is not always understood and is understimated when making tank repairs and inspections. Given that in some locations aboveground tanks have been in service for more than a few decades, and that is not uncommon to build a tank from parts used in other tanks, catastrophic tank failure is a real concern. [click to continue…]


By Carlos Molina

Tank settlement is one of the topics of the Body Of Knowledge for the API 653 exam. It is a very important subject for us tank inspectors, althought is also one of the most vague topics for a new inspector. In fact, the word “settlement” is mentioned more than 250 times in the API 653 standard. As an inspector, you should be able to determine the type  and extent of tank settlement, and decide if it can affect tank integrity. In the api 653 exam, maybe 2 questions will show up about this subject. And as complex as it may look in the api 653 standard, the limitations imposed by the BOK make it a really easy topic.


In new tanks, the API 650 standard doesn´t necessarily asks for a settlement measurement to be done during hydrostatic tests. If there is no settlement expected (for example,  a tank over a giant rock), it might not need settlement measurements, but that´s a decision that is entirely up to the owner.  In normal conditions, there will always be settlement. Anyway, you should design and construct foundations to limit any settlement at all, as impossible it is to eliminate it.

For the sake of information, you should know how setttlement measurements are made. During hydrostatic testing for new and old tanks, at least 6 sets of measurements shall be made.

1. When the tank is empty before hydrostatic testing

2. When the tank is 1/4 full

3. When the tank is 1/2 full

4. When the tank is 3/4 full

4. 24 hours after it is filled

4. With the tank empty again.

Shell elevation measurements shall be made at equally-spaced intervals around the tank circumference not exceeding 10 m (32 ft)


During operations, shell settlement measurements should be taken at a planned frequency, based on an assessment of soil settlement predictions. Bottom settlement monitoring is to be made during internal inspections, respecting the intervals given for inspections in API 653 4.4.6. Identify and evaluate any tank bottom settlement is one of the 3 key objectves of internal inspections, because it plays such an important role on many tank failures and floating-roof problems.

Settlement can be caused by the following:

  1. Lack of support under the base circumference affecting the cylindrical shell and the tank bottom. Parts or the concrete ring may be lost.
  2. Non homogeneous geometry or compressibility of the soil deposit (voids or crevices below the bottom plate)
  3. Non uniform distribution of the load applied to the foundation. Differential pressure during emptying and filling cycles
  4. Uniform stress acting over a limited area of the soil stratum
  5. Wrongly constructed foundations (deficient reinforcement of the concrete, bad quality cement, etc)
  6. Liquefaction phenomenon around the foundation generated by earthquakes. Consider the following excerpt:

The Niigata earthquake was also the first seismic disaster in Japan where the liquefaction of the ground attracted notice. Among the disaster incidents caused by the earthquake, five crude oil storage tanks in a refinery caught fire and continued burning for two weeks, spreading into the surrounding area and burning down a total of 286 adjacent houses. One of them was a 30,000kL floating roof type tank, 51,500mm in diameter, and 14,555mm in height, which was fully stocked with oil. The cause of the fire was ignition by sparks generated by the collision of the floating roof with the side wall, which in turn was caused by the movement of the crude oil by the sloshing phenomenon. Source.


Various forms of settlements could take place in tanks. The BOK considers 3 types of settlement and their evaluation.

1. Edge settlement

Edge settlement occurs when the tank shell settles sharply around the periphery, resulting in deformation of the bottom plate near the shell-to-bottom corner junction,  or the depth of the depressed area of the bottom plate. You can see a diagram for edge settlement below.


Edge settlement affects bottom parallel and perpendicular welds in different manners. It affects weld seams that are “parallel” to the shell in a more critical manner that the ones that run “perpendicular”.

How to evaluate edge settlement?

STEP 1. Annex B of API 653 separates Edge Settlement evaluations in two separate scenarios:

1. If edge settlement is in an area with a welded seam than runs parallel +-20°  to the shell, B turns into Bew

2. If edge settlement is in an area with a welded seam than runs perpendicular +-20°  to the shell, B turns into Be


STEP 2. With the value of R, B and the tank diameter, you can check the maximum allowable vertical settlement in figures B-11 of API 653 for Bew or B-12 for Be. A sample of that diagram you can see next.


See API 653 B-11 and B-12 for the whole details.

Welds in tanks with settlement greater than or equal 75 % of Bew or Be, and larger than 2 in., are to be inspected with magnetic particle of liquid penetrant method. Additionally, weld seams should be inspected vissually and if they show strains bigger than 2%, they should be repaired.  Any plate exceeding acceptable plastic strains (typically 2 % to 3 %) should be replaced.

2. Bottom settlement near the tank shell

This kind of settlement can be present in the bottom or in the annular ring zone, if there is one. It occurs when the bottom deforms showing a depression or a convexity in relation with a flat plane bottom. That deformation is caused by stresses in the bottom plate that have to be evaluated.


How to evaluate bulges in tank bottoms?

STEP 1. As per API 653 B3.3, measure the bulge or depression in its entire lenght. The half of that measure is radius R of the bulge.

STEP 2. The maximum dimension for bulges or depressions is given by the following equation:



B is the maximum height of bulge or depth of local depression, in inches;

R is the radius of an inscribed circle in the bulged area or local depression, in feet.

3. Localized bottom settlement remote from the tank shell.

Localized bottom settlement remote from tank shell are depressions (or bulges) that occur in a random manner, remote from the shell. The same equation (B3.3) used for bottom settlement near the tank shell can be used for the evaluation of this kind of settlement, granted the bottom has single-pass welded joints.


  1. Leave plenty of free space under any nozzle, to prevent any contact with the floor if there is settlement.
  2. Settlement occurs to every tank, and it can be different in practice from the measured settlement during and after hydrostatic testing.
  3. If there is uniform settled expected (If foundations werent well built), you can use flexible joints or maritime hoses that can absorb those misalignments.
  4. Edge settlement often can be predicted in advance, with sufficient accuracy from soil tests. Anyway, piping (especially buried piping) should be designed with adequate consideration to prevent problems caused by such settlement


See that it is pretty easy? I think this is a good explanation of what you will have to learn in order to answer correctly questions regarding tank settlement in the API 653 examination. If you liked this article that will help you in your inspections, then subscribe to my mail list, and you will receive a weekly article about equipment integrity and how to pass your exams.

Cheers and good luck


I want to receive APIEXAM articles

* indicates required