ASME B31.3 PROCESS PIPING PROGRESSIVE WELD SAMPLING

Download B31.3 Progressive Weld Sampling Flowchart

Progressive Sampling is the process of selecting cascading levels of additional inspection samples as the result of a rejected examination. Progressive sampling requirements can occur when working within ASME B31.3 Process Piping and Section VIII Div. 1 Pressure Vessels when performing random examinations. The focus of this article will be on ASME B31.3 Process Piping.

Random examinations are employed to sample work performed, and determine the general quality level of the tested population. This method has proven to be effective at maintaining sufficient weld quality while minimizing the cost and schedule impact of examining every weld.

When performing required random examinations reveals a reject, the code requires that more examinations be performed to determine if the initial reject represents other possible rejectable quality issues in the untested population; this is why the term “progressive” is used to define this process.

COMMON TERMINOLOGY & DEFINITIONS

ASME B31.3 paragraph 341.3.4 describes the additional examinations due to failure as “Samples.” Standard terms used in the industry for these samples are also known as “Tracers” or “Penalties.”

ASME B31.3 paragraph 344.1

100% examination: A complete examination of all a specified kind of item in a designated lot of piping.
Random examination: complete examination of a percentage of a specified kind of item in a designated lot of piping.
Spot examination: a specified partial examination of each of a specified kind of item in a designated lot of piping, e.g., of part of the length of all shop-fabricated welds in a lot of jacketed piping.
Random spot examination: a specified partial examination of a percentage of a specified kind of item in a designated lot of piping.
Lot: A designated lot is that quantity of piping to be considered in applying the requirements for examination in ASME B31.3. The quantity or extent of a designated lot should be established by agreement between the contracting parties before the start of work. More than one kind of designated lot may be established for different kinds of piping work. See Pipe Fabrication Institute Standard ES-48, Random Examination, for examples of lot selection.
Random or Spot Examination Note: Random or spot examination will not ensure a fabrication product of a prescribed quality level throughout. Items not examined in a lot of piping represented by such examination may contain defects that further examination could disclose. Specifically, if all radiographically disclosable weld defects must be eliminated from a lot of piping, 100% radiographic examination must be specified.

PROGRESSIVE SAMPLING SCOPE

B31.3 is written in such a way that progressive sampling due to rejects applies to all NDE methods. In practice, most in the industry think of and focus on the RT or UT methods when thinking about progressive sampling. This may be because the most common and sometimes the only metrics kept and tracked for reject rates focus on RT or UT. So be familiar with the general implementation within the industry and the customers you work with as well as what the code states are the requirements.

VT PRACTICES

It is common in the industry to perform 100% VT on all welds; this is a best practice and is highly encouraged as the most effective and economical way to confirm adequate welding is taking place. A careful reading of B31.3 para. 341.4 reveals that Category D & Normal Fluid Services do allow for random visual examination.

An alternate way to consider the practice of 100% VT is as follows. Consider that any “touch up,” or “pick-up” repairs marked during VT are, in fact, initial rejections. With this being the case, the welds are being rejected (and not tracked), and the rules of progressive sampling dictate that other samples be made. This progressive sampling quickly puts all welders into a 100% inspection requirement. You also need to be aware that customer specifications or in house procedures or quality manuals may require the 100% VT practice.

ADDITIONAL SAMPLES - DEFINING “SAME KIND”

When a spot or random examination reveals a defect, two additional samples of the same kind are required. One of the most common questions for those who find themselves involved in selecting additional samples is how to apply the “same kind” requirements. Situations are so diverse the Code has not provided much in the way of describing specifics, except in the case of a couple of interpretations that have been issued. ASME code interpretations can be found here: ASME Code Interpretations Link

ASME B31.3 Interpretation Same Kind 1-62 — ASME B31.3 Interpretation of Same Kind 1-62

When setting up projects it is important to know what the specifications, quality procedures, or manuals may say pertaining to the definition of “same kind”, regularly these resources will not say anything, as it is very difficult to pre-define rules due to the variety of scope and scenarios to which this may apply. So the individual running the quality effort must decide what this means as it applies to the situation. There is no Code requirement that the additional samples selected, be approved by the customer, yet good advice would dictate that it be considered to prevent disagreements later on. On some projects the contract or customer specifications may in fact state that the owner’s inspector does review or approve the additional samples, so be sure to know what the contractual documents state.

ASME B31.3 LOTS

ASME B31.3 includes the following definition footnotes in paragraph 344.1.3 Definitions.

Lot: A designated lot is that quantity of piping to be considered in applying the requirements for examination in ASME B31.3. The quantity or extent of a designated lot should be established by agreement between the contracting parties before the start of work. More than one kind of designated lot may be established for different kinds of piping work. See Pipe Fabrication Institute Standard ES-48, Random Examination, for examples of lot selection.

It also includes a note regarding the objectives of random examination as well as 100% examination.

Random or Spot Examination Note: Random or spot examination will not ensure a fabrication product of a prescribed quality level throughout. Items not examined in a lot of piping represented by such examination may contain defects that further examination could disclose. Specifically, if all radiographically disclosable weld defects must be eliminated from a lot of piping, 100% radiographic examination must be specified.

ASME B31.3 PROGRESSIVE SAMPLING

The following provides a step by step guide through the progressive sampling process. For convenience, the terms “round” and “scenario” will be used to describe the cascading options that occur when the progressive sampling yields defects; these are not used by B31.3.

When a random examination is performed and found to be acceptable, it is documented, the lot for which it represents is satisfied or closed, and monitoring for the next Lot is set up.

PROGRESSIVE SAMPLING - FIRST ROUND REJECTION

When a random examination is rejected in the first round ASME B31.3 paragraph 341.3.4 (a) states that two additional samples of the same kind, from the original designated lot, shall be given the same type of examination (as the rejected sample).

Repairs or replacements of rejects and the ramifications of each option are detailed in ASME B31.3 paragraph 341.3.3.

For documentation purposes, all documentation connected to this event needs to state or clarify that these examinations are associated with the original reject. Best practice would also dictate coordination with production that the welder in question be stopped from further welding and placed on other duties until the process follows its course. Training and investigation are other matters that should be performed, or at the very least considered at this point in the process.

B31.3 paragraph 341.3 Progressive Sampling

PROGRESSIVE SAMPLING - SECOND ROUND

If 2 Accepted: No more examinations are required for this lot.
If 1 Accepted & 1 Rejected: The rejected sample requires 2 additional tracers
If 2 Rejected: 4 additional tracers are required

PROGRESSIVE SAMPLING - THIRD ROUND

In the third round, any rejections will require that the entire lot be 100% examined.

If All accepted: No more examinations required for this lot.
If 1, 2, 3 or 4 Rejected: All items in Lot shall be
- Repaired or replaced & fully reexamined per paragraph 341.3.4 (e)(1)
- Fully examined and repaired or replaced as necessary and then fully reexamined per paragraph 341.3.4 (e)(2)

REPAIR OR REPLACE

Two options exist to address rejected welds; they can be repaired or replaced. B31.3 paragraph 341.3.3 addresses “Defective Components and Workmanship.”

Repair: Per B31.3 para. 341.3.3(a) When the defective item or work is repaired, the repaired portion of the item or works shall be examined. The examination shall use the same methods and acceptance criteria employed for the original examination.

So repair requires that the repair area be examined by the same original NDE method that was used during the rejection.

DOUBLE JEOPARDY

Per B31.3 para. 341.3.4(f) progressive sampling does not apply to rejects of repairs or replacements. Also see B31.3 interpretation 16-01 & 25-05.

PROGRESSIVE SAMPLING METRICS

Per ASME B31.3, not less than 5% of circumferential butt and miter groove welds shall be examined fully by random radiography. The welds to be examined in each designated lot shall include the work product of each welder or welding operator whose welds are part of the lot. Customer specifications may require more due to a blanket requirement or due to special service applications.

To document that this requirement has been met, a running total should be kept. In calculating this number, there are sometimes questions if accepted tracers can count towards satisfying this total. Interpretation 16-05 question and reply #2 addresses this question and clarifies that any accepted examinations which occur as a result of progressive sampling do not count towards the required percentage.

REPRESENTED ITEMS

ASME B31.3 paragraph 341.3.4(e) reads as follows “if any of the items examined as required by (c) above reveals a defect, all items represented by the progressive sampling shall be either”; it then provides two approaches of performing repairs or replacements. The question arises as to what the phrase “all items represented by the progressive sampling” refers to. The answer is supplied in B31.3 interpretation 13-12, which is, “All items within the same designated lot.” So if a welder has a reject that leads to enough rejects that they become exposed to the 100% sampling criteria, it only applies to the lot which was represented by the original defect.

This emphasizes the need to have lots well defined before starting a project, as well as keeping the random examinations very fresh on each welder so any possible quality issues don’t get too far out of hand. Also remember a contractual specification or requirement can supersede the restriction to only test within the defined lot, make sure this is well understood and that the associated costs for progressive sampling outside of defined lots is understood by those in charge of the budget.

B31.3 Interpretations Represented Items 13-12

SUMMARY

Progressive Sampling is the process of selecting cascading levels of additional samples as the result of a rejected examination. The rules by which this is to be carried out are contained in ASME B31.3 Process Piping and Section VIII Div. 1 Pressure Vessels, each for their respective scope.

Having a standardized process of documenting who has welded what, performing random examinations promptly, which welders lots do random examinations belong to, and a process to document progressive samples complex and sometimes confusing task, having tools in place helps to manage the process

A useful progressive weld sampling flow chart detailing the layered steps is provided at the following link.