What standard does this selector follow?

NACE MR0175 / ISO 15156-2, which defines material requirements and qualification limits for carbon and low-alloy steels exposed to H₂S in oil and gas production environments.

How are SSC regions determined?

The selector classifies service conditions into SSC Regions 0, 1, 2, or 3 based on H₂S partial pressure and in-situ pH per ISO 15156-2 Figure 1. Region 0 is non-sour; Region 3 is the most severe and restricts grade selection to high-performance materials.

Which API 5CT grades are evaluated?

H40, J55, K55, N80-1, N80Q, L80-1, L80-13Cr, C90, T95, P110, and Q125, with their maximum hardness limits and qualification requirements per NACE MR0175 Table B.1.

Does temperature affect sour service qualification requirements?

Yes. Above 65°C (150°F) the risk of sulphide stress cracking is significantly reduced. The selector accounts for temperature when determining applicable qualification requirements per ISO 15156-2.

Sour Service Grade Selector

Enter your well's H₂S partial pressure, in-situ temperature, in-situ pH, and chloride to classify the SSC severity region per NACE MR0175 / ISO 15156-2, then see which API 5CT grades are qualified — with their actual hardness limits and service envelopes, not just a pass/fail flag.

Grade properties from API 5CT 11th ed. · Service envelopes from NACE MR0175 / ISO 15156-2:2015 · For guidance only — verify with a qualified corrosion engineer.

Service Conditions

H₂S partial pressure

Sour threshold: 0.3 kPa (0.044 psia)

In-situ temperature

SSC risk reduces significantly above 120 °C

Chloride concentration (mg/L)

Affects 13Cr grades; enter 0 if unknown / negligible

In-situ pH

Affects region boundary; use 3.5 if unknown (conservative)

API 5CT Grade Assessment

Grade	SMYS (ksi)	Max HRC / HBW	Heat treatment	H₂S envelope	Status

Grade properties: API 5CT 11th edition · Envelopes: ISO 15156-2:2015

Region 3 — CRA Consideration

At H₂S partial pressures above 10 kPa, carbon steel OCTG grades (except C110) exceed their qualified envelopes. Duplex stainless steels qualified under ISO 15156-3 are an option. The table below shows selected duplex grades from the NACE MR0175 / ISO 15156-3 specification:

Material	Max temp (°C)	Max H₂S (kPa)	Chloride / pH
Wrought duplex SS: 30 ≤ FPREN ≤ 40, Mo ≥ 1.5%	232	10	See remarks — any combination / any
UNS S31803 produced by hot isostatic pressing (HIP): 30 ≤ FPREN ≤ 40, Mo ≥ 1.5%	232	10	See remarks — any combination / any
Wrought duplex SS: 40 < FPREN ≤ 45	232	20	See remarks — any combination / any

Source: ANSI/NACE MR0175 / ISO 15156-3 Technical Circular 1:2011 Table A.24. Verify FPREN per alloy datasheet.

SSC Severity Regions — ISO 15156-2 Figure 1

Region	H₂S pp (kPa)	In-situ pH	Qualified carbon-steel OCTG grades
0 — Not sour	< 0.3	Any	All API 5CT grades
1 — Mild SSC	0.3 – 1.5	≥ 3.5	L80-1, C90, T95, C110
2 — Moderate SSC	1.5 – 10	≥ 3.5 (L80-1 needs ≥ 4.5)	L80-1 (pH ≥ 4.5), C90, T95, C110
3 — Severe SSC	> 10 or pH < 3.5 with H₂S > 0.3	Any	C110 (no pp limit); CRAs per ISO 15156-3

Region boundaries simplified from ISO 15156-2:2015 Figure 1. Exact boundary is a pH vs H₂S partial pressure diagram — consult the standard for precise interpolation.

Why hardness determines NACE compliance

NACE MR0175 / ISO 15156-2 qualifies carbon-steel tubulars primarily through maximum hardness limits, which correlate with susceptibility to sulfide stress cracking (SSC). A grade can only be used in H₂S service if it meets the hardness limit throughout the pipe body, including the heat-affected zone of welds. Maximum hardness is verified on production pipe — it is not just a nominal specification value.

Related tools & specs

AI Pipe Grade Selector → API 5CT Spec Tables → Pressure & Weight Calculator → API 5L PSL1 vs PSL2 →

Disclaimer: This tool provides guidance based on ISO 15156-2:2015 and API 5CT 11th edition. Material selection for H₂S service must be confirmed by a qualified corrosion engineer against the current edition of NACE MR0175 / ISO 15156, the project-specific corrosion assessment, and applicable design code. Results do not constitute a fitness-for-service determination.