In this module, you shall learn about:
- Reference documents,
- General tips on document navigation,
- Important terms and definitions and
- 20 quiz.
In this module, you shall learn about:
In a nutshell, an API 510 Pressure Vessel Inspector should know about vessel construction code (ASME Sec VIII); Welding Inspection and WPS (ASME Sec IX & API 577), NDT (ASME Sec V), Corrosion (API 571); Inspection of Pressure Relief Valves (API 576); most importantly Pressure Vessel Inspection code (API 510) plus the associated API 572 and finally have sufficient general and safety knowledge.
The API 510 Pressure Vessel Inspector examination has two sets of references as study materials:
One set contains ASME codes (Section VIII- Pressure Vessels; Section IX- Welding, and Section V-Non-destructive Testing). Most of questions from these codes are in open book part of the examination and of calculation type. You need not memorize them but should know where to look for when solving the open book questions. You should have an idea how to navigate through them during open book part.
When reading a code, don’t immediately dive into the details. Get the bigger picture. First, understand what the code covers by reviewing the opening paragraphs of each code. This is generally called the Scope or Introduction. Next, look at the table of contents to understand how the code is structured. This step is often overlooked and the inspector fails to get the scenario or the purpose of the code.
The closed book exam questions coming from ASME codes are the ones that an inspector would be using on daily basis and therefore, you need to memorize them. But don’t worry, we shall supply you with enough presentation, mock question and flash cards to ensure that you would not forget them during the exam.
The second set of study materials or reference documents contain the recommended practices: API RP 572 (Inspection of Pressure Vessels); API RP 576 (Pressure-Relieving Devices); API RP 571 (Damage Mechanisms); API RP 577 (Welding Inspection), and finally the all important API 510 (Pressure Vessel Inspection Code).
Please note that only API 510 is an inspection code (mandatory), while the rest of API documents are recommended practices (good engineering practice).
Closed book questions mostly come from API 510 code and RPs because these information is supposed to be used by inspectors on daily basis.
For open book questions that need referring to tables, graphs and formulas, you shall have access to both the API RPs and API 510 code besides ASME codes.
We shall cover them within the next 8 modules combined with flash cards and mock exams.
Codes are based on scientific conclusions while recommended practices are mostly the result of past experience gathered over the years showing the trends and good practices. That’s why; you may observe that the formulas brought within RPs are empirical. The empirical formulas have no sound scientific backing and are merely formulated to show the trends and relationship between various parameters.
Why? Because, to turn an empirical formula into a scientific formula necessitates including many more parameters of less importance and this would unnecessary complicate the equation where as empirical formulas are like rule of thumbs and can be of everyday use especially when you do not need to be that accurate.
The analogy would be the difference between a WPS and a Welding Instruction. The welder does not need to know about all the essential and non essential parameters or the PQR and it’s associated test reports. All the welder needs to know is the range of amperage & voltage, the welding speed, the type and size of electrode, the welding position, the number of passes and if any pre heat required.
Empirical formulas are used when a very high accuracy is not important. They are basically the mathematical representation of trends. For example, as a rule of thumb, you need to preheat 4″ or 4t from each side of the weld whichever is more. You do not really need complicated formulas to come to the right number that you cannot even implement in practice.
Scientific formulas accurately explain the phenomena for all ranges of parameters while an empirical formula only works within a limited range.
Overall, the Codes are engineering based while RPs are experience based.
Before going to the relevant section, you need to know which document or documents you need to look at in order to find a particular topic. Therefore, you need to know what is covered in each code and recommended practice. If you are in doubt, look at the table of contents. If it does not help, look at the list of figures or tables for large volume codes, it shall give you an idea where you can find the topic. For smaller documents, peruse through table of contents or figures.
Try reading the PDF format of documents on a computer so your eyes and mindset gets used to them. It seems, the brain works differently when you are looking at a hard copy of a document than when you peruse through soft copy of the same document. Reading soft copies of reference documents help acclimatize yourself while searching for a topic. A little practice is necessary to get it right. It is particularly useful for bigger codes such as ASME Sec V, VIII & IX.
Also try to memorize the topics of codes and RPs so you know where to look for. If you can’t find the relevant section after a couple of minutes, flag off the question and note the question number on a piece of paper provided during the exam as there is a high chance that you shall find it when looking for answers for other questions. Once found, you can go back to the flagged off question and solve it within seconds. You are also advised to practice looking for topics in PDF format.
API 510 and API RP 572, 571, 577, 576 should not be a problem navigating as they are much smaller compared to ASME codes. There is also the content list available for each RP. Overall, you should refer to 510 & 572; Pressure Relief Valves are 576, Welding are 577 and damage mechanism and corrosion are 571.
Please note that the reference codes and RPs provided during the open book part of the exam are not word searchable, hence, you should know where to find each topic.
In the following modules, we have provided the list of important topics and tables coupled with flash cards and mock exams for your practice. This should help you get an idea where to look for. Fortunately, the list is not exhaustive, so, you should not find much of the problem navigating through the documents.
The followings are the important vocabulary for API 510 course explained in simple language. It not only helps you understand a few basic concepts, but some of these key words and their meaning may also come as exam questions. Please note that the list in not exhaustive but intends to explain important key words, their concepts and differences.
In case of conflict between reference documents such as code, recommended practice, standard, project specification, procedure, purchase order, etc., there shall be an order of precedence when one document over rules or vetoes another reference document.
For example, although API RP 510 is the governing document that over rides even ASME Sec VIII for in-service pressure vessels; API RP 510 cannot be in conflict with any prevailing regulatory requirement or jurisdictional regulation or government regulation unless it is more stringent than them.
Obviously, if API RP 510 is more stringent or more onerous than a regulation, this means, it is not in conflict with a regulation but is over and above that regulation.
Repair means the work necessary to restore the vessel in order to be operated safely at its original operating pressure and temperature.
Alteration means repairing the vessel such that it changes it’s original operating pressure and/or temperature range (integrity operating window).
So, any repair such as replacement of parts with same or similar parts (like for like) and any restoration work are called a ‘’repair’’ as long as it’s current allowable operating pressure and temperature (Maximum allowable working pressure (MAWP) and minimum design metal temperature (MDMT) does not change.
On the other hand, any activity that changes any of these parameters (MAWP, MDMT, IOW), it is termed as alteration.
Repair needs approval of the inspector while alteration needs the approval of both the engineer and inspector.
Repair examples are : duplicate or like for like replacement; addition of any reinforced nozzles less than or equal to the size of existing reinforced nozzles and addition of nozzles not requiring reinforcement; also any welding, cutting, grinding on pressure containing component that does not change MDMT or MAWP.
Alteration examples are: Any restorative work that results to a change in MAWP, MDMT and subsequent rerating. Now, rerating may be either upgrading (increase in allowable MAWP and decrease in MDMT) or downgrading (decrease in MAWP or increase in MDMT). If rerating leads to downgrading, then it is called de-rating which means demoting.
Please note that an increase in MAWP is an upgrade because the vessel can tolerate higher working pressure like a car that can go at a higher speed which is understandable. But a decrease (and not an increase) in MDMT is an upgrade because the lower the MDMT, the larger, the operating window. For example; a vessel that can operate at above 10 F is superior and more versatile than a vessel that operates at above 20 F.
Remember, both rerating and de-rating results in a change in MDMT and/or MAWP and hence it is termed as an alteration and not a repair.
Alteration requires a pressure test unless exempted in writing by both the engineer and inspector.
Repair does not normally require a pressure test unless specifically asked by the inspector or engineer.
Examination specifically means QC activities such as an NDT activity. It is not an inspection. The closest analogy could be the difference between a laboratory blood test (examination) and doctor’s diagnosis (Inspection which includes evaluation and interpretation or acceptance/rejection). Examination reports shall be approved by the inspector. NDT technician examines the material by an NDT method and reports the result. NDT examiner can also report the acceptance or rejection of a material or equipment against an approved acceptance criteria if authorized by the inspector.
In any event, it is the inspector who shall approve the examination report. Please remember that, the inspector is the final authority in accepting or rejecting the QC and NDT examination reports.
is the visual inspection from outside the vessel (maximum interval 5 years).
On stream inspection means external inspection of vessel using an NDT technique.
The difference between external inspection and on stream inspection is that in external inspection, only visual inspection is carried out while on-service inspection involves the NDT examination as well. Furthermore, external inspection is aimed at detecting the environmental corrosion while on-stream inspection is aimed at substituting internal inspection, that is, when it is possible to get the same necessary information and examination by on-stream inspection without opening the vessel up for internal inspection.
On- service inspection could replace periodic internal inspection if approved by the inspector and owner.
External inspection could not replace internal inspection.
Inspection from inside of vessel both visually and with NDT methods with a maximum interval of 10 years or half corrosion life which ever happens sooner.
Precision and accuracy are often used interchangeably, but in science they have very different meanings. Measurements that are close to the known value are said to be accurate, whereas measurements that are close to each other are said to be precise.
Accuracy is used for calibration purpose to determine how accurate the readings are with respect to a known value.
Precision shows variations. How close are a bunch of thickness measurement readings at a point on the vessel?
The point of measurement normally means a circular area with a diameter of 3’’.
API does not differentiate between owner and user. The owner/user is responsible for inspection and repair to meet the code. This makes sense because if owner and user were differentiated as two separate legal entities, then, none of them could be hold them accountable because the owner would say that the user was supposed to comply with jurisdictional requirements while the user would argue that that the pressure vessel belongs to owner who should be held accountable. Owner/user is accountable for any shortcoming and non compliance to codes and specifications or jurisdictional requirements.
API 510 requires that an owner/user shall employ or subcontract an inspection organization (or an inspection program and authorized inspector), a repair organization, an engineer, and examiner. Please note that the ultimate responsibility lies with the owner/user while other individuals are accountable to the owner/user within their scope of responsibilities.
Inspector means authorized API 510 pressure vessel inspector.
The inspector is responsible to the owner for inspection and approval of the vessel for continued safe operation.
The inspector can be an individual working for the government/jurisdiction, an insurance company, for a third party under contract with the owner/user or directly working for the owner/user.
The NDT examiner is responsible to carry NDT activities as per approved procedure and if authorized by the inspector, can also prepare the acceptance and rejection part of the report.
However, please note that the Inspector is the final authority in accepting or rejecting the NDT reports as well as all the inspection records.
Certification of the NDT examiner shall be maintained by his/her employer and shall be available for inspector’s review.
The pressure vessel engineer is an individual or a team who is knowledgeable in the design, review, analysis and evaluation of pressure vessels and is appointed by the owner/user.
Both the engineer and the inspector shall approve any re-rating, de-rating and alteration, however, the repairs does not normally need engineer’s approval unless the inspector opt to consult with the engineer.
An individual knowledgeable in materials, metallurgy, damage mechanism and corrosion monitoring techniques and is approved by the owner.
This is the pressure range and temperature range that the pressure vessel is allowed to work. The range is determined by design and depends on the type of material and its thickness.
Exceeding the IOW range may affect the integrity of the vessel. There could be other parameters within IOW such as process fluid, velocity, but MAWP and MDMT are the most prominent.
Any change in the process equipment or material or hardware shall be documented. It shall be determined whether such changes may affect vessel integrity (say, by increasing the corrosion rate or change in damage mechanism).
Relevant personnel such as the Engineer, corrosion specialist, inspector, examiner and maintenance personnel may be involved to cascade such changes to inspection planning, repair and maintenance.
Points or areas on the pressure vessel are identified that normally expect to have the highest corrosion rate or stress concentration. These areas are inspected and examined periodically to assess the vessel condition.
The CML locations are selected to be representative of corrosion behaviour of the vessel. It makes sense to select those points or areas where maximum corrosion or damage is expected.
The inspector selects the monitoring locations based on previous history of inspection, damages occurred on similar vessels under similar operating and environmental conditions and may seek corrosion specialist opinion on expected damage mechanisms for a particular vessel.
Quality assurance is the design and planning of quality control activities to ensure that the service or equipment has met certain requirements while the Quality Control is the implementation of those control activities in order to demonstrate or verify that the requirements are met.
Not all parts or components of the pressure vessel have equal value or effect on the integrity of equipment. Similarly, not all equipment has equal value or effect on the integrity of a plant.
It is also important to understand what would be the consequence of failure for a particular part or equipment.
Risk-based inspection considers both the probability of failure and consequence of failure.
Once, we know what are the probability and consequence of failure, inspection efforts can be directed towards more critical parts, locations, parts and equipment thereby reducing the probability of failure, downtime and inspection costs while increasing equipment reliability, equipment availability and safety.
There might be a situation when the probability of failure is low, but the consequences of failure are huge and catastrophic in terms of cost, downtime or even human lives. In such situations, the overall risk is still high.
Risk = Probability of Failure X Consequence of Failure.
Remember that the owner/user is ultimately responsible for preparing, documenting, executing, and assessing pressure vessel/pressure-relieving device inspection and repair.
Owner/User shall have QA system that shall include: Organization chart; QC and QA procedures; report and records; inspection plan; RBI assessment; determination of inspection interval; auditing; drawings; calculations; repair, rerating; Management of changes; Compliance with codes and specifications; record of qualified welders, NDE technicians and WPS; training; material traceability and material certificates.
As you can see, this is more or less, a list of ISO 9001 requirements.
Reduction in toughness when 2 ¼ Cr 1 Mo low alloy steel exposed to high temperature range of 650 F-1100 F.
Remember that embrittlement is the reverse of ductility.
Toughness is the resistance of the material to deform under force/stress. It is quantitatively the area under the stress strain curve. It depends both on amount of stress it can tolerate and it’s amount of elongation.
Toughness of a material is determined by Charpy impact test.
Hardness is the resistance of material against penetration or indentation.