Pressure Vessels

Generic Designs Revisited

The truth is, fewer CRNs are better in many ways.  

With fewer CRNs, it’s easier to keep track of CRN registration numbers, it’s easier to ensure the right CRN registration number is affixed to the right equipment, and it’s easier if the regulators need not be contacted as much.

It’s usually possible to combine several pressure equipment designs of a particular type into one design.  This is what a generic design is all about.

Generic Pressure Vessels and Boiler Components

For example, pressure vessels or boiler vessels and components with different nozzle locations in heads and shell, different nozzle sizes, and different shell lengths can be combined into one design, i.e. a generic design.  For pressure vessels, nozzle spacing tables showing required nozzle spacing distances in accordance with ASME Section VIII-1 paragraphs UG-36, UG 37, UG-39, UG-40, UG-41, UG-42, UW-14, etc., can be included on the drawing and considered as part of a design.  Similarly for boiler vessels and components, nozzle spacings are governed by paragraphs PG-32 etc.  

Only relative locations of nozzles need to be prescribed; specific locations for each nozzle need not be defined.  In this way, a virtually unlimited number of nozzle combinations and locations can thereby be included with a vessel design, as long as they reasonably represent the product line and market demand.  The idea is not to combine all possible nozzles at all possible locations, at all nozzle offset distances, and at all nozzle inclination angles.  A reasonable set of nozzle locations and sizes is acceptable to the regulators.

Generic vessels must have a fixed:

  • maximum allowable working pressure 
  • max design temperature, 
  • minimum design metal temperature (MDMT), 
  • shell diameter, 
  • corrosion allowances for each vessel component, 
  • weld configuration for each nozzle
  • head type
  • head and shell thicknesses, and
  • materials of construction, with reasonable exceptions.

A drain must be located at a location to permit drainage, if required.  And inspection openings, if required, must be located within a diameter’s distance of the heads’ circumferential seams.

Generic Fittings

Fittings designs are regularly combined into one application for CRN registration, as long as the same fitting category is considered.  For example, a catalogue of category A ASME B16.9 pipe fittings can be registered with one application.  Same thing for various different catalogues with sets of drawings: category B flanges, whether ASME B16.5 or custom in accordance with ASME Section VIII-1 Appendix 2; category C valves fittings in accordance with ASME B16.34, or ASME B31.3, etc.; category D expansion joints or hose assemblies; category E filters, separators, or steam traps; category F measurement instruments like gauge glasses, pressure transmitters, flow meters, etc.; or category G pressure relief valves, rupture disks and fusible plugs.  Such CRN registrations cover a wide range of sizes, pressure ratings, temperature ratings, materials of construction, etc.  In general, requirements for generic fittings are less stringent than for pressure vessels.

An exception to the above is for category H fittings, which typically look like little pressure vessels.  For generic CRN registrations involving category H fittings, it is advised to apply the guidelines for generic vessels  noted above. 

Revisions and Additions to Generic CRNs

After registration is obtained and before it expires, a CRN revision can add new design models or variations to the list of equipment already included with a CRN registration.  With a revision to a CRN, the same CRN number can be used for new models or for design variations, further to what was originally anticipated.

Maximum Allowable Working Pressure & Design Pressure

Revisiting Maximum Allowable Working Pressure (MAWP) and Design Pressure (DP)

Contrary to the articles referenced below, it is a mystery how some seem to believe and even encourage others to think that the true design pressure of any vessel component, as defined in the code, is ever less than the MAWP of the vessel. It would necessarily suggest a potentially perilous situation.

Back in April of 2019, CAMMAR published an article entitled “MAWP is NEVER Greater than ASME Design Pressure,” and it generated lots of attention in the ASME pressure vessel and piping forum group on LinkedIn, with a surprising number of questions and discussion suggesting that the article was wrong.

Addressing those questions and comments is what this article about. It is worth re-emphasizing that the design pressure of vessel components as defined by ASME and per the previous CAMMAR article can never be less than the MAWP of the vessel provided that the vessel has one chamber (as almost all do).

For the Alberta regulator’s perspective on this matter, please see the following link (page 3) for their related publication:

The ABSA article discusses the dangers associated with suggesting that ‘design pressure’ is less than MAWP and that “‘Design pressure’ within the scope of the vessel code (as discussed therein) is thus required to be at least equal to the vessel’s MAWP, …” In order to register a vessel with a CRN number, the design pressure of each vessel component can never be less than the MAWP of the vessel.

Per the original CAMMAR article, MAWP and design pressure are not synonymous and, if mistakenly used interchangeably, the difference can compromise the safety of your equipment. When considered properly in the context of pressure equipment, MAWP is NEVER greater than design pressure.

Questions and misunderstandings of readers, which are apparently still evident, are previously answered and clarified as part of the discussion here, in the ASME pressure vessel and piping forum: via LinkedIn. If you’re not a subscriber to that forum group, we suggest that you subscribe.

Here’s a sample of some of the questions/comments elicited, together with CAMMAR’s responses:

“MAWP is never greater than ASME DP.”

Reader A, P.E. in the USA

“MAWP can be Higher or lower; it depends on each component of our equipment. MAWP is the pressure which the weakest component of your system can handle.”

CAMMAR’s response:

In accordance with our explanations above and, at the risk of belabouring this issue but in the interest of public welfare, we maintain with good reason that MAWP is never greater than ASME DP, in accordance with code requirements, including the definition of DP via ASME Section VIII-1 paragraph UG-21, when considered properly with Appendix 3, and Appendix KK. MAWP is always less than or equal to the design pressure of vessel components. Design pressure (DP) as defined by the code relates to vessel components and is, therefore, a function of component location.

“The language of the code is not subject to preferences.”

Reader B, Engineer in the USA

“I agree with the content of the article. It encourages us to properly understand how MAWP, Design Pressure is defined in code. It cautions about a very specific case where assuming ” MAWP would always be greater than the design pressure” would be risky. I, however, do not agree with the title of the article. It is misleading. Please note the (*) mark against the article and do not accept the title at its face value. There is an interpretation in the code that does not agree with the title of the article ( . It is my experience that sometimes ASME BPVC code rules are read differently in different parts of the world. They are preference based on Industry, past industry experience, local laws. All of those preferences even though different complies with the language of the code.”

CAMMAR’s response:

Referenced articles (including titles) above are consistent with code rules, definitions, and interpretations. Note that the interpretation you mention relates to initial design conditions, not final design conditions. It is a mystery how some seem to believe and even encourage others to think that the true design pressure of any vessel component, as defined in the code, is ever less than the MAWP of the vessel. It would necessarily suggest a potentially very dangerous situation. The language of the code as understood by regulators is not subject to preferences! Definitions of design pressure and MAWP are what they are. There is no law directing the use of any different definitions for design pressure or MAWP in Alberta; they are defined as what the ASME code already requires.

“DP is always greater than or equal to MAWP.”

Reader C, Certifying Engineer in Germany

“Cameron, you are wrong. MAWP can be greater than Design Pressure. Even on one vessel. When the actual wall is thicker than required, you can calculate a MAWP that exceeds the design pressure of the vessel.”

CAMMAR’s response:

Well [name removed to preserve anonymity], it seems that we disagree! But thanks for your response. It’s an important topic, hence my article. MAWP is, of course, the maximum pressure permissible at the top of the vessel. That said, some vessel components might well be overbuilt in relation to others but, in that case, the MAWP will not change. If properly defined, as noted in the article, DP is always greater than or equal to MAWP. Period.

Have questions about getting your CDN? Find out how we can help you register your pressure vessels in Alberta/Canada.

Pressure Gauge Measurement

CRNs, Maximum Allowable Working Pressure (MAWP) and Design Pressure

Canadian Registration Numbers (CRNs) are issued by regulators before pressure equipment is sold or used in Canada. Though there are exceptions, CRN registration is generally needed for pressure equipment that contains expansible fluids at pressures greater than 15 psig. Expansible fluids include vapors, gases, and fluids that expand to a gas or vapor when exposed to atmospheric pressure or temperature.

Pressure is of utmost importance when designing wall thicknesses of pressure equipment (vessels, heat exchangers, boilers, fittings, appurtenances, pressure piping systems, thermal liquid heating systems, and so on). Obviously, thicker walls will withstand more pressure than thinner walls.

When it comes to what pressure is, the meaning of different terms is important, otherwise misunderstandings can occur and public risk can increase. Regulators certainly do not necessarily equate MAWP with design pressure, and for good reason. For starters, the MAWP of pressure equipment is never greater than design pressure (in the absence of a separated internal chamber), even though there are those in industry that would argue otherwise. Designs showing an MAWP greater than design pressure do not warrant CRN registration since they contradict code requirements, and they indicate a misunderstanding of the difference between the two.

MAWP vs Design Pressure

Per mandatory Appendix 3-2 of ASME Section VIII-1, MAWP is “the maximum gage pressure permissible at the top of a completed vessel in its normal operating position at the designated coincident temperature for that pressure. This pressure is the least of the values for the internal or external pressure to be determined by the rules of this Division for any of the pressure boundary parts, including static head…”

In contrast, design pressure is “the pressure used in the design of a vessel component together with the coincident design metal temperature, for the purpose of determining the minimum permissible thickness or physical characteristics of the different zones of the vessel. When applicable, static head shall be added to the design pressure to determine the thickness of any specific zone of the vessel (see UG-21).”

I’ve included a diagram to illustrate the point with an example. Dark blue is MAWP. Dark blue + light blue = design pressure. In this instance, design pressure includes the addition of a vacuum jacket and static pressure, like what you might see with a cryogenic vessel containing liquid nitrogen or oxygen.

Visual representation of MAVP vs. Design Pressure.

As shown, when height increases the difference between MAVP & Design Pressure is reduced.

As you can see, MAWP is never more than design pressure (in the absence of a separated internal chamber).

Just a few more points to make…Some software these days will take the design pressure input and then, with assistance of some iterative techniques, suggest a maximized pressure which is greater than the design requirements and call it MAWP. This is contrary to code requirements, promotes the wrong idea of what MAWP is and leads to incorrect understanding. But software is never supposed to be wrong! Well, think again, since design pressure is never less than MAWP.

Also, process facility piping designs might well use terms similar to design pressure or MAWP to describe the maximum process pressure. Sometimes, this pressure might be transcribed onto the mechanical equipment list or specification sheet by mistake! But beware, maximum process pressure, MAWP, and vessel design pressure are certainly not always the same, and cannot necessarily be interchanged.

And, for small fittings not subject to significant static head or vacuum, the MAWP is in some cases the same as design pressure and, for such fittings, MAWP and design pressure are thereby often used interchangeably on fitting drawings.

To summarize:

  • MAWP is never more than design pressure (in the absence of a separated internal chamber);
  • MAWP is the maximum internal pressure at the top of the pressure equipment;
  • Design pressure is dependent on location in the pressure vessel; and
  • MAWP and design pressure are significantly different.
yellow boots on the road

To Design Pressure Equipment and Get a CRN; The First Step

We continue to rapidly explain what is needed to properly design pressure equipment (vessels, boilers, fittings, piping systems) to get CRN registration. Many designs proposed to us are deficient for the same obvious reason and consequences that stem from it. Surprisingly enough, even established and accredited pressure equipment manufacturers sometimes don’t even know the first step to take towards proper design. But only proper designs warrant CRN (Canadian Registration Number) registration.

The first step in the design process is critical to getting a CRN, and it might not even be what you think:

it’s not to determine the schedule, cost, materials, or to qualify a welding procedure. And beyond generally knowing the overall industrial performance requirements and its general limits, the first step towards a CRN is not determining the specific design temperature or pressure either. Believe it or not, the first step towards a proper design is something even more basic and fundamental.

Selecting the code or standard of construction and knowing its requirements, is the first step to take. But unfortunately, manufacturers often exclude a note referencing an acceptable code or standard from their drawing, or consider such a note only as a last thought. If this first step is missed, then numerous mistakes, problems, redesign, product recalls, or even replacement can easily result. Imagine navigating a large ship that is already headed in the wrong direction; turning it around or redirecting it to avoid rocks is time consuming, costly, but still necessary. Instead of heading even near the rocks, it’s best to steer the ship in the correct direction at the outset, as a first step.

In Canada, acceptable codes of construction are adopted by jurisdictional legislation and also listed by CSA B51 – the boiler, pressure vessel, and pressure piping code. Acceptable standards are referenced in adopted codes. For pressure piping, acceptable codes of construction are ASME B31.1, B31.3, and in some circumstances, CSA Z662. For boiler external piping, only ASME B31.1 is accepted unless ASME Section I is used to design it. For pressure vessels, ASME Section VIII-1 and ASME Section VIII-2 are accepted. ASME Section I is acceptable for boiler proper designs.

For every design, the code of construction or referenced standard and the edition date used needs to be clearly stated on a unique controlled document (for example, a drawing with a document number and revision number). Otherwise, requirements that the design is meant to follow are unclear and greater risk to the public results. If an acceptable code of construction or referenced standard is not properly noted on a controlled document, then chances of that design being registered with a CRN are greatly diminished and, in our opinion, CRN registration would not be warranted in such an instance.

Codes can differ from one another with respect to their various requirements, including mechanical strengths, material specifications, allowable temperatures, hydrostatic test pressures, and so on. But code of construction requirements always need to be met; pressure equipment designs need to meet or exceed all code requirements. When adopted codes are more stringent than the standards they reference, then the code requirements take precedence.

Using a mixture of different codes, or cherry picking the requirements from different codes of construction to favorably combine them together, is unacceptable. Every design must be consistent with the selected code of construction and, to avoid backtracking and costly reparations, that code should be selected at the outset of pressure equipment design after due consideration of the overall equipment performance requirements.

We know how complicated getting a CRN registration can be. Our experts at Cammar Corporation can help you get one without any hassles.

Cammar Corporation Harmonized CRN Registration and Public Safety

Harmonized CRN Registration and Public Safety

Have you ever tried to sing along with the radio?  Sometimes, harmony just doesn’t happen easily.  Now, consider 13 people trying to sing along to the same tune.  For them to sing in harmony, even with the same music, they would need to work at it quite a bit.  But, I digress.

To get a Canada wide CRN (Canadian Registration Number), applications to 13 separate jurisdictions need to be considered and a comparable number of separate, independent regulatory reviews are required.  Why?  Well, in short, each province or territory in Canada is constitutionally responsible for legislation about public safety within their boundaries.  Hence, time for parallel and separate reviews, then separate and additive fees, and then separate registrations, etc. are currently required.  In this day and age, when ideas can flash around the globe at a key stroke, national CRN registration of designs (i.e. ideas) in Canada seems to be, well, quite awkward and glacial in December.

This is not to say that regulators do a bad job.  On the contrary, they are needed, appreciated, and certainly do contribute to the safety of the populace by helping owners of equipment (users, manufacturers, distributors, etc.) meet safety requirements.  Indeed, regulators are of particular importance at a time of increased public scrutiny in relation to safety, and responsibility.  This series of articles is about the system that pressure equipment regulators currently operate in.

But can there be improvements to the CRN registration system?  Can it be more harmonious, in better tune? Of course.  CRNs are still needed.  But in our opinion, there must be a willingness, and some proper foundation, for change.

Now, imagine a world where getting a CRN registration in Canada is harmonized.  In other words, CRN registration in this world is a one stop process, that includes just one high quality, third party regulatory review.  Safety would be maintained or even enhanced from the status quo, and barriers associated with the time for different reviews and additive costs would be gone.

“Safety would be maintained or even enhanced from the status quo.”

To get to such a new world, what sorts of foundations would properly drive this harmonized change to the CRN registration process?  In our opinion, such a drive would necessarily have at least two foundations for it to truly be in the public interest.

The first foundation would be a drive towards enhanced and maintained levels of public safety.  Owners could be encouraged, nationwide, to meet established and documented requirements prescribed from the collective experience of pressure equipment regulators across the country.  Each ‘port’ of entry to nationwide CRN registration, if you will, would enforce the exact same high requirements based on collective regulatory experience.  Selection of nationwide requirements should never be a race downhill so that in effect, the lowest common denominator, weakened or lessened, requirements would result.   No, the highest topical CRN requirement currently in place should be selected nationwide in each case.

“Barriers associated with the time for different reviews and additive costs would be gone.”

The other foundational driver would surely be economic.  A more efficient and shorter registration process would encourage foreign and domestic manufacturers.  A shorter response time from the manufacturer to the market would obviously have economic and competitive benefits for Canadian industry.  These benefits, though obvious, would be difficult to reliably quantify.  Subject to maintained and enhanced safety, this driving force must be managed well.

With these two drivers, surely there is likely a willingness amongst the public and industry, together with the provincial and federal governments, for change.  But time will tell.

As this year draws to a close, here’s hoping that the future will usher in an era where requirements across Canada are held high for the safety and economic benefit of all.

Details relating to the implementation of any harmonized CRN registration process are important.  As time permits, future Cammar Corp blog articles will explore how the implementation of a harmonization process could, in some cases, be a benefit or a disadvantage to the public interest.  Stay tuned.

British Columba Oil and Gas Facilities Cammar Corporation

British Columbia Oil and Gas Facilities; What is Going On

As of November 7, 2016, BC effected some changes to its safety legislation.  From discussions with a BC Oil and Gas Commission (BCOGC) representative, it’s reported that they are addressing these changes to ensure that no gaps in regulatory oversight occur.  It will be interesting to see how this transpires.

The BCOGC now regulates oil and gas facility pressure piping (and related refrigeration) systems in British Columbia while the British Columbia Safety Authority (BCSA) continues to regulate pressure vessels, boilers, and boiler external piping.  For more details from the BCOGC, please take a look at their Appendix A relating to the changes, the Memorandum of Understanding with the British Columbia Safety Authority (BCSA), and the Liquified Natural Gas Facility Permit Application and Operations Manual.

Governing legislation relating to codes of construction acceptable to the BCOGC for oil and gas facility pressure piping include ASME B31.3 or CSA Z662, per the BC Drilling and Production Regulation (Section 78(3)).  Pressure piping drawings must be professionally authenticated per the Drilling and Production Regulation (Section 78(4)) and the BC LNG Facility Regulation(Section 12). “A facility permit holder must submit to the commission all as-built drawings including piping and instrumentation diagrams, metering schematics and plot plans, signed and sealed by a professional engineer licensed or registered under the Engineers and Geoscientists Act, within 3 months of beginning production or completing permitted modifications, as applicable” (BC Drilling and Production Regulation (Section 78(4))), and  “An LNG facility permit holder must submit to the commission the record drawings, including process flow diagrams, metering schematics and plot diagrams, signed and sealed by a qualified professional, within 9 months after” notice of operation (BC LNG Facility Regulation (Section 12)).

The BC LNG Facility Regulation s 3(1)(f) further requires that the elements of a quality assurance program be presented to the BCOGC before the construction of the pressure piping system, but whether the program needs to (or even can, given the proprietary nature of fitting designs) address fitting design details or quality does not seem to be explicitly addressed.

PIDs and Process Flow Diagrams do not usually contain the information used to evaluate mechanical qualities of a design.

Details relating to mechanical design such as codes or standards of construction, calculations, identification markings, thicknesses and other dimensions, design pressures, design temperatures, minimum design metal temperatures, material specifications, impact testing, heat treatment, test pressures and mediums etc are ordinarily excluded from PID’s, Process Flow Diagrams, Metering Schematics and Site Plot Diagrams.

In combination, these regulations indicate that P&IDs, Process Flow Diagrams, Metering Schematics, and Site Plot Diagrams need to be professionally authenticated by a professional engineer registered in BC, within a limited time frame after completion of construction or operation of the pressure piping systems.  So, in effect, the BC Drilling and Production Regulation (Section 78(4)) and the BC LNG Facility Regulation (Section 12) do not seem to require that details relating to fitting design be provided to the BCOGC before the pressure piping can be operated.

The above approach seems to be a departure and relaxation from what was required to use fittings in British Columbia prior to November 7, 2016, when registration of all non-exempt fittings within a pressure piping system required registration before operation.

Without a requirement to follow CSA B51, there would be no requirement to register oil and gas facility fittings with CRNs.

The previous CRN registration process for non-exempt fittings in BC required a third party accreditation of the fitting manufacturer’s quality control and capability, a statutory declaration attested to by the manufacturer that stated their products complied with all requirements of the selected adopted codes and referenced standards, detailed design drawings with enough detail to permit manufacture, and other technical information from the manufacturer to justify their design.  After supplying the above proprietary information to the satisfaction of BCSA, and with BCSA’s assurance of confidentiality relating to design details, the fitting would be registered in BC.

Added to all of the above, CSA B51-2014 (The Canadian Boiler, Pressure Vessel, and Pressure Piping Code) is referred to in safety legislation across Canada and, from extensive and thoughtful deliberations, has requirements that extend beyond ASME B31.3-2014 and CSA Z662-2015 requirements.  CSA B51 is about much more than just CRNs.  So, CSA B51 includes more requirements than the codes referred to by the BC Drilling and Production Regulation.  Similarly, CSA Z662 and ASME B31.3 make no reference to CSA B52-2013, the Canadian Mechanical Refrigeration Code.

It will be interesting to see how the BC Oil and Gas Commission, together with the BC provincial government, manages the BC legislative changes that are now in effect to ensure that the safety of British Columbians is not reduced.  British Columbians, like all other Canadians, deserve nothing less.

Comparing CRN regulations is like comparing apples to oranges.

ASME B31.3 vs ASME B31.1: Are CRN Registration Requirements the Same?

Cammar Corp was recently asked, “If a fitting has a CRN registration with ASME B31.3 as the code of construction, it’s likely ok to use it as a ASME B31.1 design, and vice versa, right?”

The short answer is a qualified “no”.

Now for the long answer, with our explanation and point of view with some background.  For even more detail and elaboration, please check with the code texts.

In General

Some would say that “if a fitting has a CRN registration, what does it matter if it’s registered to a different code of construction than another?  After all, a CRN registration is a registration is a registration.”  This response would seem to be in line with the idea that, when considered in their entirety, both codes are equal.  But when considering CRN (Canadian Registration Number) requirements, this idea is incorrect in many ways.

For a fitting to be registered at all, a manufacturer must attest on a witnessed Statutory Declaration, that the fitting it manufactures completely conforms to either a referenced North American standard, code of construction, or equivalent.  This means that the fitting must meet all requirements of that standard or code of construction.  If only some rules of one code are used together with some rules of the other, then besides not meeting either code, the resulting mix will likely not be safe, and will likely not be registerable.  Cherry picking requirements from various codes is not permitted.

CRN registrations are tied to codes of construction, referenced standards, etc.

And the specific requirements of B31.3 and B31.1 differ significantly from one another.  Table 1 compares a selection of some of the most commonly encountered differences, described here.


ASME B31.3 and ASME B31.1 are the most applicable ASME codes of construction for many pressure piping and fitting CRN designs in Canada.  However, their scopes are different in at least one major respect.

ASME B31.1 covers the requirements of boiler external piping, and ASME B31.3 does not.  So, whereas some ASME B31.1 fittings can be used as part of a boiler external piping design, ASME B31.3 fittings cannot be.

For example, if some boiler external piping systems needs a valve replacement, the replacement valve must be registerable to ASME B31.1, and the material must be suitable for boiler external piping.  An ASME B31.3 valve would not be acceptable.

Allowable Strengths

ASME B31.3 generally permits higher allowable strengths in many cases and thereby somewhat thinner pressure boundary thicknesses.  For example, in ASME B31.3-2014 the allowable strength at 100F of A106B is 20 ksig and in ASME B31.1-2014 it is 17.1 ksig.  Check the allowable stress tables and methods of determining allowable strengths in each code carefully.

So as a result, some equipment with a CRN that meets the thickness requirements of ASME B31.3 would be too thin to meet ASME B31.1 requirements and therefore would not be a suitable candidate for a B31.1 based CRN.

Material Specifications

The available selection of materials in ASME B31.3 and ASME B31.1 has overlap, but is not the same.  Check to ensure that the proposed material is listed in the code that you want to use with your CRN application.

Unlisted materials are defined and treated differently by B31.3 and B31.1.  ASME B31.3 states that unlisted materials can be used provided that they are described in a suitable published specification (see ASME B31.3-2014 para 323.1.2), and in addition to this ASME B31.1 states that their use must be approved, in writing, by the end user (see ASME B31.1-2014 paragraph 123.1.2(D)).

So, for example, suppose a site glass is to be made with unlisted material conforming to the requirements of an acceptable published specification.  If the use of the unlisted material is not accepted by the end-user in writing in every instance, then code does not permit the equipment to be used as a B31.1 fitting.

Pressure Testing

Regardless of design temperature, all non-service hydro-static pressure testing for ASME B31.1-2014 designs is conducted at 1.5 times the design pressure.  But for ASME B31.3-2014 designs, all non-service hydro-static pressure testing is conducted as a function of design temperature, to account for any decrease in allowable strengths as temperature increases during operation, per paragraph 345.

So, a fitting that is shop hydro tested to only meet ASME B31.1 will quite possibly not meet ASME B31.3 requirements if the allowable strength of the construction material decreases at design temperature.

Only with the regulator’s acceptance and at the owner’s option are service tests at design pressures permitted for ASME B31.3 Category D fluid (see para 300.2) pressure piping systems.  But ASME B31.1 has no limitation in relation to fluid category for this, and with the regulator’s acceptance, pressure piping can be service tested “when specified by the owner, when other types of tests are not practical or when leak tightness is demonstrable due to the nature of the service”, per ASME B31.1 para 137.7.1.

Notwithstanding what ASME B31.1 allows for here, service testing should be avoided whenever possible, especially when high energy piping systems are concerned.

Pneumatic testing is permitted by both ASME B31.3 and B31.1, but only with the regulator’s acceptance, together with proper justifications, procedures, and safeguards.  For ASME B31.3-2014, the pneumatic test pressure would be between 1.1Pdesign and 1.33Pdesign, and for ASME B31.1-2014 it would be between 1.2Pdesign and 1.5Pdesign.  For details, refer to ASME B31.3 paragraph 345.5 and ASME B31.1 paragraph 137.5.  Pneumatic testing is obviously inherently dangerous compared to hydrostatic testing due to stored energy.

Equipment should not leave the manufacturer’s shop without being pressure tested.  It is difficult to imagine a situation where pressure tests are impractical in the shop unless, due to size, assembly in the field is required.  And, even then, field testing will likely be required.

Alternatives to Pressure Testing

With the regulator’s acceptance, proper justification and procedures, closure welds are permitted on ASME B31.3 pressure piping systems.  An ABSA document, AB-519, provides good background in relation to the type of information that is required for justification and documentation.  Weld tolerances and allowable imperfections before, during, and after joining should be specified, together with the proposed weld locations and identification on a numbered list and isometric drawing, with post weld heat treatment if any, non-destructive testing techniques, etc.  All of this information should be documented for each weld.

ASME B31.1 does not permit closure welds.

Radiography and Ultrasonic Examination

All ASME B31.3 pressure equipment designs require at least 5% acceptable random radiography (RT) or ultrasonic examination (UT) of all circumferential butt and miter groove welds per B31.3-2014 paragraph 341.4.1(b).  Depending on the category of the service, more volumetric examination might well be required.

For ASME B31.1, the level of radiography or ultrasonic examination depends on the design temperature, pressure, and size of the piping per ASME B31.1-2014 paragraph 136.4.  So, though in some instances the RT and UT requirements of B31.1 could be met in the absence of any radiography or ultrasonic testing, equipment with circumferential welds would likely not meet the requirements of B31.3 unless some RT or UT was specified

Minimum Design Metal Temperature

As part of the design conditions, ASME B31.3 designs require that the minimum design metal temperature (MDMT) be specified.  It indicates the lowest temperature at which the equipment is designed to operate at.

ASME B31.1 does not list minimum design metal temperatures even though some material specifications listed in B31.1 do have metal transition temperatures below which brittle behavior becomes evident with ambient conditions in Canada.

Instead, B31.1 somewhat indirectly includes requirements associated with low temperature design via a reference to B31T in paragraph 124.1.2.  Even though ASME B31.1 designs do not ordinarily require explicit specification of the MDMT in the application, good engineering judgement requires that the MDMT be properly considered.  B31.1 designs without a specified MDMT would not meet ASME B31.3 requirements.

Impact Testing

To ensure that materials can withstand the wear and tear required at cold, potentially embrittling temperatures, ASME B31.3 requires impact testing to help ensure safety.  Please refer to ASME B31.3 paras 323.2 and 323.3 for some more details.

As noted above, ASME B31.1 does not include an MDMT as a design condition beyond a reference to ASME B31T and in paragraph 124.1.2.

Table 1:

Summary of Some Differences Between ASME B31.3 and ASME B31.1
(See text above for more information, and codes for full details)

Difference ASME B31.1 ASME B31.3
Scope includes boiler external piping systems see above
Allowable Strengths generally less than B31.3, so wall thicknesses are greater generally greater than B31.1, so wall thicknesses are thinner
Unlisted Material Specifications written, end-user approval is required, see above see above
Non-Service Hydro Pressure Testing Ptest = 1.5Pdesign


Ptest = 1.5Pdesign*Stest/Sdesign
Pneumatic Pressure Testing 1.2Pdesign<=Ptest<=1.5Pdesign

and see above


and see above

Service Testing see above category D fluids only, see above
Alternatives to Pressure Testing no closure welds permitted
see above
closure welds permitted, subject to conditions
see above
Radiography and Ultrasonic Testing dependent on size, pressure and temperature minimum 5% random testing for circumferential and miter groove welds
MDMT needs to be considered per B31T, and paragraph 124.1.2 is a design condition that needs to be specified
Impact Testing needs to be considered per paragraph 124.1.2 is a design parameter that needs to be specified


It is possible to design equipment that meets both codes of construction, where all ASME B31.1 and B31.3 requirements are met.

Registering equipment to meet the requirements of more than one code of construction can be done.  And some manufacturers do this, so that their brand can be sold to a wider range of clientele.

An adequate design and properly prepared CRN application can assist with the CRN registration process.