ASME Code Changes

Lookout For Anticipated 2019 ASME Code Changes

As the year progresses and new codes are published, there are a few things to keep a lookout for, particularly with respect to material property requirements.

Two materials are of particular interest, and are reportedly likely to change with the 2019 edition of ASME Section VIII-1. The potential ramifications of these changes on pressure equipment designs and CRNs are quite significant and interesting.

SA-105, Specification for Carbon Steel Forgings

As many Canadians can attest, particularly this year, Canada is not a stranger to cold weather. The thermometer drops below -29C (-20F) with uncomfortable regularity here. As such, impact toughness characteristics and impact test requirements are of primary concern when designing pressure equipment for Canadian use. Nobody wants a pressure boundary to crack and lose containment.

With respect to the SA-105 material specification, somewhat recent brittle fracture incidents at relatively moderate temperatures have been reported, despite adherence to current code rules. As is, ASME Section VIII-1 2017 lists the SA-105 specification as a curve B material per ASME Section VIII-1 Figure UCS-66. We understand that the 2019 Edition of ASME Section VIII-1 will likely change this and instead list SA-105 as a curve A material, thereby requiring impact testing for SA-105 when it wasn’t required before.

We are relatively unsure about whether reclassification of A105 will immediately be reflected by the newest anticipated edition of ASME B31.3 or ASME B31T.

Regardless, the reclassification of SA-105 will be of interest to industry. SA-105 is a common choice for flanges and other forgings for all sorts of pressure piping, and would likely be one of the most, if not the most, prevalent type of carbon steel forging currently used in pressure equipment design.

Since this code change will be more stringent than recent requirements, the onus will be upon end users and manufacturers to ensure that pressure equipment being made, sold and used meets current code requirements. Over the recent past, code changes have instead relaxed requirements in general and so designs with pre-existing CRN were automatically grandfathered by subsequent code changes.

It will also be interesting to see how regulators administer this code change given it makes the code more stringent than what was originally required for pre-existing registered CRNs. Regulators maintain an archive of all registered designs and can compel manufacturers and end users to adapt to more stringent code requirements as needed.

Grade P91 Alloy Steel

This material seems to be a preferred choice for some thermal power plant station designs, given its reported relatively high strength at high temperatures.

However, concerns about P91 material failures and measurements of reduced strength in some circumstances have reportedly led the 2019 Edition of ASME Section I to consider substantial reductions in allowable strength! Minutes from a recent Pressure Equipment Sub-Council meeting report that expected allowable strength reductions are to be in the order of up to 19%!!

As you probably know, permitted pressure is directly proportional to the strength of the material containing that pressure. If code requires that the allowable strength of P91 pressure boundaries to be reduced by 19% then, excluding corrosion allowance if any, the maximum permitted pressure will also be reduced by a proportional amount.

The effect on the existing power plant operation and future designs could be substantial. For reliable and efficient operation, design conditions of power plants are carefully controlled and specified. Needless to say, a prescribed pressure reduction in maximum operating pressure could be, at best, very problematic for the power industry and the public that depends on electricity.

Similar to code changes relating to the SA105 material specifications, it will be interesting to see how regulators administer code changes relating to P91 grade material, given these changes make the code more stringent than what was originally required for pre-existing boiler CRNs. On behalf of the public, regulators must be satisfied that pressure equipment designs are as safe as, or safer than, what current code requires. Regulators maintain an archive of all registered designs and can compel manufacturers and end users to adapt to more stringent code requirements as needed.

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.